Chapter 4, 7, 9, 12 Flashcards
(285 cards)
1
Q
what is morphogenesis?
A
the formation of an organized form
2
Q
what are epithelial cells?
A
cells that are connected tightly
-often in sheets or tubes
3
Q
what are mesenchymal cells?
A
loosely associated or migrating cells
4
Q
what ways do cells construct themselves into an organized embryo?
A
- cell signalling
- cells know what types of cells to stay with (correct populations)
- signals tell cells to associate with each other
- organ formation and location
- organ growth and growth coordination
- achieving polarity
5
Q
what is paracrine signalling?
A
signals that reach long ranges
- occurs early in development unlike endocrine
- signalling molecule is released from the cell and a cell with the correct receptor will receive it
6
Q
what is juxtacrine signalling?
A
signals that are passed between touching cells (local)
- can be homophobic binding (same molecule connecting the cells)
- or could be heterophilic binding (a molecule from each cell)
- or can interact through ECM
7
Q
what is autocrine signalling?
A
a cell sending a signal to itself
8
Q
what is selective affinity?
A
germ layers or different cells types have a positive affinity for one layer and a negative one for another
-can change during dev
9
Q
what is the differential adhesion hypothesis?
A
- a model that explains patterns of cell sorting based on thermodynamic principles
- cells aggregate together in the most thermodynamically stable pattern
10
Q
how was selective affinity first described?
A
- used an amphibian neurula and separated epithelial cells and neural plate cells and dissociated them
- when they naturally reformed they found that epithelial cells went to the outside and neural cells went to the inside
- preformed by Towns and Holfreder in 1955
11
Q
what does differential adhesion have to do with surface tension?
A
- cells that have same surface tension populate together
- cells with more surface tension will sort inside
- cells with lower surface tension on the outside
- the cells with higher surface tension had more cadherins which connects surface tension to differential adhesion
12
Q
what are cadherins?
A
- calcium dependant adhesion molecules
- they are transmembrane (external domain adheres cells together)
- anchored by catenins, and bind to the actin of the cytoskeleton of the cell (provides mechanical support for sheets and tubes)
- also a signalling molecule that cells gene expression
13
Q
what are the types of cadherins in mammals?
A
E: early mammalian dev, restricted to epithelial tissues later on
P: placenta, to stick to uterus
N: developing CNS
R: retina formation
pro: lack attachment to actin cytoskeleton, help keep migrating cells together
14
Q
what is the overall structure of cadherins?
A
- ECM domain with 5 regions to interact with neighbouring cells
- calcium-binding sites
- adhesive recognition site for cadherin of same type
- transmembrane domain
- intracellular domain that interacts with a catenin complex of 3 that interacts with actin
15
Q
how do cadherins interact with each other?
A
-form homodimers then interact
16
Q
how can cadherins be inhibited?
A
-removing calcium from the environment (Cells won’t be able to interact)
17
Q
how do you get different amounts of gene expression for cadherins?
A
-depends on what amount of TFs are present at the enhancers, the more TFs the more cadherin production
18
Q
how is E cadherin used in epiboly in zebrafish?
A
- the ectoderm cells surrounding the embryo need to be held together to migrate around the embryo
- the endoderm moves inwards and pulls the ectoderm around the embryo
- if E-cadherin isn’t present the embryo is half-baked (endoderm isnt wrapped around)
19
Q
what is radial intercalation?
A
- movement of deep epiblast cells to more superficial layer (powers epiboly)
- involves E-cadherins
20
Q
why does the type of cadherin matter for interactions?
A
- if they aren’t the right type they won’t bind
- ex. R and B don’t bind
- sheets of cells of the same type form this way
21
Q
why is it important that the egg stays inside the zona pellucida?
A
-cells on the outside of the egg express P-cadherin so that the egg can be implanted into the placenta but if the egg hatches from the zona pellucida in the Fallopian tube it can bind there and the pregnancy must be terminated otherwise the mother will be killed
22
Q
what is the extracellular matrix?
A
- an insoluble network consisting of macromolecules secreted by cells into their immediate environment- between cells
- most cells are secreted for ECM are fibroblast cells
23
Q
what four proteins are important for the ECM?
A
- proteoglycan: delivers paracrine factors in high conc.
- fibronectin: glycoprotein dimer, general adhesion molecule, proper alignment of cells with ECM and cell migration (pathways guide cells over dorsal blastopore lip)
- laminin: part of basal lamina
- collagen: type IV part of basal lamina
24
Q
what do all of the proteins of the ECM provide?
A
- site of attachment
- path for migration
- directions for movement
- signal for a development event
25
what are the three cell receptors (domains/integrins) for ECM molecules?
1. extracellular domain: binds to arg-gly-asp sequence found in fibronectin, vitronectin, and laminin
2. transmembrane domain
3. cytoplasmic domain: bind to talin and alpha actin to connect
- allows cells to move by contracting actin against ECM and helps them know where to migrate
- signals to inside of the cell to alter gene expression
- bound integrin prevents activation of genes that promote apoptosis (if a cell doesn't follow the right path it won't have proper gene expression so it dies which is good so dev. isn't screwed up)
26
what are the similarities and differences between interns and cadherins?
Similarities:
-both have extracellular domain and transmembrane domain
-both interact internally with actin cytoskeleton forming dimers (in integrins beta subunits bind to talin and alpha actinin binds to actin filament)
Differences:
-cadherins bind to other cadherins in extracellular domain but integrins bind to proteins in ECM
-cadherins from homodimers, integrins form heterodimers that come together interacting with ECM, the cellular beta subunits bind to two parts of actin
-extracellular region of integrin is rigid and cellular region is dynamic to allow cells to move and change shape
27
what are the steps of the epithelial to mesenchymal transition?
1. cells need to be activated: paracrine factors activate gene expression in target cells to down regulate cadherins
2. the cell is released from the basal lamina
3. cytoskeleton (actin) is rearranged
4. cell secretes new ECM molecules characteristic to mesenchymal cells
28
what cellular junctions are cadherins involved in?
- adherin junctions
| - desmosomes
29
what cellular junctions are integrins involved in?
-hemidesmosomes
30
why is cell signalling important during development?
-through development all cells must change gene expression to go from undetermined to a differentiated cell and to do this, signals are taken from the environment or other cells near by
31
what is cell induction?
one group of cells changes the behaviour of an adjacent set of cells, causing them to change shape, mitotic rate, or cell fate
-the cells being signalled to must be competent
32
what is cells competence?
- the ability to respond to an inductive signal
| - has correct receptor
33
what is an inducer in cell signalling?
-cells or tissue that produces the signal that tells other cells to change (signal is usually paracrine)
34
what is a responder in cell signalling?
the competent cell with the receptor
35
what is reciprocal induction?
the inducer becomes the induced
36
what is instructive interaction?
a signal from the inducing cell is necessary for initiating new gene expression in the responding cell
37
what is permissive interaction?
responding tissue has already been specified and needs only an environment that allows the expression of these traits (instructive interaction has probably already occurred)
38
how does instructive interaction in the eyes work?
- signal fgf8 is sent by paracrine factor from the neural ectoderm to the ectoderm above it that has an fgf8 receptor
- when the signal is received, the lens of the eye forms
39
how can instructive interaction in the eyes get messed up?
-if the optic vesicle is removed, fgf8 signal can't be sent so the epidermal ectoderm can't form a lens
40
how does the lens ectoderm differentiate and become competent in the right region to be able to accept the fgf8 signal?
- a signal from the ventral foregut causes the change mid gastrula stage
- that region then turns on Otx2 gene expression and ectoderm that forms neural plate in late gastrula stage signals for lens ectoderm to turn on Pax6
- in early neurula stage the mesoderm and formed neural plate interact with lens ectoderm, signalling to express Sox3 and L-Maf
- Sox3, L-Maf, Otx2, and Pax6 transcription factors are expressed and finals signal from the optic vesicle can be sent (fgf8 and bmp4
41
what can Pax6 deficiency result in?
-iris problems (aniridia)
42
what is an example of permissive interaction?
-the heart, it has everything ready for expression just needs correct ECM environment
43
what are the 4 types of paracrine factors?
1. fibroblast growth factor family (sequencing and protein)
2. the hedgehog family (important in dev. for boundaries between tissues)
3. the Wnt family (establishing polarity)
4. transforming growth factor beta superfamily: TFG-beta family, activin family, bone morphogenic proteins, nodal proteins the Vg1 family, and several related proteins
44
what is a signal transduction cascade?
- response to a signal ends in regulation of TFs and/or regulation of cytoskeleton
- cells will know what pathway to take and how to differentiate
45
what is the job of morphogens?
-secrete signalling molecules by a signalling cell that produces a gradient
46
how many structurally related members of FGF family are there?
- about 24
| - they can generate hundreds of different isoforms
47
what does fgf1 do?
-acidic, for regeneration
48
what does fgf7 do?
-keratinocyte growth factor, for skin development
49
what is the breathless FGF?
- in drosophila
| - for tracheal development
50
what does fgf8 do?
-limb and lens induction
51
what is often the fibroblast growth factor receptor and how does it work when the morphogen binds?
- receptor tyrosine kinases
- once to morphogen binds to this receptor, the tyrosine kinase region inside the cytoplasm is phosphorylated that triggers protein to be active which will active responding protein, the signal transduction cascade travels through the cell until there is a change in gene expression or cytoskeleton
52
why can the fgf8 trigger formation of so many different things in a chick when its the same signal?
-it uses the same morphogen but each type of cell went through a different path earlier in dev so the signal does different things since each cell type already has a set of genes being expressed
53
what is the tyrosine kinase pathway that is activated by FGF?
1. FGF binds to receptor that makes the receptor form a dimer
2. a conformational change inside the cell allows it to phosphorylate receptor tyrosine kinase)
3. guanine exchange factor is activated by phosphorylated RTK
4. GEF helps exchange guanine diphosphate for guanine triphosphate which activates Ras protein
5. Ras activates Raf
6. Raf activates MEK
7. MEK activates ERK which is in the nucleus of the call
8. ERK activates TFs in the nucleus
9. transcription occurs (expression will depend on what chromatin is open)
54
how does FGF activate the JAK-STAT pathway?
1. prolactin that released from pituitary gland binds to cytokine receptor
2. interior is phosphorylated which phosphorylates JAK 2
3. JAK 2 activation triggers STAT 5 phosphorylation and STAT dimerizes which gives a nuclear localization signal
4. STAT 5 enters nucleus and initiates transcription with TFs
- casein gene expression which makes milk production occur
55
what happens when the FGFR3 is mutated?
- fgf3 binds to FGFR3 to activate the JAK-STAT pathway
- if FGFR3 is mutated, the kinase domain keeps phosphorylating itself so JAK and STAT are always on
- the mutated receptor ends up stopping cartilage growth before birth so fetus has a narrow chest, short limbs and rib cage can't support the developing lungs (Thanatophoric dysplasia)
56
why does the hedgehog family need closterol to function?
- only 2/3 of the amino terminal is secreted
| - it helps anchor the Hedgehog to the receptor cells cell membrane
57
what is the function of sonic hedgehog, shh?
-motor neurons, somites, feathers, pinkies
58
what is the function of desert hedgehog, dhh?
-seroli cells of the testes
59
what is the function of Indian hedgehog, ihh?
-gut and cartilage
60
how is transcription often activated with hedgehog?
-inhibiting an inhibitor
61
in what forms can hedgehog be secreted outside of the cell?
- monomer
- multimer
- lipoprotein
- exovesicle
62
what is the drosophila pathway for hedgehog signalling?
1. hedgehog ligand is released (cholesterol recognized patched protein and hedgehog binds to it)
2. patched gets internalized by endocytosis
3. smoothened protein is phosphorylated because of patched and starts signal cascade
4. smoothened inhibits Cos2/Kif7 (inhibitor) which releases CI from a protein complex
5. CI enters nucleus binding enhancers and activating a subset of genes
- transcription then occurs
63
how is the vertebrate pathway for hedgehog signalling different from drosophila?
-same, except instead of CI its Gli
64
how many members of the Wnt family are there for vertebrates?
about 15
65
what are the Wnt family signals important for?
- establishing polarity in insect and vertebrate limbs
- promoting proliferations of stem cells
- important during gastrulation to help make sure that cells divide in same place
66
what is the wnt signalling pathway when no wnt is bound?
- the disheveled protein cannot be bound so it can't interact with GSK-3 which normally doesn't phosphorylate
- GSK-3 then phosphorylates beta-catenin which then gets tagged with ubiquitin and degraded by a proteasome
67
what is the wnt signalling pathway when wnt is bound?
-wnt interacts with frizzled and LRP5/6
-LRP5/6 is phosphorylated and changes shape of frizzled and LRP5/6
allowing for interaction with disheveled that also changes shape and is allowed to interact with Axin and GSK3
-since GSK3 is bound, it can't phosphorylate Beta-catenin
-Beta-catenin can enterthe nucleus and with the correct TFs bound, gene expression is turned on
68
what is the planar polarity pathway for Wnt?
-LRP and frizzled are present so they can interact with disheveled that will interact with Rho GTPases (changes cytoskeletal organization or gene expression (by JAK)) or Wnt
69
what is the Wnt/calcium pathway?
- requires internal stores of calcium
| - calcium regulates multitude of target proteins (activates and inactivates)
70
wnt4 is needed for kidney dev and female sex gonads, what happens when wnt4 is knocked down/out?
- no kidneys form
| - ovaries begin synthesizing testosterone and ducts become modified to male duct system
71
how can wnt be post-translationally modified?
- the palmitoleic acid attached to wnt interacts with herparan sulphate proteoglycan to help concentrate wnt so that wnt can interact with frizzled and LRP5/6
- therefore palmitoleic acid is needed for wnt to interact with receptor
72
how is the concentration of wnt that cells get controlled?
wnt is being concentrated and activating frizzled but as that's being done, the notum being expressed by wnt pathways is clipping off palmiteoleic acid to down regulate the signal (unless signal is being continuously received)
- negative feedback system
- notum makes it so 40\5 of wnt is expressed
73
what protein helps wnt diffusion?
-swim
74
how many members of the TGF-beta family?
-about 30
75
what is the anti-Mullerian hormone important for?
-mammalian sex determination
76
what is the Smad pathway activated by TGF-beta?
- receptors type 1 and 2 dimerize and get phosphorylated in the the cytoplasmic portion to initial the signal cascade
- if activin, nodal or TGF-beta ligand binds to the receptor, Smad 2,3 get activated
- Smad 4 recognizes Smad 2,3 and the two enter the nucleus together
- transcription occurs
- if BMP binds to receptor, Smad 1,5 is activated instead
77
what are the types of receptors for juxtacrine signalling?
Notch: Delta, jagged, serrate
eph: ephrin ligand
78
why are juxtacrine interactions only from direct contact?
the signalling molecule is attached to only the signalling cell so only neighbouring cells can receive the signal
79
what organs are juxtacrine signals important for?
-kidneys, pancreas, heart, nervous system
80
what experiment was preformed to show the fgf8 gradient?
- a cell was injected with mRNA that was made up of fgf8 and GFP
- the protein that got made from this would glow so it would show where fgf8 is
- showed that close cells had a lot of fgf8 and farther cells had less (diffusion gradient)
- the experiment was done with cells that were +dynamin (lost endocytosis function) and cells that were +Rab5c (gained endocytosis function)
- LOF: fgf8 diffused further because cells near the fgf8 signal were endocytosing the signal so it could travel farther
- GOF: fgf8 was internalized faster so there was less of a gradient
81
why are signal gradients important?
depending on how much of a dose of signal a cell gets will affect their gene expression so cells will have different fates
82
what factors can play a role in fgf8 signalling and gradient?
1. mRNA decay (speed of decay determines how much fgf8 is translated)
2. free diffusion (if nothing inhibits it, it can go quite far)
3. HSPG (cell help diffuse and direct fgf8 if it needs to go to a specific spot)
4. a lot of HSPG around a cell (can help to concentrate fgf8 around nearby cells)
83
how can filopodia help sent signals?
-paracrine factors can be delivered by filopodia projections that reach out to cells that are multiple cells away
84
what are the signalling filopodia called?
-cytonemes (actin based)
85
hedgehog has a primary cilium that can be used for signalling, how does this work?
-hedgehog is hyperactivated, smoothened is expressed and has to move into the primary cilium to prevent Cos/Kis7 which then prevents the cleavage of Gle proteins and then can activate proteins
86
what is Notch?
-a transmembrane protein with a cytoplasmic domain
87
what is the mechanism of Notch activity?
- the Notch receiving molecule comes in direct contact with Delta signalling molecule which changes the Notch conformation and allows it to be recognized by protease in the cytoplasm
- protease then cleaves the cytoplasmic domain off Notch which then enters the nucleus and recognizes proteins that are already in the nucleus and bound to a specific subset of genes (CSL)
- other factors are also recruited like histone acetyl transferases
- the enhancer region is linked to the target gene and transcription occurs
88
how are the vulval precursor cells for c. elegans induced?
- anchor cells induce them
- they trigger the closest cells to become the primary vulval cells which activate LIN-12 signal for neighbour secondary cells
- farther cells get less LIN-3 signal and become secondary vulval cells
- the farthest cells are tertiary and become hypodermis (no LIN-3 signal)
89
what is fertilization?
-fusion of gametes
90
what are the four steps in fertilization?
1. contact and recognition: sperm has to get to the egg and recognize that it needs to fertilize it
2. regulation of sperm entry: only one sperm should be entering the egg so that there are only 2 copies of genetic info
3. fusion of genetic material: once sperm fertilizes the egg, the nuclei has to come together so that genetic info is in one nuclei
4 activation of egg metabolism to start development: drosophila doesn't need this but humans do
91
what are the steps of male gametogenesis?
```
mitosis: spermatogonia
meiosis I: primary spermatocyte
meiosis II: secondary spermatocyte
spermatid
differentiation: sperm (goes through capacitation in female reproductive system after this then is ready to fertilize the egg)
```
92
what modifications are done to the germ cells to form mammalian sperm?
- first there is a spermatid with one centriole, a nucleus, and a Golgi apparatus
- the centriole duplicates and flagellum forms
- the Golgi turns into acrosomal vesicle that contains enzymes that digest protein and complex sugars to gain access to the egg cell membrane
- centriole moves to behind the nucleus
- sperm has a lot of mitochondria for engird production
93
what do the outer dense fibres of the sperm do?
-cytoskeletal structures that help maintain elastic structure, recoil, and protect from constant movement
94
what is the function of the dynein arms in sperm?
-uses ATP to slide doublets on outside relative to others to provide motile force of sperm
95
what are the steps of female gametogenesis?
- germs cells are set aside that have marks on them that will eventually go through meiosis
- mitosis: oogonia
- meiosis I: arrested primary oocyte, first polar body and the egg (occurs during ovulation)
- meiosis II: second polar body and mature ovum (happens after fertilization)
96
what is present in a sea urchin egg cytoplasm?
- nutritive proteins
- ribosomes and tRNA
- mRNA
- morphogenetic factors
- protective chemicals
97
what are the cortical granules in a sea urchin egg?
- derived from the Golgi like the acrosomal vesicle in sperm
- located directly underneath the egg membrane of the gg
- about 15000 in sea urchins
98
what happens as soon as the first sperm touches the egg cell membrane?
- the egg reacts to prevent other sperm from getting through the vitelline envelope
- cortical granules under plasma membrane release contains once sperm gets to the cell membrane which causes changes to the egg
99
what events take place that lead to the egg and sperm fusion in sea urchins (external)?
1. chemoattraction of sperm to egg by soluble molecules secreted by the egg
2. exocytosis of sperm acrosomal vesicle and release of its enzymes
3. binding of the sperm to the ECM (vitelline envelope or zone pellucida) of the egg
4. passage of sperm through ECM
5. fusion of egg and sperm cell membranes
100
how do sea urchins ensure that sperm will find egg because of their external fertilization?
- different species release at different times
- the timing is very important
- called species-specific attraction (right egg to right sperm) and species-specific activation (egg won't be activated unless the sperm is of the right species)
101
when and how is sperm motility activated?
- acquired when sperm are spawned into seawater
- movement: the pH in the testes is 7.2 and in the seawater is 7.6, the slightly more basic seawater activates dynein ATPase
- direction: sperm-activating proteins are released from the egg jelly in order or sperm to find the egg
102
how does the resact protein from the egg help the sperm?
- it binds to a receptor on the outside of the sperm (receptor guanylyl cyclase)
- GTP gets turned into cyclic cGMP which activates Ca2+ channel that lets Ca2+ in from the seawater
- this activates mitochondria ATP generation which triggers dynein ATPase to activate and allow sperm tail to move
- only resact from the same species can bind to the receptor on the sperm
103
when is the acrosome reaction initiated and what happens?
- initiated by contact of sperm with egg jelly
- species specific sulphate-containg polysaccharides in the egg jelly binds to specific receptors above the acrosome vesicle with the sperm cell membrane
- the acrosrome vesicle fuses with the sperm cell membrane by exocytosis
- acrosomal process extends (helps sperm find their way through the jelly to the vitelline membrane)
- the proteolytic enzymes and proteosomes digest a path through the jelly to access the cell surface
104
other than digesting the jelly of the egg, what is the acrosomal reaction important for?
- the acrosomal process forms with Binding which is needed to interact with the microvilli of the the vitelline membrane
- binds to egg bindin receptor protein 1 (EBR1)
105
how is the sperm passed through the ECM of the egg?
-the sperm makes contact with egg bindin receptor protein and egg produces fertilization cone what helps the sperm into the egg
106
what is monospermy?
-when one sperm enters the egg (diploid)
107
what happens to the sperm and egg centrioles once the sperm has entered the egg?
-the sperm centriole is divided to form two poles of the mitotic spindle and the egg centriole is degraded
108
what is polyspermy?
- when multiple sperm enter the egg (triploid)
| - each sperms centriole divides
109
what is fast block?
-electrical change in the egg cell membrane to prevent other sperm from entering
110
what is slow block?
-exocytosis of the cortical granules to prevent sperm entry
111
what happens if two sperm do end up entering one egg?
- there will be an extra pronuclei
- two sets of centrioles replicate
- at first cleavage, the egg is pulled in 4 directions instead of just two
- the number is chromosomes is not evenly distributed (54 chromosomes divided unevenly)
- the embryo will not survive
112
what happens when fast block occurs?
- an influx of Na2+ ions through sodium channels in the egg
- happens when sperm contacts the cell membrane of the egg
- changes the membrane potential which stops more sperm from entering until the cortical granules can release and slow block occurs
113
why might be a reason the fast block does not occur in mammals?
-fertilzation is internal sp not many sperm get through to the egg anyways, no need for something to be happening before slow block occurs
114
where does slow block occur in the egg?
-starts where the sperm enter and continues around the egg
115
what do the cortical granules do during slow block?
- they release a serine protease:
- cleaves protein posts connecting vitelline membrane proteins to egg cell membrane
- clips off binding receptors and any sperm attached
116
what is the sequence of events during fertilization envelope formation?
- sperm enters
- cortical granules fuse to egg cell membrane and release contents between cell membrane and vitelline envelope, Ca2+ is also released from the ER
- space absorbs water
- fertilization envelope is stabilized by cross-linking proteins including hyalin
- egg extends microvilli to attach to hyaline layer, the provides support for blastomeres during cleavage
117
what is inside to cortical granules?
- serine protease
- peroxidase enzymes
- transglutaminase
- hyalin
118
what triggers cortical granule exocytosis?
-the sperm fusing to the egg triggers release of Ca2+ from the internal store in the ER
119
what do the contents of the cortical granules do?
- serine protease: cleaves vitelline envelope from cell membrane
- mucopolysaccharides: help cause osmotic gradient (the water being absorbed into the space between the egg and the fertilization envelope
- vdx1: catalyzes hydrogen peroxide which is a substrate for ovoperoxidases
- ovoperoxidase and transgutimase and hylin: make fertilization envelope which protects developing embryo from external environment and gives egg something solid to attach to
120
what two things does the release of Ca2+ do?
- no more sperm can fertilize the egg
| - helps activate egg metabolism
121
how does Ca2+ activate egg metabolism?
- releases inhibitors from maternally stored messages, allowing mRNA translation
- release nuclear inhibition allowing cleavage to occur
- all timed with Ca2+ release
122
what are the possible mechanisms to trigger the internal stores of Ca2+?
1. could be a soluble factor from the sperm that's introduced into the egg at the time of cell fusion (this would activate the egg by changing ionic composition of cytoplasm (mammals))
2. could be from the sperm binding to receptors on the egg cell surface and changing the conformation (initiates reaction within the cytoplasm activate the egg (sea urchin))
- both cases go through tyrosine kinase which activates phosphates C then you end up with IP3 and DAG
123
what do IP3 and DAG do?
- IP3: binds to Ca2+ channel to release stores
- DAG: with help of Ca2+, activates Na+/H+ pump which changes the internal composition of the egg (helps stimulate cell division, DNA synthesis, RNA translation)
124
how is the G protein involved in sea urchin activation?
-if its inhibited, wave of Ca2+ doesn't occur
125
what is the proposed mechanism for egg activation in sea urchins?
- sperm contact and fuse with egg
- G protein is activated
- Src is activated
- PLC-gamma is activated
- PIP2 is turned into IP3 and DAG
- triggers Ca2+ release
- release triggers cortical granule exocytosis (slow block) and inactivates MAP kinase (recitation of cell cycle occurs)
126
what is acid efflux?
- happens with release of Ca2+ and activation of PLC and IP3 and DAG
- its a Na+-H+ exchange
127
how long does it take for the zygotic nuclei to form?
- 2-12 minutes for sperm nucleus to get to the centre of the egg
- 5-10 mins or the egg nucleus to migrate to the sperm nucleus
128
why isn't the zygotic DNA needed for the first cleavage?
-stored maternal mRNA is translated due to Ca2+ release (the protein protecting the mRNA gets degraded)
129
what are the early effect of Ca2+ release?
- activation of NAD kinase which turns NAD+ into NADP+
- NADP+ is used as a coenzyme for lipid biosynthesis
- reduction of oxygen for cross linking in fertilization envelope by UDX1 depends on NADPH
- NADPH also helps regenerate glutathione and ovothiols (molecules that may be critical scavengers of free radicals
130
what are the late effects/responses of the Ca2+ release?
- resumption of protein and DNA synthesis
- NA+ - H+ exchange - increased pH - stored mRNA gets translated
- Ca2+ inactivates MAP kinase which removes DNA synthesis inhibition (more membrane and protein transcription can occur so DNA can be copied and produce more cells
131
what happens during the burst of protein synthesis that occurs during fertilization?
-mRNA stored in oocyte cytoplasm gets used
132
how did they find out that the stored mRNA was being used at fertilization and not the zygotic mRNA?
-treated the seawater with actinomysin which prevents RNA synthesis
in the first 5 hours there was a burst of ribosomes and polysomes (must be the stored mRNA)
-then once own mRNA from zygotic nuclei was needed, the amount od ribosomes and polysomes decreased and the mRNAs couldn't be synthesized
133
how is the genetic material in sea urchins fused leading to DNA synthesis?
- the sperm nucleus decondenses to become a pronucleus (which rotates 180 degrees so the centriole is positioned between sperm and egg pronuclei)
- the nuclear envelope vesiculates into small packets exposing chromatin to egg cytoplasm
- chromatin decondenses
- histone proteins of sperm are exchanged or egg-derived histones (starting translation)
- DNA adheres to egg nuclear envelope (fusion)
- DNA pol can initiate replication
134
where does the internal fertilization of mammals occur?
-the ampulla region of the oviduct
135
how long after intercourse can fertilization occur for mammals?
- up to 6 days after intercourse
| - the opportunity ends after ovulation
136
how is the oocyte translocated inside the oviduct?
- the oocyte is surround by cumulus cells that can enter the oviduct
- ciliary beating and muscle contractions of the oocyte move it along the oviduct
137
how is the sperm translocated inside the oviduct?
1. uterine muscle contractions release sperm to oviduct
2. the sperm is slowly released to the ampulla
3. sperm gain motility in the oviduct
4. the sperm get directions cues from temp and chemicals and current that sperm swim against
5. the sperm mature so that they can fertilize the egg
138
instead of a vitelline envelope like sea urchins, what surrounds the mammalian ovum?
-zona pellucida
139
what does it mean for sperm to be capacitated?
- the sperm gets prepared acrosome reaction
| - motility is enabled so sperm can become hyperactive and sense the egg location be rheotaxis and chemotaxis
140
what are the five major molecule changes that happen for a sperm to become capacitated?
1. removal of cholesterol by albumin proteins in the female reproductive tract (cholesterol efflux)
2. particular proteins or carbohydrates on sperm surface are lost
3. membrane potential becomes more negative as K+ ions leave the sperm
4. protein phosphorylation occurs inside sperm
5. outer acrosomal membrane changes and comes into contact with sperm cell membrane
141
how can we fertilize an egg in a Petri dish?
- due to research of mammalian sperm capacitation
- fluid from the oviduct can be incubated with the egg and sperm
- pr the sperm and egg can be incubated with Ca2+ ions, bicarbonate and serum albumin proteins
- serum albumin pretins cause cholesterol to flux oit and for sperm to activate Ca2+ channels and bicarbonate channels
142
why does sperm capacitation allow the sperm to move much faster and enter the ampulla?
- before capacitation the sperm is held in place by eptitheial cells,
- åter capacitation, the sperm can move very fast to break free for the hold
143
what are some of the reasons mammals may not need fast block?
- some sperm are never capacitated
- sperm that are, are at different times so only small amounts of sperm are released at once
- some sperm go to the wrong oviduct
144
there are two pathways the sperm can get to the egg, what happens when the sperm recognized the Egg ZP2 (pathway 1)?
- if the Egg ZP2 is recognized, the sperm moves through the zone pellucida
- the cell membranes fuse (fertilization)
- cortical granules reaction is triggered inside the egg
- the ZP2 and ZP3 are inactivated on the outside of the egg so that other sperm can bind there
145
what is the pathway for sperm entry is the sperm recognized the ZP3 (pathway 2)?
-after the ZP3 is recognized, the acrosome reaction is triggered, then the acrosome reacted sperm is activated and can recognize ZP2, the rest of the pathway is the same as pathway 1
146
what are the sperm and egg proteins that recognize each other and allow the sperm and egg to fuse?
- izumo for sperm
| - juno for egg
147
what do the cortical granules from mammal eggs release?
-ovastacin: cleaves off ZP2 so other sperm can't bind to make contact with the egg cell membrane
148
what is the second slow block to polyspermy that happens in mammals
- zinc is released that is stored in vesicle in the periphery of the egg
- this inhibits capacitation and acrosomal enzymes
- the since must diminish quickly though or else the egg won't be able to go through cleavage
149
what is the third slow block to polyspermy in mammals?
-juno is released from oocyte cell membrane and can bind to sperm in pervitelline space, this prevents sperm that have gone through acrosomal reaction from binding to cell membrane
150
what are the modifications sperm go through before fusing with the egg?
-sperm DNA is bound by protamines that are cross linked with disulphide binds
151
what are the modifications that an egg goes through before fusion with a sperm?
-egg nuclei is arrested in metaphase II- increased Ca2+ from cortical granules levels lead to proteolysis of cyclin (Cell cycle progression) and securing (protein holding metaphase chromosomes together) and haploid maternal pronucleus completion
152
how is the DNA synthesis different in mammals than sea urchins?
- in mammals, DNA synthesis occurs separately for sperm and egg and chromosome orient themselves on a common mitotic spindle, the true diploid is in 2-cell stage inside of 1-cell stage
- in sea urchins, ptronculi merge then go through the first cell division
153
where does the mammalian PLC(phospholipase) come from?
sperm, stored in the sperm head and delivered during gamete fusion
154
who is Thomas Morgan and what did he discover?
- white eyed mutations occurred more in males
- found that it was a mutation on the X chromosome which showed genes are past off through chromosomes and are responsible for specific phenotypes
155
why is drosophila a great model organism?
- a lot of info is shared about them
- short generations
- easy to care for
- cheap
156
how do drosophila change x regulation to match female compared to humans?
- drosophila males up-regulate X chromosome
| - human females down regulate X chromosome
157
what happens during fertilization in drosophila?
- sperm enters a pre-activated egg through micropyle
- the egg is activated by ovulation a few minutes before fertilization
- females can store sperm from multiple makes
- when the sperm enters the egg, specification of body axes have already began- Ca2+ channels open at ovulation before fertilization, no cortical granules though
158
what is the life cycle of drosophila?
-an egg is oviposited and within 10 days at 25 degrees, the egg becomes adult fly
-in the first 24h the embryo goers from single cell, through cleavage, gastrulation, and produced larval structures by differentiation, adult structures are set aside in imaginal discs
(embryo to 1st instar larva)
-in the next 24h the larva eats and grows a lot
(1st instar to 2nd)
-next 24h 3rd instructive curls up and becomes prepupa then pupa
-in 5 days, the drosophila emerges from the pupa (eclose)
159
what type of cleavage do drosophila go through?
- syncithial (lots of nuclei but not cell membranes)
| - superficial (centrally located yolk confines cleavage to cytoplasmic rim of the egg)
160
what is happening in the 8th cell cycle and on in drosophila?
- 8th: each cycle takes 8 minutes, 256 nuclei are produced
- 9th: about 5 cells reach posterior end of cell and generate the pole cells
- 10th: the nuclei migrate to cortex (periphery) of egg and are surrounded by microtubules and microfilaments (energids)
- after 11th: zygotic nuclei begin to express genes
- after 13th cycle: about 6000 cells, about 4 hours post-fertilization, cell membrane folds inward to partition off each energy to create cellular blastoderm (from the syncytial)
161
what is an energid?
-a nuclei associated with cytoplasmic islands/regions around them as individual cells form
162
what is bazooka?
-a scoffolding protein that is an early polarity mark (helps to organize cells)
163
when and how does that maternal to zygotic transition occur?
cycle 11: zygotic gene transcription begins
cycle 13: takes 25 minutes, mid-blastula transition
cycle 14: asynchronous, 75-175 mins (only zygotic transcripts now)
164
what is the maternal to zygotic transition controlled by?
1. ratio of chromatin to cytoplasm (only at a certain threshold of chromatin can you start the maternal to zygotic transition)
2. Zelda (zinc-finger early Drosophila activator) transcription factor (maternal) binds to CAGGTAG motif in promoter region (turns on zygotic transcripts, increased what is needed over time)
3. smaug protein (maternal) RNA binding protein that is a translational repressor of maternal mRNA by binding to 3' end of RNA and helps increase translation as cell goes through divisions
165
when does gastrulation of drosophila start?
-shortly after the mid-blastula transition
166
what are the steps of drosophila gastrulation?
1. segregate the presumptive mesoderm, endoderm, and ectoderm (major movements of cells)
2. about 1000 cells of mesoderm fold inward to produce the ventral furrow which will become the ventral tube by invagination
3. endoderm invaginate to form pockets at the anterior and posterior ends of the ventral furrow (pole cells too)
4. germ band that will form trunk of embryo is formed from the ectoderm and mesoderm and wraps around the top dorsal surface (extended position; imaginal discs are formed)
6. the germ band retracts back and body segments appear dividing the ectoderm and mesoderm
7. dorsal closure as two sides of epidermis are brought together (the larva is formed)
167
what is the amniosersa important for in drosophila?
germ band extension
168
what patterning do maternal transcripts set up?
- anterior to posterior
| - dorsal to ventral
169
how is the ventral furrow set up?
- expresses myosin unevenly through cells
| - the myosin proteins help constrict apical end by pinching it which causes those cells to invaginate inward
170
what is the ventral nervous system?
- derived from ectoderm over invaginated mesoderm
| - the ventral mesoderm does inside and induces neural ectoderm below it
171
what is responsible for the anterior to posterior patterning in drosophila?
-determined by interactions between the developing oocyte and its surrounding follicle cells (oocyte traps things from the from the follicle cells in certain regions)
172
how does the drosophila oocyte form?
- oogonium (immature reproductive system) divides 4 times in the egg chamber with incomplete cytokinesis
- this gives us 16 germline cells, 15 of which become nurse cells, 1 becomes oocyte
173
what do follicle cells do before degrading?
-secrete chorion (outer shell of egg) which is important for setting up gradient of gene expression inside the egg
174
where does the nucleus end up in the developing oocyte?
gurken mRNA in the dorsal side of the egg surrounds the oocyte nuclei and gets localized there
175
what differentiates the two ends of the oocyte?
- bicoid is anterior
- nanos is posterior (bound in place by oskar)
- they both form gradients
176
what genes do bicoid and nanos turn on then what's turned on after that?
- gap genes: create more defined regions
- gap genes turn on pair-rule genes: creates even smaller specifically defined regions (ex. fushi terazoo)
- pair-rule turn on segment polarity genes (ex. engrailed) and homeotic genes (form and function)
177
what initiates the pattern formation of anterior to posterior polarity?
-gurken mRNA made in nurse cells are transported along microtubules into oocyte
178
where does the turkey mRNA localize?
-between oocyte nucleus and cell membrane, gets translated there
179
what does the Gurken protein do?
- binds to Torpedo receptors in follicle cell membrane
- the follicle cells send an unknown signal that's thought to involve protein kinase A back which recruits Par-1 to the posterior edge of the oocyte (Par1 organizes the microtubules so the minus ends point s anterior)
180
what is transported on the microtubules that Par-1 orientated?
- kinesin transports Oskar from follicle cells to posterior end
- oskar then gets translated in the posterior cortex so now there is a distinctive pole plasm by cycle 9 (will eventually become abdomen and germ cells)
- bicoid is transported to anterior end
181
how is nanos kept the to posterior end of the oocyte?
- the 3'UTR is associated with oskar, Valois, vasa, staffer, and tudor that trap nanos in the posterior end
- oskar and Staufen are transported by kinesin motors and are bound to actin microfilaments or cortex
- Staufen allows oskar to be translated into Oskar and bind nanos
- the nanos that's in the cytoplasm is inhibited to translate by Smaug (by binding to 3'UTR) and Cup which prevents ribosome binding and recruits deadenylation proteins
182
when do bicoid and nanos get translated?
- after fertilization
| - once they are translated they create gradients which happens when oocyte is going through mitosis
183
how do bicoid and nanos affect hunchback expression?
- bicoid activates it (these high concentrations of bocoid and hunchback anteriorly activate head gap genes (buttonhead, empty spiracles, and orthodenticle))
- nanos inhibits it (no expression posteriorly)
184
what does Caudal protein activate?
- knirps and giants that are important for abdominal development
- bicoid inhibits caudal
185
when does cellularization occur?
-when segment polarity genes are being expressed
186
what are the 5 segments that form in drosophila?
- acron
- head
- thorax
- abdomen
- telson
187
what does it mean when a pair-rule gene is in a parasegment?
- it is part way into one segment and partway into another
- the segment have their own anterior and posterior ends
- the overlapping gives unique gene expression in every cell
- fushi tarazu is an example
188
what are the three toggle switches of the gap gene network?
1. Knipps and Hunchback are inhibiting each other
2. Hunchback inhibits Kruppel, but can also enhance its expression if only moderate levels of Hunchback are around
3. Kruppel and Giant inhibit each other
189
in what cycle do pair-rule genes get expressed?
cycle 13
- they form at periphery by parasegments
- are expressed in 7 stripes
190
which genes activate and repress segment 2 for pair-ruled even skipped gene?
activate: bicoid, Hunchback, caadal
repress: Kruppel, giant, knurls, tailless
191
when do segment polarity genes get turned on?
-cycle 14 when all interactions must take place through cell-cell signalling to establish cell fate
192
what proteins do segment polarity genes encode?
-wnt and hedgehog signalling pathways proteins
193
what is the normal patterning of segment polarity genes in drosophila?
-one row of cells expressed wingless (drosophila wnt protein) and one row of cells expresses hedgehog in each parasegement
194
what is engrailed activated by?
- even skipped
- fushi tarazu
- paired
195
what is engrailed repressed by?
- odd-skipped
- runt
- slopped-paired proteins
196
which compartment of each parasegment does engrailed mark?
-the anterior compartment
197
where were the Hox gene first discovered in? what are they important for?
- drosophila
| - important for A-P patterning
198
what are the two complex of homeotic selector genes?
1. Antennapedia
| 2. Bithorax
199
what chromosome are homeotic selector genes on?
-3
200
what are homeotic selector genes responsible for?
-regulating development of anatomical structures (form and function)
201
what locks in place the homeotic selector gene expression?
- polycomb and thrithorax (repressive and active chromatin)
| - if these are mutated, form and function is lost
202
why does the oocyte nucleus get pushed to the anterior dorsal position and what happens when it does?
- gets pushed because of the volume of the oocyte increasing
- as it gets pushed there, gurken gets localized between oocyte nucleus and oocyte cell membrane and Gurken forms A-P gradient along dorsal surface
- this signals follicle cells to become columnar dorsal follicle cells
- this signals a cascade of gene activates that specifies the D-V axis
203
what are amniotes?
- vertebrates whose embryos form an amnion or water sac
| - includes reptiles, birds, mammals
204
what is the function of the shell in chick embryos?
-helps from drying out
205
what is the function of the chorion?
-contain blood vessels that exchange gases with outside environment
206
function of the amnion?
-fluid filled sac: protects from drying out also absorbs movement from shock
207
function of yolk sac?
- enables nutrient uptake and helps development of circulatory system
- present in chick embryo and mammal but smaller in mammals
208
what is the placenta and its function?
- organ that contains tissues and blood vessels from embryo and mother
- provides gas exchange, waste elimination. embryo can develop inside another organism
- only mammals have placentas
209
when does fertilization happen for chicks?
-occurs in oviduct before albumin and shell are secreted (before hard shell is present)
210
how long after fertilization do hens lay the egg?
-about 24 hours
211
what type of yolk do chicks have?
- telocithal (dense)
| - disc of cytoplasm, blastodisc, sits on top of yolk
212
what kind of cleavage occurs for chicks?
- discoidal mesoblastic (only portion of egg cytoplasm is used to make the embryo)
- happens in oviduct
- also for fish and reptiles
213
when does the maternal to zygotic transition occur for chicks?
- 128 cell stage (around 7-8 divisions)
| - this is earlier than drosophila (11-14 divisions)
214
what happens when cells are about 4 cells layers thick in chicks?
- they form tight junctions
- absorb water from albumin and secrete the fluid between the cells and the yolk to form the sub-germinal cavity (like a blastocoel, allows gastrulations to occur)
215
what is the area pellucida and area opaca in chicks?
- pellucida: deep cells in centre of blastoderm die and pellucida forms which forms most of actual embryo
- opaca: peripheral ring of blastoderm cells that have not shed deep cells
216
what is between the area pellucida and opaca?
-marginal zone (some of these cells are very important for determining cell fates)
217
what is the function of the chalaza (chick)?
-holds yolk in place
218
what is the function of albumin (chick)?
-stores protein
219
where does cleavage start from for chick embryo?
-blastodisc
220
what is happening in chick egg right before laying?
- the egg is 50 000 cells thick
- upper layer of area pellucida has formed epiblast
- the posterior end of the area pellucida has thickened at the marginal zone (cells are signalled to be Kollers sickle)
- posterior marginal zone is located between area opaca and Kollers sickle
- anterior region of epiblast stay attached to form hypoblast islands - 5-20 cells migrate and become primary hypoblast
- the primary hypoblast combine with anteriorly migrating cells to form complete hypoblast layer (secondary hypoblast)
221
what happens when cold temperatures affect primary hypoblast formation?
-increased chance of two primitive streaks forming (twins)
222
what do primary hypoblast cells become?
-extra-embryonic membranes (include yolk sac and stalk (links yolk to endodermal digestive tube))
223
what happens 12-14 hours after the egg is laid?
- primitive streak first arises from Koller's sickle and epiblast above it, extending posterior to anterior
- primitive groove is formed by cells converging, creating a depression
- hensons node is produced by cells thinking at the anterior end (the lead of the primitive streak)
- cells start moving through Hensons node to ventral side
- epiblast cells remain on outside to close the streak and form the dorsal structures (closest to streak) and epidermis (farther from streak)
224
depending on where and when they enter Hensons node, what do the migrating cells become?
- first through becomes pharyngeal endoderm of fore gut; that migrate anteriorly and displace hypoblast cells
- cells that enter the anterior end give rise to prechoral mesoderm, notochord, and medial part of somites
- cells that enter the middle become maternal part of somites, heart, and kidneys
- cells that enter posterior end become lateral plate and extra embryonic mesoderm
225
when does gastrulation occur in the chick embryo?
-after the egg is laid
226
when does the primitive streak start forming and when does it begin regression?
- forms at 12-14 hours after being laid
- regresses at 23-25 hours
- at 27 hours there is presence of somites
227
what are the events occurring during gastrulation in the chick embryo?
the primitive streak elongates:
- cells that enter undergo E-M transition and the basal lamina beneath them breaks down so that the cells have room to migrate where they need to in the blastocoel
- streak elongates towards future head region (convergent extension, gets narrower)
- secondary hypoblast cells migrate anteriorly from posterior marginal zone with the primitive streak (hypoblast directs streak movement)
- the streak eventually extends 60-75% of the area pellucida before receding
228
how is the endoderm and mesoderm formed in early chick development?
-established before gastrulation but is controlled by inductive signals as cell migrate through primitive streak
229
what is the Hensons node focus, what do the cells that migrate through the primitive streak in this area become?
endoderm, head mesoderm, notochord
230
what does the germinal crescent that's formed during gastrulation contain?
- located anteriorly
| - contains precursors for germ cells that will migrate though blood vessels to the gonads
231
as the primitive streak is forming, what triggers cell mirgration?
-FGFs from hypoblast activate Wnt planar polarity pathway in epiblast to begin cell migration around streak and in through it
232
what are the signals being produced as cells migrate through primitive streak? (when streak is moving from P-A)
- fgf8: expressed in the streak, repels migrating cells away from it
- Wnt5a (anterior): opposed by Wnt3a which inhibits migration and cells form paraxial mesoderm
- Wnt5a (posterior): directs cells to migrate broadly and become lateral plate mesoderm
233
what molecular mechanisms are occurring when the primitive streak is regressing?
- mesodermal ingression continues
- hensons node moves closer to the centre of the area pellucida to more posterior position leaving notochord formation in head-tail direction (as Hensons node regresses, notochord increases)
- the pharyngeal endoderm and head mesoderm induce anterior parts of the brain and notochord to induce hindbrain and spinal cord
234
what molecular mechanisms are happening during epiboly of the ectoderm?
- ectodermal precursors proliferate and migrate along underside of vitelline envelope to surround the yolk sac
- only outer cells of area opaca attach firmly to vitelline envelope (filopodia binds to fibronectin and helps marginal cells pull ectodermal cells around yolk)
235
what forms axis specification in chick embryos?
- gravity (radial symmetry to bilateral symmetry)
- egg gets rotated for 20 hours at 15 revolutions per hour in hens reproductive tract
- the lighter components lie beneath one side of blastoderm (becomes posterior marginal zone where primitive streak formation begins)
- posterior marginal zone controls the other regions of margin and initials gastrulation and prevents other regions of margin from forming their own primitive streak
236
what are the specific signals involved in axis specification that begins during cleavage?
- the entire marginal zone is producing Wnt8c that can induce Beta catenin, and cells are secreting Vg1
- the wnt8c and Vg1 work together to induce nodal expression in future epiblast (next to Kollers sickle and PMZ)
- nodal is needed to intimate primitive streak and secretion of cerebrum (inhibitor of nodal) by the primary hypoblast prevents primary streak formation in other areas
- after the streak is formed, it produces lefty which is an nodal inhibitor too and prevents further streak formation
- the hypoblasts that secrete Cerberus are pushed anteriorly to ensure neural cells become forebrain
237
what cells form ectoderm in the chick?
- initial neural plate becomes future head and forebrain- ear vesicle (induced by hypoblast)
- small region lateral and anterior to Hensons node become hindbrain- spinal cord (induced by notochord)
238
what determines anterior to posterior patterning in the chick?
- cells receive signal while they are in epiblast for where they are along to A-P axis
- specified as a function of time of emergence from primitive streak and Hensons node
- depending on how long cells were in the primitive streak determines which Hox genes are expressed (and FGF snf RA gradients)
239
what keeps cells undifferentiated and what induced differentiation?
FGF: keeps cells undifferentiated as cell regress
| Retinoic acid: induced differentiation as cells leave Hensons node
240
what are Hox genes important for?
- A-P patterning
| - form and function of cells
241
how is retinoic acid produced to induce differentiation?
-fgft8 promotes wnt8c which helps retinoic acid production
242
what signals regulate axis extension in chicks?
- Raldh2/RARbeta
- Ffg8
- Shh
243
how many gene clusters do vertebrates have for Hox genes?
4: a, b, c, and d
244
when does Hox gene expression occur?
-before gastrulation
245
what signals regulate left-right axis formation in chicks?
-left-sided expression of nodal and pitx2
-activin signalling and BMP4 block expression of Shh and activate fgf8 on the right side (this ends up blocking Cerberus)
transcription of Shh is resricted to left side
-Shh activates Cerberus and with BMP this stimulates Nodal expression
-nodal activates pitx2 and represses snail
-lefty1 in ventral midline prevents Cerberus from crossing to right side
246
what are trophoblast cells and what do they become (mammals)?
-outermorula, becomes placenta
247
when does egg finish meiosis in mammals?
-fertilization
248
when is first cleavage for mammals?
-about 1 day post fertilization
249
what type of cleavage occurs in mammals?
-meridional
250
how long is between each cleavage in mammals?
- 12 to 24 hours (drosophila is every 8 mins, chick was laid in 24 hours)
- very slow compared to others
251
what happens during the second cleavage for mammals?
-one cell division is meridionally and the other is equatorially (causes rotational cleavage)
252
when are zygotic genes being used in humans?
- at 8 cell stage (faster than drosophila)
| - gamete specific DNA methylation is removed (except in imprinted genes), new DNA methylation occurs
253
when are is the genome of mammals pluripotent instead of totipotent?
- at 16-cell stage
| - because some cells become inner cell mass (embryo) and others become trophoblasts cells (extra embryonic tissue)
254
when does compaction occur in mammals?
between 8-cell stage and 16-cell stage
255
what signals help cells become pluripotent again?
yamanaka factors: oct4 and sox2
| -also nanog (pioneer TF that can break compact DNA to revert cells back to pluripotent cells)
256
how do cells know to become trophoblast or inner cells mass?
- know by 8-cell stage
- both are producing cdx2 and oct4 (reciprocally inhibit each other) but trophoblast is producing just cdx2 eventually
- in trophoblast cells its thought that something inhibits Hippo which then can't activate lats, this causes yap to enter the nucleus activating tead4 and allow more cdx2 expression
- in inner cell mass cells, hippo activates lats which phosphorylates yap so it can't activate tead4 no cdx2 expression occurs
257
what is compaction?
- E cadherin is expressed which is stabilized by tight junctions on outside of cells and gap junctions between inside cells
- this is when outer cells become trophoblast and inner cells become inner cell mass
258
how is the blastocoel created?
- trophoblast cells secrete fluid into morula to create blastocoel (oviduct signals this to occur)
- water is drawn in because of Na+-K+ ATPase and Na+H+ exchanger
259
what is formed after the 16-cell morula?
-the blastocyst
260
what happens if embryo escapes from zona pellucida escapes from egg too early?
-eptopic or tubopregnancy can occur (egg is implanted in Fallopian tubes instead of uterus)
261
how is the small hole created from the blastocyst to hatch from?
-trypsin-like protease that secreted from trophoblast cells
262
after the blastocyst hatches from the zona pellucida, what does it adhere to?
- endometrium (epthelial lining of uterus)
- makes a ECM to catch the blastocyst (Controlled by estrogen and progesterone)
- composed of sugars, collagen, laminin, fibronectin, cadherins, hyaluronic acid, and her-area sulphate receptors (if any of these are missing, blastocyst won't be caught)
263
what happens right after initial binding of blastocyst?
- trophoblast cells synthesize integrins which is important to attach embryo to uterus
- P cadherins on trophoblast and endometrium also help dock embryo to uterus
264
how does the blastocyst burry itself into the uterine wall?
wnt proteins from trophoblast and endometrium cause trophoblast to secrete proteases that digest ECM
265
when do 1/3 of twins occurs during development?
- before day 5, before implantation
| - each embryo will have own chorion and amnion
266
when do 2/3 of twins occur during development?
- before day 9, after day 5
- after implantation
- each have own amnion but share a chorion
267
what happens if twins occur after 9th day of development?
-they share a chorion and amnion
268
what would happen if a chick epiblast was divided into 4 parts?
- four primitive streaks would form
| - could be reason for conjoined twins
269
what are the two layers of the inner cell mass?
1. upper layer (epiblast) forms embryo and amnion
2. lower layer (primitive endoderm) like chick hypoblasts (form yolk sac, important for positioning during gastrulation and helps movement of epiblast)
- together they form bilaminar germ disc structure
270
when cells enter inner cell mass from 8-16 cell stage, what do they express?
- nanog at stage 32, lower levels of FGF
| - form upper layer
271
when cells enter inner mass from 16-32 cell stage, what do they express?
- Gata6, higher levels of FGF
| - form lower layer
272
what does the primitive endoderm become?
- expands to line blastocoel cavity (giving rise to yolk sac) forms parietal endoderm
- when its contacting epiblast its visceral endoderm
273
what happens to start gastrulation in mammals?
- epiblast layer splits to separate embryonic epiblast from epiblast that forms amnion
- after this occurs, amniotic cavity fills with fluid and gastrulation can begin
274
where does gastrulation begin and what is happening during it?
- begins at posterior end and nose cells arise
- mesoderm and endoderm originate in epiblast, undergo E-M transition, lose E cadherin, migrate through primitive streak as individual cells
- node cells give rise to notochord (become integrated into endoderm, converge medially and bud off in dorsal direction from roof of gut at day 16)
- fgf8 expressed in primitive streak
275
what signals direct mesodermal migration, specification, and patterning?
- snail
- brachyury
- tbx5
276
what are the two signalling centres that for the A-P axis in mammals?
1. node organizer: posterior (most of body)
| 2. anterior visceral endoderm: conjunction with node for anterior patterning and streak prevention
277
how is node organizer formed?
- trophoblast-derived BMP4 expressing extra embryonic ectoderm induced wnt3a and nodal in epiblast
- wnt3a activates brachyury in posterior cells
278
what does the node organizer do?
-secretes chordin (head process and notochord will later add noggin (a BMP antagonist))
279
what does the anterior visceral endoderm do?
- prevents wnt3a and nodal from having an effect on anterior side of embryo
- does this by secreting lefty-1 and cereberus
280
what signals are present anteriorly in the head region of developing mammal embryos?
-lefty and cerberus
281
what signals are present posteriorly in the developing mammal embryo?
-nodal, BMPs, FGFs, and wnts
282
how many genes are present in how genes
- 13
| - not all are present in every box gene though
283
how can you alter expression of Hox genes?
- knockout (gene targeting)
- they respond by having receptor sites in enhancers or by responding to cdx (activated by retinoic acid) so if you shift RA gradient, hox genes expression can be shifted
284
how are hox genes comparative?
the constellation of Hox gene expression predicts type of vertebrate formed
285
how do ciliary cells of node start the left-right axis?
- clilia cause fluid to flow right to left
- crown cells beside the node sense flow through their immobile cilia and activate pkd2 that inhibits Cerberus synthesis and activates nodal
- nodal binds in autocrine manner and activates pitx2 while maintaining own transcription
left: nodal and pitx2
right: cerberus (nodal inhibitor)
