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ANAT 381 > Ryan Lecture 2 > Flashcards

Ryan Lecture 2 Flashcards

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1
Q

Fertilized egg —>

A

Blastula —> gastrula

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2
Q

What happens after fertilization - blastula formation

A

Cleavage occurs in almost all species
Extremely rapid mitotic divisions
Divides zygotic cytoplasm into numerous smaller cells = blastomeres
No increase in cytoplasmic vol

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3
Q

What is mid blastula transition

A

Slow down in rate of mitosis
All proteins/mRNA used = from oocyte/sperm
Onset of zygotic transcription - exception is mammals

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4
Q

When is blastula formed

A

End of cleavage
Variety of types = blastula, blastodisc, blastocyst (depends on Shape but all the same)

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5
Q

Describe xenopus blastula

A

Ectodermal = animal cap
Blastocoel = vegetal cap
Mesoderm, endoderm

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6
Q

Describe mouse blastula

A

Te = extraembryonic
Icm = embryo proper
Blastocoel = large, filled with fluid

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7
Q

Describe human (rabbit, chick) blastula

A

Flat blastodisc
Cavity becomes fluid filled
Epiblast = embryo
Hypoblast
Replaced by future cells of embryos, flat layered of cells

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8
Q

How many cells does human blastodisc/blastocyst have

A

70-100cells

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9
Q

When does human blastodisc formation begin

A

~5 days post fert

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10
Q

Describe early embryogenesis in drosophila- gen

A

Syncytial blastoderm - mitosis w/o cytokinesis
One nucleus, initial yolks cytoplasm (30 mins) —> 70 mins

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11
Q

Describe early embryogenesis in drosophila - first important thing

A

Nuclei move to periphery during 10th mitosis division
Cells surround yolks mass in early drosophila embryo

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12
Q

Describe early embryogenesis in drosophila - second important thing

A

After 13th division
Cell membranes form to create cellular blastoderm = single layer of cells around a yolky core
Mitotic divisions =synchronized, no longer at mid blastula transition, size of embryo stays the same
Dorsal, ventral and ant and post = many Nuclei important

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13
Q

Describe early embryogenesis in drosophila - third important thing

A

Cycle 14= mid blastula transition, zygotic transcription and asynchronous divisions, gastrulation begins
Cellularization = compartmentalize nucleus to single cell

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14
Q

Describe single cell to blastula In xenopus - gen

A

Fertilized egg —multiple rounds cell Division—> blastula, hollow sphere of cells (blastocoel)

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15
Q

Describe single cell to blastula In xenopus - features

A

Animal cap gives rise to embryo proper
Localization of proteins even at one cell stage
Important info that affects dev of cells, and axis of embryo

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16
Q

Describe single cell to blastula In zebrafish

A

Cleavage and blastoderm formation
Single cell - zygote to 512 cell, - now cell not that much bigger than single cell embryo

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17
Q

Describe single cell to blastula In mouse - gen

A

Totipotent stage =egg—>rotational cleavage—>4 cell stage —> morula
Pluripotent stage = compacted morula (tight junctions) —> blastocyst (te-extraembryonic, icm=embryonic relatively small compared to blastocoel cavity)

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18
Q

What is truly the most important time in your life

A

It is not birth, marriage, or death, but gastrulation

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19
Q

What is gastrulation

A

Series of cell movements and migration involving entire embryo
Extensive cell movements that establish final spatial relationship of the 3 germ layers = ectoderm, mesoderm, endoderm (also sometimes 4th=neural crest cells)
Species specific differences in pattern of gastrulation but only a few basic types movements

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20
Q

Describe the germ layers - gastrulation generally

A

Cells that wil form endoderm and mesoderm are brought to inside - MOUSE EXCEPTION
Ectoderm (skin and nervous system, surface and neuro ectoderm) spread over outside surface

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21
Q

Describe intercalaton - gastrulation cell movements

A

Rows of cells move between one another, creating an array of cells that is longer, in one or more directions (or another shape of cell)
Like zipper merge

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22
Q

Describe convergent extension - gastrulation cell movements

A

Cells intercalate in highly directional manner
Causes embryo to elongate
Lateral —> midline side in embryo
Longer, more directional group of cells
Correlated with planar cell polarity, now which direction is ant and post and where neighbours are

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23
Q

What does convergent extension depend on

A

Non canonical want/pcp (planar cell polarity) pathway

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24
Q

Describe model showing convergent extension

A

Bead model
Move in and spread out
Cluster of cells more likely to stick togetehr

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25
Describe convergent extension in an Embryo
Happens during time of lots of mitosis Dorsal side,rod like structure formed Ball of cells = somites Movement to middle gives embryo shape and structure
26
Describe invagination - gastrulation cell movements
Sheet of cells (epthelial sheet) bends inwards Apically constrict, on one side Get narrow and move into liumen = gives pop of cells = mesoderm or endoderm Depends when they move in
27
Describe gastrulation in drosophila
Same outcome - 3 germ layers Slightly diff process- happens through invagination
28
Describe gastrulation in drosophila - mesoderm
Derived from 1000 cells at Ventral midline that fold inwards to form ventral furrow
29
Describe gastrulation in drosophila - endoderm
Invaginates as 2 pockets at anterior and posterior ends of ventral furrow
30
Describe stage 4 drosophila embryo
Syncytial stage Just before cellularization
31
Describe gastrulation in drosophila - invagination
Ventral view Becomes mesoderm 2 pockets at ends = endoderm, ant and post Overlying ectoderm will close up around
32
Describe invagination during drosophila gastrulation
Endoderm = more triangular in shape
33
Describe involution - gastrulation cell movements
Partially important in xenopus Process by which an epithelial sheet rolls inwards to form an underlying layer Dorsal lip of blastopore - cells involute, and move along surface of embryo, in opp dir
34
What is required for involution
Initial turn requires apical constriction Dorsal leading edge - head-mesoderm = push in against cells that become later ectoderm = happens In dorsal blastopore lip Bottle cells = change shape as involution happens
35
Describe process of involution - needed steps
Movement of nuclei - to basal side helps change shape - and apical actomyosin complex undergoes contraction to buckle epithelium- constriction, like hoodie
36
Describe amphibian gastrulation
Involution Blastula —> gastrula —> neurula Neurula = only future ectoderm on surface = surface ectoderm, neural plate ectoderm Cells involute at dorsal blastopore lip
37
Describe xenopus cell movements during gastrulation - dorsal view of gastrulation
Cells move Cells left on surface = forms start of neural tube and other cells will be the surface ectoderm
38
Describe xenopus cell movements during gastrulation - vegetal view of involuting cells
Surface ectoderm eventually covers neural tube - 15h elapsed time
39
Describe xenopus cell movements during gastrulation - internal view of gastrulation
See movement and involution - as come through dorsal lip of blastopore and move up and around that surface
40
Describe epiboly - gastrulation cell movements
Process in which a sheet of cells spreads by thinning movements of cells over another later of cells Cells change shape Especially important in zebra fish Cell movement - by thinning Can see in early xenopus
41
What does epiboly do in zebrafish
Movement important = over surface of yolk - brings yolk yo indifferent of embryo so can nourish embryo
42
Describe epiboly of zebrafish over time
30% epiboly, 4hr, embryo spreads over surface = c shape, epiboly cells gradually move down surface —> 75% epiboly, 7.55 hr —> 90% epiboly, 9hrs = stage embryo by how much these cells have moved down 1cell—>100% epiboly, as epiboly movement = cells contribute to grow on surface
43
Describe ingression - gastrulation cell movements
Individual cells leave epithelial sheet and become freely migrating mesenchyme Similar to epithelial to mesenchymal transition In most blastodisc shaped embryos = humans, rabbits, chicken and mouse, but mouse do not form blastodisc at this point Fall out and migrate down - but lose connections with neighbours = lose cell cell tight junctions
44
Describe EMT (epithelial to mesenchymal transition) - stage 1
Initially = attached to neighbour via cell attachments = Epithelial cell layer, epiblast = junctions complexes intact (tj, adherens, gap junctions) Basement membrane intact
45
Describe EMT (epithelial to mesenchymal transition) - stage 2
Junctional complexes begin to breakdown Induced
46
Describe EMT (epithelial to mesenchymal transition) - stage 3
Junctional complexes break down Basement membrane breaks down Ingresssing cell takes on mesenchymal phenotype - so cell can slip down
47
Describe EMT (epithelial to mesenchymal transition) - stage 4
Cells leaves epithelial layer of epiblast Becomes mesenchymal Will contribute to mesoderm or endoderm Migrate out, cells that remain in epithelial layer = become ectoderm
48
Are all germ layers mesenchymal
NOOOOO Any germ layer can be epithelial and any germ layer can be mesenchymal = refers to cell state
49
Describe gastrulation in Chick embryos - ingression
Cells that fall out and moves towards midline embryo = primitive groove Once cells reach primitive groove= eat go and they migrate into place Result =ectoderm, mesoderm, endoderm
50
Name important parts of chick embryo
Hesens node Primitive groove Epiblast Blastocoel Hypoblast Migrating mesenchyme = will contribute to lateral plate mesoderm
51
Describe gastrulation movements in chick embryos - formation of primitive streak, dorsal view
Formed post to ant
52
Describe gastrulation movements in chick embryos -dorsal view
Cells stained with red dye Get there and u turn = mostly on one side Left and right patterning very early and carry info with them as they go forwards
53
How do human embryos gastrulate - describe
Flat blastodiscs - most similar to chick and rabbit embryos 3rd week post fert ~14 days —> 21 days, now have definite germ layers
54
Describe gastrulation in mouse
NOT FLAT Blastocyst Icm forms structure - embryo proper Endoderm and mesoderm come to outside of embryo - day 6.5 Different tho
55
What is most mammalian embryos gastrulation similar to
Birds/reptiles
56
Describe mouse and human - single cell thru gastrulation
Blastocyst stages similar, humans = more blastodisc shape Early gastrula = diff Late gastrula = MOUSE (tail end swings around and lateral parts ectoderm start to encompass embryo) HUMAN (tissues enclose yolk sac)
57
What is at the end of gastrulation
3 germ layers Tissues gain memory as go through all this Germ layers = also patterned with respect to d-v and a-p axes
58
Describe ectoderm
Outer cell layer Epidermis, neural tissue, placodes (optic, optic, olfactory, hypophyseal)
59
Describe mesoderm
Middle cell layer Demis, muscle, bone, kidney, gonads
60
Describe endoderm
Inner cell layer Epithelial lining of gut, lung, liver, pancreas
61
Describe 4th germ layer
Neural crest cells Arise at boundary of neural and non neural ectoderm during neural tube closure - after gastrulation has happened Cells in peripheral and enteric nervous systems, muscle, craniofacial bones and cartilage, melanocytes, VERY DIVERSE
62
DESCRIbe neural crest cells and their derivatives
What is left after gastrulation = neural plate border Will give rise to neural tube, brain and spinal cord - MEDIAL Gives rise to surface ectoderm = LATERALLY Cells migrate away = epi to mesenchymal transition, and migrates to diff parts of body as neural tube closes
63
How do neural crest cells become what they do
Migratory path= where they end up determines what they become From from ectodermal region originally Smooth muscle cells, osteoblasts, osteoclasts, adipocytes, chondrocytes, melanocytes, Schwann cells, neurons Bones in head = diencephalic Heart and components, vasculature and neurons in brain
64
What is an organizer
Group of cells capable of organizing neighbouring cells Provide important info to surrounding cells
65
What can organizer do
Can induce ectopic cell fates in host tissue following heterotopic transplantation Important for endogenous structures but can also re pattern cells that are competent in other regions
66
Describe Hilde mangold
Student, cut and paste experiment in amphibian embryos Not awarded cause dead
67
Describe hilde mangolds experiment
Take pieces of early blastula embryo and transplant them into other parts Normal = primary endogenous axis, neural tube, notochord, sortie and ganglia form Then she used tissue derived from transplanted dorsal blastopore lip = no pigment and could induce whole other axis, regions of embryo can induce axis Secondary induced axis = new tissues, can tell since og structures pigmented
68
What did hilde conclude basically
Dorsal blastopore lip = region where cells would pass by during gastrulation and get info Transplantation of dorsal blastopore lip induces a secondary axis
69
Is it a fate mapping exp - hilde
It didn’t become something else but it did induce other cells to
70
Does this tell you about the potential of dorsal blastopore lip - hilde mangold
Inducing tissue Then what will target become, or what will it induce = WHAT IS POTENTIAL OF TISSUE WE ARE TRANSPLANTING OR WHAT IS POTENTIAL OF IT TO INDUCE SOMETHING ELSE
71
WHAT Happens when transplant embryonic shield of zebrafish
Embryonic shield = specialized region embryo In sit exp - looking at shh = gives 2 diff embryos - similar effect of hilde exp
72
What happens when transplant hensens node from chick embryos
Hensens node = ant end primitive streak Can induce another embryo to dev Can also induce a regionally structured a-p neural axis Leads to = tissues from host being induced to start new ap structure Spinal cord - donor Forebrain Forebrain Spinal cord - host
73
What is spemann mangold organizer
In amphibians Sets up v early = at blastocyst stage At dorsal blastopore lip
74
Describe molecules required for induction of spemann mangold organizer
B cate + VegT, Vg1 (both needed to form organizer)—> nodal related high —> organizer VegT, Vg1 —> nodal related low —> ventral mesoderm (lower nodal signal)
75
Describe molecular signals required for patterning germ layers - ventral centre
Bmp4, bmp7 (Cv2, sizzled, Bambi, xlr, tsg)
76
Describe molecular signals required for patterning germ layers - spemann mangold organizer
Antagonists inhibit activity fo signalling molecules, dampens signal at that place Chordin, noggin, follistatin, frzb1, sfrp2, crescent, dickkopf-1, cerberus
77
Describe the mutiple cell signalling inhibitors the organizer produces
Frzb1, dickkopf-1, crescent = inhibit wnts Cerberus = inhibits xwnt-8, xnrs , bmps (Nodal related) Chordin, noggin, follistatin = inhibit bmps Inhibits of pathway = v imrpoatnt in organizers themselves
78
Name the major axes in early embryo - 3
Dorsal - ventral, back to front Anterior - posterior, top to bottom Left - right (int vs ext human body = look symmetrical but not inside)
79
What is an axis
Axis usually defines a direction or orientation Asymmetrical - may be initially symmetrical
80
Name additional axes in older embryos
Proximal -distal = close to far
81
How does asymmetry - polarity happen
Unfertilized egg = single cell, usually radially symmetrical Initial divisions after fert can generate functionally equivalent daughter cells (Autonomous specification exception, bc first division asymmetric Eventually cells must become different
82
Name the 2 ways cells can become different - cell divisions
Asymmetric cell division = localization of cytoplasmic determinants followed by asymmetric cell division = recall, spindle parallel to determination gradient Asymmetric patterning through inductive signals = cell cell signalling within fields of identical cells (closer = more signal info) or across boundaries (groups of cells that can stick together)
83
Describe dorsal ventral axis in mammals
Forms from icm cells that are in contact with trophoblast Icm = tells that undergo gastrulation Dorsal axis, do not know much about it overall, but do know it form individual organs and spinal cord
84
Describe d-v axis in chick - gen
Formation depends on pH Occurs at blastodisc stage
85
Describe d-v axis in chick - specificallly
Water and sodium ions transported from basic albumen (egg white above blastodisc) = basic through cells to acidic sub germinal cavity below in Hypoblast area Creates a membrane potential diff Side facing albumen becomes dorsal Side facing yolk becomes ventral - got cells RESULTS= in endodermal/future gut next to yolk, food source
86
Where is d-v axis initiated in drosophila
Syncytial blastoderm = before cellularization in single cell
87
Describe d-v axis formation in drosophila - gen protein
Depends on tf dorsal Dorsal = product if maternal effect gene = mRNA deposited in egg from female/mom - around from beginning
88
Describe d-v axis in drosophila-specifics
Dorsal initially found throughout syncytial blastoderm -so present throughout cytoplasm Dorsal protein comes nuclear only on future ventral side of embryo, dorsal regulates ventral phenotypes
89
How are many proteins named in drosophila
Based on phenotype caused when gene mutated When dorsal mutated = causes dorsal phenotype
90
What happens of absence of dorsal - in drosophila
Or if dorsal doesn’t enter nucleus = embryo becomes dorsalized Has 2 dorsal sides of Emrbyo
91
What happens if dorsal enters all the nuclei in drosophila
Embryo becomes centralized 2 ventral sides
92
Describe dorsal entering nucleus
Dorsal triggered to enter nuclei in regions of embryo where spatzle ligand binds its receptor (toll) Ligand present in ventral superficial surface (only on ventral side) = binds to receptors on surface of future cells Toll activation = Triggers another series of events = casues dorsal enter nucleus
93
Describe Nobel prize 1995 discovery
If mutate toll = no ventral phenotype
94
When does d-v axis patterning start for all species - name
At blastula stage in mouse At blastoderm stage in chick At blastoderm stage in drosophila At fertilization in xenopus

ANAT 381 (24 decks)

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