Final Flashcards
(309 cards)
1
Q
What is the phylotypic stage?
A
The stage after gastrulation and formation of the neural tube, where vertebrate embryos pass through a stage where they all look similar
2
Q
What features are present on embryos in the phylotypic stage?
A
All embryos have developed a body with a neural tube, somites, a notochord and a head
3
Q
What does the animal pole consist of?
A
Small cells that divide rapidly
4
Q
What does the vegetal pole consist of?
A
Large yolky cells that divide very slowly
5
Q
When does the development of the animal-vegetal axis occur?
A
Prior to fertilization
6
Q
Where does the sperm enter the egg? (xenopus)
A
Anywhere in the animal hemisphere
7
Q
What defines the dorso-ventral axis in the xenopus?
A
The point of sperm entry. The cells opposite the region of sperm entry eventually form the dorsal portion of the body.
8
Q
What type of eggs are xenopus eggs?
A
Mesolethical
9
Q
Where are maternally-supplied mRNAs localized in the xenopus egg?
A
Localized along the animal-vegetal axis during the development of the egg and many end up in the vegetal region
10
Q
What happens when sperm enters a xenopus egg?
A
Cortical cytoplasm at the edge of the egg cell rotates 30 degrees towards site of sperm entry
11
Q
What does rotation of the egg cytoplasm do in the xenopus zygote?
A
Rotation exposes a wedge of the grey cytoplasm underneath, sometimes producing a visible zone of lighter colour called the grey crescent
12
Q
What does the grey crescent correspond to? (xenopus)
A
Corresponds to future dorsal side of embryo
13
Q
What does inhibition of cortical rotation lead to? (xenopus)
A
Loss of dorsal structures
14
Q
What happens when you impose a second cortical rotation? (xenopus)
A
Leads to conjoined twin formation
15
Q
What happens when you separate a 2-celled embryo along the plane of cleavage so that each have of the embryo gets half of the grey crescent? (xenopus)
A
Each half develops normally and forms a normal embryo
16
Q
What happens if a 4-celled embryo is split so that one have gets the dorsal region and the other does not? (xenopus)
A
- ventral half develops into a ventralized embryo
- dorsal half develops most of the structures of the embryo but lacks the gut (which develops from ventral blastomeres)
17
Q
In what cell stage are the dorsal and ventral regions established in an embryo? (xenopus)
A
4-cell stage
18
Q
What type of cleavage occurs in the xenopus?
A
- displaced radial
- holoblastic
19
Q
Where does the blastocoel form in the xenopus blastula?
A
In the animal hemisphere above the larger yolk cells
20
Q
Where are the ectodermal cells located in the xenopus blastula and what do they form?
A
- located in the animal pole
- forms epidermis of skin and the nervous system
21
Q
Where are the endodermal cells located in the xenopus blastula and what do they form?
A
- located in the vegetal pole
- forms the gut and lungs
22
Q
Where are the mesodermal cells located in the xenopus blastula and what do they form?
A
- located in the marginal zone in the vegetal pole
- form dermis of skin, notochord, heart, kidneys, bone, gonads and blood
23
Q
Where does xenopus gastrulation begin?
A
On future dorsal side of the embryo ~180 degrees of point of sperm entry
24
Q
What is the first thing to occur in xenopus gastrulation?
A
Invagination of endodermal cells on dorsal side creates the blastopore
25
What is the second thing to occur in xenopus gastrulation?
Involution of endodermal cells at the site of the future blastopore
26
What is the archenteron? (xenopus)
The precursor of the gut
27
What is the result of the involution of endodermal cells in xenopus blastula?
- acrchenteron forms
| - blastocoel is desplaced to side opposite the blastopore lip
28
Are frogs deuterostomes or protostomes?
- deuterostomes
29
What also occurs during the involution of cells? (xenopus)
- the ectoderm undergoes epiboly by spreading downwards and eventually covers the whole embryo
30
What is convergent extension? (xenopus)
The process that drives the movement of cells underneath the ectoderm
31
What is a yolk plug? (xenopus)
A patch of large endodermal cells which remain exposed on vegetal surface of blastula that will eventually be internalized by epiboly
32
What occurs as xenopus gastrualtion continues?
- the archenteron becomes larger and displaces the blastocoel
- the blastocoel diminishes
- embryo becomes surrounded by ectoderm
- endoderm is internalized, and mesoderm is positioned between ectoderm and endoderm
33
What is the Spemann-Mangold organizer?
- embryonic organizer
| - found on the dorsal blastopore lip
34
What are the 2 key roles of the spemann-mangold organizer?
- to specify dorsal fate
| - to make nearby ectoderm turn into neural tissue
35
What happens when the spemann-mangold organizer is transplanted to the opposite side of an embryo?
- the graft induces the formation of a new body axis with a neural tube and somites
- transplanted cells induce the formation of a second embryo
36
What happens when the spemann-mangold organizer is grafted midway through gastrulation?
- leads to the induction of secondary heads
37
What happens when the spemann-mangold organizer is grafted late in gastrulation?
- leads to the induction of secondary tails
38
What are involved in controlling D/V effects in the xenopus?
Maternal proteins located in the vegetal cortical cytoplasm
39
What happens to dorsalizing factors after cortical rotation? (xenopus)
They are relocated from their initial position at the vegetal pole to a position opposite the site of sperm entry
40
What are two examples of dorsalizing factors that are relocated to the dorsal side after cortical rotation? (xenopus)
- Wnt mRNA
| - Dishevelled
41
What do dorsalizing factors do when present in cells? (xenopus)
They activate Wnt signaling pathway which allows the protein beta-catenin to enter nuclei and turn on expression of genes needed for dorsalization in cels
42
What happens in the absence of the Wnt signal? (xenopus)
- Beta-catenin is bound by a destruction complex of protiens in the cytoplasm
- this destruction complex phosphorylates beta-catenin and targets it for ubiquitination and degradation
43
How the activation of the Wnt signaling pathway begin? (xenopus)
With Wnt binding to cell surface receptor (Frizzled)
44
How is the signal that Wnt has bound transmit across the membrane? (xenopus)
- frizzled
| - an associated co-receptor called Arrow
45
What does the activation of signals in the wnt pathway cause? (xenopus)
Causes the same protein kinases that phosphorylated beta-catenin in the destruction complex to now become associated with the membrane and phosphorylate arrow
46
What proteins are recruited to arrow and frizzled at the membrane? (xenopus)
- the intracellulare signaling protein dishevelled
| - the protein axin
47
What does beta-catenin do in the nucleus?
binds to t-cell transcription factor (TCF) to displace the co-repressors, and enables target genes to be expressed
48
What happens if the Wnt signaling pathway is activated everywhere in the embryo? (xenopus)
Results in hyper-doralized embryos
49
What does lithium do in the wnt signaling pathway? (xenopus)
Lithium is know to block GSK-3 and lithium treatment promotes formation of dorsal and anterior structures at expense of ventral and posterior structures
50
What allows a ventralized embryo to be rescues? (xenopus)
- injection of RNA extracts from hyperdorsalized embryo into the ventralized embryo
- injection of beta-catenin in ventral vegetal cells
51
What is the Nieuwkoop center?
- induces the spemann-mangold organizer
52
When does the Nieuwkoop center arise?
In early blastula stage
53
How does the Nieuwkoop center aris?
by the action of beta-catenin and other maternal factors on the dorsal side of the vegetal region leads to the formation of this signaling center
54
How does the mesoderm form in the marginal zone? (xenopus)
As a result of inductive signals released by vegetal blastomeres
55
What do low levels of nodal proteins give rise to? (xenopus)
Ventral mesoderm
56
What do high levels of nodal protein give rise to? (xenopus)
The spemann-Mangold organizer (as part of the dorsal mesoderm)
57
What happens to embryos that are depleted of the maternal VegT mRNA? (xenopus)
They do not form an endoderm
58
What happens when a blastula is split and one half lacks the Nieuwkoop center? (xenopus)
Develops an abnormal embryo lacking all dorsal and anterior structures
59
What happens when a blastula is split and the dorsal half contains the signaling center? (xenopus)
Develops most of the structures of the embryo but lacks the gut, which develops from ventral blastomeres
60
What is goosecoid?
a transcription factor that can activate genes whose proteins are responsible for the organizer's activities
61
What happens during organogenesis? (xenopus)
Specialized cells such as muscle, cartilage and neurons differentiate
62
What are the steps associated in neurulation?
- edge of neural plate forms neural folds which rise towards midline
- the folds fuse to form neural tube
- the neural tube sinks below epidermis
63
What do neural crest cells become?
- sensory and autonomic nervous systems
- skull
- pigment cells
- cartilage
64
What does the anterior neural tube become? (xenopus)
The brain
65
What does the mid and posterior neural tube become? (xenopus)
the spinal cord
66
What does organogenesis result in? (xenopus)(which stage)
Tailbud embryo stage
67
Where is the egg fertilized in the mammal?
In the ampulla region of the oviduct
68
Why is it difficult to study embryonic development in mammals?
- eggs are very small
- zygotes are not produced in large numbers
- development occurs inside the mother rather than in the external environment
69
Why is the mouse an important model organism?
- it has a short life cycle (for a mammal)
- the mouse genome has been sequenced
- specific genes can be mutated or removed (both forward and reverse genetic approaches can be taken to study the roles of genes on developmental processes)
70
What type of cleavage to mammals have?
rotational holoblastic
71
What is a major difference in mammalian cleavage?
- mammalian blastomeres do not all divide at the same time
72
What is compaction?
- after the 3rd cleavage, blastomeres "huddle" together
- contact between blastomeres is maximized
- compacted cells are sealed together by tight junction between the outside cells of the sphere
- cells within the sphere form gab junction (allowing molecules and ions to pass between them)
73
When does compaction occur? (mammal)
- at the 8-celled stage
74
What does compaction result in? (mammal)
- the formation of a solid ball of cells called the morula
75
What is the chorion? (mammal)
- the embryonic portion of the placenta
76
Where is the inner cell mass attached at the blastocyst stage? (mammal)
- attached to epithelium at one end
77
What doe the epithelium form? (mammal)
The trophoectoderm
78
What does the trophoectoderm give rise to? (mammals)
Gives rise to extra-embryonic structures
79
What does the inner cell mass give rise to?
Gives rise to the embryo
80
What is the inside-outside hypothesis? (mammals)
The fate of a blastomere derives from its position within the embryo, rather than from its intrinsic properties
81
What is the cell polarity model? (mammals)
- if the plane of cleavage of a blastomere is perpendicular to the surface of the embryo each daughter cell becomes trophoblast
- if the plane of cleavage is parallel to the surface, the daughter blastomere located at the surface becomes trophoblast, whereas the daughter cell located on the interior becomes part of the inner cell mass
82
What happens to the embryo as it moves through the oviduct? (mammal)
The blastocyst expands within the zona pellucida
83
What does the Na/K-ATPase pump do in the plasma membrane of trophoblast cells? (mammal)
- pump Na ions into central cavity
| - this causes water to be drawn in, thus enlarging the blastocoel
84
What prevents the blastocyst from adhering to oviduct walls?
Zona Pellucida
85
What does the embryo do once it reaches the uterus?
- it must "hatch" from the zona so that it can adhere to the uterine wall
86
How does the blastocyst hatch from the zona pellucida?
- by lysing a small hole in it and squeezing through the hole as the blastocyst expands
87
What are the three stages of implantation? (mammal)
- apposition
- adhesion
- invasion
88
What is appostition? (mammal)
- the initial adhesion of blastocyst to endometrial surface (very unstable stage as the blastocyst could still detach)
89
What is adhesion? (mammal)
- occurs when a stronger connection is established between embryo and endometrium
90
What is invasion? (mammal)
- involves trophoblastic cells invading the endometrium
91
How does the endometrium (uterine epithelium) "catch" the blastocyst? (mammal)
- catches blastocyst on an extracellular matrix containing collagen, laminin, fibronectin, hyaluronic acid and heparan sulfate receptors
92
What does the trophoblast secrete once in contact with the endometrium? (mammal)
- secretes another set of proteases (collagenase and plasminogen activator)
- these digest the extracellular matrix of the uterine tissue, enabling the blastocyst to bury itself within the uterine wall
93
What is the fetal organ capable of absorbing maternal nutrient? (mammal)
Chorion
94
What is the chorion derived from? (mammal)
- primarily from embryonic trophoblast cells, supplemented with mesodermal cells derived from the inner cell mass
95
What forms the fetal portion of the placenta? (mammal)
Chorion
96
What forms the maternal portion of the placenta?
The decidua
97
What does the blastocyst separate in to? (mammal)
- trophoblast
| - inner cell mass
98
What does the trophoblast form? (mammal)
- first the cytotrophoblast
| - which divides to form the syncytiotrophoblast
99
What does the segregation of inner cell mass cells result in? (mammal)
- hypoblast
| - epiblast
100
What does the hypoblast divide into? (mammal)
- extraembryonic endoderm
| - which then forms the yolk sac
101
What does the epiblast divide into? (mammal)
- amnionic ectoderm
| - embryonic epiblast
102
What does the embryonic epiblast divide into? (mammal)
- embryonic ectoderm
| - primitive streak
103
What does the primitive streak divide into? (mammal)
- embryonic endoderm
- embryonic mesoderm
- extraembryonic mesoderm
104
What is the bilaminar embryonic disc (blastodisc)? (mammal)
- refers to the two layers (epiblast and hypoblast) that evolved from the embryoblast
105
What form the lining of the amnionic cavity?
- embryonic epiblast
| - amnionic ectoderm
106
What is the purpose of amniotic fluid?
- serves as a shock absorber for the developing embryo while preventing its desiccation
107
What do cytotrophoblast cells do?
- initially adhere to the endometrium through a series of adhesion molecules
- contain proteolytic enzymes that allow them to enter uterine wall and allow fetal blood vessels to bathe in maternal blood
108
What do synctiotrophoblast cells do?
- have finger-like processes that further progress the embryo into uterine wall by digesting uterine tissue
109
What seals the site of initial penetration of blastocyst into endometrium? (mammal)
a blood clot (fibrin plug)
110
What is the function of the yolk sac in mammals?
- acts as a source of primordial germ cells and hematopoiesis
111
What is the function of the connecting stalk? (mammals)
- suspends the embryonic disc in the chorionic cavity
- joins the embryo to the cytotrophoblast
- ultimately becomes the umbilical cord
112
What is the primitive streak?
- gives rise to left/right and anterior/posterior body axes
| - marks the beginning of gastrulation
113
What in mammals is analogous to the amphibian blasopore?
primitive groove
114
What in mammals is analogous to the dorsal lip of the amphibian blastopore?
Primitive knot (hensen's node)
115
What is Hensen's nod (primitive knot)?
- regional thickening of cells at the anterior end of the primitive streak
116
Where does gastrulation begin? (mammal)
- at the primitive streak
| - starting at posterior end and working toward anterior end
117
What does the bilaminar embryonic disc give rise to? (mammal)
- gives rise to dorsal-ventral body axis
118
What do ingressing cells at hensen's node form? (mammal)
- move anterior to form head processes and notochord
119
What internal cavity develops in the mouse that gives it a cup-shape?
- proamniotic cavity
120
How is the proamniotic cavity formed?
- by a process called programmed cell death
121
What is unique process during development of mouse embryo?
- undergoes a complex conformational change and "turns" to be completely enclosed in the protective amnion and amniotic fluid
122
What is situs solitus?
-refers to the normal position of the thoracic and abdominal organs
123
What is situs inversus?
- refers to the rare condition where individuals have organs that are positioned in a mirror image from normal positions
124
When does gastrulation occur in the chicken?
after the egg is laid
125
Where is the location of the blastoderm (embryo) prior to gastrulation in the chicken?
lying on top of the yolk
126
What is the chorion in the chicken?
the outermost membrane that lines the inside of the eggshell
127
What are the components of the yolk sac in the chicken?
- surrounds the egg yolk
- has a well-developed vascular system
- transports nutrients from the egg yolk to the developing chick embryo
128
What is the amnion in the chicken?
- surrounds the developing embryo
- filled with fluid to serve as a shock absorber
- protects embryo against any jarring impacts or movements
129
What is the allantois? (chicken)
- a sac-like extraembryonic membrane that removes waste from the chick embryo
- disposal site for uric acid
130
How does the chick embryo get oxygen?
- as the chick embryo grows, so does the allantois, which eventually presses against the chorion, which alllows the allantois to exchange oxygen and carbon dioxide with the air outside the shell
131
Where does cleavage occur in the chicken?
in the blastodisc
132
How does the egg move down the uterus? (chicken)
- moves pointed end first and rotates slowly around its long axis (each revolution taking a~6 minutes)
133
What part of the blastoderm becomes the posterior side? (chicken)
The upper edge (that is positioned at a ~45 degree angle)
134
What type of eggs are chicken eggs?
telolecithal
135
What type of cleavage do chickens have?
- discoidal
| - meroblastic
136
What are the first cleavages of the chicken embryo?
- occur downwards from the surface but do not extend into the yolky area (blastoderm remains continuous with the yolk)
137
What is the subgerminal space? And how is it formed? (chicken)
- a cavity that forms between the blastoderm and the yolk
| - the cells near the yolk in the center of the blastoderm are shed and die giving rise to a larger central cavity
138
What is the area pelucida? (chicken)
- the region of the blastoderm that overlies the subgerminal space and is translucent in appearance
139
What is the area opaca? (chicken)
- the surrounding area around the area pellucida (darker in appearance)
140
Where does the hypoblast develop? (chicken)
- develops over the yolk (forms the floor cavity)
141
What is the first observable sign of the anterior-posterior axis? (chicken)
- the formation of a crescent-shaped ridge of smalls cells at the posterior end of the embryo
- Koller's sickle
142
What does gastrulation begin in the chicken embryo?
At koller's sickle
143
Where is the blastocoel located in relation to the epiblast and hypoblast? (chicken)
- between the epiblast and hypoblast
144
Where is the subgerminal cavity located in relation to epiblast, hypoblast and yolk? (chicken)
- located under the hypoblast and above the yolk
145
When does the primitive streak begin to form? (chicken)
- when hypoblast are displaced by a layer of cells (endoblast) that grows outward from the posterior marginal zone
146
What is hensen's node equivalent to?
- the spemann-mangold organizer
147
Where is Vg-1 expressed in the chicken embryo?
- in the posterior marginal zone
148
What is the posterior marginal zone? (chicken)
- makes up the border between area opaca and area pellucida
149
What are two of the earliest signaling proteins for initiation of primitive streak in chickens?
- Vg-1
| - Wnt-8C
150
What is the posterior marginal zone? (chicken)
- an organizing center
151
What happens when the posterior marginal zone of one chick embryo is grafted onto another position in a second blastoderm?
- it can induce the formation of another primitive streak
152
What is the posterior marginal zone analogous to in the xenopus? (chicken)
- the Nieuwkoop center (because it can induce the formation of a new body axis when it is transplanted into a new location on another embryo
153
What happens when a blastoderm is cut up into fragments? (chicken)
- each fragment undergoes gastrulation
| - a new body axes is induced in each fragment
154
Why does only one primitive streak form? (chicken)
- once a primitive streak has formed, it inhibits other areas of the marginal zone from forming additional primitive streaks
155
Why does the primitive streak not form while the hypoblast is intact? (chicken)
- hypoblast secretes a protein that inhibits streak formation
- once displaced by the endoblast the inhibitory protein is no longer made, and the primitive streak can begin to form
156
What does the secretion of Vg-1 and Wnt signals by the posterior marginal zone induce? (chicken)
- induce the expression of Nodal in adjacent epiblast cells
157
What prevents Nodal from binding to its receptor? (chicken)
- Cerberus (released from hypoblast)
158
What signals induce the internalization of epiblast cells? (chicken)
- Nodal
- Fibroblast Growth Factor (FGF)
- both from Koller's sickle
159
What is the process of the FGF signaling pathway? (chicken)
- FGF signals through transmembrane receptors
- binding of FGF to its receptor causes two ligand-bound receptors to dimerize
- this activates the intracellular kinase domains and they phosphorylate each other
- phosphorylated receptor tails recruit Grb and Sos which activate Ras
- MAPK enters the nucleus and phosphorylates transcription factors
- cause gene expression in epiblast cells
160
What does the formation of the primitive streak rely on? (chicken)
- on a complex network of signaling pathways that work together to ensure that this process is highly regulated
161
What are bone morphogenetic proteins (BMPs) (chicken)
- a group of growth factors that are important for regulating streak formation
162
What concentration of BMP signals does the site of primitive streak formation have? (chicken)
- low BMP signals
| - while the rest of the epiblast displays high levels of BMP
163
What did studies using the BMP inhibitor Chordin show? (chicken)
- that streak formation requires BMP inhibition
164
What are somites?
blocks of mesoderm tissue from which the muscles and skeleton will form
165
What does the anterior region of the primitive streak give rise to? (chicken)
- axial and paraxial mesoderm (notochord and somites)
| - the heart
166
What does the posterior region of the primitive streak give rise to? (chicken)
- the lateral mesoderm (blood and blood vessels, extra-embryonic mesoderm)
167
What happens when the Hensen's node is transplanted? (chicken)
- induces a new embryo
168
In what direction does somite formation in the chick proceed?
- antero-posterior direction
169
Where do somites form in the chick?
- form on either side of the notochord behind Hensen's node as it moves towards the posterior pole of the embryo
170
What do the first 5 somite pairs contribute to? (chicken)
- the posterior part of the skull
171
What is pre-somitic mesoderm? (chicken)
- the posterior unsegmented paraxial mesoderm
172
When does the head process form? (chicken)
- after the primitive streak reaches its full length
173
Where do the cell that generate somite arise from? (chicken)
- arise from the epiblast on either side of the primitive streak
- these cells move in through the node during gastrulation and form a population of stem cells located around Hensen's node
174
What cells form the pre-somitic paraxial mesoderm? (chicken)
- cells left behind as the node regresses
175
Where are somites patterned along? (chicken)
- along dorso-ventral and meio-lateral axies
176
What does the dermomyotome give rise to? (chicken)
- gives rise to the myotome, from which muscle cells originate, along with dorsal dermis
- also contains cells that contribute to vasculature
177
Where are sclerotome cells located and what do they develop in to? (chicken)
- located in ventral part of medial somite
| - surround the notochord and develop into vertebrae, intervertebral discs and ribs
178
How do somites acquire their identity? (chicken)
- somites differentiate into particular structures based on their position along the A/P axis
179
What is an early indication of left-right asymmetry in the chick embryo?
- asymmetric activity of a proton potassium pump (H+/K+-ATPase) in Hensen's node
180
Where is Nodal preferentially expressed in the chick embryo?
- on the left side
| - upregulated by Shh
181
What represses Nodal expression on the right side? (chicken)
- activin
| - FGF
182
What does increased Nodal levels on the left side lead to? (chicken)
- allows for expression of a transcription factor Pitx2
183
What does a lack of Nodal on the right side lead to? (chicken)
- leads to the expression of Snail and no expression of Pitx2
184
Why are sea urchins important models?
- it is easy to obtain large numbers of zygotes and embryos
- they are transparent so you can visualize early development processes
- the genome has been sequenced
- suitable for micromanipulation experiments
185
What type of eggs are sea urchin eggs?
- isolecithal
186
What type of cleavage do sea urchins have?
- radial
| - holoblastic
187
What type of cells are located at the animal pole of sea urchins?
- mesomeres
188
What type of cells are located at the vegetal pole of sea urchins?
- macromeres and micromeres
189
At what stages of sea urchin development do they contain the complete animal-vegetal axis and give rise to mostly normal larvae is separated or fused together?
- two cell stage
| - four cell stage
190
What happens in development to the animal half of cells if lysed at the 8-cell stage? (sea urchin)
- form a hollow sphere of ciliated ectoderm
191
What happens in development to the vegetal half of cells if lysed at the 8-cell stage? (sea urchin)
- larvae is variable in form but usually vegetalized ( has a large gut and skeletal rods, but a reduced ectoderm lacking the mouth region)
192
What does the animal half of the 32-cell embryo of the sea urchin form if removed?
ectoderm
193
What happens when micromeres from a 16 cell embryo are combined with the animal half of a 32-cell embryo? (sea urchin)
- a normal larvae is produced
194
What happens if micromeres from a 16-celled embryo are transplanted onto the side of a 32-cell embryo? (sea urchin)
- another gut will form at the site where the micromeres were planted
195
What is a unique function of micromeres in the sea urchin embryo?
- they can act as inducers to cells on the animal half of the embryo
196
What do the micromeres of the sea urchin embryo give rise to?
- mesoderm (namely, the primary mesenchyme that forms skeleton)
197
What does the vegetal plate give rise to in the sea urchin?
- endoderm
- mesoderm ( namely, secondary mesenchyme that forms muscle, pigment cells and immunocytes
- some ectoderm
198
What do the mesomeres in the sea urchin give rise to?
- the ectoderm
| - divide into future oral and aboral ranges
199
How does sea urchin gastrulation begin?
- blastula hatches from the fertilization envelope
| - vegetal side begins to thicken and flatten
200
What cell movements does sea urchin gastrulation involve?
Ingression: micromeres pass into blastocoel
Invagination: the vegetal pole folds inward forming a pocket
Involution: archenteron forms (the pocket continues to expand as a tube toward the animal pole)
201
What are the two axes defined in the sea urchin embryo?
- animal-vegetal axis
| - oral- aboral axis
202
What is the mesenchyme? (sea urchin)
- loosely organize undifferentiated mostly mesodermal cells that give rise to such structures as connective and skeletal tissues
203
In what stage of sea urchin development are skeletal rods laid down?
- pluteus stage
| - laide down by the mesenchyme
204
What characterizes the left-right asymmetry in echinoderms?
- asymmetric positioning of the imaginal rudiment on the left side of the bilateral pluteus larva
205
What forms the rudiment in the sea urchin?
the left coelomic pouch proliferates and differentiates to form the rudimetn
206
What occurs in sea urchin metamorphosis?
- the larva settle on the sea floor and the imaginal rudiment separates from the larva (which then degenerates)
207
What does Lithium treatment of sea urchin embryos result in?
- causes vegetalization (embryos with reduced ectoderm and enlarged gut)
- embryo has proportionately large archenteron or even an archenteron that bulges outward from surface rather than invaginating properly into the blastocoel
208
What does lithium block in the sea urchin?
- blocks GSK-3 kinase (a beta-catenin regulating molecule that negatively regulates the Wnt pathway)
- leads to increased nuclear beta-catenin
209
Why are C. elegans an important model in developmental biology?
- embryos are transparent
- adult worm is made up of a small number of cells
- each adult has invariant lineage (there is little room for randomness)
- has a rapid period of embryogenesis
- complete genome has been sequenced
- animal can be maintained in the laboratory
210
What type of eggs are c. elegans?
isolecithal
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What type of cleavage do c. elegans go through?
rotational, holoblastic
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What does the first cleavage of c. elegan egg result in?
- Large anterior AB cell
| - smaller p1 cell
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What side does the site of sperm entry become in the c. elegan?
- becomes the posterior pole
214
At what pole is the egg nucleus located at the time of fertilization?
- the anterior pole
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What happens during the second division of the c. elegan embryo?
- AB cell divides equatorially to form ABp and ABa cells
| - P1 cell divides meridionally to produce EMS and P2 cell (posterior stem cell)
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What cell defines the future dorsal side of the c. elegan embryo?
- ABp cell
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What cell marks the future ventral surface of the c. elegan embryo?
- EMS cell
218
Where are p granules located in the c. elegan embryo?
- p granules remain in p daughters of cell dividsion
| - eventually become localized to the P4 cell
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What does the ABa cell of the c. elegan embryo give rise to?
- ectodermal tissue, such as the epidermis
- nervous system
- small portion of the mesoderm of the pharynx
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What does the ABp cell of the c. elegan embryo give rise to?
- neurons
| - hypodermis
221
What does the MS cell of the c. elegan give rise to?
- gives rise to many of the body's muscles
| - posterior half of pharynx
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What does the E cell in the c. elegan embryo give rise to?
- endoderm of the mid gut
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What do the C cells of the c. elegan embryo give rise to?
- forms hypodermis, neurons and body-wall muscle
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What do the D cells of the c. elegan embryo give rise to?
- muscle
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What do P4 cells of the c. elegan embryo give rise to?
- germ lines
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When is the left-right axis set in the c. elegan?
- after the third cleavage
- ABal and ABpl on the left side
- ABar and ABpr on the right side
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What is a founder cell? (c. elegans)
- produces differentiated descendants
228
What is a stem cell? (c. elegans)
- produces other founder cells and the germ line
229
What kind of specification do c. elegans have?
- conditional and autonomous
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What type of specification occurs in the P1 lineage of c. elegan embryo?
- autonomous specification
| - cell fates are determined by internal cytoplasmic factors rather than by interactions with neighbouring cells
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What proteins intrinsically determine the fates of P1 cells in c. elegans?
- SKN-1
- PAL-1
- PIE-1
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What do c. elegan embryos of skn-1 deficient mothers lack?
- mesoderm and endoderm derivatives of EMS
| - make extra hypodermal and bodywall tissue where their intestine and pharynx should be
233
What happens to c. elegan embryos that lack PAL-1?
- no somatic cell types are derived from C and D cells
234
What do mutation in the PIE-1 gene in c. elegans result in?
- germ line blastomeres adopting somatic fates
| - P2 cell behaves similar to wild-type EMS blastomere
235
Where is SKN-1 active in c. elegan?
EMS
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Where is PAL-1 active in c. elegans?
C and D cells
237
Where is PIE-1 active in c. elegans?
P cells (P4)
238
Where can conditional specification be seen in c. elegans?
- seen in the development of the endoderm cell lineage
239
What happens if the P2 cell is removed at the early four cell stage in the c. elegan?
- the EMS cell will divide into two MS cells
| - endoderm will not be produced
240
Where is the MOM-2 peptide produced? (c. elegans)
- in the P2 cell (homologue of a Wnt protein)
241
What protein recieves the MOM-2 peptide and where does this occur? (c. elegans)
- MOM-5 protein
| - in the EMS cell
242
What is the result of the MOM-2 and MOM-5 signaling cascade? (c. elegans)
- to down-regulate the expression fo the pop-1 gene in the EMS daughter destined to become the E cell
243
What happens to pop-1 deficient embryos? (c. elegans)
both EMS daughter cells become E cells
244
What happens to c. elegan embryos that have mutant GLP-1?
- ABp is transformed into an ABa cell
245
What is the first tissue to internalize in the c. elegan?
- endoderm
246
What do PAR genes do? (c. elegans)
- encode proteins that are critical for positioning the asymmetric cell division and proper partitioning of cytoplasmic determinants
- maternal-effect genes
247
What happens during contraction in actomyosin network around the outer edge of c. elegan embryo?
- cause certain PAR proteins to become asymmetrically localized
248
What PAR proteins are located at the anterior location in the c. elegan egg?
PAR-3 and PAR-6
249
What PAR proteins are located at the posterior location in the c. elegan egg?
PAR-1 and PAR-2
250
What type of eggs are drosophila?
centrolecithal
251
What type of cleavage to drosophila have?
- superficial
| - meroblastic
252
Where do sperm enter the drosophila egg?
- throught the anterior end of the egg through a pore called the micropyle
253
What do the dorsal appendages in the drosophila embryo do?
- thought to facilitate gas exchange by projecting above the substrate in which the developing egg is embedded
254
Where does fertilization occur in the drosophila?
- in the female fly
| - then the fertilized egg is laid
255
What occurs after fertilization of the drosophila?
- the zygote nucleus undergoes a series of rapid mitotic division
- unlike in most embryos, there is initially no cleavage of the cytoplasm and no formation of cell membranes to separate the nuclei
256
What is a syncytium? (drosophila)
- a cell with many nuclei in a common cytoplasm
257
What is the syncytial blastoderm and when does it form? (drosophila)
- occurs after nine nuclear divisions
- most of nuclei move to periphery
- comprised of superficial layer of nuclei and cytoplasm, and surrounds a central mass of yolky cytoplasm
- equivalent to the blastual stage in xenopus embryos
258
What is the cellular blastoderm and when does it occur? (drosophila)
- after 14 mitoses
| - membranes grow in from the surface and enclose the nuclei and form cells
259
What are pole cells? (drosophila)
- nuclei that have moved to the posterior end of the embryo
| - eventually give rise to germ cells
260
What does the blastoderm give rise to in the drosophila?
- gives rise to the somatic cells of the embryo
261
What is the process of cellularization? (drosophila)
- pulls membrane down between nuclei and deposits new membrane to envelop each nucleus in its own plasma membrane
262
What are the first movements of drosophila gastrulation?
- segregate the presumptive mesoderm, endoderm and ectoderm
263
What occurs during gastrulation at the future mesoderm site? (drosophila)
- ventral furrow is formed after invagination of mesoderm cell in the ventral region
264
How is mesodermal tissue formed and internalized in the drosophila embryo?
- the ventral furrow pinches off from the ventral surface to become a ventral tube
- these cell are flattened to form a layer of mesodermal tissue beneatch the venctal ectoderm
265
What do ectodermal cells of the ventral region do after the mesoderm has invaginated? (drosophila)
- leave the surface individually and form a layer of prospective neural cells between mesoderm and remaining outer ectoderm
266
What do endodermal cells do after the invagination of the mesoderm? (drosophila)
- endoderm invaginates as two pockets at the anterior and posterior ends of the ventral furrow
- grow inward towards each other and eventually fuse to form the midgut (ectoderm is dragged inward behind them to form foregut and hind gut)
267
What happens when the drosophila embryo bends during gastrulation?
- forms the cephalic furrow
268
What are the four morphogenetic events involved in drosophila gastrulation?
- ventral furrow formation
- posterior/anterior- mid gut invagination
- cephalic furrow formation
- germ band extension
269
What is the germ band? (drosophila)
- collection of cells that will form the segmented trunk of embryo
270
How is the germ band formed in a drosophila embryo?
- the ectodermal cells on the surface and the mesoderm undergo convergent extension, migrating toward the ventral midline
271
What is the process of germ band extension? (drosophila)
- the germ band extends posteriorly and wraps around the dorsal surface of the embryo
272
What is an imaginal disc? (drosophila)
- a sac-like epithelial structure found inside the larva of insects that undergo metamorphosis
- once the larva turns into a pups, almost all the larval tissues degenerate and the imaginal discs turn into the external structures of the head, thorax, limbs and genitalia
273
How does germ band extension occur? (drosophila)
- by intercalation of the cells in the tissue
| - when the cells intercalate, the tissue gets longer and thinner
274
What does germ ban retraction do? (drosophila)
- brings the embryo to its final fosterior position and the segments that will form the head, thorax and abdomen form
275
When does dorsal closure begin? (drosophila)
- when germ-band retraction starts
276
What drives the dorsal closure process in drosophila embryos?
- an actomyosin purse string forms at the boundary between the epithelial and amnioserosa cells
- cells in the amnioserosa undergo cycles of actomyosin contractions (brings the margins of the amnioserosa together
- when the epidermal cells meet at the anterior/posterior ends they fuse to create a "zipper" that seals the epidermis closed
277
What is a morphogen?
- a molecule whose non-uniform distribution in a embryo governs the pattern of tissue development in the process of morphogenesis or pattern formation
278
What are maternal effect genes?
- genes whose productes are produced or deposited during egg formation
279
What do maternal effect genes do in the drosophila embryo?
- encode transcriptional and translational regulatory proteins that diffuse through syncytial blastoderm
280
What are zygotic genes and what is their role in the drosophila embryo?
- expressed by an embryo and respond to maternal gene expression
- includes gap genes, pair-rule genes, segmentation genes and selector genes
281
What are gap genes and what are their role in the drosophila embryo?
- participate in early patterning along the A-P axis of embryo
- encode trancription factors that regulate the expression of pair-rule genes
282
What are pair-rule genes? (drosophila)
- determine the position of the parasegments
| - encode transcription factors that regulate the expression of the segment polarity genes
283
What are segment polarity genes? (drosophila)
- set A/P axis of each parasegment
- segment polarity genes make the true gements out of the parasegments
- expression of these genes is closely associated with the process of morphological sementation
284
What are homeotic selector genes? (drosophila)
- determine the final developmental fate of each segment
| - determine which physical structures will develop in each segment
285
What proteins regulate the production of anterior structures of the drosophila embryo?
- bicoid
| - hunchback
286
What proteins regulate the formation of posterior structures in the drosophila embryo?
- nanos
| - caudal
287
How are terminal regions specified in the drosophila?
- by an interesting mechanism that involves the localized activation of a recepto protein that is itself present throughout the plasma membrane of the fertilized egg
288
What happens in a bicoid mutant drosophila embryo?
Anterior mutation: partial loss of head and thorax at the anterior end which is replaced with posterior structures (including another telson)
289
What happens in a nanos mutant drosophila embryo?
Posterior mutation: loss abdominal segments within embryo
290
What happens in a torso mutant drosophila embryo?
Terminal mutation: missing acron and telson ends of embryo
291
What occurs if toll is absent from the drosophila embryo?
- dorsal protein is prevented from entering nuclei by being bound in the cytoplasm to another maternal gene product called cactus
292
Where is the dorsal protein located? (drosophila)
- in high abundance on the ventral side
| - absent from nuclei on the dorsal side
293
Where is Dpp expressed?
| drosophila
- expressed where dorsal is absent
| - highest Dpp activity occurs at the dorsal-most region of the embryo
294
Where is twist expressed in the drosophila embryo?
- in nuclei of cells where dorsal levels are high (takes a lot of dorsal to activate their expression)
295
What does the gradient of the dorsal protein specify in the drosophila embryo?
- specifies the initial pattern of zygotic gene activity along the dorsal- ventral axis
- further patterns the mesoderm and neuroectoderm by activating other target genes
296
At what concentrations does hunchback activate or repress kruppel? (drosophila)
- At low concentrations, hunchback activates kruppel
| - At high concentrations, hunchback represses kruppel
297
What genes define the expression zone of kruppel? (drosophila)
- Bicoid
| - Hunchback
298
What are denticle belts? (drosophila)
- alternating patches of denticle hairs anc cuticle on each segment (used for locomotion)
299
What are pair-rule genes defined by? (drosophila)
- by the effect of a mutation in that gene, which causes the loss of the normal developmental pattern in alternating segments
300
What happens after parasegmental boundaries are set? (drosophila)
- the pair- rule and gap genes interact to regulate the homeotic selector genes, which will determine the identity of each segment
301
What are halteres? (drosophila)
- small knovved structures modified from hind wings in flies (they vibrate during flight to help flies remain stable)
302
Where are homeotic genes clustered? (drosophila)
- Antennapedia complex (ANT-C)
| - Bithorax complex (BX-C)
303
Where are ANT-C complex genes expressed and what are they responsible for? (drosophila)
- expressed in the head and anterior thoracic regions
| - responsible for the formation of head and most thoracic structures
304
Where are BX-C complex genes expressed and what are they responsible for? (drosophila)
- expressed in the posterior thorax and abdominal regions
| - responsible for the formation of posterior thoracic and abdominal segments
305
What happens when homeotic genes are inactivated or expressed in unusual locations? (drosophila)
- they may cause body segments to take on new identities
306
What does the homeotic gene Antennapedia do in the drosophila?
- acts as a master regulator, turning on the genetic program that makes the fly's second pair of legs and other segment-specific structures
307
What happens if a genetic mutation causes expression of the Antennapedia gene to expand into the fly's head?
- causes legs to grow from the fly's head in place of antennae
308
What does the Ultrabithorax gene do in the fly?
- expressed in the third segment of the thorax, which bears the fly's rearmost pair of legs
- represses second-segment identity and formation of wings in the third segment
309
What happens when Ultrabithorax is inactivated in the fly?
- the halteres will be converted to a second set of wings (neatly positioned behind the normal set)
