[LE 02] Gastrulation Flashcards
end goal of gastrulation
form the 3 germ layers
t or f: blastomere cell fate is already specified prior to gastrulation
t
difference between specification and determination
specification: cell fate is reversible
determination: cell fate is irreversible
what is “presumptive”
can’t say if specified or determined
cell movement which forms the dorsal lip of the blastopore
invagination
three cell movements involved in gastrulation
- invagination
- involution
- epiboly
- ingression
- intercalation
- convergent extension
what is the goal of epiboly?
to cover the cell
when will the yolk plug close during gastrulation?
when it is covered with ectoderm via epiboly
cell rearrangements that drive gastrulation
- epiboly
- vegetal rotation
- bottle cell formation
- tissue separation
- cell migration
- convergence and extension
- convergent thickening
it is the rearrangement of cells which initiates invagination and involution
bottle cell formation
bottle cell formation forms via
apical constriction
t or f: apical constriction promotes tissue remodeling
t
what happens during apical constriction?
constriction of apical side, expansion of basal side
cell rearrangement wherein the cells go around the animal hemisphere
epiboly
cellular movement that is like EMT
ingression
what drives epiboly?
morphology change
cellular movement that is the specialized form of intercalation
convergent extension
t or f: direction does not matter in intercalation
f; intercalation is highly directional
where do bottle cells form?
at sites of invagination
bottle cells initiate what type of cell movement?
involution
these are the apically constricting cells
bottle cells
what happens during tissue separation in gastrulation?
- there is a cycling between attachment and detachment
- attachment triggers repulsion
- there is reestablishment of contact when the cells are apart
t or f: during tissue separation, the mesoderm can invade the ectoderm
f; but it can still use the cells as a substrate for movement
explain the process of involution happening after bottle cell formation
- apical constriction
- outer marginal zone is pulled vegetally
- mass of large vegetal cells is pulled directly inward
- anterior mesoderm is pushed toward the animal pole
- IMZ is rotated outward
what is the result of involution?
reorientation of the anterior marginal zone making it the leading movement into the blastocoel
how does ventral lip of the blastopore form?
forms from the progression of ectoderm surrounding the vegetal hemisphere
t or f: convergent extension occur during epiboly
t
cellular movement wherein the tissue elongates along one axis and narrows in one or both orthogonal axes
convergent extension
steps in the convergent extension of the dorsal mesoderm
- several deep IMZ layers intercalate radially to form one, thin broad layer
- IMZ extends vegetally because of the intercalation
- deep cells reach the blastopore lip then involute
- initiation of 2nd type of intercalation
- intercalation causes convergent extension along the mediolateral axis
- formation of a long, narrow band
why is there mediolateral intercalation in the convergent extension of the dorsal mesoderm?
to drive migrating mesoderm
effect of the continuous migration of the mesoderm to the animal pole
forms an endodermal roof of the archenteron
t or f: derivatives of bottle cells contribute to internal cell arrangements
t
processes present in the epiboly of the prospective ectoderm
cell division and intercalation
how does the cells of the prospective ectoderm migrate when it undergoes epiboly?
it uses fibronectin which assembles into fibrils
t or f: all cells in gastrulation move via convergent extension
f
steps in the epiboly of the prospective ectoderm
- 3 rounds of cell division to increase the number of deep layers in the animal hemisphere
- at the same time, complete integration of the numerous deep cells into one layer
- superficial layer expands by cell division and flattening
t or f: epiboly of the prospective ectoderm involves convergent extension for cell movement
f; it uses fibronectin for migration
different Wnt-related signaling pathways
- beta-catenin pathway
- PCP/CE pathway
- Ca2+ pathway
ligands in the beta-catenin pathway
Wnt1 and Wnt3a
ligands in the PCP/CE pathway
Wnt5a and Wnt11
ligands in the Ca2+ pathway
Wnt5a
process of the beta-catenin pathway
- Wnt1 and Wnt3a bind
- Dvl inhibits GSK-3beta, APC, and axin complex
- beta-catenin is expressed
- beta-catenin binds to Tcf/Lef
- there is gene expression: cell proliferation and differentiation
end result of the beta-catenin pathway
gene expression: cell proliferation and differentiation
steps of the PCP/CE pathway
- Wnt5a and Wnt11 binds
- Dvl produces either RhoA or Rac
- RhoA:Rho-kinase and Rac:JNK
- act on cytoskeleton
- cell polarity, cell migration
result of the PCP/CE pathway
cell polarity and migration
steps in the Ca2+ pathway
- Wnt5a binds
- Dvl induces production of Ca2+
- Ca2+: CaMK or PKC
- inhibits binding of beta-catenin to Tcf/Lef
- cell migration, inhibition of beta-catenin pathway
draw the different wnt-related signaling pathways
gow
how is polarity established/regulated in cells?
thru the differential recruitment of protein complexes on opposite sides of the cell
protein that is responsible for the regulation of cell polarity
wnt gradient
how is polarity established by the complexes?
there is inhibition so that the complexes do not form on the same side
t or f: in regulation of polarity, the complexes inhibit extracellularly
f; bati sila extracellularly
proteins in polarity regulation that antagonize each other
Dgo and Dsh against Pk and vanguard
pathway regulated in the regulation of polarity
PCP pathway
pathway that regulates apical constriction during epithelial morphogenesis
PCP pathway
what triggers contraction in the process of apical constriction
myosin II
epithelial markers
- E-cadherin
- epithelial cell adhesion
- occludins
- claudins
- alpha6 beta4 integrin
- cytokeratins
mesenchymal markers
- N-cadherin
- Vimentin
- Fibronectin
- beta1 and beta3 integrins
- MMPs
transcription factors in the maintenance of the epithelial state of cells
- Crumbs
- PATJ
- LGL
t or f: fibrillogenesis can be in the folded state
t; if there is no need for long distance migration
mesenchymal marker which degrades ECM
MMPs
why do MMPs degrade the ECM?
it can be a barrier to cell movement
mesenchymal markers which are important for transient adhesions
beta1 and beta3 integrins
epithelial marker which is found in hemidesmosomes and keeps the cell attached to cell
alpha6 beta4 integrins