Gastrulation in Xenopus Flashcards
what are the most important cell movements in gastrulation (and what do they result in)?
invagination (formation of blastopore)
involution (animal pole cells = future endoderm and marginal zone cells, aka future mesoderm; will “roll in” layers at blastopore)
convergent extension (of future mesoderm)
epiboly (spreading of ectoderm as presumptive endoderm and mesoderm move inside)
what is present in the marginal zone?
thin layer of putative endoderm outside of putative mesoderm here
this region of putative endoderm will form the bottle cells (initiates gastrulation)
what is the first event of gastrulation? what does it entail, what drives change?
vegetal rotation - movement of blastocoel floor upward toward animal pole, but preferentially toward presumptive dorsal side.
amoeboid movements largely drive this change in position
what follows from vegetal rotation? how does this occur?
formation of the blastopore - a group of cells on the dorsal side change their shape st they become constricted at apical ends + somewhat elongated
these cells = bottle cells, thought that B-catenin they’ve inherited allows for this change, which causes a small groove (blastopore) to form.
what/where is the dorsal lip of blastopore?
dorsal lip = Spemann’s organizer, ledge of cells on animal side of blastopore
what happens w/ putative mesoderm/endoderm after blastopore formation?
putative mesoderm/endoderm on animal side of blastopore start to involute inward around blastopore. this movement starts on dorsal side, spreads laterally + vegetally st blastopore becomes circular
what happens w/ ectoderm in relation to mesoderm + endoderm movement?
as mesoderm + ectoderm cells move inside + line roof of blastocoel, ectodermal cells of the animal cap change their shape (divide and expand laterally while becoming thinner and intercalate radially), initiating epiboly (spreads down over vegetal region)
what is the yolk plug?
a yolky plug of endodermal cells that remain exposed at vegetal pole.
blastopore will eventually contract and yolk plug cells will be forced into interior, forms floor of gut.
what happens to first mesodermal cells to involute?
1st mesodermal cells to involute eventually migrate as mesenchyme over blastocoel roof, will form head structures (head + neck connective tissues, muscles, etc)
what happens to the mesoderm cells following the 1st set of cells?
mesoderm in sheet that follows are thought to get somewhat constricted (and also intercalate) as they pass thru blastopore; results in convergent extension along A-P axis. (think merging of traffic)
how are the bottle cells affected in this movement of mesoderm?
bottle cells are pulled along passively and will contribute to endodermal roof of archenteron
what is the geometric result of convergent extension of the mesoderm? what forms from part of this mesoderm?
the mesoderm that used to be found in an equatorial ring now forms a distorted partially open teepee-shape inside of the embryo (elongated along A-P axis).
notochord forms from band of mesoderm up the steep side of the teepee.
how is the archenteron formed, what is the result of its formation?
involution creates the archenteron, which is primordial gut (formed by primitive endoderm); first displaces then destroys blastocoel
what happens with the mesoderm toward the embryo midline?
continued intercalation of mesoderm toward midline along A-P axis occurs; eventually, notochord separates itself out from somitic (contributes to somites) mesoderm on either side; noto. cells start to elongate
what are somites?
chunks of mesoderm that form certain muscles, the ribcage, etc.
