1- How does the convergence of multiple signal pathways due to the formation of
ID: 3166351 • Letter: 1
Question
1- How does the convergence of multiple signal pathways due to the formation of the gray crescent lead to the formation of the primary organizer in Amphibians? Describe these pathways, the key molecules they effect, and how they lead to the primary organizer forming opposite the site of sperm entry.
2- What cellular events lead to the formation of different germ layers during gastrulation in amphibians. Discuss the role and function of superficial and deep cells, bottle cells, the blastocoel, the blastopore lip, the IMZ, the NIMZ, the archenteron, mediolateral intercalation, convergent extension, the yolk plug, and epiboly.
Explanation / Answer
1)Upon fertilization of an amphibian egg, there are many changes in the cytoplasm via which a gray area of the cytoplasm , crescent shaped, is exposed opposite to the site of sperm entry, because gray crescent area gives rise to cells that initiate gastrulation, these cells are the ones that form the dorsal lip of the blastopore.Upon sperm entry , there is an axis formation via which molecules are shifted upwards to animal pole of the zygote,their are resulting molecular interactions via which events lead to a dorsal fate.Via this shift there is interaction with molecules apart from those at the vegetal pole.There is a dorsal signalling centre formed which triggers self differentiation of tissues, morphogenesis and inducing more signals for furher development of gastrula.
2)Post the convergence of various pathways , sperm entry leading to gray crescent formation,there is a blastula stage with a hollow in the middle.following this stage is the gastrula stage wherein cells that migarte into the embryo,the specific site being blastopore with cells from gray crescent making up the dorsal lip (blastopore lip).The cells from the blastopore lip form the primary organizer (also known as Spemann organizer) which determines the dorsal fate, and the change of ectoderm to neural tissue.
Blastocoel is a fluid filled cavity formed during early embryogenesis ,and is a key inititiator of the gastrula stage.It also allows migration of cells in gastrulation and stops cells below it from intercalation with cells above it before time.
Epiboly is a set of cell movements during the gastrula stage via which differnt layers form. For instance formation of epithelial cell layer
The superficial cells, deep cells, yolky cells are a part of the blastula.The superficial cells of the marginal zone lead to the archentron.
As more cells enter the blastocoel, it is positioned at one side, there is yolk plug formation with the endoderm remaning after blastopore forms a ring around large endodermal cells that are towards the egetal surface.
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