Gastrulation movements
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in sea urchin embryos what do cells of the vegetal region undergo transition to
the primary mesenchyme and then they enter the blastocoel at the vegetal pole
in sea urchin embryos what happens after the vegetal mesoderm entering the blastocoel
the invagination of the endoderm which extends to the animal pole and contacts the blastocoel to form the mouth
in sea urchin embryos how is invagination of the endoderm initiated
it is initiated by contraction of the contractile ring of cytoskeletal elements in the apex of some cells
in sea urchin embryos how do actin filaments allow high versatility
they can polymerise and depolymerise rapidly
for does fog stand for
fold of gastrulation
in drosophila what does snail gene regulate
the epithelial to mesenchymal transition - it is required for the repression of cadherin gene expression and cadherin endocytosis
in drosophila what forms when the primary mesenchyme cells migrate to the blastocoel
a pattern forms on the inner blastocoel wall - first arranged in a ring around the gut then some migrate to form 2 extensions toward the animal pole on the ventral side - migration varies in diff embryos but final pattern is fairly constant
in drosophila how do mesenchymal cells more over the inner surface of the blastocoel well
by filipodia which contain cross linked actin filaments which extend by polymerisation to push out the edge of the filipodium, they adhere to the basal lamina living in the blastocoel wall and then contract to pull the cell body towards the point of contact
in drosophila what happens to the filipodia as cells migrate?
they fuse forming cable like interactions
in drosophila what affect does the stability of contacts between the filipodia and blastocoel have?
it is the determining factor for pattern of cell migration
in drosophila what 2 growth factors are guidance cues for cell migration?
fibroblast growth factor A and vascular epithelial growth factor
in drosophila where is FGF-A expressed in blastula and what does the inhibition of it result in
expressed on primary mesenchymal cells - inhibition stops the migration of cells and skeleton formation
in drosophila what is VEGF expressed by, where is it expressed and what happens when it isnt present
expressed by prospective ectoderm cells at the most ventral sites to which mesenchyme cells migrate if VEGF isnt present the cells do not reach their prospective positions so the skeleton isnt formed
in drosophila how many phases is there in gut formation
two
in drosophila what are the stages in gut formation
• ectoderm invaginates to form a short, squat cylinder extending halfway across the blastocoel there is then a short pause and the extension continues • cells at the tip of the invaginating gut form long filipodia which make contacts with the blastocoel wall. the extensions pull the gut all the way across the blastocoel until it contracts and fuses with the mouth region
what does extension of the germ band lead to
doubling in length of the thorax and embryo
what is the germ band made up of
the mesoderm, ventral ectoderm and dorsal epidermis
what is germ band extension driven by
convergent extension of the ventral part of epithelial layers
how does the narrowing of cells occur
adjacent cells intercalate laterally narrowing the tissue and causing it to extend in an antero-posterior manner
how is the change in cell shape seen as it occurs
the cells firstly appear as hexagonal shapes, as the extension begins adherens junctions on the faces of parallel to the dorso-ventral axis disappear and cells become diamond shaped, new junctions parallel to the antero-posterior axis appear and make boundaries hexagonal again and intercalation occurs along the dorso-verntal axis
what are junctional dynamic regulated by in germ band extension
by localised myosin activation activity of myosin is co-localised with beta-catenin-E-cadherin-actin complexes at adherens junctions
what prevents cells being held together in germ band extension
regulated mysoin contractions at junctions prevents e cadherins holding cells together so that new contacts can be made
what in frog embryos sets up the body plan
gastrulation
what is involution
the rolling in of coherent sheet of endoderm and mesoderm at blastospores