Gastrulation movements Flashcards
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
what is epiboly
the thinning and spreading of ectoderm and mesoderm
what characteristic do cells need for coherent extension
planar cell polarity - one end of the cell differs molecularly and structurally to the other
when does the blastopore close
when the mesoderm and ectoderm have moved inside
how does epiboly of the ectoderm occur
the blastospore initially forms a crescent shaped indentation, then the dorsal and ventral lips are formed in succession
when the ventral lips are formed the endoderm moves progressively inside then the ectoderm massively extends
how does involution and the formation of the blastopore lip occur
the small groove, blastospore, has a dorsal lip at the site of the speman organised
coherent sheet of the mesoderm and ectoderm begin to involute around the blastospore rolling into the interior of the blastula against its own under surface
involution spreads and the blastospore forms a circle around a plug of yolky cells
the blastospore then contracts forcing the yolky cells to the interior where they form the floor of the gut
what is the anterior migration of the mesoderm involving chemotaxis responding to
platelet derived growth factor secreted by the ectoderm
what does radial intercalation result in
the thinning of the blastocoel roof and drives ectodermal epiboly
what is epiboly of the ectoderm mediated by
radial cell intercalation
what does radial intercalation cause
thinning of a multicellular layer of cells to a thinner sheet causing extension
where does intercalation occur
in the multilayered ectoderm of the animal cap
what does radial intercalation cause
increased surface area of the cell
what are the driving forces of body axis elongation
convergence and extension movements
what is the initial form of the mesoderm and when does this change
initially in the form of an equatorial ring, during gastrulation it converges and extends along the antero-posterior axis
what happens to cells on opposite sides from each other during convergence
they become v close together
what happens to cells opposite ends of the long axis
they become further away from one another
what direction are migrating mesoderm cells polarised
the direction of the animal pole, its migration id dependent on interactions with fibroconectin fibrils in extracellular matrix lining the blastocoel roof
what layers does convergent extension occur in and when
in the mesoderm and endoderm as they involute
what does convergent extension of the mesoderm and future neural tube drive
elongation of embryos
what is the future mesoderm identified by
the expression of the brachyury gene - it is seen as narrowing around the blastospore
what is convergent extension mediated by
mediolateral cell intercalation - cells shuffle in between each other along the medio-lateral axis some cells move medially and some laterally
how does dishevelled controls signalling work
either canonical Wnt signalling pathway through beta catenin stabilisation resulting in changes in gene expression
or cells signal to PCP pathway which is involved in the control of cell:cell intercalation
finally signals to calcium dependent pathways control tissue separation
what does PCP stand for
planar cell polarity
what does the PCP signalling pathway involve and what is it required for
involves Wnt signalling and is required for cell polarisation during convergent extension
what drives streak formation
apical contraction of the myosin dependent directional cell : cell intercalation
how is the primitive streak formed
through the epiblast cell movement into the interior of the embryo and specialisation into endoderm and mesoderm as they become internalised - the embryo elongates by a combination of cell proliferation and convergent extension
in primitive streak formation where does epithelial and mesenchymal transitions start
the posterior end of the blastoderm and it progresses forward
what occurs at the same time as primitive streak formation
convergent extension of the epiblast
in the chick epiblast, what is primitive streak formation preceeded by
extensive bilateral symmetric movements of the anterior epiblast outward from the midline backwards toward the posterior where the streak will begin
