BIOL 443 Lecture Notes - Lecture 12: Epithelial–Mesenchymal Transition, Sea Urchin, Archenteron
Document Summary
Large micromeres conditionally specify the fates of their neighbors above them, inducing endoderm fate and invagination to make the gut. They can do so even if placed adjacent to animal cell layers: signaling is by juxtacrine and paracrine factors, including notch-delta for non- skeletogenic mesoderm and activin (a tgfb family member) for endoderm. Non-skeletal mesenchyme cells then ingress and form filopodia, connecting the tip of the archenteron to the other end of the blastocoel wall. It is expressed in the oral ectoderm starting at the. Separation at this stage leads to incomplete embryos, unlike in sea urchins: the 3rd cleavage plane is equatorial. Dorsal-ventral axis: before fertilization, dorsal side is at the vegetal pole (and is where gastrulation is initiated) As in sea urchins, tunicate gastrulation is characterized by invagination of the endoderm, but mesoderm is formed later, by involution.
