Practice question

Veg2 tier lies just above large micromeres at 60-cell stage and represents upper vegetal region with conditional specification responsive to induction. Upon receiving Delta signal from neighboring micromeres via direct Notch receptor activation, Veg2 cells activate gene regulatory network genes Gcm, GataE and FoxA. Its descendants undergo epithelial-mesenchymal transition and ingress as secondary mesenchyme cells that diversify into pigment cells containing echinochrome, blastocoelar immune cells, coelomic pouch muscle and esophageal muscle fibers. Large micromeres form primary skeletogenic mesenchyme, Veg1 mainly forms archenteron. Thus major derivative of Veg2 is secondary mesenchyme population essential for immunity.