Practice question

Adjacent to micromeres, macromeres and large micromeres receive inductive signal mediated by direct cell contact requiring juxtacrine interaction. Micromeres express transmembrane ligand Delta following derepression of HesC by Pmar1. Neighboring cells express Notch receptor; Delta binding triggers gamma-secretase cleavage releasing Notch intracellular domain NICD that translocates to nucleus activating transcription of secondary mesenchyme genes gcm, gataE, foxA for pigment and blastocoelar cells and endoderm. This Delta-Notch induction specifies non-skeletogenic mesoderm. Blocking Notch with DAPT inhibitor eliminates secondary mesenchyme, while Delta misexpression induces ectopic mesoderm, proving essential vegetal patterning mechanism.