Gastrulation

Gastrulation

1. Epiblast

   • Primitive Streak forms at Caudal end of embryo (3 wks)
     • Epiblast Cells migrate to the cranial end of the streak (node)
       • Cells move through cranial region
         • Form prechordal plate
           • Form notochord (both induce CNS)
             • Form nucleus pulposus in intervertebral discs
       • Node (organizer)
         • Cranial-caudal axis extablished by Anterior Visceral Endoderm (AVE) by secretion of genes for head formation
         • Goosecoid and other genes antagonize BMP4, organizing head mesoderm
           • BMP4 from embryonic disc ventralizes mesoderm, forming internediate and lateral plate mesoderm
         • Brachyury (T) gene controls formation of dorsal mesoderm in regions caudal to the head
           • W/o T gene -> caudal dysgenesis
             • Sirenomelia (Mermaid Syndrome) = insufficient mesoderm formed -> missing kidneys and fused lower limbs
           • PITX2 controls laterality (left sidedness) and is regulated by seratonin (5HT), NODAL and FGFs
             • Situs inversus = transposition of viscera w/ no other side effects
               • Laterality sequences -> incomplete sidus inversus (generally have other defects)(some caused by anti-depressants
   • Ectoderm
     • skin, CNS, PNS, eyes, internal ear, nerual crest cells (bones and connective tissue of the face and part of the skull
   • Mesoderm
     • bones, connective tissue, urogenital system, cardiovascular system
   • Endoderm
     • gut and gut derivatives (liver, pancreas, lungs, etc)