MCD BIO 138 Lecture Notes - Lecture 12: Primitive Streak, Epiblast, Germ Layer

• School: UCLA
• Department: Molecular, Cell, and Developmental Biology
• Course: MCD BIO 138
• Professor: Lyons

Document Summary

Lec 12 gastrulation & mesoderm formation in birds & mammals. Primitive streak development: bird embryo as mammalian gastrulation model, start with flat sheet of cells sitting on yolk, epiblast: yolk-free cells that divide & give rise to embryonic structures, cells from epiblast move towards midline convergent extension. Streak initiates at posterior marginal zone: posterior marginal zone marked by high level b-catenin (from high wnt, unlike frog: mammals & birds don"t have maternal determinants. In birds: marginal zone location due to gravity (probably difference in cytoplasmic tension) In mammals: how location established unknown (probably mechanical effect: high level b-catenin -> posterior marginal zone -> convergent extension. Posterior marginal zone analogous to frog nc: both high b-catenin & overlapping expression of multiple tfs -> area with high level nodal, transplantation expt. Transplant posterior marginal area to host embryo -> twinned axis. Primitive streak initiation: wnt -> b-catenin -> nodal (homologous to nodal-related) Wnt turns on nodal in adjacent epiblast cells.