Question

1. How do Cerberus, Noggin, Chordin, BMPs and Wnt establish cell fate along the Dorsal-ventral and anterior-posterior axis?

Answer 1

→ Just after fertilization, maternai B-caterin protein is concentrated on the dorsal side of the egg. One of its downstream target protein is siamois , a 24 gotic transcription factor expressed in the dorsal endodeon. Siamois activates the transcription of neural inducer genes (chordin; Noggin, and cerberus) and repress the transcoiption 'ob BMP. Neural inducers inhibit BMP signalling. BMP signalling, promotes epidermal and Ventral mesodermal fater, and repress necral ectodermal and dorsal mesodermal fares.: Neural ectoderm is formed when BAP Signalling is prevented. Epidermis Ventral Mesoderm B catenin (dorsal side of egg) + siamois ('n dorsal epdo ochoderm) + Chondin noggin / Cerberus y BMP (vem toal) besoderm * Neural eetoderne * Dorsal Meso derm

wint lligand) binds to its receptor called frizzled in the presence of the ligand Wmt, Axin is removed from the destruction complex'. Destruction complex consists of Axin , APC, GSK which phospborylares B-catenin in the absence of klot, and ß-catenin is destroyed for proteosomes bars B-catenin then moves into the nuclects, and transcribes the target gemen.

Role of wint signalling in all axis specification is by the establishment of a simple activity gradient whereby high levels of wat leads to posterior Fates and low levels to anterior fares. Thu WIDE signalling leads to activation of ß-catenin in posterior part of the embryo, and the target genes of B-catenin further helps in posteriorisation •