Practice question

BMP morphogen gradient patterns ectoderm: highest ventrally, lowest dorsally. High BMP4/7 activates Smad1/5/8 complexing with Smad4, translocating to nucleus inducing epidermal keratin genes XK81, AP2 and GATA2 while repressing Sox2 and Neurogenin. Animal caps exposed to BMP become ciliated epidermis. In intact embryo lateral and ventral ectoderm receiving high BMP becomes epidermis covering embryo, dorsal ectoderm protected by organizer antagonists becomes neural plate. Neural crest forms at intermediate BMP border. Thus high BMP specifies epidermis rather than neural, crest or endoderm fates. This illustrates conserved developmental logic of morphogen gradients patterning embryonic axes through Wnt and BMP antagonism.