Practice question

Primary embryonic induction defined by Spemann and Mangold as organizer dorsal mesoderm inducing overlying ectoderm to become neural plate rather than epidermis, mediated by BMP antagonists Chordin, Noggin. This mesoderm-ectoderm interaction is archetypal induction: dorsal mesoderm secreting inhibitors instructs competent ectoderm whose fate changes upon contact requiring time for transcription. Secondary inductions like lens or limb involve similar principles. Although endoderm and blastocoel form earlier and neural crest arises later via Wnt and BMP border signals, fundamental conceptual breakthrough concerned mesoderm signaling to ectoderm generating central nervous system and body pattern.