Practice question

Classic embryology experiment transplanting optic vesicle to trunk ectoderm demonstrates regional restriction of lens competence. Trunk ectoderm lacks Pax6-primed head ectoderm program and fails to activate Sox2, L-Maf, and crystallin genes despite receiving BMP4 and FGF8 signals from transplanted optic vesicle. Consequently no ectopic lens forms, Pax6 remains silent in trunk cells, Sox2 not induced lens-wise, confirming necessity of pre-existing competence factors restricted to head region. This result established concept of competence: inductive signal alone insufficient without appropriate receiving tissue transcriptional context enabling response and differentiation.