Practice question

Competence requirement was proven by tissue recombination. Fujiwara et al. used rSey rats carrying Pax6 mutation. Wild-type optic vesicle grafted onto wild-type head ectoderm induces lens efficiently. When same wild-type vesicle is apposed to Pax6 mutant ectoderm, no lens forms despite normal inductive signals. Reverse combination, mutant optic vesicle with wild-type ectoderm, still induces lens, showing Pax6 needed in responding tissue not inducer. This demonstrates transcription factor acts cell-autonomously in ectoderm to confer ability to interpret BMP and FGF cues, rather than affecting signaling source or neural crest components.