Hair cell differentiation following tissue interactions for induction of otocyst morphogenesis

The 12th-12.5th gestational day inner ear otocyst from the CBA/CBA mouse was explanted to organ culture with and without surrounding mesenchyme. One group of otocysts from which the mesenchyme had been removed was cultured in conditioned medium (i.e., medium in which mesenchyme alone had been cultured but had been removed prior to explantation of the "stripped" otocyst, without adjacent mesenchyme). Morphogenesis was good in organ cultures with preserved mesenchyme, acceptable in "stripped" otocysts cultured in conditioned medium, but very poor (or even lacking) in specimens deprived of mesenchyme and cultured in normal medium. In the two latter groups, only a small number of hair cells were identified. Although morphogenesis can be induced in specimens initially deprived of adjacent mesenchyme, a normal tissue relationship seems essential for cytodifferentiation of a normal number of hair cells.