Formation of junctional complexes in otocysts developed in vitro. A freeze-fracture study.

The thirteenth gestational day inner ear anlage (otocyst) was explanted to an in vitro system and cultured for 8 days, i.e. to a time corresponding to birth. The freeze fracturing technique was used to evaluate morphological differentiation, particularly as regards cell membrane specializations. The epithelial cells were found fully differentiated, e.g. there were regularly arranged stereocilia on the hair cells. The development of tight junctions and gap junctions followed the same pattern as in vivo, but tight junctions did not reach the same degree of regularity and maturation as they did in vivo. There were very few gap junctions in our in vitro specimens. Several tight junctions had an odd appearance, with loss of the normally punctate structure of the strands and areas with considerable thickening. It is possible that this specific morphology can be explained by differentiation in the in vitro system.