The kinocilium of auditory hair cells and evidence for its morphogenetic role during the regeneration of stereocilia and cuticular plates.

Auditory hair cells that survive mechanical injury in culture begin their recovery by reforming the kinocilium. This study is based on cultures of the organ of Corti of newborn mice and two control animals. The axonemal patterns were examined in 165 kinocilia in cross-section. In the immature and regenerating kinocilium, one of the normally peripheral doublets is frequently located inward, forming the modified 8 + 1 (double) form; the distribution of the remaining microtubules is irregular. As the cell matures, the 9 + 0 form predominates. Overall, 34-61% of auditory kinocilia consist of 9 + 0 microtubules. The 9 + 2 (single) form, previously thought to characterize the organelle, occurs only in about 3-14%, whereas the remaining population comprises the modified 8 + 1 (double) form. Normally, the kinocilium lasts only about 10 postnatal days; however, post-traumatic hair cells reform their kinocilia regardless of age. Concomitant with the regrowth of the kinocilium, the basal body and its cilium take a central location in the cuticular plate, stereocilia regrow, and the cytoplasmic area adjacent to the basal body displays pericentriolar fibrous densities, growth vesicles, and microtubules, all surrounded by actin filaments. Pericentriolar bodies nucleate microtubules. Involvement of microtubules is seen in the alignment of actin filaments and in the formation of the filamentous matrix of the cuticular plate. We propose that reformation of the kinocilium in recovering post-traumatic hair cells indicates the possible role of its basal body in the morphogenesis and differentiation of cuticular plates and stereocilia.