LOCALIZATION OF MICROTUBULES CONTAINING POSTTRANSLATIONALLY MODIFIED TUBULIN IN COCHLEAR EPITHELIAL-CELLS DURING DEVELOPMENT

In the adult gerbil inner ear, hair cell microtubules contain predomin antly tyrosinated tubulin while supporting cell microtubules contain a lmost exclusively other isoforms. This cell-type specific segregation of tubulin isoforms is unusual, and in this respect the sensory and su pporting cells in this sensory organ differ from other cells observed both in vivo and in vitro. Thus, we hypothesized there must be a shift in the presence and location of tubulin isoforms during development, directly associated with the onset of specialized functions of the cel ls, We describe the appearance and/or disappearance of tubulin isoform s in sensory hair cells and fr iie different supporting cells (inner a nd outer pillar cells, Deiters cells, cells of Kolliker's organ, and c ells of the tympanic covering layer) during development of the gerbil organ of Corti from birth to 14 days after birth. Tyrosinated tubulin was initially present in all cells and remained predominant in cells t hat decrease in number (Kolliker's organ and tympanic covering layer) and exhibit active processes such as secretion and motility (sensory c ells). Posttranslational modifications occurred in the supporting cell s in a time-dependent manner as the number and length of microtubules increased and development proceeded, but the establishment of elongate d cell shape and polarity occurred prior to the appearance of acetylat ion, detyrosination, and polyglutamylation of tubulin. In the pillar a nd Deiters cells, posttranslational modifications progressed from cell apex to base in the same direction as microtubule elongation. In the pillar cells, posttranslational modifications occurred first at the ap ical surfaces. in the pillar cells, tile appearance of acetylated tubu lin was rapidly followed by the appearance of detyrosinated tubulin. I n Deiters cells, the appearance of acetylated tubulin preceded the app earance of detryosinated tubulin by one or more days. At onset uf coch lear function, detyrosinated tubulin and acetylated tubulin had achiev ed their adult-like pattern, but polyglutamylated tubulin had not. (C) 1997 Wiley-Liss, Inc.