Microtubule assembly in the cochlea of the mouse

Abstract

Pillar cells of the organ of Corti of the mouse were examined after fixation and embedding for transmission electron microscopy. These specialised epithelial cells have transcellular microtubule arrays which are parallel to the longitudinal axes of the cells. Array microtubules have diameters of about 28 nm and are probably composed of 15 protofilaments. These microtubules have, in Inner pillar cells, nucleating sites which are associated with the lateral plasmalemma. Microtubules of the inner pillar cell array start to elongate during the second day post-partum. Assembly of microtubules of outer pillar cells Is temporally distinct. This assembly does not appear to start until about the third day post-partum. Array assembly in inner pillar cells occurs at the same stages in vitro as in vivo but with a reduction in the overall number of microtubules present. These have the same diameter as those which elongate in vivo and also exhibit similar end-on anchorage to the lateral plasmalemma. After culturing the organ of Corti in vitro, the microtubule array is similar in structure to that which assembles in situ, the arrays have a tubular configuration. This is produced by the annular configuration of lateral plasmalemma-associated microtubule nucleating sites. This contrasts with the array configuration in outer pillar cells. Nucleatlon sites in these cells are situated in a small apical turret-like process which produces the rod-like configuration of the microtubule array. In both inner and outer pillar cells, microtubules which have small diameters of about 21 nm, are associated with the centrosome. These microtubules are randomly oriented at the apical region of each cell.