An electronmicroscopic study of microtubules in the development of marginal cells of the mouse stria vascularis.

This study provides an ultrastructural evaluation of cytoplasmic microtubules during the maturation of marginal cells of the mouse stria vascularis. Postnatal marginal cells are cuboidal in structure and over a period of days develop the numerous cellular processes typical of transporting epithelia. Immediately after birth, marginal cells contain numerous microtubules randomly oriented throughout the cytoplasm. Golgi bodies and vesicles are also abundant. The initiation of cellular extension is characterized by the presence of sheet-like extensions of plasma membrane about areas of the cell periphery. Subsequently, large organelle-containing processes form, whose plasmalemma appear pleated due to the presence of the above mentioned sheet-like extensions. Typically, these processes contain microtubules oriented parallel to the direction of their extension. Within these processes, microtubles are closely associated with organelles, such as mitochondria, and may function to displace and stratify these organelles within the processes. The number and length of microtubules increase as the processes grow larger. In the adult mouse, the strial marginal cell processes are attenuated and contain almost exclusively microtubules and mitochondria. The membrane pleats unfold, apparently to provide plasma membrane for cellular extension. The data strongly implicate microtubules in strial development. Furthermore, it is suggested that the depolymerization of microtubules in the adult may underlie strial atrophy.