CYTOSKELETON OF CARTILAGE CELLS

The cytoskeleton of chondrocytes consists of microfilaments made of ac tin, microtubules made of tubulin, and intermediate filaments made of a variety of subunits. Actin filaments are not prominent in vivo but m ay form in vitro. In culture, changes in filament polymerisation are i mportant in determining cell shape, initiating chondrogenesis, and mai ntaining the chondrogenic phenotype. Microtubules, besides their role in cell division, organise the distribution of organelles and are invo lved in secretory transport mechanisms in collagen and proteoglycan sy nthesis. A variety of intermediate filaments may be present, frequentl y forming large whorled aggregates. The filaments include vimentin, cy tokeratins, and glial fibrillary acidic protein. These may occur at di fferent depths in articular cartilage. Vimentin accumulates during dev elopment of some fibrocartilages with increased mechanical loading. To gether with other elements of the cytoskeleton, intermediate filaments could form part of a mechanotransduction system by which cells respon d to external forces and sense changes in their external environment. (C) 1994 Wiley-Liss, Inc.