Phenotypic modulation of nasal septal chondrocytes by cytoskeleton modification

The reversion to the initial round shape of chondrocytes in monolayer cultu res is one of the initial events required for the expression of cartilage-s pecific macromolecules. Thus, considerable research efforts have focused on developing reliable procedures to maintain a round morphology of cultured chondrocytes. Our study focuses on evaluating the response of dedifferentia ted fetal rat chondrocytes to cytochalasin D, an actin-disrupting agent, wi th special emphasis on the morphological events. Immediately after exposure to the drug, cells round up but Batten again after removing the agent. How ever, immunocytochemical procedures revealed a disorganization of microfila ments and intermediate filaments. Phase-contrast and scanning electron micr oscopic observations revealed that on day 6 of culture, cells located at th e top of the cell layer adopted a spherical morphology. Prominent differenc es were noted in control cultures where cells had to aggregate prior to ove rt chondrogenesis. These morphological changes occurred parallel to the exp ression of type II collagen, marker of the chondrocytes phenotype, strongly expressed in experimental cultures, but relatively weak in control culture s, and only restricted on areas of polygonal cellular aggregates. Furthermo re, [S-35]-sulphate incorporation into sulphated glycosaminoglycans increas ed rapidly with the period of culture to a maximum after 7 days and was the n two-fold in treated cultures. Taken together. these findings indicated th at cytochalasin-D stimulates chondrogenesis in response to modification of cytoskeleton architecture and the subsequent rounding up of the cells.