Characterization of Ca 2+-dependent and -independent aggregation mechanisms among mouse cerebellar cells

Abstract

To gain insight into the cellular and molecular mechanisms underlying cell interactions in the early postnatal mouse cerebellum, Ca 2+-dependent and -independent aggregation mechanisms were characterized using single cell suspensions under conditions that allow discrimination between the two mechanisms. When cerebellar cells were derived from newborn to 10-day-old mouse cerebellum, both mechanisms were active and showed no major change in activity during this time period. Mg 2+ could not replace Ca 2+ in the Ca 2+-dependent mechanism. In contrast to the Ca 2+ -independent mechanisms, the Ca 2+-dependent mechanism was inactive at low temperatures, suggesting a necessity for molecular rearrangement within the surface membrane during aggregation. Neuraminidase, chondroitinase, heparinase or hyaluronidase treatment of cells did not influence the aggregation of cells under Ca 2+-dependent and -independent conditions. Chondroitin sulfate inhibited and hyaluronic acid stimulated the Ca 2+-dependent mechanism, whereas chondroitin sulfate only slightly and hyaluronic acid strongly inhibited the Ca 2+-independent one. Dextran sulfate slightly inhibited both mechanisms, whereas heparin and fucoidan, a complex sulfated carbohydrate, did not influence cell aggregation, while they strongly inhibited attachment of cells to laminin. The polycation poly- l-lysine slightly stimulated the Ca 2+-independent mechanism, but inhibited the Ca 2+-dependent one. Interestingly, chondroitin sulfate and hyaluronic acid strongly stimulated cell aggregation under conditions where both mechanisms were almost destroyed or inactive. Dextran sulfate showed only a small effect under these conditions. These observations indicate that different molecular mechanisms are active in cell—cell versus cell—extracellular matrix interactions and suggest a hitherto unknown complexity in molecular mechanisms during early postnatal cerebellar development.