HIGH GELSOLIN CONTENT OF DEVELOPING OLIGODENDROCYTES

The actin-binding protein gelsolin that severs and caps the actin micr ofilaments under the control of the cytoplasmic free calcium and the m embranous phosphatidylinositol 4,5-bisphosphate, is essentially restri cted to the oligodendroglia in the central nervous system. Immunocytoc hemistry showed that gelsolin is an early marker of oligodendrocytes, both in vivo, in the rat cerebellum, and in vitro, in oligodendrocyte culture. We report the early appearance of gelsolin in A2B5-positive p recursor oligodendrocyte cells and the specific expression of gelsolin in OL-1-, GC-, and MBP-positive oligodendrocytes in culture. The prot ein was distributed throughout the cell body and in the branched cell processes of cultured oligodendrocytes, but not in the MBP-positive me mbrane sheets. Gelsolin is thus cytosolic and not a myelin component. The quantitative study demonstrated that the cerebellar gelsolin conte nt changes significantly with age, with the maximal value at the age o f 21 days, confirming that large amounts of gelsolin are transiently s ynthesized during development, especially from the first events of mye linogenesis. The results are consistent with gelsolin being involved, through its effects on the actin cytoskeleton, in the motile events oc curring during the growth of the oligodendroglial processes towards th e axons and the wrapping of the myelin sheaths around the axons.