High gelsolin content of developing oligodendrocytes.
The actin-binding protein gelsolin that severs and caps the actin microfilaments under the control of the cytoplasmic free calcium and the membranous phosphatidylinositol 4,5-bisphosphate, is essentially restricted to the oligodendroglia in the central nervous system. Immunocytochemistry 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 precursor oligodendrocyte cells and the specific expression of gelsolin in OL-1-, GC-, and MBP-positive oligodendrocytes in culture. The protein was distributed throughout the cell body and in the branched cell processes of cultured oligodendrocytes, but not in the MBP-positive membrane sheets. Gelsolin is thus cytosolic and not a myelin component. The quantitative study demonstrated that that the cerebellar gelsolin content changes significantly with age, with the maximal value at the age of 21 days, confirming that large amounts of gelsolin are transiently synthesized during development, especially from the first events of myelinogenesis. The results are consistent with gelsolin being involved, through its effects on the actin cytoskeleton, in the motile events occurring during the growth of the oligodendroglial processes towards the axons and the wrapping of the myelin sheaths around the axons.