Developmental regulation of tyrosine kinase substrate p36 (calpactin heavy chain) in rat cerebellum.

The tyrosine kinase substrate p36 (calpactin heavy chain) is a calcium-dependent membrane- and cytoskeletal-binding protein. Using an affinity-purified antiserum raised against the p36 heavy chain from bovine adrenal medulla, we have examined the cellular distribution of p36 in developing and adult cerebellum. From immunoblotting, the level of p36 in cerebellum was found to decline during development. In dissociated cell cultures of P4 cerebellum, all cell types were labeled by anti-p36. In vibratome sections from cerebella of P10 rats, anti-p36 stained Purkinje cell bodies strongly and all other cell types less strongly, with the exception of cells in the external germinal layer, which were unstained. By 18 days postnatally p36 was present at higher levels in Bergmann glia and astrocytes of the white matter. In sections of adult cerebella, anti-p36 staining was restricted to Bergmann glial processes and to the processes of a subclass of astrocytes in the granular layer and the white matter. At no developmental stage was anti-p36 staining detectable in axons or dendrites in vibratome sections. These results suggest that p36 plays a role in some aspect of cellular differentiation common to all cerebellar cell types and may have additional functions in astrocytes of the adult cerebellum.