Immunological evidence that the β isoform of Ca²⁺/calmodulin-dependent protein kinase IV is a cerebellar granule cell-specific product of the CaM kinase IV gene

Ca2⁺/calmodulin-dependent protein kinase IV (CaM kinase IV) exists as two monomeric isoforms, α and β. In this study, we raised an antibody against the β isoform and provided immunohistochemical evidence for specific expression of the β isoform in cerebellar granule cells as a single gene-derived translational product distinct from the α isoform. Immunohistochemical examination showed that the β-immunoreactivity was confined to the nuclei of the cerebellar granule cells, in contrast to the more widespread immunoreactivity for the α isoform in both nuclei and cytoplasm of the cerebellar granule cells and many other neurons with dominant nuclear localization. In developing cerebella, the β-immunoreactivity gradually appeared in the internal granule cells during the postnatal 2nd and 3rd weeks, while the α-immunoreactivity had already appeared in the internal granule cells in the 1st postnatal week. Unlike the α isoform, β-immunoreactivity was not detected in the Purkinje cells at any developmental stages. The differential expression of the α and β isoforms suggests that each isoform may be involved in different cerebellar functions.