Presence of protein I, a phosphoprotein associated with synaptic vesicles, in cerebellar granule cells

The cerebellar levels of Protein I, a synapse-specific neuronal phosphoprotein, have been investigated in the cerebellar mouse mutants stagger (sg), weaver (wv), nervous (nr), and Purkinje cell degeneration (pcd). The Protein I concentration was reduced by about 66% in sg and wv mutants, representing a 90% loss of Protein I per cerebellum. A heterozygote effect was observed in the wv mutant. These results indicate that a great majority of Protein I in the normal cerebellum may be present in the granule cells. In nr mutants the cerebellar Protein I concentration was reduced by only 12% in 62-day-old mice, suggesting that Purkinje cells contribute little to cerebellar Protein I. However, a greater reduction was observed in pcd mutants, which may reflect on the nature of the pcd mutation.