Postnatal apoptosis in cerebellar granule cells of homozygous leaner (tg1a/tg1a) mice.

Leaner mice carry a homozygous, autosomal recessive mutation in the mouse CACNA1A gene encoding the Alpha1A subunit of P/Q-type calcium channels, which results in an out-of-frame splicing event in the carboxy terminus of the Alpha1A protein. Leaner mice exhibit severe ataxia, paroxysmal dyskinesia and absence seizures. Functional studies have revealed a marked decrease in calcium currents through leaner P/Q-type channels and altered neuronal calcium ion homeostasis in cerebellar Purkinje cells. Histopathological studies of leaner mice have revealed extensive postnatal cerebellar Purkinje and granule cell loss. We examined the temporospatial pattern of cerebellar granule cell death in the leaner mouse between postnatal days (P) 10 and 40. Our observations clearly indicate that leaner cerebellar granule cells die via an apoptotic process and that the peak time of neuronal death is P20. We did not observe a significant increase in microglial and astrocytic responses at P20, suggesting that glial responses are not a cause of neuronal cell death. We propose that the leaner cerebellar granule cell represents an in vivo animal model for low intracellular [Ca2+]-induced apoptosis. Since intracellular [Ca2+] is critical in the control of gene expression, it is quite likely that reduced intracellular [Ca2+] could activate a lethal cascade of altered gene expression leading to the apoptotic granule cell death in the leaner cerebellum.