Alternative splicing in the C-terminal tail ofCa_v2.1 is essential for preventing a neurological disease in mice

Alternative splicing (AS) that occurs at the final coding exon (exon 47) of theCa_v2.1 voltage-gated calcium channel (VGCC) gene produces two major isoforms in the brain, MPI and MPc. These isoforms differ in their splice acceptor sites; human MPI is translated into a polyglutamine tract associated with spinocerebellar ataxia type 6 (SCA6), whereas MPc splices to an immediate stop codon, resulting in a shorter cytoplasmic tail. To gain insight into the functional role of the AS in vivo and whether modulating the splice patterns at this locus can be a potential therapeutic strategy for SCA6, here we created knockin mice that exclusively express MPc by inserting the splice-site mutation. The resultant Cacna1a^CtmKO/CtmKO mice developed nonprogressive neurological phenotypes, featuring early-onset ataxia and absence seizure without significant alterations in the basic properties of the channel. Interactions of Ca_v2.1 withCa_vβ4 and Rimbp2 were significantly reduced while those with GABA_B2 were enhanced in the cerebellum of Cacna1a^CtmKO/CtmKO mice. Treatment with the GABAB antagonist CGP35348 partially rescued the motor impairments seen in Cacna1a^CtmKO/CtmKO mice. These results suggest that the carboxyl-terminal domain ofCa_v2.1 is not essential for maintaining the basic properties of the channel in the cerebellar Purkinje neurons but is involved in multiple interactions ofCa_v2.1 with other proteins, and plays an essential role in preventing a complex neurological disease.