entla, a Novel Epileptic and Ataxic Cacna2d2 Mutant of the Mouse

Abstract

entla (ent) is a novel recessive phenotype of mice. The underlying mutation was mapped to chromosome 9 (60.1 centimorgans) and identified as an allele of the Cacna2d2 gene encoding the α2δ-2 subunit of voltage-gated calcium channels. The Cacna2d2entla allele harbors a 38-kb duplication comprising the 117 nucleotides of exon 3. The predicted duplication of 39 amino acid residues near the subunit's N terminus results in the expression of a full-length, membrane-associated protein. Western blot data were consistent with correct cleavage of the α2δ-2entla precursor into α2entla and δ2 proteins but indicated loss of the disulfide linkage between the two proteins. ent/ent mice develop ataxia by postnatal day 13-15, followed by paroxysmal dyskinesin a few days later. Two distinct types of cortical and hippocampal epileptic activity at 2 and 4 Hz were recorded, indicative of absence epilepsy. Homozygotes display reduced size and weight, increased mortality before weaning, and female infertility. No overt neuroanatomical abnormalities were detected. Ca 2+ current densities recorded from acutely dissociated Purkinje cells of homozygous entla animals were reduced by 50% compared with wild type. Ligand binding assays using the antiepileptic drug [3H]gabapentin, a specific ligand of the α2δ-1 and α2δ-2 subunits, revealed a >60% reduced maximum binding to cerebellar membranes of ent/ent compared with unaffected littermates. entla is allelic to ducky and ducky 2J, representing the third murine Cacna2d2 allele identified and so far the only one encoding an untruncated protein that is incorporated into membranes.