Abstracts

RATIONALE: Calcium channels mediate a variety of cellular functions and are involved genetic epilepsy syndromes in mice. The channel complex is a hetero-multimer of four distinct subunts, ?1, ?, ?2? and ?, stochiometrically linked 1:1:1:1. There are mouse mutants for each subunit all with generalized epilepsy. In stg, a spontaneous mutant with generalized epilepsy and ataxia, the defect is in the ?2-subunit (CACNG2). Currently the role of the gamma subunit in calcium channel function remains elusive, although they appear distantly related to the claudin family of tight junction proteins. Our laboratory has reported a family of CACNG genes, 1-5, on human chromosomes 16, 17 and 22 (Burgess et. al. 1999). More recently we found an additional subset, CACNG 6-8 located in a cluster on human chromosome 19 (manuscript in progress). In this study we sought to determine the localization of the gamma subunits in mice, both to define a functional role and to search for potential epilepsy causing genes. METHODS: Screening was performed by PCR amplification of reverse transcribed cDNAs from mouse total RNA samples of brain, cerebellum, heart, skeletal muscle, lung, liver, kidney, spleen, ovary and testes. PCR primers were generated using published mouse sequences (1&2), mouse ESTs (3,4,6), redundant human sequences (5,7,8). Products were sequenced and screened against human and mouse databases to confirm specificity. RESULTS: CACNG 2-4,and 7 were amplified from brain and CACNG7 was also amplified from mouse testes. CACNG1 was found only in skeletal muscle. CACNG6 was found in skeletal muscle, heart and lung. CACNG5, previously found in fetal human kidney RNA, was not seen in any adult or fetal murine samples. CACNG 8 appears localized to brain. CONCLUSIONS: We report the distribution of a large family of calcium channel gamma subunits in mice which includes three novel members of the family, CACNG6-8. Five of the subunits, CACNG2-4, 7 and 8 appear to be expressed in brain and like CACNG2 may be candidates for epilepsy causing genes. Further studies with in situ hybridization are in progress.