Genomic organization, expression, and phylogenetic analysis of Ca2+ channel β4 genes in 13 vertebrate species

Ebert AM, McAnelly CA, Handschy AV, Mueller RL, Horne WA, Garrity DM. Genomic organization, expression, and phylogenetic analysis of Ca2+ channel beta 4 genes in 13 vertebrate species. Physiol Genomics 35: 133-144, 2008. First published August 5, 2008; doi: 10.1152/physiolgenomics.90264.2008.-The Ca2+ channel beta-subunits, encoded by CACNB genes 1-4, are membrane-associated guanylate kinase ( MAGUK) proteins. As auxiliary subunits of voltage-gated Ca2+ channels, the beta-subunits facilitate membrane trafficking of the pore-forming alpha 1 subunits and regulate voltage-dependent channel gating. In this report, we investigate whether two zebrafish beta 4 genes, beta 4.1 and beta 4.2, have diverged in structure and function over time. Comparative expression analyses indicated that beta 4.1 and beta 4.2 were expressed in separable domains within the developing brain and other tissues. Alternative splicing in both genes was subject to differential temporal and spatial regulation, with some organs expressing different subsets of beta 4.1 and beta 4.2 transcript variants. We used several genomic tools to identify and compare predicted cDNAs for eight teleost and five tetrapod beta 4 genes. Teleost species had either one or two beta 4 paralogs, whereas each tetrapod species contained only one. Teleost beta 4.1 and beta 4.2 genes had regions of sequence divergence, but compared with tetrapod beta 4s, they exhibited similar exon/intron structure, strong conservation of residues involved in alpha 1 subunit binding, and similar 5' alternative splicing. Phylogenetic results are consistent with the duplicate teleost beta 4 genes resulting from the teleost whole genome duplication. Following duplication, the beta 4.1 genes have evolved faster than beta 4.2 genes. We identified disproportionately large second and third introns in several beta 4 genes, which we propose may provide regulatory elements contributing to their differential tissue expression. In sum, both mRNA expression data and phylogenetic analysis support the evolutionary divergence of beta 4.1 and beta 4.2 subunit function.