Profiling the array of Ca_v3.1 variants from the human T-type calcium channel gene CACNA1G: Alternative structures, developmental expression, and biophysical variations

We describe the regulated transcriptome of CACNA1G, a human gene for T-type Ca_v3.1 calcium channels that is subject to extensive alternative RNA splicing. Fifteen sites of transcript variation include 2 alternative 5′-UTR promoter sites, 2 alternative 3′-UTR polyadenylation sites, and 11 sites of alternative splicing within the open reading frame. A survey of 1580 fetal and adult human brain full-length complementary DNAs reveals a family of 30 distinct transcripts, including multiple functional forms that vary in expression with development. Statistical analyses of fetal and adult transcript populations reveal patterns of linkages among intramolecular splice site configurations that change dramatically with development. A shift from nearly independent, biased splicing in fetal transcripts to strongly concerted splicing in adult transcripts suggests progressive activation of multiple "programs" of splicing regulation that reorganize molecular structures in differentiating cells. Patch-clamp studies of nine selected variants help relate splicing regulation to permutations of the gating parameters most likely to modify T-channel physiology in expressing neurons. Gating behavior reflects combinatorial interactions between variable domains so that molecular phenotype depends on ensembles of coselected domains, consistent with the observed emergence of concerted splicing during development. We conclude that the structural gene and networks of splicing regulatory factors define an integrated system for the phenotypic variation of Ca_v3.1 biophysics during nervous system development.