Developmental and cell-specific expression of Cacna1d splice variants
CaV1.3 is an L-type voltage-gated calcium channel implicated in several functions including gene expression, pacemaking activity, and neurotransmitter release. The gene that encodes the CaV1-pore forming subunit of CaV1.3 (Cacna1d) is a multi-exon gene that undergoes extensive alternative splicing, which provides functional versatility to this gene across tissues and cell-types. The function and expression of several Cacna1d splice variants within the C-terminus have been previously characterized. These splice variants differ in their voltage-dependence of activation, Ca2+-dependent inactivation, and their sensitivity to dihydropyridines. However, less is known about alternatively spliced exons in Cacna1d located downstream of domain I and upstream of the C-terminus (e11, e22a/e22, e31a/e31b/e32). Here, we performed a systematic study to determine the developmental and cell-specific expression of several Cacna1d splice variants. We found that the cassette e11 is upregulated during brain development, and in adult cortical tissue is more abundant in excitatory neurons relative to inhibitory interneurons. This exon is also upregulated upon nerve growth factor (NGF) induced differentiation of pheochromocytoma cells, PC12. At the functional level, the splice variants resulting from e11 alternative splicing (+e11-Cacna1d and {Delta}e11-Cacna1d) form functional CaV1.3 channels with similar biophysical properties in expression mammalian systems. Of the pair of mutually exclusive exons, e22a and e22, the later dominates at all stages. However, we observed a slight upregulation of e22 from embryonic to adult human brain. A second pair of mutually exclusive exons, e31a and e31b, was also studied. We found that e31a increases during brain development. Finally, the cassette exon 32 is repressed in adult brain tissue.