Redundant, exclusive, and cooperative functions of alternative exons in Drosophila Cav2 channels

Abstract

The diversity of voltage gated calcium channel (VGCC) functions greatly outnumbers the count of voltage gated calcium channel genes. One of the ways to increase VGCC functional diversity is alternative splicing. In this thesis I could show for the Drosophila VGCC cacophony, a homolog to the vertebrate Cav2 calcium channel family, that functional diversity is indeed linked to alternative splicing. By using CRISPR/Cas for exon excision as well as electrophysiological methods, confocal microscopy, and behavioral assays, both isoform-specific properties and degenerate functions of exon dependent isoform subsets could be identified. Two alternative exon pairs encoding part of the voltage sensor or accessory subunit binding sites, respectively, were investigated. Differences in isoform localization as well as channel kinetics suggest a division of labor in some parts of the nervous system. Indeed, some of the isoforms fulfill essential functions with behavioral relevance, while others function in a degenerate manner. Although, whether these degenerate ones also exert unique functions under specific conditions remains to be determined. In addition to this, a novel collaborative interaction between two isoforms of the same gene could be discovered. Specifically, lethality resulting from the deletion of one essential isoform and behavioral impairments resulting from the deletion from the other alternative isoform are both fully rescued in trans heterozygous flies carrying both deletions. Both alternative exons have rather similar channel properties but different global and subcellular localizations. They are both required in concert throughout the nervous system for survival and normal motor behavior.