Deletion of a specific exon in the voltage-gated calcium channel gene cacophony disrupts locomotion in Drosophila larvae

TAR DNA-binding protein 43 (TDP-43) is an RNA-binding protein that regulates transcription, translation and alternative splicing of mRNA. We have shown previously that null mutations of the Drosophila ortholog, Tar DNA-binding homolog (tbph), causes severe locomotion defects in larvae that are mediated by a reduction in the expression of a type II voltage-gated calcium channel, cacophony (cac). We also showed that TDP-43 regulates the inclusion of alternatively spliced exons of cacophony; tbph mutants showed significantly increased expression of cacophony isoforms lacking exon 7, a particularly notable finding as only one out of the 15 predicted isoforms lacks exon 7. To investigate the function of exon 7, we generated Drosophila mutant lines with a deletion that eliminates exon 7. This deletion phenocopies many defects in tbph mutants: a reduction in cacophony protein (Dmca1A) expression, locomotion defects in male and female third instar larvae, disrupted larval motor output, and also reduced activity levels in adult male flies. All these defects were rescued by expression of cacophony transcripts containing exon 7. By contrast, expression of a cacophony cDNA lacking exon 7 resulted in reduced cacophony protein levels and failed to rescue larval locomotion.