Tissue and life stage specific alternative splicing of a Kir channel in mosquitoes

Inward-rectifier potassium (Kir) channels are key players in nerve, muscle, and epithelial function in mammals, but a comprehensive understanding of their physiological roles in insects remains to be determined.  Mosquitoes (Aedes aegypti) possess five different genes encoding Kir channel subunits: Kir1, Kir2A, Kir2B, Kir2Bʹ, and Kir3.  Previously, we have 1) cloned the cDNAs of Kir1, Kir2B, and Kir3 expressed in the renal (Malpighian) tubules and 2) shown that Kir channels are important to the excretory physiology of adult female mosquitoes (Ae. aegypti).  Here we characterize the expression of Kir2A in various tissues and life stages of Ae. aegypti.  Notably, we find that Kir2A mRNAs are expressed as three distinct splice variants that encode three different Kir2A proteins with novel N-terminal and/or C-terminal domains.  Genomic databases of Anopheles gambiae and Drosophila melanogaster confirm similar splicing patterns of Kir2A mRNAs in these dipteran insects.  Examination of the genomic structure of Kir2A reveals that each species uses 1) an upstream 5ʹ exon to encode a unique N-terminus and 2) a downstream cassette exon or intron retention to vary the C-terminus.  Furthermore, RT-PCR analyses show that in Ae. aegypti, the relative expression of the splices varies by tissue and life stage, which suggests that the encoded proteins may perform specific physiological roles.  Funded by a grant from the Foundation for the NIH, VCTR program.