ADrosophilaCalcium Channel α1 Subunit Gene Maps to a Genetic Locus Associated with Behavioral and Visual Defects

Abstract

We have cloned cDNAs that encode a complete open reading frame for a calcium channel alpha1 subunit from Drosophila melanogaster. The deduced 1851 amino acid protein belongs to the superfamily of voltage-gated sodium and calcium channels. Phylogenetic analysis shows that the sequence of this subunit is relatively distant from sodium channel alpha subunits and most similar to genes encoding the A, B, and E isoforms of calcium channel alpha1 subunits. To indicate its similarity to this subfamily of vertebrate isoforms, we name this protein Dmca1A, for Drosophila melanogaster calcium channel alpha1 subunit, type A. Northern blot analysis detected a single 10. 5 kb transcript class that is regulated developmentally, with expression peaks in the first larval instar, midpupal, and late pupal stages. In late-stage embryos, Dmca1A is expressed preferentially in the nervous system. Variant transcripts are generated by alternative splicing. In addition, single nucleotide variations between cDNAs and genomic sequence are consistent with RNA editing. Dmca1A maps to a chromosomal region implicated in, and is the likely candidate for, the gene involved in the generation of behavioral, physiological, and lethal phenotypes of the cacophony, nightblind-A, and lethal(1)L13 mutants.

Presynaptic N-type Calcium Channels Regulate Synaptic Growth

“…Previous genetic analysis of Dmca1A revealed several lethal mutations that map to the locus (19). Out of five embryonic lethal alleles of Dmca1A, we examined Dmca1A 6 , Dmca1A 10 , Dmca1A 13 , Dmca1A 20 , and Dmca1A 24 ; Dmca1A 13 behaves similar to a deficiency in complementation testing with our TS mutants and has been reported previously (19) to act as a null mutant in complementation testing with other cacophany and nightblind alleles of the Dmca1A locus. Therefore, we performed immunocytochemistry on Dmca1A 13 embryos in trans to a small deficiency (Df(1)RC29) that removes the Dmca1A locus.…”

“…Dmca1A NT27 was the most severe allele isolated, requiring progressively longer recovery times with increased length of exposure to 38°C. The temperature-sensitive phenotype of each allele was rescued with a small chromosomal duplication (Dp(1;2)v65b) encompassing the wild-type Dmca1A locus (19), indicating the behavioral defects result from disruption of the N-type calcium channel. Behavioral analysis of the TS mutants as well as complementation testing with other Dmca1A alleles suggest an allelic series of decreasing severity, NT27 Ͼ TS3 Ͼ TS4 Ͼ TS5.…”

“…Dmca1A is abundantly expressed in the Drosophila nervous system (19) and encodes the presynaptic N-type calcium channel responsible for calcium influx that triggers synaptic vesicle fusion (24). Null mutations in Dmca1A are embryonic lethal (lethal(1)L13), whereas partial loss-of-function mutations disrupt synaptic transmission, leading to defects in various behaviors, including courtship (cacaphony) and phototaxis (nightblind-A) (19,24,42).…”

“…Recombination mapping was performed with a y cho cv v f marked strain. Rescue experiments were performed using a duplication (Dp(1;2)v65b) covering the Dmca1A locus (19). The Dmca1A 13 mutant has also been referred to as l(1)L13 and l(1)11Aa13 (19,42).…”

“…In both cases, the R876C charge neutralization reduces the sensitivity of the channel to voltage, shifting the conductance-voltage relationship and requiring more depolarization for channel activation. Indeed, the third arginine in the S4 voltage domain has been shown to contribute more than any other S4 charged residue in (19), and the P1385S change found in Dmca1A TS2 (62). B, the Arg-876 amino acid (circled) is conserved in all voltage-gated ion channels through evolution and forms the third charged residue in the S4 voltage sensor transmembrane helix.…”