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.

Messenger RNA editing of transcripts encoding voltage-sensitive ion channels has not been extensively analyzed--least of all in Drosophila, for which several channel-encoding genes are known. Previous sequence studies of D. melanogaster's cacophony gene, which encodes an alpha 1 calcium-channel subunit called Dmca1A, suggested that several nucleotides within the ORF of the primary transcript are edited such that "A-to-G" substitutions occur (these two nucleotides being the adenine that is found at the relevant sites in the sense strand of genomic DNA or the primary transcript, compared to the substitution of guanine that is detected at the level of cDNA analysis). Such A-to-G changes are the same kind of post-transcriptional variations originally discovered--in a neurobiological context--for a ligand-sensitive channel in vertebrates. Here, we extracted RNA from adult flies and revealed, by RT-PCR and restriction-enzyme analyses, that transcript heterogeneity exists in vivo for three distinct edited sites within the cac-encoded RNA. Each such nucleotide would lead to channel variability at the level of the Dmca1A polypeptide. Owing to cacophony being originally identified as a "behavioral gene," the possible significance of Dmca1A RNA editing for influencing the relevant neuro-functional phenotypes is discussed.

The voltage-gated Na (+) channels (VGSC) are complex membrane proteins responsible for generation and propagation of the electrical signals through the brain, the skeletal muscle and the heart. The levels of sodium channels affect behavior and physical activity. This is illustrated by the maleless mutant allele (mle (napts)) in Drosophila, where the decreased levels of voltage-gated Na(+) channels cause temperature-sensitive paralysis. Here, we report that mle (napts) mutant flies exhibit developmental lethality, decreased fecundity and increased neurodegeneration. The negative effect of decreased levels of Na(+) channels on development and ts-paralysis was more pronounced at 18 and 29°C than at 25°C, suggesting particular sensitivity of the mle (napts) flies to temperatures above and below normal environmental conditions. Similarly, longevity of mle (napts) flies was unexpectedly short at 18 and 29°C compared with flies heterozygous for the mle (napts) mutation. Developmental lethality and neurodegeneration of mle (napts) flies was partially rescued by increasing the dosage of para, confirming a vital role of Na(+) channels in development, longevity and neurodegeneration of flies and their adaptation to temperatures.