The dominant cold-sensitive Out cold mutants of Drosophila melanogaster have novel missense mutations in the voltage-gated sodium channel gene paralytic

Here we report the molecular characterization of Out cold (Ocd) mutants of Drosophila melanogaster, which produce a dominant, X-linked, cold-sensitive paralytic phenotype. From its initial 1.5Mb cytological location within 13F1-16A2, P-element and SNP mapping reduced the Ocd critical region to less than 100kb and to six candidate genes, hangover, CG9947, CG4420, eIF2a, Rbp2 and paralytic (para). Complementation testing with para null mutations strongly suggests Ocd and para are allelic, as does gene rescue of Ocd semi-lethality with a wild-type para transgene. Pesticide resistance and electrophysiological phenotypes of Ocd mutants support this conclusion. The para gene encodes a voltage-gated sodium channel. Sequencing the Ocd lines revealed mutations within highly conserved regions of the para coding sequence, in the transmembrane segment S6 of domain III (I1545M & T1551I), and in the linker between domains III and IV (G1571R), the location of the channel inactivation gate. The G1571R mutation is of particular interest as mutations of the orthologous residue (G1306) in the human skeletal muscle sodium channel gene SCN4A are associated with cases of periodic paralysis and myotonia, including the human cold-sensitive disorder paramyotonia congenita. The mechanisms by which sodium channel mutations cause cold sensitivity are not well understood. Therefore, in the absence of suitable vertebrate models, Ocd provides a system in which genetic, molecular, physiological and behavioral tools can be exploited to determine mechanisms underlying sodium channel periodic paralyses.

Key Words: Drosophila, SCN4A, cold sensitivity, paralysis, sodium channels

Online ISSN: 1943-2361  Print ISSN: 0016-6731
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