Originally published as Genetics Published Articles Ahead of Print on August 24, 2008.

Genetics, Vol. 180, 873-884, October 2008, Copyright © 2008
doi:10.1534/genetics.108.090951

The Dominant Cold-Sensitive Out-Cold Mutants of Drosophila melanogaster Have Novel Missense Mutations in the Voltage-Gated Sodium Channel Gene paralytic

Helen A. Lindsay^*,,1, Richard Baines, Richard ffrench-Constant, Kathryn Lilley^**, Howard T. Jacobs^*, and Kevin M. C. O'Dell^*,2

^* IBLS Division of Molecular Genetics, University of Glasgow, Glasgow G11 6NU, United Kingdom, Institute of Medical Technology and Tampere University Hospital, FI-33014 University of Tampere, FI-33014 Tampere, Finland, Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, United Kingdom, Centre for Ecology and Conservation, Cornwall Campus, University of Exeter, Penryn, Cornwall TR10 9EZ, United Kingdom and ^** Cambridge Centre for Proteomics, Cambridge System Biology Centre, Department of Biochemistry, University of Cambridge, Cambridge CB2 1QR, United Kingdom

² Corresponding author: IBLS Division of Molecular Genetics, Anderson College Complex, University of Glasgow, 56 Dumbarton Rd., Glasgow G11 6NU, UK.
E-mail: k.odell{at}bio.gla.ac.uk

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 1.5-Mb cytological location within 13F1-16A2, P-element and SNP mapping reduced the Ocd critical region to <100 kb 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 semilethality 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 and 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.

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