DEVELOPMENTAL ANALYSIS OF THE SMELLBLIND MUTANTS - EVIDENCE FOR THE ROLE OF SODIUM-CHANNELS IN DROSOPHILA DEVELOPMENT

We have recently found evidence that two smellblind mutants, originall y identified as olfactory mutants, define a new class of mutation in t he para (paralytic) sodium channel gene (Lilly et al., in press). Thes e two mutants have previously been shown to be heat-sensitive developm ental lethals: animals raised at elevated temperatures die as embryos or as young larvae (Lilly and Carlson, 1990, Genetics 124, 293-302). T his article shows, surprisingly, that both mutants are not only heat-s ensitive lethals, but also cold-sensitive lethals: when raised at redu ced temperatures, the mutants develop to the adult stage, but then die prematurely. Moreover, this effect is sexually dimorphic, in that let hality is substantially greater for females than males. The associatio n of cold-sensitivity with mutations of a sodium channel gene has rece ntly been found in the case of a cold-sensitive human muscle disease, paramyotonia congenita, in which sodium channel function is defective (Ptacek et al., 1992, Neuron 8, 891-897). The heat-sensitive and cold- sensitive periods for the two smellblind mutants are determined throug h a series of reciprocal temperature shift experiments and are found t o be different. Most, if not all, of the contribution to the heat-sens itive lethality occurs before metamorphosis, whereas the cold-sensitiv ity is particularly pronounced after the onset of metamorphosis. These results are discussed in terms of the developmental role of the para sodium channel and the role of electrical activity in Drosophila devel opment. (C) 1994 Academic Press, Inc.