We examined a number of Drosophila mutants with increased susceptibility to
We examined a number of Drosophila mutants with increased susceptibility to seizures following mechanical or electrical stimulation to better understand the underlying factors that predispose neurons to aberrant activity. their increased seizure susceptibility (Kuebler and Tanouye 2000). Additionally, administration of valproate, phenytoin, gabapentin, and potassium bromide, all of which act as anticonvulsants in humans, suppresses seizures in bang-sensitive mutants (Kuebler and Tanouye 2002; Reynolds 2004; Tan 2004). The affected loci of several of the bang-sensitive mutations have been identified, including two mitochondrial proteins, a mitochondrial ribosomal protein (1987; Zhang 1999). Additionally, mutations in an ethanolamine kinase (1994; Zhang 2002). Although molecular identification of two mutants with mitochondrial defects suggests that impaired aerobic metabolism may generate this seizure phenotype, the physiological mechanism remains unclear (Jan and Jan 1978; Ganetzky and Wu 1982; Royden 1987; Schubiger 1994; Zhang 1999). TABLE 1 Summary of phenotypes and gene products among known bang-sensitive Drosophila mutants To further characterize the mechanisms underlying bang sensitivity in Drosophila and to test the hypothesis that these seizure phenotypes are due to metabolic disruption, we have characterized a new bang-sensitive mutant and performed additional analysis of previously studied mutants. We molecularly identified (as well as in several other bang-sensitive mutants. Electrophysiological analysis revealed alterations in neuronal firing patterns in the giant fiber (GF) pathway of these mutants. Our results demonstrate that metabolic perturbations can alter membrane excitability and increase seizure susceptibility. MATERIALS AND METHODS Fly strains: Flies were cultured on cornmealCmolasses agar medium at 22C29. Bang-sensitive mutant strains used in this study include (diagrammed in Figure 1A)were utilized for complementation analysis and mapping of locus (CG3861) were isolated elsewhere [(Bourbon 2002) and (Berkeley Drosophila Genome Project)]. Aconitase lines and were used for genetic interaction experiments. Wild type and control refer to Canton-S, unless otherwise stated. Figure 1. Genetic mapping of the locus. (A) Complementation testing of bang sensitivity using X chromosome deficiencies in the 5AC6A region resulted in failure of complementation by two deficiencies, and homozygotes are developmentally delayed; time to eclosion is 4C7 days longer than wild type at room temperature. This delay is similar to that reported for and as well as that for other mutants with deficits in cellular metabolism, including mutants. Bang-sensitive paralysis in homozygotes shows incomplete penetrance and variable expressivity that is independent of differences in age, rearing density, time of eclosion, or time of day. On the basis of previous recombinational mapping (Ganetzky and Wu 1982), we performed deficiency mapping of in the region between cytological positions 5A and 9F on the X chromosome. failed to complement did complement by R. Kreber (personal communication) revealed breakpoints at 5D2C3;5E4C6, which defined a distal limit for was heterozygous with a noncomplementing deficiency than in homozygotes. Females carrying a single wild-type allele of (males, which carry X-chromosome region 5A;6D inserted into the Y chromosome. Attempts to align the cytological map with the genomic sequence in the 5E interval indicated that the alignment given in FlyBase is incorrect. Primer pairs designed to cover cytological regions 5E2 through 5E8 (domains ACF in Figure 1A) gave positive PCR products for templates isolated from embryos homozygous for each of the deficiencies examined except and and either of these elements displayed the same increase in severity of the bang-sensitive phenotype as in flies, buy Angiotensin 1/2 (1-6) suggesting that the insertions are null alleles. Transposase-mediated precise excision of each element resulted in viable revertants that complemented (Figure 2). The and are within the same large intron of CG3861 (Figure 1B), identifying it as the locus. Consistent with this, RTCPCR analysis revealed that of the four genes neighboring these elements, only CG3861 showed a Rabbit Polyclonal to MAP2K3 (phospho-Thr222) buy Angiotensin 1/2 (1-6) marked reduction in expression in embryos homozygous for the genotypes. Animals of the genotype indicated were observed for their time to recover following 15 sec of mechanical stimulation (> 10 for each sample; error bars represent SEM). Wild-type and control animals … Molecular identification of mutant revealed an R95H substitution in the encoded protein (Figure 3). buy Angiotensin 1/2 (1-6) This change was not found in the wild-type background in which was generated, nor were any sequence changes found in the neighboring gene, CG3446. The arginine residue altered in is highly conserved in all species from yeast to humans (Figure 3) and corresponds to R94 in the human protein. This residue has not been implicated previously in enzymatic function (Wiegand and Remington 1986). Figure 3. Sequence alignment of citrate synthase in the region of the mutation. This region is definitely highly conserved buy Angiotensin 1/2 (1-6) in all known eukaryotic.