enhancer of seizure: A New Genetic Locus in Drosophila melanogaster Defined by Interactions With Temperature-Sensitive Paralytic Mutations

摘要

Mutations in the enhancer of seizure ( e ( sei )) locus have been isolated on the basis of their ability to cause temperature-induced paralysis of alleles at the seizure ( sei ) locus at temperatures at which these mutations ordinarily do not paralyze. This enhancer is specific to the seizure locus and is without effect on other temperature-sensitive paralytic mutants including para, nap, tip-E and shi . This suggests that the enhancer responds specifically to the mechanism of paralysis mediated by the seizure mutations. The e ( sei ) is a recessive mutation which maps to 39.0 on the left arm of chromosome 3 . Deficiency mapping has placed it at 69A4-B5 on the salivary gland polytene chromosome map. When a new enhancer allele was isolated following P-M hybrid dysgenesis, there was a concomitant P -element insertion at 69B. In the absence of seizure mutations, the enhancer mutation causes non-temperature dependent hyperactivity when agitated and interferes with the climbing response. Electrophysiological studies examined the effects of increasing temperature on electrical activity in the adult giant fiber/flight muscle system. Neuronal hyperactivity was seen in both e ( sei ) and sei single mutant homozygotes, but not in wild type. The hyperactivity was more severe in the sei ; e ( sei ) double mutants. The correlation between the physiological effects and the mutant behavior suggests that both sei and e ( sei ) cause membrane excitability defects. Since previous work has shown that seizure mutants affect [3H]saxitoxin binding to the voltage-sensitive sodium channel, e ( sei ) may code for a gene product which interacts with this channel.