Mutational Analysis of the Shab-encoded Delayed Rectifier K+ Channels in Drosophila

Abstract

K؉ currents in Drosophila muscles have been resolved into two voltage-activated currents (I A and I K ) and two Ca 2؉ -activated currents (I CF and I CS ). Mutations that affect I A (Shaker) and I CF (slowpoke) have helped greatly in the analysis of these currents and their role in membrane excitability. Lack of mutations that specifically affect channels for the delayed rectifier current (I K ) has made their genetic and functional identity difficult to elucidate. With the help of mutations in the Shab K ؉ channel gene, we show that this gene encodes the delayed rectifier K ؉ channels in Drosophila. Three mutant alleles with a temperature-sensitive paralytic phenotype were analyzed. Analysis of the ionic currents from mutant larval body wall muscles showed a specific effect on delayed rectifier K ؉ current (I K ). Two of the mutant alleles contain missense mutations, one in the aminoterminal region of the channel protein and the other in the pore region of the channel. The third allele contains two deletions in the amino-terminal region and is a null allele. These observations identity the channels that carry the delayed rectifier current and provide an in vivo physiological role for the Shab-encoded K ؉ channels in Drosophila. The availability of mutations that affect I K opens up possibilities for studying I K and its role in larval muscle excitability.

Robustness of Neural Coding inDrosophilaPhotoreceptors in the Absence of Slow Delayed Rectifier K+Channels

“…The gene encoding the slow delayed rectifier in Drosophila photoreceptors has so far not been identified. Because mutations at the Shab locus are known to affect sustained K ϩ currents in Drosophila muscles (Hegde et al, 1999), we performed voltage-clamp recordings of isolated photoreceptors from Shab 3 flies. The results show that the Shaker current was unaffected but the slowly inactivating current was eliminated (Fig.…”

“…Three alleles of the Shab gene (Shab 1 , Shab 2 , and Shab 3 ) were used either in ebony or WT background. Shab 1 and Shab 2 are missense mutations, whereas Shab 3 is a null allele (Hegde et al, 1999). The Shaker 14 null allele (a missense mutation in the core region resulting in nonfunctional Shaker channels) and Shaker 14 ;Shab 3 double mutants were also used in red-eyed flies.…”

Mutations in Cytochrome c Oxidase Subunit VIa Cause Neurodegeneration and Motor Dysfunction in Drosophila

“…Isolation of levy mutations and identification of the gene: The levy 1 mutation was isolated in a screen in which a number of temperature-sensitive paralytic mutants were identified in Drosophila (Hegde et al 1999;Singh and Singh 1999;Chopra et al 2000). The mutation was induced with EMS using compound chromosomes (Singh et al 1987).…”

Large Neurological Component to Genetic Differences Underlying Biased Sperm Use in Drosophila

“…Shab encodes the Shaker cognate b-subunit and is solely responsible for the delayed rectifier current in neurons and muscles of Drosophila (Hegde et al 1999).…”