In Vivo Analysis of a Gain-of-Function Mutation in the Drosophila eag-Encoded K+ Channel

Abstract

Neuronal Na 1 and K 1 channels elicit currents in opposing directions and thus have opposing effects on neuronal excitability. Mutations in genes encoding Na 1 or K 1 channels often interact genetically, leading to either phenotypic suppression or enhancement for genes with opposing or similar effects on excitability, respectively. For example, the effects of mutations in Shaker (Sh), which encodes a K 1 channel subunit, are suppressed by loss-of-function mutations in the Na 1 channel structural gene para, but enhanced by loss-of-function mutations in a second K 1 channel encoded by eag. Here we identify two novel mutations that suppress the effects of a Sh mutation on behavior and neuronal excitability. We used recombination mapping to localize both mutations to the eag locus, and we used sequence analysis to determine that both mutations are caused by a single amino acid substitution (G297E) in the S2-S3 linker of Eag. Because these novel eag mutations confer opposite phenotypes to eag loss-of-function mutations, we suggest that eag G297E causes an eag gain-of-function phenotype. We hypothesize that the G297E substitution may cause premature, prolonged, or constitutive opening of the Eag channels by favoring the ''unlocked'' state of the channel.

Ion channels to inactivate neurons in Drosophila

“…However K + channel mutants, like other channel chromosomal mutants, maybe of limited use to suppress neuronal electrical activity, especially as unlike human or worm channel mutants, few are gain-of-function alleles required for electrical inactivation (Ashcroft, 2006; Cardnell et al, 2006). Increased repolarising current can also be achieved by mutants that contain a chromosomal rearrangement that result in duplicated copies of a K + channel translocated onto an additional chromosome (Haugland and Wu, 1990).…”

“…K + channels are the most diverse ion channel family, with over 30 such channels in Drosophila , therefore mutations are seldom lethal with the possibility of having adult flies lacking two major classes of K + channel (Littleton and Ganetzky, 2000 ; Vähäsöyrinki et al, 2006 ). However K + channel mutants, like other channel chromosomal mutants, maybe of limited use to suppress neuronal electrical activity, especially as unlike human or worm channel mutants, few are gain-of-function alleles required for electrical inactivation (Ashcroft, 2006 ; Cardnell et al, 2006 ). Increased repolarising current can also be achieved by mutants that contain a chromosomal rearrangement that result in duplicated copies of a K + channel translocated onto an additional chromosome (Haugland and Wu, 1990 ).…”