The Journal of Neuroscience, August 15, 2000, 20(16):5958-5964
A Novel Leg-Shaking Drosophila Mutant Defective in a
Voltage-Gated K+ Current and Hypersensitive to Reactive
Oxygen Species
Jing W.
Wang1,
James M.
Humphreys2,
John P.
Phillips2,
Arthur J.
Hilliker2, and
Chun-Fang
Wu1
1 Department of Biological Sciences, University of
Iowa, Iowa City, Iowa 52242, and 2 Department of Molecular
Biology and Genetics, University of Guelph, Guelph, Ontario, N1G 2W1
Canada
1,1'-Dimethyl-4,4'-bipyridinium dichloride (methyl viologen;
paraquat), an herbicide that causes depletion of NADPH and
generates excessive reactive oxygen species (ROS) in
vivo, has been used to screen for ROS-sensitive
Drosophila mutants. One mutant so isolated, named
quiver1
(qvr1), has a leg-shaking phenotype.
Mutants of the Shaker (Sh),
Hyperkinetic (Hk), and ether a
go-go (eag) genes, which encode different
K+ channel subunits that regulate the A-type
K+ current (IA) in
different ways, exhibit leg shaking under ether anesthesia and have
heightened metabolic rates and shortened life spans. We found that
Sh, Hk, and eag mutant
flies were all hypersensitive to paraquat. Double-mutant combinations
among the three channel mutations and
qvr1 had drastically enhanced
sensitivity to paraquat. Synaptic transmission at the larval
neuromuscular junction was increased in the
qvr1 mutant to the level of
Sh mutants. Similar to eag Sh double
mutants, double mutants of eag and
qvr1 showed striking enhancement in
synaptic transmission and a wings-down phenotype, the hallmarks of
extreme hyperexcitability. Voltage-clamp experiments demonstrated that
the qvr1 mutation specifically
disrupted the Sh-dependent IA
current without altering the other currents
[IK, Ca2+-activated fast
(ICF) and slow
(ICS) currents, and
ICa] in larval muscles. Several deficiency
strains of the qvr locus failed to complement
qvr1 and confirmed that ether-induced
leg shaking, reduced IA current, and
paraquat hypersensitivity map to the same locus. Our results suggest
that the qvr gene may encode a novel
K+ channel-related polypeptide and indicate a strong
link between a voltage-activated K+ current and
vulnerability to ROS.
Key words:
Shaker; Hyperkinetic; ether a
go-go; quiver; potassium channel; synaptic
transmission; paraquat; free radical
Copyright © 2000 Society for Neuroscience 0270-6474/00/20165958-07$05.00/0
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