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The Journal of Neuroscience, 1999, 19:RC28:1-8
RAPID COMMUNICATION
Neuronal Polymorphism among Natural Alleles of a
cGMP-Dependent Kinase Gene, foraging, in
Drosophila
John J.
Renger1,
Wei-Dong
Yao1,
Marla B.
Sokolowski2, and
Chun-Fang
Wu1
1 Department of Biological Sciences, University of
Iowa, Iowa City, IA 52242, and 2 Department of Zoology,
York University, Toronto, Ontario, M3J 1P3, Canada
Natural variation in neuronal excitability and connectivity has not
been extensively studied. In Drosophila melanogaster, a
naturally maintained genetic polymorphism at a cGMP-dependent protein
kinase (PKG) gene, foraging (for),
is associated with alternative food search strategies among the allelic
variants Rover
(forR; higher PKG activity)
and sitter
(fors; lower PKG activity). We
examined physiological and morphological variations in nervous systems
of these allelic variants isolated from natural populations. Whole-cell
current clamping revealed distinct excitability patterns, with
spontaneous activities and excessive evoked firing in cultured
sitter, but not Rover, neurons. Voltage-clamp examination demonstrated reduced voltage-dependent K+ currents in sitter neurons. Focal
recordings from synapses at the larval neuromuscular junction
demonstrated spontaneous activity and supernumerary discharges with
increased transmitter release after nerve stimulation. Immunolabeling
showed more diffuse motor axon terminal projections with increased
ectopic nerve entry points in sitter larval muscles. The
differences between the two natural alleles was enhanced in
laboratory-induced mutant alleles of the for gene. The
pervasive effects of the for-PKG on neuronal
excitability, synaptic transmission, and nerve connectivity illustrate
the magnitude of neuronal variability in Drosophila that
can be attributed to a single gene. These findings establish the
consequences in cellular function for natural variation in an isoform
of PKG and suggest a role for natural selection in maintaining
variation in neuronal properties.
Key words:
Drosophila; foraging; neuronal
polymorphism; natural variation; cultured neurons; neuromuscular
junction; membrane excitability; K+ currents; cGMP-dependent protein kinase; focal recording; patch clamping
Copyright © 0000 Society for Neuroscience 0270-6474/0/$05.00/0
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