Worm Breeder's Gazette 14(4): 73 (October 1, 1996)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Department of Genetics, University of Washington, Seattle, WA 98195
We have previously described mutants with muscle activation
defective (Mac-d) or hyper-activated muscle (Mac-h) phenotypes. Mac
genes were proposed to encode ion channels or other regulators of cell
excitability. Mutants for a third class of genes are Mac-d in some
tissues and Mac-h in others (Mac-m; muscle activation mixed). Perhaps
Mac-m genes encode regulatory proteins that act on different effectors
in different tissues (1).
Animals with gain-of-function mutations in unc-43 (unc-43(gf))
are Mac-d in the egg-laying and enteric muscles and Mac-h in the
body-wall muscles. Loss-of-function mutations (unc-43(lf)) confer the
reciprocal muscle phenotypes. unc-43 appears to function widely in the
nervous system, since unc-43 mutations also confer defects in functions
other than muscle activation. unc-43(gf) causes an abnormally long
defecation cycle period, while unc-43(lf) confers an inappropriate
repeat or "echo" of the defecation motor program. We have shown that
the previously described dec-8(sa200) mutation (2) is a partial
loss-of-function allele of unc-43. unc-43(gf) causes sluggish
locomotion, while unc-43(lf) causes a "jumpy" phenotype, apparently
consisting of rapid, sequential initiation and cessation of locomotion.
Finally, we observed that unc-43(gf) can promote dauer formation in
combination with other Daf-c or syn-Daf (3) mutations (our observations;
E. Malone, M. Ailion and J. Thomas, pers. comm.).
We mapped unc-43 to a small region between daf-14 and mec-3,
which was recently sequenced by the C. elegans genome sequencing
consortium. Using the candidate gene approach, we found that unc-43
encodes a putative type II Ca++/calmodulin-dependent protein kinase
(CaMKII). In other systems, CaMKII has been well-characterized
biochemically but not genetically. We have sequenced eleven unc-43
mutations, including an early stop mutation and a change of an aspartate
that is universally conserved in serine/threonine kinases. These
putative null mutations confer phenotypes comparable to most
loss-of-function alleles.
CaMKII is thought to function in short-term learning and memory,
and to exist as a homododecamer that autophosphorylates upon activation
by Ca++/calmodulin. The resulting activated kinase has relatively low
specific activity, but can remain activated for hours, giving it the
potential to provide a long-term molecular memory of Ca++ influx. Based
on in vitro studies, CaMKII is thought to modulate ion channel function
directly by phosphorylation.
We have previously reported that loss-of-function mutations in
unc-103 suppress the unc-43(gf) enteric muscle defect, but not other
defects. unc-103 is closely related to the human erg K+ channel, which
is defective in some individuals with the hereditary cardiac arrhythmia
disorder Long QT Syndrome (4). We have also found that mutations in the
tax-4 cyclic-nucleotide gated cation channel (5) suppress the Mac-h
body-wall muscle defect conferred by unc-43(gf). We speculate that
unc-43 regulates the function of the unc-103 and tax-4 gene products by
directly phosphorylating the channels, and tests of this are in
progress.
(1) Reiner, Weinshenker and Thomas (1995) Genetics 141: 961-976.
(2) Liu and Thomas (1994) J. Neurosci. 14: 1953-1962.
(3) Thomas, Iwasaki, Malone and Ailion (1995) WBG 13(5): 45.
(4) Reiner, Nishiwaki, Miwa, Levitan and Thomas (1996)WCWM Abstract 129.
(5) Komatsu, Mori and Ohshima (1995) IWM abstract 318.