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.