Worm Breeder's Gazette 16(2): 41
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.
The Netherlands Cancer Institute, Division of Molecular Biology, Center for Biomedical Genetics, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands
Heterotrimeric G proteins are an important class of signal-transducing molecules that couple seven transmembrane receptors to several intracellular effectors. In C. elegans, one homologue of each of the 4 mammalian classes of Ga subunits (Gai/o, Gaq, Ga12 and Gas) has been found.
Previously, the C. elegans Gas gene, gsa-1, was characterized (Korswagen et al, 1997). gsa-1 is an essential gene that is ubiquitously expressed in neurons and muscle cells. Partial loss of Ga s expression or overexpression of the protein results in reciprocal defects in movement and egg-laying. Furthermore, it was shown that expression of a constitutively active Gas subunit in C. elegans results in neuronal degeneration of a specific subset of ventral nerve cord motoneurons. Extragenic suppressors of this latter phenotype have been isolated, and one of these suppressors, sgs-1, encodes an adenylyl cyclase (Korswagen et al, 1998).
Currently, we have isolated 23 sgs-1 alleles. Animals containing an sgs-1 mutation do not show any obvious defects in development or behavior. All the suppressor alleles have been sequenced. In 18 alleles, mutations were found that change amino acids at 14 different positions. 3 independent alleles contained an identical splice donor site mutation. One allele had a mutation in the promoter of sgs-1, and in one allele no mutation in the sgs-1 gene could be detected thus far. None of the alleles contained mutations that result in early termination or frame-shift of the SGS-1 protein. The mutations that change amino acids are located in the first transmembrane domain or in the catalytic domains of sgs-1, but none of them seem to affect the residues know to be involved in the catalytic activity of the protein. Therefore, probably none of the mutations represent a complete null allele of sgs-1.
Recently, we isolated a Tc1 insertion derived deletion allele (pk1279te) of sgs-1. In this allele, a 2.9 kb region of the sgs-1 sequence is deleted, removing the second transmembrane region and the second catalytic domain of sgs-1. This is highly likely a null allele. Animals homozygous for sgs-1 (pk1279te) arrest in larval development. This phenotype was rescued by introduction of an sgs-1(+) containing plasmid.
Our results indicate that sgs-1 is an essential gene. Presumably, the sgs-1 mutants that suppress the activated Gas-induced neuronal degeneration are reduction-of-function alleles, and not complete loss-of-function alleles.
References:
H.C. Korswagen, J.-H. Park, Y. Ohshima, and R.H.A. Plasterk. 1997. An activating mutation in a Caenorhabditis elegans Gs protein induces neural degeneration. Genes Dev. 11: 1493-1503
H.C. Korswagen, A.M. van der Linden, and R.H.A. Plasterk. 1998. G protein hyperactivation of the Caenorhabditis elegans adenylyl cyclase SGS-1 induces neuronal degeneration. EMBO J. 17: 5059-5065