clk-1 encodes an enzyme involved in the biosynthesis of ubiquinone (UQ), a redox active lipid that is found in all cellular membranes, including in the mitochondrial respiratory chain.
clk-1 mutants display slow and deregulated physiological rates, including slow embryonic and post-embryonic development, retarded germline development, slow behaviours, and an increased lifespan. We have shown that several of the phenotypes of
clk-1 mutants can be suppressed by disrupting the expression of enzymes that detoxify reactive oxygen species (ROS). For example, RNAi knockdown of SOD-1, the cytoplasmic superoxide dismutase, suppresses the slow embryonic, post-embryonic and germline development of
clk-1 mutants but not the slow defecation cycle (1 and unpublished results). As the only known function of the SODs is the detoxification of superoxide, these findings indicate that the phenotype of
clk-1 mutants is due to low levels of superoxide and that superoxide regulates physiological rates in C. elegans.We have identified 9 additional genes (
clk-2 to -10) whose mutants have a phenotype similar to that of
clk-1, including the presence of a strong maternal rescue (2 and unpublished results). The mutants share a number of features, including a mean slowing down of physiological rates such as development, reproduction, behaviour and lifespan. We have been analysing all mutants by knocking down
sod-1 and
sod-2 by RNAi, and scoring Clk phenotypes. The phenotypes of several mutants are partially suppressed by treatment with
sod-1 RNAi. Interestingly, only one mutant,
clk-4, and only one phenotype of this mutant, slow post-embryonic development, is suppressed by
sod-2 (but not
sod-1) RNAi. Together these results indicate that ROS from various sub-cellular compartments can regulate physiological rates. We are also analysing the characteristics of the lifespan increase of the new clk genes, in particular their interactions with
daf-2.
daf-2 clk-1 double mutants display a much more than additive increase in lifespan. We are investigating whether this is a property that is unique to
clk-1 or a general property of mutants with a
clk-1-like phenotype, and whether the ability to synergize with
daf-2 can be related to the pattern of altered ROS metabolism that we are uncovering.1.Y. Shibata,R. Branicky,I.O. Landaverde,S. Hekimi,Science 302,1779-82 (2003).2.S. Hekimi, P. Boutis, B. Lakowski, Genetics 141, 1351-64 (1995).