Understanding the molecular basis of ageing is a necessary precursor to developing therapies to counter deleterious aspects of human ageing including frailty and age-related diseases. The widely-studied premature ageing Werner syndrome (WS) phenocopies normal human ageing but is caused by mutation of a single gene, WRN, encoding both helicase and exonuclease activities. In order to dissect the distinct roles of WRN helicase and exonuclease throughout development and ageing, we have identified homologues of both the helicase and exonuclease activity of human WRN in C. elegans.
Our comparative genomic analysis in C. elegans suggests that
wrn-1 is the closest homologue of the human WRN helicase domain and
mut-7 is the closest homologue of the human WRN exonuclease domain. Ageing phenotypes and shortened lifespan have been previously associated with reduction of function of
wrn-1 by RNA interference [1], while mutation of
mut-7 results in genetic instability by activating transposons in the germline [2], but there have been no reported lifespan studies. We suggest that together,
wrn-1 and
mut-7 constitute the same domain architecture as human WRN, as in other invertebrates (Drosophila) and plants (Arabidopsis).
We have established out-crossed worm lines mutant for the WRN exonuclease, and for the WRN helicase (
mut-7 and
wrn-1, respectively), and have used these strains to generate
wrn-1;
mut-7 double mutants. Ageing phenotypes and lifespan of the mutant worms will be presented, as will the phenotype of our novel double mutants lacking both WRN helicase and exonuclease. In addition, further data highlighting how this worm model can be used to dissect at the molecular level the relative contributions of the WRN helicase and exonuclease to DNA damage responses and genome stability will also be given.
References 1.Lee, SJ; Yook, JS; Han, SM; Koo, HS. A Werner syndrome protein homolog affects C. elegans development, growth rate, life span and sensitivity to DNA damage by acting at a DNA damage checkpoint. Development, 2004. 131(11): p. 2565-2575. 2.Ketting, RF; Haverkamp, TH; van Luenen, HG; Plasterk, RH. Mut-7 of C. elegans, required for transposon silencing and RNA interference, is a homolog of Werner syndrome helicase and RNaseD. Cell, 1999. 99(2): p. 133-141.