A Werner syndrome protein homolog affectsC. elegansdevelopment, growth rate, life span and sensitivity to DNA damage by acting at a DNA damage checkpoint

Abstract

A Werner syndrome protein homolog in C. elegans (WRN-1) was immunolocalized to the nuclei of germ cells, embryonic cells, and many other cells of larval and adult worms. When wrn-1 expression was inhibited by RNA interference (RNAi), a slight reduction in C. elegans life span was observed, with accompanying signs of premature aging, such as earlier accumulation of lipofuscin and tissue deterioration in the head. In addition, various developmental defects, including small, dumpy, ruptured, transparent body, growth arrest and bag of worms, were induced by RNAi. The frequency of these defects was accentuated by γ-irradiation, implying that they were derived from spontaneous or induced DNA damage. wrn-1(RNAi) worms showed accelerated larval growth irrespective of γ-irradiation, and pre-meiotic germ cells had an abnormal checkpoint response to DNA replication blockage. These observations suggest that WRN-1 acts as a checkpoint protein for DNA damage and replication blockage. This idea is also supported by an accelerated S phase in wrn-1(RNAi) embryonic cells. wrn-1(RNAi) phenotypes similar to those of Werner syndrome, such as premature aging and short stature, suggest wrn-1-deficient C. elegans as a useful model organism for Werner syndrome.

Developmental Modulation of Nonhomologous End Joining in Caenorhabditis elegans

“…It was previously reported that L1 larvae of C. elegans strains deficient for the Werner's helicase wrn-1 display a radiation-induced Egl phenotype that can be suppressed by the neurotransmitter serotonin (Lee et al 2004). Given that WRN has been shown to physically interact with Ku , the Egl phenotype that occurs in irradiated late-stage NHEJ mutant embryos might be similar to that previously observed for wrn-1 mutants.…”

“…of NHEJ mutants is different from that reported for the wrn-1 Egl phenotype (Lee et al 2004). Defects in vulval morphogenesis may be responsible for the radiationinduced NHEJ mutant Egl phenotype ( Figure 4D).…”

“…Given that WRN has been shown to physically interact with Ku , the Egl phenotype that occurs in irradiated late-stage NHEJ mutant embryos might be similar to that previously observed for wrn-1 mutants. However, wrn-1 mutants failed to display Late Egg Rad phenotypes, although irradiation of L1 larvae produced weak effects, as previously reported (Lee et al 2004). The possibility that the radiationinduced Egl defect of NHEJ mutants was caused by a defect in neurons innervating egg-laying muscles was examined using an excess of serotonin, but this failed to rescue the Egl phenotype (Figure 7) (Bastiani et al 2003).…”

WRN helicase regulates the ATR–CHK1-induced S-phase checkpoint pathway in response to topoisomerase-I–DNA covalent complexes

“…Interestingly, RNAi-mediated depletion of WRN-1 or CHK1 in C. elegans leads to accelerated progression through S phase in the developmental stage. A similar phenotype is also observed in double RNAi knockdown of WRN-1 and CHK1, suggesting that WRN and CHK1 are involved in the same S-phase checkpoint pathway (Lee et al, 2004).…”

Werner syndrome as a hereditary risk factor for exocrine pancreatic cancer

“…This exonuclease function enables repair of DNA damage by facilitating resolution of hindered DNA replication forks during synthesis of complicated sequences, or by base pair excision and recombination when DNA polymerase encounters an obstruction. 22,31 Further supporting its dual roles in DNA replication and repair, the WRN protein is known to interact with DNA repair enzymes such as Polb, Ku, DNA-PK cs , PARP-1 and APE1. 22 In addition to directly proofreading DNA base pairs, WRN also plays roles in maintaining genomic integrity through a cell cycle "gatekeeper" function by inducing p53-dependent transcription of the cyclin-dependent kinase inhibitor p21 CDKN1A .…”