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

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.

The Caenorhabditis elegans XPA homolog of human XPA

The Xeroderma pigmentosum complementation group A (XPA) protein that is indispensable for nucleotide excision repair of DNA damage in eukaryotes participates in photoproduct recognition. A search of the current Caenorhabditis elegans database allowed us to identify a good candidate for the XPA protein homolog. We cloned a complete cDNA of C. elegans XPA (Ce-XPA) by using RT-PCR. Northern blot analysis showed that the Ce-xpa gene is expressed in all of the stages, including embryos. Ce-XPA encodes a 241-amino acid protein that is homologous to all known eukaryotic XPA. Ce-XPA RNAi caused embryonic lethality and survival lethality to UV radiation. This result suggests that Ce-XPA is involved in the repair of UV-damaged DNA in C. elegans.