Based on our previous observation that gene encoding cell cycle checkpoint functions determined lifespan in C. elegans, we aimed to define the genetic pathways at play. Three observations prompt this study. First we isolated a mutation in the gene checkpoint gene
cid-1 which causes thermotolerance, increased lifespan and resistance to hydroxyurea (HU). Second we also found that mutations in other checkpoint genes and the tumor suppressor
p53 confer resistance to HU. Third, since the nematode is post-mitotic, it is possible to study the effect of knocking down these genes in a whole organism without occurrence of lethal cancers. When wild-type eggs are placed on NGM plates spotted with HU the worms arrest development in a dose dependent manner. We screened for RNAi clones that suppressed this arrested development. All hits were re-tested at multiple doses of HU and resistance quantified as body size at three days of age. ~ 50 clones reproducibly result in HU resistance (hur genes) We are currently examining the hur genes for abnormal germline development, sterility and embryonic lethality. Many known cell cycle and checkpoint mutants show sensitivity to DNA damage. Therefore, to further test for cell cycle / checkpoint phenotypes we are exposing young worms to ionizing radiation and studying three different markers of DNA damage/checkpoint inefficiency, embryonic lethality, cell cycle arrest and apoptosis in the germline. We observed thermotolerance for 21 of the hits but not for all of them. Thus, HU resistance does not stem from a generalized increase in stress resistance but from a more specific mechanism. One of the clones increases thermotolerance of
daf-2,
daf-16 and
eat-2 mutants and seems to function independently from insulin signaling and caloric restriction. Aging is one of the biggest risk factors for cancer. Our ongoing analysis suggests that the hur gene list is highly enriched for increased lifespan although some result in shortened lifespan. We are investigating these and similar genes in a number of neuronal cell death models including human cells.