Keywords: t. circadian rhythms and sleep; s. circadian rhythms
Long-term night shift work has been associated with increased risk of certain cancers, although this link is not consistently supported. The most obvious difference between shift workers and non shift workers is increased disruption of circadian rhythms in shift workers. If circadian rhythm disruption increases use of mutagenic DNA double strand break repair (DSBR) pathways such as non-homologous end joining (NHEJ), that would provide a potential mechanistic link between shift work and cancer initiation.
To test the hypothesis that circadian rhythm disruption increases use of NHEJ DSBR, we used the Rr3 system. The Rr3 system is based on a chromosomally integrated DsRed gene that is rendered nonfunctional by an inserted I-SceI site flanked by a short direct repeat. Rr3 containing flies are crossed to I-SceI expressing flies and DSBs are induced in the F1 generation premeiotic germline. Individual repair events are recovered and scored in the F2 generation by appropriate crosses. Repair by base pairing at the direct repeats (single strand annealing, SSA) reconstitutes expression of the DsRed gene. Repair by NHEJ does not reconstitute DsRed expression. We compared relative usage of SSA and NHEJ repair pathways between flies maintained on 12:12 and 8:8 light:dark schedules. Disruption of circadian rhythms by the 8:8 schedule was confirmed by actimetric analysis. We found no significant difference in NHEJ or SSA repair pathway usage between 12:12 and 8:8 flies. Current experiments are investigating the effect of circadian rhythm disruption on use of homologous recombination repair.