Worm Breeder's Gazette 8(1): 5
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Synchronized N2 populations were obtained by growth on chicken egg plates, followed by hypochlorite treatment. Embryos were plated on seeded NG plates, removed at various times, and subjected to UV irradiation. After incubation in phosphate buffered saline to allow time for repair, worms were frozen in liquid nitrogen. The DNA was extracted and treated with a UV-specific endonuclease, partially purified from Micrococcus luteus, which introduces single strand breaks between adjacent nucleotides of pyrimidine dimers. The number of single-strand breaks, and hence the number of dimers present in the DNA, was measured in two ways. First, samples were subjected to alkaline gel electrophoresis. Weighted average molecular weights were calculated by comparison with molecular weight standards. Second, samples were incubated with DNA polymerase I and supplied with all factors necessary for polymerization, including tritiated deoxycytidine. The amount of radioactive incorporation was proportional to the number of dimers. The techniques yielded similar results. Repair was evident in animals irradiated 24 hours after hypochlorite treatment (as L1's), with a maximum of 70% to 90% of the dimers removed 24 hours after irradiation. The number of dimers did not change when either L4 larvae or adults were held after irradiation. In fact, in most experiments, DNA from adults was partially degraded after irradiation. The simplest conclusion is that DNA repair is developmentally regulated in the worm; specifically, young larvae have substantial ability to excise DNA damage but this capacity diminishes throughout development. This regulation correlates well with the animal's cellular development,in which many somatic cells undergo the terminal round of DNA replication during larval development. Taken together, our results suggest that dpy-21+ is a negative regulator and dpy-22+ is a positive regulator of X-expression in both XO and XX animals. The finding that dpy-22(e652) is apparently epistatic to dpy-21(e428) in the double mutant suggests further that dpy-21+ may act by negatively regulating dpy-22. We have preliminary evidence that the one known dpy-23 mutation does not affect the three X-linked hypomorphs. We would like to have a larger collection of both X-linked and autosomal hypomorphs, and will welcome any contributions.