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.

Developmental Regulation of DNA Repair in C. elegans

P.S. Hartman, K. Lowery

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 
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