Worm Breeder's Gazette 8(2): 8
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.
X-linked hypomorphs provide a genetic assay for X-chromosome expression (Meneely & Wood, Newsletter vol. 8, #1, p.6). To test genetically whether C. elegans compensates for differences in X dosage between males and hermaphrodites, we have used the hypomorphs unc-3(e54) (severely Unc when present over a deficiency in XX animals; moderately Unc as a homozygote) and let-2(mn114) (L1 lethal when present over a deficiency in XX animals; adult sterile as a homozygote) . XO males hemizygous for either of these alleles show the same phenotype as the corresponding homozygous hermaphrodite rather than that of the hemizygous deficiency hermaphrodite, indicating compensation for X dosage, at least for these two genes. To test biochemically for compensation, we compared the activity of the DNase encoded by nuc-1 X (Dew & Sulston, Newsletter, vol. 1, #1 p. 17) in males and hermaphrodites. Enzyme activities were assayed by measuring release of acid-soluble radioactivity during incubation of 100 l reaction mixtures containing a high-speed supernatant fraction of sonicated worms, 100 nmoles of DNA nucleotides in the form of sonicated salmon sperm and [3H]-labelled E. coli DNA, 1mM EDTA, and 40mM sodium phosphate buffer. The assay gave good proportionality with both time and extract concentration up to >40% of radioactivity released. The activity showed a broad pH optimum of 5-6 and was routinely assayed at pH 6.0. Under these conditions E. coli extracts had no detectable DNase activity. Sonicates of nuc-1(e1392) showed <1% the specific activity of N2 sonicates. Sonicates of staged N2 populations showed similar specific activities for L1 - L4 and adult worms, and about 50-fold lower specific activities for early embryos and dauer larvae. Sonicates of young adult males and hermaphrodites, separated (to >95%) from staged populations of him-5(e1490) using Nitex filters, showed the same specific activity +/-5%. Although other interpretations of this result are possible, it is most simply explained by compensation for differences in nuc-1 dosage between males and hermaphrodities.