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.

C. elegans Compensates for Differences in X Dosage

W.B. Wood, P. Meneely

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.