Worm Breeder's Gazette 7(2): 11

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.

Somatic Damage to the X Chromosome of C. elegans Induced by Gamma Radiation

P.S. Hartman, R.K. Herman

Wild-type males are more sensitive than wild-type hermaphrodites to 
inactivation by gamma radiation.  This sex-specific difference is 
observed when eggs are irradiated immediately after collection by the 
hypochlorite method, but it is more pronounced when irradiation is 
delayed for 22 hours after egg collection.  In the latter case, for 
example, at a dose of 50 kr, survival of males was only about 5% that 
of hermaphrodites.  In both cases, the difference between the 
inactivation curves of males and hermaphrodites is in the extent of 
the shoulders and not in the final inactivation slopes.
We considered three explanations for this sex-specific difference.  
First, the difference could be caused by some artifact in scoring the 
heavily irradiated males and hermaphrodites.  Second, the difference 
could be due to the different sexual phenotypes per se.  And third, 
the difference could be due to the difference in chromosome 
composition of the two sexes, that is, hermaphrodites are more 
radiation resistant because they have two X chromosomes rather than 
one.  These possibilities were tested by examining the gamma radiation 
sensitivities of animals in which the normal correspondence between X 
chromosome constitution and sexual phenotype was altered by either a 
her-1 or tra-1 mutation.  A her-1 dpy-21 triple 
mutant was constructed and assayed for radiation sensitivity.  The him-
5 mutation insures the constant generation of XO animals; the dpy-21 
mutation allows distinction of XO (non-Dpy) versus XX (Dpy) animals; 
and her-1 transforms XO animals into hermaphrodites.  The inactivation 
curves for non-Dpy (XO) and Dpy (XX) her-1 hermaphrodites were 
strikingly similar to the curves obtained for wild-type males and 
hermaphrodites.  respectively.  Moreover, XX animals transformed into 
fertile males by a tra-1 mutation did not show increased 
radiosensitivity relative to their tra-1/dpy-18 sibs.  We conclude 
that the wild-type sex-specific difference is caused by the difference 
in X chromosome constitution and that inactivation of XO animals by 
gamma radiation is predominantly due to X-chromosome damage.  No sex-
specific difference in inactivation was observed after UV irradiation.