Worm Breeder's Gazette 8(2): 7
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.
In the previous newsletter, we described the use of X-linked hypomorphs to provide a genetic assay for X-chromosome expression. We have used them to examine the effects of four mutants on X-chromosome expression. Mutations in two autosomal genes, dpy-21 V and dpy-26 IV, lead to abnormally high expression of the X, based on their ability to suppress the hypomorphs. Three alleles of dpy-21 do not differ appreciably in suppression, whereas the maternal (and presumed null) allele of dpy-26, n199 is a much stronger suppressor of the hypomorphs than the non-maternal allele ct14. We also reported that the X-linked gene dpy-22 is an apparent enhancer of the hypomorphs. None of the three dpy genes affects autosomal hypomorphs or null alleles of X- linked genes. From this, we postulate that dpy-21 and dpy-26 are negative regulators of X-expression and that dpy-22 is a positive regulator. We had shown previously that duplications of the X can interact with dpy-21; in particular, a dpy-21 XO animal with a large X duplication may be a Dpy intersex. There are at least two possible explanations for this: 1) the duplication turns on dpy-21 in some manner, for example by supplying an X-linked inducer; or 2) The duplication competes with the normal X for something that represses X-chromosome expression, and this effect is more evident when dpy-21 is mutant. To distinguish these hypotheses, we looked at the effect of the large X- duplication mnDp25 on a hypomorph it does not cover, lin-15(n767), in dpy-21+ strains. The duplication suppresses the hypomorph, albeit somewhat weakly, suggesting that X-duplications increase overall X expression by titrating an X repressor. One candidate for this postulated X repressor is dpy-26. Thus, the dpy-21 product may not interact with the X at all. We are testing other X-duplications, both singly and in combinations, to see if this effect is limited to mnDp25. We are also asking how dpy-26(null) XO animals are affected by X duplications.