Worm Breeder's Gazette 9(1): 74
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.
We have used X-linked hypomorphic (i.e., leaky) mutations as a simple and versatile assay for the expression of X-linked genes. Particularly useful mutants are lin-15 (n765) and let-2 (b246), which result in a temperature-sensitive Muv phenotype and lethality (or sterility), respectively. From this assay, we have suggested that dpy- 21 and dpy-26 mutants have higher X expression than wild-type and that dpy-22, and possibly dpy-23, have lower expression than wild-type. The fact that dpy-21 is an effective suppressor of X-linked hypomorphs led to a simple scheme for finding new dosage compensation mutants: Mutagenizing lin-15 (n765) hermaphrodites (or lin-15 [n765] let-2 [b246] hermaphrodites) and picking non-mutant animals in the F1 and F2. We have found more than 20 suppressors, at least 7 of which suppress both hypomorphs. Such suppressors do not appear to be particularly rare. Most of them are Dpy, some are male-abnormal, and some are Him. Because some mutants are dominant suppressors we do not know yet how many genes are represented; at least one, a recessive suppressor, is a dpy-21 allele. Another mutant is a heterozygous suppressor and semi- Dpy, but a homozygous lethal and extremely Dpy. In a previous newsletter, and in our CSH poster, we reported that mnDp25, a fairly large X duplication, suppressed a lin-15 hypomorph. We have extended this to other duplications and hypomorphs, and the conclusion is quite clear: X duplications suppress hypomorphs in the regions they do not duplicate. Although the data are limited, the effect appears to be size-dependent; a big duplication like mnDp25 suppresses better than a medium-sized duplication like mnDp57, and both suppress better than a small duplication like (mnDp57 includes the region from unc-2+ to lon-2+, and was kindly provided by Bob Herman). Likewise, two copies of a duplication suppress better than a single copy. This is consistent with the simple idea that the duplication competes with the normal X for the 'repressors' encoded by dpy-21, s elevating overall X expression. Working on the old dogs and new tricks principle, we are isolating more X- chromosome duplications and deficiencies.