Worm Breeder's Gazette 8(3): 37
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.
1. Sex-linked amber suppressors are not dosage compensated. An amber allele of dpy-20 IV, e2017, has been isolated, which provides a convenient assay for the level of amber suppression. The unsuppressed phenotype is 'piggy', i.e. an extreme dumpy phenotype with a rounded nose, like other strong dpy-20 alleles such as e1362 or e1422, which are non-amber. The three amber suppressors sup-5 III, sup-7 X, and sup-21 X are roughly equal in the efficiency of suppression in hermaphrodites: the sup/+ phenotype is a medium dumpy, and the sup/sup phenotype is wildtype. The effect of suppressor dosage on expression of e2017 in the two sexes has been compared: [See Figure 1] Thus, suppression in hemizygous males is markedly weaker than in homozygous males for both sup-7 and sup-21, indicating that these genes are not dosage compensated. It follows that not all sex-linked genes of C. elegans are dosage compensated. It may be that C. elegans tRNA genes, such as sup-7 and probably sup-21, are in general not compensated, in contrast to Drosophila sex-linked tRNA genes, at least some of which are dosage compensated. 2. Another chauvinistic dumpy. Mutations in the genes dpy-21 V and dpy-26 IV are expressed much more strongly in XX animals than in XO animals, irrespective of sexual phenotype (see Mol.Gen.Genet. 192: 452). A possible explanation is that these two genes are involved in controlling X chromosome dosage compensation. A new mutation of this type has been identified: dpy-27( rh18) III, mapping about 0.5% right of unc-93 III. The rh18 mutation is recessive, and has properties intermediate between those of dpy-26( n199) and dpy-21(e428). Homozygous dpy-27(rh18) XX hermaphrodites are dumpy and very slow growing, while dpy-27 XO males are non-dumpy, grow normally, and are almost wildtype (mating efficiency 64% of wildtype). As with dpy-26, there is a maternal effect: dpy-27 XX daughters of dpy-27/+ mothers are dumpy, but grow better than dpy-27 XX daughters of homozygous mothers. However, unlike dpy-26, XX strains homozygous for dpy-27 can be maintained, though they grow very slowly. Also unlike dpy-26, odites do not have a Him phenotype. The interactions of dpy-27 with sex-determining genes resemble those of dpy-26 and dpy-21: r-1 XO animals are non-dumpy hermaphrodites, while dpy-27 ls are dumpy males with abnormal bursae.