Worm Breeder's Gazette 11(2): 120
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.
Three independently isolated X-linked suppressors of the dominant masculinizing her-1 allele n695 (Burgess et al., WBG 9.2, 1986) are large X-chromosome duplications (Tanner et al. C. elegans Meeting Abstracts 1989) that result in a high incidence of XO lethality with the surviving XO worms variably transformed toward hermaphrodite. The endpoints of these duplications have now been more precisely mapped by quantitative Southern blotting and each has been shown to include the sdc-2 locus. All three, ct28, ct30, and ct31 have left endpoints between xol-1 and lin-14. On the right ct30 terminates between myo-2 and unc-3, while ct28 and ct31 terminate between unc-3 and let-2. Thus ct30 can be estimated to duplicate between 14% and 51% of the X chromosome; ct31 and ct28 between 24% and 54%. ct31 has been shown genetically not to include Unc-15, and therefore does not include sdc- 1. All three duplications result in virtually indistinguishable phenotypes although they probably duplicate different amounts of the X chromosome. XO animals, carrying one copy of the duplication, are non- mating, slow-growing, and variably feminized. Nomarski observation of 140 ct31 XO and ct31 lon-2(e678) XO animals showed that 77% had defective tails, 18% had a mid-ventral hypodermal protrusion, 16% had a sac-like or a two-armed gonad, and 8% contained oocytes. Immunofluorescent staining of 193 ct31 XO animals with an anti- vitellogenin antibody indicated 11% (21 animals) produced yolk protein. Three ct31 XO animals have been observed to contain developing embryos. Homozygous ct28, ct30. and ct31 XX animals carrying two copies of the duplication are slow-growing Dumpy hermaphrodites. This phenotype is very different from that of animals carrying mnDp10, another large homozygous-viable X-chromosome duplication ( between 22% and 38% of the X chromosome), that includes much of the same region as ct28, ct30, and ct31 but does not include sdc-2. XO animals homozygous for mnDp10 are healthy mating males, although their fertility is reduced. XX animals homozygous for mnDp10 are perhaps very slightly dumpy but grow normally. These observations and the apparently different sizes of ct28, ct30, and ct31 suggest that their resulting phenotypes are not due simply to increased X-chromosome dosage, but rather to the duplication of specific sequences. In addition to feminizing XO animals, the ct31 duplication results in significant XO lethality. The ratio of XO to XX cross progeny counted in two separate crosses was 226/399, indicating 43% XO lethality. This lethality is XO specific since the self progeny of ct31 homozygous hermaphrodites show only 5% lethality. Similar experiments with ct28 and ct30 are in progress. We suggest that the feminization and reduced viability of XO animals containing these duplications is due primarily to increased copy number of sdc-2. Loss-of-function alleles of sdc-2 result in masculinization of XX animals, XX lethality and increased X-chromosome expression (Genetics 122; 579-593, 1989). If sdc-2 is a developmental switch gene, the gain-of-function phenotype should be hermaphroditization of XO animals, XO lethality and reduced X chromosome expression, as predicted by Nusbaum and Meyer (ibid.). Previous results from this lab indicate that the X-linked duplications affect X-chromosome expression, suggesting effects on dosage compensation as well as sexual phenotype. The ct31 duplication increases the penetrance of the hypomorphic lin-15 allele n765, consistent with a general decrease in X expression caused by ct31 ( Burgess et al. WBG 9.2, 1986). RNA dot-blot analyses indicated a slightly higher level (1.24x) of myo-2 mRNA in ct31 than in wild type. Since the ct31 strain has four copies of myo-2 compared to two copies in N2, this result may still reflect a reduction of X-chromosome expression. Further analysis of dosage compensation effects of ct28, ct30 and ct31 is in progress, as are experiments on the results of specifically varying sdc-2(+) dosage in the presence of these duplications.