Worm Breeder's Gazette 9(2): 68
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 an effort to further our understanding of germ-line sex- determination, we have isolated more alleles of the fog-2 locus (fog for feminization of the germ-line). As described at the 1985 CSH meeting, XX animals homozygous for fog-2 mutations are female, while XO animals are wild-type males. Thus, this single recessive mutation converts C. elegans from an hermaphrodite to an obligate bisexual mode of reproduction. These observations suggest that the fog-2 product is required for the brief period of spermatogenesis which occurs prior to oogenesis in the hermaphrodite. Seven independent fog-2 alleles have now been isolated by three different protocols; (a) three (q70, q71 and q154) were from screens of F1 clones that segregated F2 females, (b) three (q86, q123 and q124) were obtained in complementation screens for F1 females, and (c) one (q113) was obtained as a recessive suppressor of the fem-3 gain-of- function allele q20 (also see below). All alleles are essentially identical. None are temperature sensitive (although all were isolated at 25 C). No maternal effects are observed - either maternal rescue by wild-type product (like fem-1, Diniach and Hodgkin (1984), Dev. Biol. 106: 223-235) or zygotic feminization due to maternal absence ( like fem-3, Hodgkin, et. al., (1985), CSHSQB 50: 585-593). No feminization has been observed in males of any age. In XX animals, oogenesis begins among the most proximal germ-line cells at a time when spermatogenesis would normally occur. One allele (q124) is slightly leaky with about 1 in 250 XX animals being self-fertile in one or both ovotestes. The fog-2 locus maps very near to unc-51 on the tip of the right arm of chromosome V. Epistasis analysis with the fog-2 allele q71 and putative null mutations in other sex-determination loci has yielded the following results: For the fog-2;her-1(e1518) double, XX and XO animals are female. For the fog-2;tra-2(e1425) XX animal, the tra-2 phenotype is observed in both the germ-line and the soma. For the fog-2;tra-1 and the fog-2;tra-3 doubles, XX animals show the tra-1 and tra-3 phenotypes respectively in the soma, while the germ-line phenotype is complex and will be discussed elsewhere. Thus far, phenotypic effects of fog-2 mutations are observed in the germ-line but not the soma. Doniach (WBG Vol. 8, #3, p. 34 and Genetics, in press) has previously suggested that a gene(s) might negatively modulate the tra- 2 gene or gene product so as to allow the fem genes to be temporarily active resulting in the brief period of spermatogenesis in the hermaphrodite germ-line. The fog-2 gene product is an excellent candidate for a negative regulator of tra-2 based on both the fog-2 mutant phenotype and the fact that tra-2 mutations are epistatic to it. The phenotype of the fog-2;her-1 double mutant suggests that the fog- 2 product is expressed/active regardless of the X/A ratio. This could be a result of fog-2 being normally active in both XX and XO animals. The fact that spermatogenesis is uneffected in fog-2 XO mutant could then be a consequence of fog-2 function being redundant in males or that we do not yet have a null allele. Alternately, fog-2 could be active only in the absence of her-1.Note: That a her-1 mutant XO is an hermaphrodite and that in XX animals, the her-1 gene or product is thought to be inactive (Hodgkin, (1980), Genetics, 96: 649-664). In the course of complementation screens for new fog-2 alleles, two other mutations were recovered from F1 females. The first, q126 is a mutation with a fog phenotype that is distinct from fog-2. Both XX and XO animals have feminized germ-lines. In XX animals, the feminization is semidominant, although it is slightly leaky in q126 homozygotes. In XO animals, the germ-line has first sperm and the oocytes; q126 maps in the region of unc-13 to unc-29 on chromosome I. The second mutation, q122, is a dominant gain-of-function (gf) tra-2 allele. It was shown to be a tra-2 allele by map position and by isolation of intragenic revertants that have the tra-2 loss-of- function masculinizing phenotype which fail to complement canonical tra-2 alleles. The phenotypes of q122 are similar to those of the tra- 2(gf) allele e2020 described by Doniach (op. cit.): (a) q122 XX animals homozygous, heterozygous or in trans to a tra-2 null are female. (b) q122 XO animals are wild-type males, although some begin to make oocytes and yolk (as judged by Nomarski) when old. Like fog-2 mutants, tra-2(q122gf) male/female strains can be constructed. Furthermore, both the fog-2 allele q71 and the tra-2(gf) allele q122 are unselected suppressors of fem-3 gain-of-function mutations. In XX animals, fem-3(gf) alleles completely masculinize the germ-line so that spermatogenesis and no oogenesis occurs (Barton, et. al., (1985), CSH, p. 97). In both the fog-2(q71);fem-3(q20gf) and the tra-2(q122gf) ;fem-3(q20gf) double mutants self-fertility is restored (q71 is a recessive suppressor while q122 is a dominant suppressor). In summary, the similiarities between fog-2 loss-of-function and tra- 2 gain-of-function phenotypes are consistent with the idea that fog-2 negatively regulates tra-2 which in turn negatively regulates the fem genes to allow hermaphrodite spermatogenesis.