Worm Breeder's Gazette 12(2): 102 (January 1, 1992)
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.
Previous research has identified two genes required specifically to determine that germ cells develop as sperm: fog-1 I (Barton and Kimble 1990) and fog-2 V (Schedl and Kimble 1988). Mutations in either of these genes feminize the germline (the Fog phenotype) by causing germ cells that would have differentiated as sperm to become oocytes instead; these mutations do not affect the soma. However, the fog-1 and fog-2 genes play distinct roles in germline development: (1) Mutations in fog-1 affect the germ cells of both sexes, whereas mutations in fog-2 -onlyaffect hermaphrodites. (2) Mutations in fog-1 prevent spermatogenesis in all genetic background tested, whereas mutations in fog-2 can be suppressed by mutations in tra-1 , tra-2 ,and tra-3 ,as well as by fem-3 (gf)mutations. These results suggest that fog-2 acts early in the process of germline sex-determination in hermaphrodites, whereas fog-1 acts late in both sexes to specify spermatogenesis.
We have characterized four new Fog mutations ( q441 , q443 , q469 ,and q470 )that were isolated by Phil Balandyk in screens for sterile mutants. These recessive mutations all fail to complement each other, but do complement fog-1 mutations. Furthermore, they map just to the left of lin-11 on LGI, far from fog-1 .Thus these mutations define a new gene, fog-3 .Because fog-3 mutations complement the deficiencies nDf23 , nDf24 ,and nDf25 , fog-3 is probably located to the right of these deficiencies, and thus lies between the genes mel-26 and lin-11 .This region is spanned by the duplication sDp1 .As expected from the recessive behavior of the fog-3 mutations, unc-13 fog-3 ; sDp1 animals (which are fog/fog/+) produce sperm.
In both tests discussed above, the fog-3 gene behaves like fog-1 and differs from fog-2 .In both fog-1 and fog-3 XO animals, all germ cells differentiate as oocytes. Furthermore, in fog-3 ; tra-2 ( e1425a m)mutants, in fog-3 ; tra-1 ( e1099 lf)mutants, and in fog-3 ; fem-3 ( q95 gf)mutants all germ cells differentiate as oocytes. These results suggest that fog-3 acts at the same place in the process of sex-determination as does fog-1 ,and that both genes are absolutely required for spermatogenesis to occur.
Although the germ cells of fog-1 and fog-3 mutants develop identically, two genetic tests discriminate between these genes. First, fog-1 mutations are semi-dominant in males: fog-1 /+XO animals produce both sperm and oocytes. Second, fog-1 mutations are semi-dominant suppressors of fem-3 (gf)mutations (Barton and Kimble 1990). By contrast, fog-3 mutations show no semi-dominance in either test. These results suggest that the amount of fog-1 gene product might be limiting in some situations in which the amount of fog-3 gene product is adequate.
To learn whether the fog-3 mutations reduce or eliminate gene function, we are now screening for new fog-3 mutations and deletions by non-complementation. Furthermore, to better understand the interactions between fog-1 and fog-3 we are continuing our efforts to clone these genes for molecular analysis.
Schedl, T. and Kimble, J. 1988 Genetics 119: 43-61.