Worm Breeder's Gazette 14(2): 56 (February 1, 1996)

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.

laf-1 and translational repression of tra-2.

Elizabeth Goodwin1, Judith Kimble2

1 Northwestern University Medical School, Chicago Il.
2 Howard Hughes Institute, University of Wisconsin, Madison Wisconsin The sex determination gene tra-2 promotes female development; reduction of function mutations in tra-2 cause XX animals to be transformed into males. tra-2 activity must be repressed for male development to occur. Six dominant gain-of-function tra-2 mutations result in inappropriate feminization in both XX and XO animals: the germ line of tra-2(gf) XX animals produces only oocytes, and the intestine of tra-2(gf) XO animals makes yolk and the germ line oocytes. The tra-2(gf) mutations map to a 60 nt direct repeat located in the tra-2 3'UTR. The direct repeat controls the activity of tra-2 by repressing the translation of the tra-2 mRNA (Goodwin et al. 1993). We have identified a gene, laf-1, that promotes male development by repressing the translation of tra-2 mRNA. Several lines of evidence support this conclusion. First, translational control of a reporter transgene fused to the tra-2 3'UTR is disrupted by reduction of function mutations in laf-1. Second, a proportion of laf-1(lf)/+ XX animals develop as females, a predicted phenotype for mutations in a translational repressor. Third, laf-1 appears to act upstream of tra-2 in the sex-determination genetic hierarchy, the expected position for a repressor of tra-2. In addition to its effect on sexual phenotype, laf-1 appears to have an essential function; laf-1 homozygotes die as embryos, suggesting it may control other genes besides tra-2. Previous genetic analyses suggested that the somatic sex determination genes (her-1, tra-2 and tra-3, fem-1,2,3, and tra-1) act in a linear hierarchy, with tra-1 being the terminal regulator. At the 1995 International Worm Meeting, one of us (B.G.) presented evidence that the functional relationships among these genes may be more complex. First, double mutant analysis of laf-1 with tra-1 demonstrated that female development could occur in the absence of tra-1 activity: laf-1(lf) tra-1(null)/+ tra-1(null) animals were found to be partially feminized and in fact were occasionally self-fertile. Second, double mutant analysis of tra-2(gf) with tra-1(null) suggested that a release of tra-2 translational repression could feminize tra-1(null) mutants. The latter result suggested that the feminization detected in laf-1(lf) tra-1(null)/+ tra-1(null) animals might be due to increased tra-2 activity. However, this last result appears to be wrong. Jonathan Hodgkin, using the original isolate of tra-2(e2020gf) mutation, did not detect feminization in tra-2(e2020gf);tra-1(null) animals (see abstract this gazette). He kindly sent us the double mutant strain, and we too were unable to see feminized animals. Presently, it is unclear why our tra-2(e2020gf) strain can feminize tra-1(null) mutations. Because of the discrepancy of the tra-2(gf);tra-1(null) double mutant analysis, we reexamined the relationship between laf-1 and tra-1. We first backcrossed two laf-1 alleles, q349 and q217 (which had already been six times back crossed) an additional two times and marked them with unc-93(e1500sd). [unc-93(e1500sd) has a semi-dominant UNC phenotype and maps 3.16 map units to the right of laf-1]. Previous epistasis analysis relied on unmarked strains. We next allowed laf-1(lf)unc- 93(e1500sd) +/++tra-1(e1834null) animals to lay progeny and examined UNC males. [tra-1(e1834) removes the 5'half of the gene, and is likely to be a null allele.] Approximately, 11% of the laf-1(q349)unc-93(e1500sd))tra-1(e1834null)/++tra-1(e1834) animals (n=74) and 7% of the laf-1(q217)unc-93(e1500sd)tra-1(e1834null)/++tra-1(e1834null) animals (n=73) were feminized. Most feminized animals showed severe truncation of tail structures. Occasionally, an animal developed a vulva and a bilobed gonad. Since tra-1(e1834null) is a deletion, PCR was used to confirm the genotype of the feminized animals. These experiments were repeated with two other tra-1(lf) alleles, e1099 and e1781, with essentially the same results as tra-1(e1834). In conclusion, two different laf-1 mutations can feminize each of three tra-1(lf) alleles, suggesting it is possible to get feminization in the absence of tra-1 activity. However, it is unclear how mutations in laf-1 cause this feminization. One simple possibility is that laf-1(+) acts to inhibit female development not only by repressing the translation of tra-2, but also by acting on genes downstream of tra-1. We would like to thank Jonathan Hodgkin for graciously sharing his results with us. Goodwin, E.B., Okkema, P.G., Evans, T.C., and J. Kimble (1993) Translational regulation of tra-2 by its 3' untranslated region controls sexual identity in C. elegans. Cell 75, 329-339.