Is Involved in Drosophila Sex Determination

Females homozygous for sans jille'62' (= fs(1)1621) have an abnormal germ line. Instead of producing eggs, the germ-line cells proliferate forming ovarian tumors or excessive numbers of nurse cells. The Sex-lethal gene product(s) regulate the branch point of the dosage compensation and sex determination pathways in the soma.The role of Sex-lethal in the germ line is not clear but the germ line of females homozygous for female sterile Sex-lethal alleles or germ-line clones of loss-of-function alleles are characterized by ovarian tumors. Females heterozygous for sansj l le '621 or Sex-lethal are phenotypically wild type with respect to viability and fertility but females trans-heterozygous for sans fille'621 and Sex-lethal show ovarian tumors, somatic sexual transformations, and greatly reduced viability. A DULT fruit flies show extensive sexual dimorphism. A number of genes have been identified that are specifically required for morphological aspects of sexual identity (BAKER and BELOTE 1983; CLINE 1985; BAKER, NAGOSHI and BURTIS 1987) and/ or sex-specific regulation of X-linked gene expression (LUCCHESI and MANNING 1987). The development of a female (diplo-X) somatic cell appears to be controlled by a cascade of regulatory gene products. In diplo-X cells Sxl+ is "on" resulting in the activation of transformer+ ( tra) and transformer-2+ (tra-2). tra+ and tra2+ are required for expression of female specific doublesex+ ( d s x ) gene product(s) that, along with intersex+ gene product(s), repress male differentiation. Sxl+ activity is also believed to repress the expression of dosage compensation genes. The absence of S x P expression in diplo-X flies probably leads to heightened levels of X-linked gene expression and a resultant lethal imbalance of gene products (LUCCHESI and SKRIPSKY 198 1). While failure to initiate S x P expression is lethal to diplo-X flies, failure to maintain Sxl+ expression in diplo-X somatic cells results in male morphology (SANCHEZ and NOTHIGER 1982; CLINE 1985). Sex determination and dosage compensation in the germ line is different than in the soma. The absence of Sxl+ expression does not kill diplo-X germ-line cells but does block oogenesis (SCHUPBACH 1985) resulting in the accumulation of large numbers of small germline cells in the ovary (ovarian tumor phenotype). None of the other genes of the somatic sex determination pathway are required in the female germ line ' Present address: Department of Genetics, Harvard Medical School and Howard Hughes Medical Institute, 25 Shattuck Street, Boston, Massachusetts 021 15. Genetics 1 5 0 159-171 (September, 1988) (MARSH and WIESCHAUS 1978; S C H ~ B A C H 1982; BELOTE and BAKER 1983) and only one sex determination gene, tra-2 (BAKER and RIDGE 1980; BELOTE and BAKER 1983), and one dosage compensation gene, maleless (BACHILLER and SANCHEZ 1986), are known to be required in the male germ line. It is also known that germ line cells transplanted into hosts of the wrong chromosomal sex do not function (VAN DUESEN 1976) and that haplo-X germ cells do not proceed (if they even survive) as far in oogenesis as Sxl+ diplo-X germ cells in a diplo-X soma (SCHUPBACH 1985). If there are more undiscovered or unrecognized germ-line sex determination genes one approach to finding those genes lies in the analysis of female sterile mutations characterized by "Sxl-like" ovarian tumors or mutations resulting in other early "blocks" in oogenesis (LEUTHOLD 1986). We have examined the interaction of sans Elle (snf) (= fs(1)1621) (GANS, AUDIT and MASSON 1975; GOLLIN and KING 1981; PERRIMON et al., 1986) with Sxl and find that mutations in these genes interact to produce a variety of defects in both the soma and the germ line of diplo-X flies. MATERIALS AND METHODS Stocks: Visible mutants and balancers are described in LINDSLEY and GRELL (1968). The following stocks were obtained from the Bowling Green stock center: y cho, rb, peb v, rg, y cv v f , yJ sc ec cv ct gf, bi ct6 8. The recessive female sterile mutationsfs(1)575,fs(I)IO7,fs(1)456 a n d f s ( l ) s n . 6 2 1 (=fs(1)1621) are marked with vZ4 and balanced with FM3 (CANS, AUDIT and MASSON 1975).fs(~)ov0~"~' is maintained in FM3 or C(I)DX, y f / Y stocks (OLIVER, PERRIMON and MAHOWALD 1987a). Sxlf*', fs(1)ovo"' (= f s ( l ) M I ) , fs( I)ovo"~ (= fs( I)M38), fs( I)M40 and fs( I)M66 are marked with y cv v f and were maintained in FMO or FM3 stocks 160 B. Oliver, N. Perrimon and A. P. Mahowald