In C.elegans, most tissues are sexually dimorphic between hermaphrodites and males. Notable examples include the musculature, the nervous system, the germline, and the somatic gonad. The somatic gonads of the two sexes arise from two precursor cells, Z1 and Z4, which undergo different lineages, migration, and morphogenetic movements to generate very different organs. The adult hermaphrodite somatic gonad is two-armed and symmetrical, with each arm comprised of a uterus, spermatheca, and sheath cells, while the male somatic gonad is single-armed and asymmetrical with a seminal vesicle and vas deferens. To identify genes that control sex-specific gonad development, we have performed a genetic screen. We used a GFP marker expressed in the male vas deferens and seminal vesicle (see Thoemke et al abstract), and examined F2 males for abnormal expression or gonad morphology (see abstract by Illi et al). We isolated a number of mutants, including one we have tentatively named
tog-1 (transformer of gonad). The
tog-1(
ez16) mutant male gonad develops into a mass of disorganized tissue and about 25% of the mutant males have hermaphrodite vulval structures. The tail and other structures of the
tog-1 males are normal. Most mutant males express
lim-7::gfp, a hermaphrodite sheath cell marker, and
cdh-3::gfp, an anchor cell marker.
tog-1 males express male-specific GFP markers for valve cells, seminal vesicle, and vas deferens, indicating that feminization of the male gonad is not complete.
tog-1 hermaphrodite gonads have normal overall morphology with two symmetrical arms, although the spermatheca appears abnormal and does not function properly. We have mapped the
tog-1 locus to chromosome II and found that
tog-1 encodes a novel forkhead transcription factor. The
ez16 allele appears to be null: the phenotype is the same in trans to a deficiency, and the
ez16 mutation changes the start AUG to AUA. Lineage analysis (described in Tilmann et al abstract) showed that
tog-1 is required for male-specific early asymmetrical cell division and cell migration. The global sex determining gene
tra-1 also regulates the symmetry of early cell division and migration, and we are currently analyzing how
tra-1 and
tog-1 function together to direct sexually dimorphic gonadogenesis.