| In C. elegans, sex is determined by the ratio of X chromosomes to sets of autosomes (X:A). The X portion of the sex signal consists of the nuclear receptor sex-1, the RNA-binding protein fox-1, and other X signal elements (XSEs) that dose-dependently repress the developmental switch gene xol-1 via multiple mechanisms. We report the mapping and initial characterization of the three alleles y323, y324, and y326, which likely define a new XSE. These mutations map to the same region of the X chromosome, enhance other xse(lf), and suppress Dp(xse).; Prior to this work, the molecular components of the autosomal sex signal were unknown; however, genetically this signal opposes the X signal to promote the male fate. We have identified and characterized the gene sea-1 (Signal Element on an Autosome), which possesses the hallmarks of an autosomal signal element (ASE): it acts early in the sex determination pathway to oppose the X signal in a zygotic dose-dependent manner.; sea-1(y356), a recessive suppressor of fox-1 sex-1 hermaphrodite-specific lethality, also suppresses the lethality and dumpiness of all other XSE double mutant combinations but does not rescue the hermaphrodite phenotypes of mutations acting downstream of xol-1 in the sex determination/dosage compensation pathway, indicating that it is not gene-specific and acts early in this genetic hierarchy. Whether sea-1 directly regulates xol-1 is under investigation. sea-1 dominantly enhances the male lethality caused by an XSE duplication. Enhancement of male lethality is even greater when sea-1 is homozygous, indicating that the effect of sea-1 is dose-sensitive, as expected of an ASE. Suppression of xse(lf) and enhancement of Dp( xse) by sea-1 depends on the zygotic dose. Thus, these data are consistent with the identity of sea-1( y356) as the first known C. elegans autosomal signal element.; sea-1 belongs to the T-box class of transcriptional regulators. Members of this class of site-specific DNA-binding proteins, including the founding member brachyury, are important regulators of cell fate in early development across species. Thus, C. elegans appears to have co-opted an evolutionarily important mechanism of developmental regulation and applied it to another vital embryonic decision, the determination of sexual fate. |
