Evidence from mosaic analysis of the masculinizing gene her–1for cell interactions inC. eleganssex determination

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Abstract
SEX in Caenorhabditis elegans is determined by a regulatory cascade of seven interacting autosomal genes controlled by three X-linked genes in response to the X chromosome-to-autosome (X/A) ratio1,2. XX animals (high X/A) develop as self-fertile hermaphrodites, and XO animals (low X/A) develop as males. The activity of the first gene in the sex-determining cascade, her-1, is required for male sexual development3. XO her-l loss-of-function mutants develop as self-fertile hermaphrodites, whereas XX her-l gain-of-function mutants develop as masculinized intersexes4. By genetic mosaic analysis using a fused free duplication linkingher-l to a cell-autonomous marker gene, we show here thather-lexpression in a sexually dimorphic cell is neither necessary nor sufficient for that cell to adopt a male fate. Our results suggest thather-l is expressed in many, possibly all, cells and that its gene product can function non-autonomously through cell interactions to determine male sexual development.