The nematode C. elegans naturally develops as either an XO male or XX hermaphrodite, The sex-determining gene,
tra-2, promotes hermaphrodite development in XX animals, This gene encodes a predicted membrane protein, named TRA-2A, which has been proposed to provide the primary feminising activity of the
tra-2 locus, Here, we show that transgenic TRA-2A driven from a heat shock promoter can fully feminise the somatic tissues of XX
tra-2 loss-of-function mutants, which would otherwise develop as male. TRA-2A is thus likely to provide a component of the
tra-2 locus that is both necessary and sufficient to promote female somatic development, Transgenic TRA-2A driven by the heat shock promoter can also transform XO animals from male to self-fertile hermaphrodite, This result establishes the role of
tra-2 as a developmental switch that controls somatic sexual cell fate, We show that a carboxy-terminal region of TRA-2A, predicted to be intracellular, can partially feminise XX
tra-2 loss-of-function mutants and XO
tra-2(+) males, We suggest that this intracellular domain of TRA-2A promotes hermaphrodite development by negatively regulating the FEM proteins.