The development of sex-specific neurons in C. elegans depends on convergence of pathways mediating sex-determination and neuronal fate specification. A striking sexual dimorphism among ventral nerve cord (VNC) neurons arises from the sex-specific division of Pn.aap neuron precursor cells. In hermaphrodites, P3.aap-P8.aap differentiate into VC motor neurons; in males, these cells divide to produce CA and CP neurons. Despite common origins, VCs, CAs, and CPs are distinct in target specificity, neurotransmitter expression, and morphology. Both the terminal sexual regulator TRA-1 and the Hox proteins LIN-39 and MAB-5 contribute to differentiation of Pn.aap-derived neurons.1,2 However, the details of this molecular collaboration and identities of additional effectors of sex-specific VNC neurogenesis remain unknown. To identify these additional effectors, we seek genes whose loss of function alters sex-specific expression of the CP-specific marker
tph-1::gfp. We have adopted several approaches. First, in a pilot RNAi screen, we found that RNAi targeting the Hox cofactors CEH-20 and UNC-62 reduces the number of
tph-1::gfp-expressing CP motor neurons in males. CEH-20 and UNC-62 were previously found to act with LIN-39 to ensure VC survival by blocking
egl-1-mediated cell death; our findings suggest similar interactions occur in the male Pn.aap lineage.3,4 Second, the male-specific division of Pn.aap has led us to adopt a candidate gene approach to investigate the relationship between cell lineage and sexual fate in the VNC. Previous studies showed that in
unc-3(lf) hermaphrodites, Pn.aaa-derived cells adopt a Pn.aap-like fate, leading to extra VC-like neurons.5 Consistent with this, we have found that
unc-3(lf) males develop supernumerary
tph-1::gfp expressing CP-like cells. Surprisingly, our preliminary analysis also revealed that
unc-3(lf) hermaphrodites sometimes have
tph-1::gfp-positive VNC neurons, and we are further investigating this phenotype. We are exploring the ideas that division and sexual fate are tightly coupled in the VNC, and that an additional division of Pn.aap-like cells could be sufficient to define aspects of male fate in this lineage. Finally, we continue to seek regulators of sex-specific Pn.aap neurogenesis in a genetic screen for mutations that alter sex-specific
tph-1::gfp expression. Early analysis of one mutation,
ccc1, reveals normal locomotion and expression of
tph-1::gfp in head and tail neurons, but a reduced number of
tph-1::gfp positive neurons in the male VNC. We hope that our studies will lead us to better understand how Hox-mediated patterning intersects with sexual regulation to specify neurons that execute unique functions in each sex. 1Salser SJ, et al., Genes & Dev 7:1714-1724; 2Clark SG, et al. Cell 74: 43-55; 3Liu H, et al., Development 133: 641-650; 4Potts MB, et al. Dev Biol 329: 374-85; 5Prasad BJ, et al. Dev Biol 323: 207-15