C. elegans males and hermaphrodites crawl into postembryonic life with identical complements of ventral cord neurons (VCNs). By the end of L1, VCN lineages begin to diverge to take on sex-specific roles that support reproduction. In hermaphrodites, P3.aap-P8.aap become VC neurons that regulate egg laying. In males, P3.aap-P11.aap divide to generate CA and CP neurons (Pn.aapa/p), which innervate targets including male-specific neurons, muscles, and gonad1. How does Pn.aap differentiate into VCs in hermaphrodites, but divide to produce CAs and CPs in males? Pn.aap fates in both sexes are dependent on the activity of the Hox transcription factor LIN-392,3. Not surprisingly, the sex determination pathway is also instrumental. Our experiments using a
tra-2(ts) allele reveal that active TRA-1 is postembryonically required to prevent male fate in the Pn.aap lineage. XX
tra-2(ts) worms raised at the restrictive temperature after hatching display the male-specific pattern of serotonin expression in VCNs. While it is evident that Hox proteins converge with sexual regulators to instigate sexually dimorphic neurogenesis, the details of this interaction remain unclear.
To identify new regulators of sex-specific VCN fates, we are screening for mutations that alter VCN expression of the normally CP-specific marker
tph-1::gfp. Preliminary analysis reveals mutants in three phenotypic classes: 1) Mutants with sexual transformation in multiple tissues including VCNs. These mutants confirm a role for sex determination in determining VCN fate. 2) Mutants with reduced expression of
tph-1::gfp in CPs. Some mutants in this class are Unc, suggesting a disruption of general VCN neurogenesis. More interesting are mutants with CP-specific reduction of
tph-1::gfp expression and normal locomotion. We have mapped one such mutation,
ccc1, to a small region of the X chromosome (X:12.6 to X:13.95) containing about 50 candidate genes. 3) Mutants with increased VCN expression of
tph-1::gfp. This class includes alleles of
pag-3 and
unc-3, both of which cause supernumerary
tph-1::gfp(+) VCNs in males. This is consistent with previous studies demonstrating a similar role for these genes in hermaphrodite Pn.
aap4. Surprisingly, we find that
unc-3, but not
pag-3, hermaphrodites occasionally have
tph-1::gfp(+) CP-like neurons, suggesting a link between
unc-3 and sex determination in VCNs. Further analysis of these mutants will reveal mechanistic links between sex determination and neurogenesis. 1Male Wiring Project (worms.aecom.yu.edu); 2Salser SJ, et al., Genes & Dev 7:1714-1724; 3Clark SG, et al. Cell 74: 43-55; 4Prasad BJ, et al. Dev Biol 323: 207-15.