During Caenorhabditis elegans male spicule development, four pairs of precursor cells respond to multiple positional cues and establish a pattern of fates that correlates with relative anterior-posterior cell position. One of the extracellular cues is provided by the F and U cells, which promote anterior fates. We show that the genes in the
lin-3/let-23 signalling pathway required for hermaphrodite vulval induction also mediate this F/U signal. Reduction-of-function mutations in
lin-3,
let-23,
sem-5,
let-60 or
lin-45 disrupt hte fate of anterior cells. Likewise, activation of the pathway with ubiquitously produced signal results in posterior cells inappropriately adopting the anterior fates even in the absence of F and U. We have further used this genetic pathway to begin to understand how multiple positional cues are integrated to specify cell fate. We demonstrated that
lin-15 acts in spicule development as it does in vulval induction, as a negative regulator of
let-23 receptor activity. A second extracellular cue, from Y.p, also acts antagonistically to the
lin-3/let-23 pathway. However, this signal is apparently integrated into the
lin-3/let-23 pathway at some step after
lin-45 raf and is thus functionally distinct from
lin-15. We have also investigated the role of
lin-12 in forming the anterior/posterior pattern of fates. A
lin-12 gain-of-function defect is masked by redundant positional information from F and U.