THE PHA-4 GENE IS REQUIRED TO GENERATE THE PHARYNGEAL PRIMORDIUM OF CAENORHABDITIS-ELEGANS

In the 4-cell Caenorhabditis elegans embryo, two blastomeres are desti ned to generate pharyngeal cells, each by a distinct developmental str ategy: one pathway is inductive, while the other is autonomous. Here, we identify the pha-4 locus. In animals lacking pha-4 activity, an ear ly step in pharyngeal organogenesis is blocked: no pharyngeal primordi um is formed and differentiated pharyngeal cells are absent. Most othe r tissues are generated normally in pha-4 mutants, including cells rel ated to pharyngeal cells by cell lineage and position. Thus, pha-4 act ivity is required to form the pharyngeal primordium. We propose that p ha-4 marks a convergence of the inductive and autonomous pathways of p haryngeal development and suggest that establishment of pharyngeal org an identity is a crucial step for pharyngeal organogenesis.