A C. elegans patched gene, ptc-1, functions in germ-line cytokinesis

Patched (Ptc), initially identified in Drosophila, defines a class of multipass membrane proteins that control cell fate and cell proliferation. Biochemical studies in vertebrates indicate that the membrane proteins Ptc and Smoothened (Smo) form a receptor complex that binds Hedgehog (Hh) morphogens. Smo transduces the Hh signal to downstream effectors. The Caenorhabditis elegans genome encodes two Ptc homologs and one related pseudogene but does not encode obvious Hh or Smo homologs. We have analyzed ptc-1 by RNAi and mutational deletion and find that it is an essential gene, although the absence of ptc-1 has no detectable effect on body patterning or proliferation. Therefore, the C. elegans ptc-1 gene is functional despite the lack of Hh and Smo homologs. We find that the activity and expression of ptc-1 is essentially confined to the germ line and its progenitors. ptc-1 null mutants are sterile with multinucleate germ cells arising from a probable cytokinesis defect. We have also identified a surprisingly large family of PTC-related proteins containing sterol-sensing domains, including homologs of Drosophila dispatched, in C. elegans and other phyla. These results suggest that the PTC superfamily has multiple functions in animal development.