The membrane protein Patched (Ptc) and the morphogen Hedgehog (Hh) control cell patterning and proliferation in Drosophila and vertebrates. Hh functions as a repressive ligand that binds Ptc and alleviates the inhibition of the membrane protein Smoothened (Smo), which is essential for transducing the Hh signal. The role of Ptc in this signalling cascade appears to be confined to its inhibition of Smo. In C. elegans, obvious Hh and Smo homologues are absent despite the presence of two PTC orthologues, PTC-1 and PTC-3, and 24 PTR (for Patched-related) proteins. Despite the absence of Hh and Smo, the ptc and ptr genes play diverse roles in C. elegans development. We have shown that PTC-1 is essential for germline cytokinesis, and others have shown that PTR-7 promotes tissue morphogenesis (Perens and Shaham, 2005). RNAi studies have also revealed that the ptr genes have Smo-independent functions. To gain further insights into the Smo-independent roles of PTC proteins, we have analysed the C. elegans
ptc-3(
ok121) deletion mutant and shown that
ptc-3 is an essential gene during embryogenesis.
ptc-3(RNAi) shows that
ptc-3 also has a range of post embryonic roles. In the most severe cases,
ptc-3(RNAi) animals became paralysed and accumulate large vesicles; weaker RNAi effects include molting and vulval morphogenesis defects. Sytox green staining of live
ptc-3(RNAi) worms reveals that the integrity of their plasma membranes is compromised. We have generated a PTC-3::GFP reporter and find that PTC-3 expression is highly dynamic. In the late embryo, prior to hatching, PTC-3::GFP is strongly expressed in the hypodermis, excretory duct and cuticle. During later larval stages, PTC-3::GFP expression is associated with 2 pi cells, the H-shaped uterine seam cell (utse), vulE and possibly vulD. In addition, expression is detected in the cephalic neurons and the VC4/VC5 neurons. In males, PTC-3::GFP is expressed in the valve region of the seminal vesicle, precursor and mature sensory rays, cloaca and cephalic neurons. Two domains that could provide clues to the function of PTC-3 are the sterol sensing domain (SSD) and the RND transporter domain. Site-directed mutagenesis was performed and it was found that the SSD domain D(780)N appears to be dispensable for PTC-3 function. By contrast, mutation of the GxxxD motif in TM4 of the RND domain led to a loss of PTC-3 function.