Characterisation of a second patched gene in the zebrafish Danio rerio and the differential response of patched genes to Hedgehog signalling.

Hedgehog signalling has been implicated in a variety of processes in vertebrate development, and in each case, the activity of Hh proteins is thought to be mediated by their interaction with a large multipass transmembrane protein encoded by the patched (ptc) gene. In this study we present the full-length coding sequence and describe the wild-type expression pattern of a second ptc gene in zebrafish, Zf-ptc2. We find that at the sequence level Zf-ptc2 is more closely related than Zf-ptc1 to the ptc genes initially characterised in other vertebrate species. We also show that transcription of Zf-ptc2, like Zf-ptc1, is dependent upon Hh signalling and present evidence that it is activated in response to lower levels of Hh activity than is Zf-ptc1. In addition we find no evidence for any specificity in the regulatory interactions between the various Hh proteins and the two ptc genes in the zebrafish.