PARAPINOPSIN, A NOVEL CATFISH OPSIN LOCALIZED TO THE PARAPINEAL ORGAN, DEFINES A NEW GENE FAMILY

Multiple sites of extraretinal photoreception are present in vertebrat es, but the molecular basis of extraretinal phototransduction is poorl y understood. This study reports the cloning of the first opsin specif ically expressed in the directly photosensitive pineal and parapineal of cold-blooded vertebrates. This opsin, identified in channel catfish and termed parapinopsin, defines a new gene family of vertebrate phot opigments and is expressed in a majority of parapinealocytes and a sub set of pineal photoreceptor cells. Parapinopsin shows a caudal-rostral gradient of expression within the pineal organ. This study also repor ts the cloning of partial cDNAs encoding the channel catfish orthologu es of rhodopsin and the red cone pigment-the full complement of retina l opsins in the species. In situ hybridization studies using probes de rived from these retinal opsins, together with parapinopsin, reveal no expression of retinal opsins in pineal and parapineal organ and no ex pression of any opsin tested in the ''deep brain,'' iris, or dermal me lanophores. These data imply that phototransduction in these sites of extraretinal photoreception must be mediated by novel opsins.