Meeting Abstract
Extraocular photoreceptors are common throughout animals, and many of these photoreceptors function using opsin proteins expressed in many tissues and cellular structures. Cephalopods, crustaceans, and fish represent phyla where extraocular opsin expression appears to be common. Cephalopods express their retinal rhodopsin and several other phototransduction proteins in chromatophore organs, parolfactory vesicles, mantle muscles, arm ganglia, sucker peduncle nerves, and a distributed array of hair cells that covers the outer epidermis. This protein expression throughout cephalopod tissues suggests that they have many extraocular photoreceptors, particularly since these tissues express the same proteins found in other photoreceptive tissues such as retinas and parolfactory vesicles. Similarly to cephalopods, crustaceans appear to have many extraocular photoreceptors. Retinal short- and long-wavelength sensitive (SWS and LWS) opsins are expressed in cell body clusters in the cerebral ganglion of the crayfish, Procambarus clarkii. From those cell bodies extend two pairs of nerve fibers that express LWS opsin protein. One pair of fibers terminates in the subesophageal ganglion (SEG) while the second pair continues through the SEG, thoracic and abdominal regions of the nerve cord, ultimately terminating in the sixth abdominal ganglion where the caudal photoreceptor exists. Like cephalopods, flounder have opsin transcripts located within the skin. The flounder, Paralichthys dentatus, has both visual opsin transcripts (RH1, RH2, SWS1, SWS2, LWS) and melanopsin in many skin regions, suggesting that putative extraocular photoreceptors may function using more than one phototransduction pathway. Opsin expression that likely contributes to extraocular light detection appears to be a common occurrence that is not well understood in these and many other animals.
