Meeting Abstract
R-type (rhabdomeric) opsins are common light-sensitive proteins in invertebrate eyes. R-opsins have been identified in the eyes, brain and skin of numerous molluscs, but not in nudibranchs, which was the goal of this study. We focused on Berghia stephanieae, Hermissenda opalescens and Melibe leonina, the latter two of which have publicly available transcriptomes. From these, we identified multiple types of opsins in both species. Using these sequences, we developed RNA probes for fluorescent in situ hybridization (FISH) and found r-opsin mRNA expression in all dermal tissues that we examined. Immunohistochemistry with antibodies to octopus r-opsin corroborated the FISH results and also indicated a similar localization in dermal tissues of Berghia. In behavioral experiments to test for extraocular photoreception, Berghia and Melibe both responded to extraocular stimulation using both white and red light, but not infrared wavelengths. R-opsins were not detected in the brains of Berghia and Hermissenda, but were expressed in a small number of neurons in the brain of Melibe in a similar location to previously identified circadian clock neurons. Double-label FISH experiments confirmed the colocalization of r-opsin with core clock transcripts in the brain. Additional experiments extended this colocalization to dermal tissues. Together, these data suggest that r-opsins are prevalent in dermal tissues of nudibranchs and may play a role in both extraocular photoreception and direct input to central and peripheral circadian clocks.
