Meeting Abstract
MSP analysis of isolated photoreceptors from the Atlantic stomatopod species Squilla empusa reveals that all photoreceptors absorb light maximally at 507 nm. This suggests that a single visual pigment is present in all retinal photoreceptors. However, multiple distinct opsin transcripts, encoding the protein component of the visual pigment, have been isolated. Six opsin sequences have been published and additional ones obtained by transcriptomics. Phylogenetic analysis reveals that all these opsins localize to several major arthropod middle/long wavelength opsin clades. In this study, we examined the expression of opsins in the retina using in situ hybridization and use bioinformatics and structural modeling to analyze amino acid sequences and predict 3D structures of the visual pigments to search for potential functional or spectral differences among the various expressed opsins. In situ hybridization of S. empusa retinal sections was done using riboprobes that target the 3’UTR of transcripts of two specific opsin genes, Se5 and Se6. The results suggest co-expression of multiple opsins in the same regions of the retina, and also suggest possible preferential expression of opsin Se6 in a subset of photoreceptor cells in the peripheral regions of the retina. Amino acid sequence and structural analysis suggests that spectral differences between opsins Se5 and Se6 are unlikely, due to very high sequence homology, particularly in the amino acids in close proximity to the chromophore binding pocket. Taken together, these data suggest that the monochromatic stomatopod Squilla empusa possesses a higher level of molecular complexity than predicted, but the exact function of multiple opsin expression remains unclear.
