An EvoDevo Study of Salmonid Visual Opsin Dynamics and Photopigment Spectral Sensitivity

• Published in: Frontiers in Neuroanatomy
• Main Authors: Eilertsen, Mariann, Davies, Wayne Iwan Lee, Patel, Dharmeshkumar, Barnes, Jonathan E., Karlsen, Rita, Mountford, Jessica Kate, Stenkamp, Deborah L., Patel, Jagdish Suresh, Helvik, Jon Vidar
• Format: Text
• Language: English
• Published: Frontiers Media S.A. 2022
• Subjects: Neuroanatomy; Sockeye; Atlantic salmon; Salmo salar
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC9309310/; http://www.ncbi.nlm.nih.gov/pubmed/35899127; https://doi.org/10.3389/fnana.2022.945344

Salmonids are ideal models as many species follow a distinct developmental program from demersal eggs and a large yolk sac to hatching at an advanced developmental stage. Further, these economically important teleosts inhabit both marine- and freshwaters and experience diverse light environments during their life histories. At a genome level, salmonids have undergone a salmonid-specific fourth whole genome duplication event (Ss4R) compared to other teleosts that are already more genetically diverse compared to many non-teleost vertebrates. Thus, salmonids display phenotypically plastic visual systems that appear to be closely related to their anadromous migration patterns. This is most likely due to a complex interplay between their larger, more gene-rich genomes and broad spectrally enriched habitats; however, the molecular basis and functional consequences for such diversity is not fully understood. This study used advances in genome sequencing to identify the repertoire and genome organization of visual opsin genes (those primarily expressed in retinal photoreceptors) from six different salmonids [Atlantic salmon (Salmo salar), brown trout (Salmo trutta), Chinook salmon (Oncorhynchus tshawytcha), coho salmon (Oncorhynchus kisutch), rainbow trout (Oncorhynchus mykiss), and sockeye salmon (Oncorhynchus nerka)] compared to the northern pike (Esox lucius), a closely related non-salmonid species. Results identified multiple orthologues for all five visual opsin classes, except for presence of a single short-wavelength-sensitive-2 opsin gene. Several visual opsin genes were not retained after the Ss4R duplication event, which is consistent with the concept of salmonid rediploidization. Developmentally, transcriptomic analyzes of Atlantic salmon revealed differential expression within each opsin class, with two of the long-wavelength-sensitive opsins not being expressed before first feeding. Also, early opsin expression in the retina was located centrally, expanding dorsally and ventrally as eye development ...