title: The two-step development of a duplex retina involves distinct events of cone and rod neurogenesis and differentiation.
abstract: Unlike in mammals, persistent postembryonic retinal growth is a characteristic feature of fish, which includes major remodeling events that affect all cell types including photoreceptors. Consequently, visual capabilities change during development, where retinal sensitivity to different wavelengths of light (photopic vision), -and to limited photons (scotopic vision) are central capabilities for survival. Differently from well-established model fish, Atlantic cod has a prolonged larval stage where only cone photoreceptors are present. Rods do not appear until juvenile transition (metamorphosis), a hallmark of indirect developing species. Previously we showed that whole gene families of lws (red-sensitive) and sws1 (UV-sensitive) opsins have been lost in cod, while rh2a (green-sensitive) and sws2 (blue-sensitive) genes have tandem duplicated. Here, we provide a comprehensive characterization of a two-step developing duplex retina in Atlantic cod. The study focuses on cone subtype dynamics and delayed rod neurogenesis and differentiation in all cod life stages. Using transcriptomic and histological approaches we show that different opsins disappear in a topographic manner during development where central to peripheral retina is a key axis of expressional change. Early cone differentiation was initiated in dorso-temporal retina different from previously described in fish. Rods first appeared during initiation of metamorphosis and expression of the nuclear receptor transcription factor nr2e3-1, suggest involvement in rod specification. The indirect developmental strategy thus allows for separate studies of cones and rods development, which in nature correlates with visual changes linked to habitat shifts. The clustering of key retinal genes according to life stage, suggests that Atlantic cod with its sequenced genome may be an important resource for identification of underlying factors required for development and function of photopic and scotopic vision.
authors.affiliation: Department of Biology, University of Bergen, NO-5020 Bergen, Norway.
authors.forename: Ragnhild
authors.initials: R
authors.lastname: Valen
authors.affiliation: Department of Biology, University of Bergen, NO-5020 Bergen, Norway.
authors.forename: Mariann
authors.initials: M
authors.lastname: Eilertsen
authors.affiliation: Institute of Marine Research, Nordnes, NO-5005 Bergen, Norway.
authors.forename: Rolf Brudvik
authors.initials: RB
authors.lastname: Edvardsen
authors.affiliation: Institute of Marine Research, Nordnes, NO-5005 Bergen, Norway.
authors.forename: Tomasz
authors.initials: T
authors.lastname: Furmanek
authors.affiliation: Department of Biology, University of Bergen, NO-5020 Bergen, Norway.
authors.forename: Ivar
authors.initials: I
authors.lastname: Rønnestad
authors.affiliation: Institute of Marine Research, Austevoll Research station and Hjort Centre for Marine Ecosystem Dynamics, NO-5392 Storebø, Norway.
authors.forename: Terje
authors.initials: T
authors.lastname: van der Meeren
authors.affiliation: Institute of Marine Research, Austevoll Research station and Hjort Centre for Marine Ecosystem Dynamics, NO-5392 Storebø, Norway.
authors.forename: Ørjan
authors.initials: Ø
authors.lastname: Karlsen
authors.affiliation: UniResearch AS, NO-5006 Bergen, Norway.
authors.forename: Tom Ole
authors.initials: TO
authors.lastname: Nilsen
authors.affiliation: Department of Biology, University of Bergen, NO-5020 Bergen, Norway.
authors.forename: Jon Vidar
authors.initials: JV
authors.lastname: Helvik
mesh_terms: D000818:Animals; D005136:Eye Proteins / Q000096:biosynthesis / Q000235:genetics; D048389:Gadus morhua / Q000196:embryology / Q000235:genetics / Q000254:growth & development*; D020440:Gene Duplication; D018507:Gene Expression Regulation, Developmental; D007814:Larva; D008018:Life Cycle Stages; D008675:Metamorphosis, Biological; D055495:Neurogenesis; D055355:Opsins / Q000235:genetics; D018160:Receptors, Cytoplasmic and Nuclear / Q000096:biosynthesis / Q000235:genetics; D012160:Retina / Q000166:cytology / Q000196:embryology / Q000254:growth & development*; D017948:Retinal Rod Photoreceptor Cells / Q000166:cytology*; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics; D059467:Transcriptome; D014785:Vision, Ocular
chemical_list: D005136:Eye Proteins; D055355:Opsins; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors
keywords: Atlantic cod; Cone; Indirect development; Metamorphosis; Nr2e3; RNA-Seq; Rod; Visual opsins