title: Cone photoreceptor types in zebrafish are generated by symmetric terminal divisions of dedicated precursors.
abstract: Proper functioning of sensory systems requires the generation of appropriate numbers and proportions of neuronal subtypes that encode distinct information. Perception of color relies on signals from multiple cone photoreceptor types. In cone-dominated retinas, each cone expresses a single opsin type with peak sensitivity to UV, long (L) (red), medium (M) (green), or short (S) (blue) wavelengths. The modes of cell division generating distinct cone types are unknown. We report here a mechanism whereby zebrafish cone photoreceptors of the same type are produced by symmetric division of dedicated precursors. Transgenic fish in which the thyroid hormone receptor β2 (trβ2) promoter drives fluorescent protein expression before L-cone precursors themselves are produced permitted tracking of their division in vivo. Every L cone in a local region resulted from the terminal division of an L-cone precursor, suggesting that such divisions contribute significantly to L-cone production. Analysis of the fate of isolated pairs of cones and time-lapse observations suggest that other cone types can also arise by symmetric terminal divisions. Such divisions of dedicated precursors may help to rapidly attain the final numbers and proportions of cone types (L > M, UV > S) in zebrafish larvae. Loss- and gain-of-function experiments show that L-opsin expression requires trβ2 activity before cone differentiation. Ectopic expression of trβ2 after cone differentiation produces cones with mixed opsins. Temporal differences in the onset of trβ2 expression could explain why some species have mixed, and others have pure, cone types.
authors: Department of Biological Structure, University of Washington, Seattle, WA 98195-7420.
authors: Sachihiro C
authors: SC
authors: Suzuki
authors: Adam
authors: A
authors: Bleckert
authors: Philip R
authors: PR
authors: Williams
authors: Masaki
authors: M
authors: Takechi
authors: Shoji
authors: S
authors: Kawamura
authors: Rachel O L
authors: RO
authors: Wong
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001483:Base Sequence; D002454:Cell Differentiation; D002455:Cell Division; D019070:Cell Lineage; D055358:Cone Opsins / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D055785:Gene Knockdown Techniques; D007814:Larva / Q000166:cytology / Q000254:growth & development / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000235:genetics; D017949:Retinal Cone Photoreceptor Cells / Q000145:classification / Q000166:cytology* / Q000378:metabolism; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism; D037042:Thyroid Hormone Receptors beta / Q000037:antagonists & inhibitors / Q000235:genetics; D015027:Zebrafish / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D055358:Cone Opsins; D008164:Luminescent Proteins; D011994:Recombinant Proteins; D037042:Thyroid Hormone Receptors beta; D029961:Zebrafish Proteins
keywords: cone genesis; in vivo time-lapse imaging; vertebrate cone photoreceptors; zebrafish retina
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