Department of Biological Sciences, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada.
Department of Biology, University of Victoria, Victoria, BC, V8W 2Y2, Canada.
Sci Rep. 2022 May 16;12(1):8062. doi: 10.1038/s41598-022-11998-9.
Fishes often have cone photoreceptors organized in lattice-like mosaic formations. In flatfishes, these lattices undergo dramatic changes during metamorphosis whereby a honeycomb mosaic of single cones in the larva is replaced by a square mosaic of single and double cones in the adult. The spatio-temporal dynamics of this transition are not well understood. Here, we describe the photoreceptors and mosaic formations that occur during the larva to juvenile transition of Atlantic halibut from the beginning of eye migration to its completion. To gauge the possibility of colour vision, visual pigments in juveniles were measured by microspectrophotometry and the opsin repertoire explored using bioinformatics. At the start of eye migration, the larva had a heterogeneous retina with honeycomb mosaic in the dorsonasal and ventrotemporal quadrants and a square mosaic in the ventronasal and dorsotemporal quadrants. By the end of metamorphosis, the square mosaic was present throughout the retina except in a centrodorsotemporal area where single, double and triple cones occurred randomly. Six cone visual pigments were found with maximum absorbance (λ, in nm) in the short [S(431) and S(457)], middle [M(500), M(514) and M(527)], and long [L(550)] wavelengths, and a rod visual pigment with λ at 491 nm. These pigments only partially matched the opsin repertoire detected by query of the Atlantic halibut genome. We conclude that the Atlantic halibut undergoes a complex re-organization of photoreceptors at metamorphosis resulting in a multi-mosaic retina adapted for a demersal life style.
鱼类的视锥细胞通常呈晶格状镶嵌排列。在比目鱼中，这些晶格在变态过程中发生剧烈变化，幼虫的蜂窝状单锥细胞镶嵌被成虫的单、双锥细胞正方形镶嵌所取代。这个转变的时空动态还不是很清楚。在这里，我们描述了大西洋比目鱼从眼睛迁移开始到完成的幼鱼到幼鱼过渡期间发生的视锥细胞和镶嵌形成。为了评估颜色视觉的可能性，我们通过微分光光度法测量了幼鱼中的视觉色素，并使用生物信息学探索了视蛋白库。在眼睛迁移开始时，幼虫的视网膜具有异质性，背-鼻侧和腹-颞侧象限呈蜂窝状镶嵌，腹-鼻侧和背-颞侧象限呈正方形镶嵌。在变态结束时，除了在中心背-颞侧区域，整个视网膜都存在正方形镶嵌，那里随机出现单、双和三锥细胞。发现了六种视锥细胞视觉色素，最大吸收波长（λ，nm）在短（S(431)和 S(457)）、中（M(500)、M(514)和 M(527)）和长（L(550)）波长，以及一种视杆细胞视觉色素，λ 在 491nm。这些色素仅部分与通过大西洋比目鱼基因组查询检测到的视蛋白库匹配。我们的结论是，大西洋比目鱼在变态过程中对视锥细胞进行了复杂的重新组织，形成了适应底栖生活方式的多镶嵌视网膜。
