Organoid replicates and cell lines.

Trichromacy is unique to primates among placental mammals, enabled by blue (short/S), green (medium/M), and red (long/L) cones. In humans, great apes, and Old World monkeys, cones make a poorly understood choice between M and L cone subtype fates. To determine mechanisms specifying M and L cones, we developed an approach to visualize expression of the highly similar M- and L-opsin mRNAs. M-opsin was observed before L-opsin expression during early human eye development, suggesting that M cones are generated before L cones. In adult human tissue, the early-developing central retina contained a mix of M and L cones compared to the late-developing peripheral region, which contained a high proportion of L cones. Retinoic acid (RA)-synthesizing enzymes are highly expressed early in retinal development. High RA signaling early was sufficient to promote M cone fate and suppress L cone fate in retinal organoids. Across a human population sample, natural variation in the ratios of M and L cone subtypes was associated with a noncoding polymorphism in the NR2F2 gene, a mediator of RA signaling. Our data suggest that RA promotes M cone fate early in development to generate the pattern of M and L cones across the human retina.

在胎盘类哺乳动物中，三色视觉为灵长类所独有，其生理基础依赖于蓝（短波长/S型）、绿（中波长/M型）与红（长波长/L型）三种视锥细胞。在人类、类人猿及旧世界猴中，视锥细胞会在M型与L型视锥亚型的命运间做出一种目前尚未阐明的选择。为明确调控M型与L型视锥细胞命运的分子机制，我们开发了一种可可视化高度同源的M型与L型视蛋白mRNA表达的实验方法。在人类胚胎早期眼球发育过程中，M型视蛋白的表达先于L型视蛋白出现，这提示M型视锥细胞的生成早于L型视锥细胞。在成人人体组织中，发育较早的中央视网膜区域同时存在M型与L型视锥细胞；而发育较晚的外周视网膜区域则以L型视锥细胞占绝对多数。视黄酸（retinoic acid, RA）合成酶在视网膜发育早期呈现高表达状态。在视网膜类器官中，早期高水平的视黄酸信号足以诱导M型视锥细胞命运，并抑制L型视锥细胞的分化。通过对人类人群样本的分析，我们发现M型与L型视锥细胞亚型的比例存在自然变异，该变异与NR2F2基因中的一段非编码多态性位点相关，而NR2F2基因正是视黄酸信号通路的介导因子。本研究数据表明，发育早期的视黄酸信号可促进M型视锥细胞命运，从而塑造人类视网膜中M型与L型视锥细胞的分布模式。