Retina-derived signals control pace of neurogenesis in visual brain areas but not circuit configuration. Retina-derived signals control pace of neurogenesis in visual brain areas but not circuit configuration

Brain development is orchestrated by both innate and experience-dependent mechanisms, but their relative contributions are often difficult to resolve. Here we asked if and how central visual areas are altered in a vertebrate brain depleted of any and all signals from retinal ganglion cells throughout development. We transcriptionally profiled neurons in pretectum, thalamus and other retinorecipient areas of larval zebrafish and searched for changes in lakritz mutants that lack all retinal connections. Although individual genes are dysregulated, the complete set of 77 neuronal types develops in apparently normal proportions, at normal locations, and along normal differentiation trajectories. Strikingly, the cell-cycle exits of proliferating progenitors in these areas are delayed, and a greater fraction of early postmitotic precursors remain uncommitted or are diverted to a glial fate. Optogenetic stimulation targeting groups of neurons normally involved in processing visual information evokes behaviors indistinguishable from wildtype. In conclusion, we show that signals emitted by retinal axons influence the pace of neurogenesis in visual areas, but do not detectably affect the specification or wiring of downstream neurons. Overall design: Tg(HGn12C:GFP) or [Tg(Gal4s1026t) X Tg(UAS:GFP)] larvae were sorted for GFP expression 24 hours after fertilization. All single-cell experiments were performed at 6 days after fertilization. To obtain unrelated WT, pigmented larvae were used from Tg(HGn12C:GFP) pigmented males or females crossed with WT TLN, which are homozygous mutant for mitfa. To obtain lakritz mutant and sibling WT larvae, Tg(HGn12C:GFP) lakritz heterozygote adults were crossed with adult lakritz heterozygotes. For experiments with lakritz larvae, only lakritz mutants were collected; for other experiments, they were discarded. For single-cell experiments larvae were rapidly decapitated and processed for cell dissociation followed by FACS of labelled cells.

大脑发育由先天机制与经验依赖型机制共同调控，但二者的相对贡献度往往难以厘清。本研究旨在探讨：在整个发育过程中完全缺失视网膜神经节细胞（retinal ganglion cells）信号的脊椎动物大脑内，其中枢视觉脑区是否会发生改变，以及如何改变。我们对斑马鱼幼体顶盖前区、丘脑及其他视网膜接收脑区的神经元开展转录组谱分析，并在完全缺失视网膜连接的lakritz突变体中筛选差异变化。尽管存在单个基因的表达失调，但77种神经元类型的完整集合仍能以正常比例、正常位置及正常分化轨迹发育形成。值得注意的是，上述脑区中增殖性神经祖细胞的细胞周期退出过程出现延迟，且更大比例的早期有丝分裂后前体细胞仍处于未定向状态，或被转向胶质细胞命运。靶向通常参与视觉信息处理的神经元集群的光遗传刺激，所诱发的行为与野生型个体无显著差异。综上，本研究证实：视网膜轴突释放的信号可调控视觉脑区的神经发生速率，但未对下游神经元的命运定向或神经环路搭建产生可检测到的影响。
实验设计：于受精后24小时，根据绿色荧光蛋白（Green Fluorescent Protein, GFP）表达情况，分选Tg(HGn12C:GFP)或[Tg(Gal4s1026t) × Tg(UAS:GFP)]转基因斑马鱼幼体。所有单细胞实验均于受精后6天开展。为获取无关野生型（Wild Type, WT）个体，将携带色素的Tg(HGn12C:GFP)成鱼与mitfa纯合突变的野生型TLN品系成鱼杂交，所得带有色素的幼体即为无关野生型样本。为获取lakritz突变体及其同窝野生型幼体，将携带Tg(HGn12C:GFP)的lakritz杂合子成鱼与lakritz杂合子成鱼进行杂交。在针对lakritz幼体的实验中，仅收集lakritz突变体幼体；其余实验则弃用该类幼体。单细胞实验中，先将幼体快速断头，再进行细胞解离，随后对标记细胞开展荧光激活细胞分选（Fluorescence-Activated Cell Sorting, FACS）。