Division of Molecular and Developmental Biology, Institute of Medical Science, University of Tokyo, Tokyo, Japan.
Medical Proteomics Laboratory, Institute of Medical Science, University of Tokyo, Tokyo, Japan.
Exp Eye Res. 2018 Jun;171:142-154. doi: 10.1016/j.exer.2018.03.017. Epub 2018 Mar 17.
During development of the retina, common retinal progenitor cells give rise to six classes of neurons that subsequently further diversify into more than 55 subtypes of neuronal subtypes. Here, we have investigated the expression and function of Fezf2, Fez zinc finger family of protein, in the developing mouse retina. Expression of Fezf2 transcripts was strongly observed in the embryonic retinal progenitors at E14.5 and declined quickly in subsequent development of retina. Then, in postnatal stage at around day 8, Fezf2 was transiently expressed then declined again. Loss-of-function analysis using retinas from mice in which Fezf2 coding region was substituted with β-galactosidase showed that Fezf2 is expressed in a subset of cone OFF bipolar cells and required for their differentiation. Using electroretinogram, we found that Fezf2 knockout retina exhibited significantly reduced photopic b-wave, suggesting functional abnormality of cone ON bipolar cells. Furthermore, reduced expression of synaptic protein Trpm1 and structural alteration of ON bipolar cell invagination, both of which affected cone photoreceptor terminal synaptic activity, was identified by transmission electron microscopy and immunohistochemistry, respectively. Taken together, our results show that Fezf2 is indispensable in differentiation of bipolar precursors into cone OFF bipolar cells and in functional maturation of cone ON bipolar cells during development of mouse retina. These results contribute to our understanding of how diversity of neuronal subtypes and hence specificity of neuronal connections are established in the retina by intrinsic cues.
在视网膜发育过程中，普通视网膜祖细胞产生六种神经元，随后进一步多样化为超过 55 种神经元亚型。在这里，我们研究了 Fezf2（Fez 锌指蛋白家族蛋白）在发育中的小鼠视网膜中的表达和功能。Fezf2 转录本的表达在 E14.5 的胚胎视网膜祖细胞中强烈观察到，并在随后的视网膜发育中迅速下降。然后，在出生后的第 8 天左右，Fezf2 短暂表达，然后再次下降。使用 Fezf2 编码区被β-半乳糖苷酶取代的小鼠视网膜进行功能丧失分析表明，Fezf2 在一组 cone OFF 双极细胞中表达，并需要其分化。通过视网膜电图，我们发现 Fezf2 敲除视网膜表现出明显减少的明视 b 波，表明 cone ON 双极细胞的功能异常。此外，通过透射电子显微镜和免疫组织化学分别鉴定到突触蛋白 Trpm1 的表达减少和 ON 双极细胞内陷的结构改变，这两者都影响了 cone 光感受器末端的突触活动。总之，我们的结果表明，Fezf2 对于双极前体细胞分化为 cone OFF 双极细胞以及在发育中的小鼠视网膜中 cone ON 双极细胞的功能成熟是必不可少的。这些结果有助于我们理解内在信号如何在视网膜中建立神经元亚型的多样性和神经元连接的特异性。
