Kiyama Takae, Altay Halit Y, Badea Tudor C, Mao Chai-An
Ruiz Department of Ophthalmology and Visual Science, McGovern Medical School at The University of Texas Health Science Center at Houston (UTHealth), Houston, TX 77030, USA.
Research and Development Institute, Transilvania University of Brasov, School of Medicine, Brasov 500484, Romania.
Front Ophthalmol (Lausanne). 2023;3. doi: 10.3389/fopht.2023.1175568. Epub 2023 May 18.
More than 40 retinal ganglion cell (RGC) subtypes have been categorized in mouse based on their morphologies, functions, and molecular features. Among these diverse subtypes, orientation-selective Jam2-expressing RGCs (J-RGCs) has two unique morphologic characteristics: the ventral-facing dendritic arbor and the OFF-sublaminae stratified terminal dendrites in the inner plexiform layer. Previously, we have discovered that T-box transcription factor () is expressed in J-RGCs. We further found that is essential for the expression of , and Tbr1 regulates the formation and the dendritic morphogenesis of J-RGCs. However, Tbr1 begins to express in terminally differentiated RGCs around perinatal stage, suggesting that it is unlikely involved in the initial fate determination for J-RGC and other upstream transcription factors must control expression and J-RGC formation. Using the Cleavage Under Targets and Tagmentation technique, we discovered that Pou4f1 binds to on the evolutionary conserved exon 6 and an intergenic region downstream of the 3'UTR, and on a region flanking the promoter and the first exon of . We showed that Pou4f1 is required for the expression of and , indicating Pou4f1 as a direct upstream regulator of and . Most interestingly, the Pou4f1-bound element in exon 6 of possesses high-level enhancer activity, capable of directing reporter gene expression in J-RGCs. Together, these data revealed a genetic hierarchy as a critical pathway in the formation of J-RGC subtype.
基于视网膜神经节细胞（RGC）的形态、功能和分子特征，在小鼠中已分类出40多种RGC亚型。在这些多样的亚型中，表达Jam2的方向选择性RGC（J-RGC）具有两个独特的形态学特征：面向腹侧的树突状分支以及在内网状层中位于OFF亚层的分层终末树突。此前，我们发现T-box转录因子（）在J-RGC中表达。我们进一步发现，对于的表达至关重要，并且Tbr1调节J-RGC的形成和树突形态发生。然而，Tbr1在围产期左右开始在终末分化的RGC中表达，这表明它不太可能参与J-RGC的初始命运决定，而其他上游转录因子必定控制的表达和J-RGC的形成。使用靶向切割和标签化技术，我们发现Pou4f1与进化保守的外显子6以及3'UTR下游的基因间区域结合，并且与的启动子和第一个外显子侧翼的区域结合。我们表明，Pou4f1对于和的表达是必需的，这表明Pou4f1是和的直接上游调节因子。最有趣的是，中位于外显子6的Pou4f1结合元件具有高水平的增强子活性，能够在J-RGC中指导报告基因的表达。总之，这些数据揭示了一种基因层级结构，作为J-RGC亚型形成中的关键途径。
