Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas, 77030, USA.
Development. 2010 Mar;137(5):725-34. doi: 10.1242/dev.040568.
Transcriptional networks, which are initiated by secreted proteins, cooperate with each other to orchestrate eye development. The establishment of dorsal/ventral polarity, especially dorsal specification in the optic vesicle, is poorly understood at a molecular and cellular level. Here, we show that COUP-TFI (Nr2f1) and COUP-TFII (Nr2f2) are highly expressed in the progenitor cells in the developing murine eye. Phenotype analysis of COUP-TFI and COUP-TFII single-gene conditional knockout mouse models suggests that COUP-TFs compensate for each other to maintain morphogenesis of the eye. However, in eye-specific COUP-TFI/TFII double-knockout mice, progenitor cells at the dorso-distal optic vesicle fail to differentiate appropriately, causing the retinal pigmented epithelium cells to adopt a neural retina fate and abnormal differentiation of the dorsal optic stalk; the development of proximo-ventral identities, neural retina and ventral optic stalk is also compromised. These cellular defects in turn lead to congenital ocular colobomata and microphthalmia. Immunohistochemical and in situ hybridization assays reveal that the expression of several regulatory genes essential for early optic vesicle development, including Pax6, Otx2, Mitf, Pax2 and Vax1/2, is altered in the corresponding compartments of the mutant eye. Using ChIP assay, siRNA treatment and transient transfection in ARPE-19 cells in vitro, we demonstrate that Pax6 and Otx2 are directly regulated by COUP-TFs. Taken together, our findings reveal novel and distinct cell-intrinsic mechanisms mediated by COUP-TF genes to direct the specification and differentiation of progenitor cells, and that COUP-TFs are crucial for dorsalization of the eye.
转录网络由分泌蛋白启动，相互协作以协调眼睛发育。在分子和细胞水平上，对背腹极性（尤其是视泡中的背侧特化）的建立知之甚少。在这里，我们显示 COUP-TFI（Nr2f1）和 COUP-TFII（Nr2f2）在发育中的小鼠眼睛祖细胞中高度表达。COUP-TFI 和 COUP-TFII 单基因条件敲除小鼠模型的表型分析表明，COUP-TFs 相互补偿以维持眼睛的形态发生。然而，在眼睛特异性 COUP-TFI/TFII 双敲除小鼠中，背腹远侧视泡中的祖细胞不能适当分化，导致视网膜色素上皮细胞采用神经视网膜命运和异常的背侧视神经鞘分化；近端腹侧身份、神经视网膜和腹侧视神经鞘的发育也受到损害。这些细胞缺陷反过来又导致先天性眼部裂孔和小眼症。免疫组织化学和原位杂交检测显示，几种对早期视泡发育至关重要的调节基因的表达，包括 Pax6、Otx2、Mitf、Pax2 和 Vax1/2，在突变眼的相应隔室中发生改变。通过 ChIP 测定、siRNA 处理和体外 ARPE-19 细胞的瞬时转染，我们证明 Pax6 和 Otx2 被 COUP-TFs 直接调节。总之，我们的发现揭示了由 COUP-TF 基因介导的新型、独特的细胞内在机制，以指导祖细胞的特化和分化，并且 COUP-TFs 对于眼睛的背侧化至关重要。
