Department of Ophthalmology, Kyoto Prefectural University of Medicine, Kyoto, Japan.
Department of Life Science Frontiers, Center for iPS Cell Research and Application, Kyoto University, Kyoto, Japan.
Cornea. 2019 Nov;38 Suppl 1:S34-S41. doi: 10.1097/ICO.0000000000002074.
In its early stages, an embryo polarizes to form cell subpopulations that subsequently produce specific organ cell types. These cell subpopulations are defined by transcription factors (TFs) that activate or repress specific genes. Although an embryo comprises thousands of TFs, surprisingly few are needed to determine the fate of a given cell. The ectoderm divides into the neuroectoderm and surface ectoderm, the latter of which gives rise to epidermal keratinocytes and corneal epithelial cells (CECs). Meanwhile, neuroectoderm cells give rise to other parts of the eye such as the corneal endothelium and retina. To investigate the regulatory role of TFs in CECs, we overexpressed the "core TFs" (PAX6, OVOL2, and KLF4) in human fibroblasts and found that the cells adopted a CEC-like quality. OVOL2 overexpression was even able to directly induce cells with a neuroectoderm fate toward a surface ectoderm fate, designated "direct reprogramming." Conversely, suppression of OVOL2 or PAX6 expression induced CECs to show qualities consistent with neural lineage cells or epidermal keratinocytes, respectively. This suggests that these core TFs can maintain the CEC phenotype through reciprocal gene regulation. Direct reprogramming has important implications for cell therapies. The potential benefits of cells derived by direct reprogramming compared with induced pluripotent stem cells include the fact that it requires less time than reprogramming a cell back to the pluripotent state and then to another cell type. Further understanding of the reciprocally repressive mechanism of action for core TFs could lead to alternative treatments for regenerative medicine not requiring cell transplantation.
在胚胎发育的早期，胚胎会极化形成细胞亚群，这些细胞亚群随后会产生特定的器官细胞类型。这些细胞亚群由转录因子（TFs）定义，这些转录因子激活或抑制特定基因。尽管胚胎包含数千种 TFs，但决定特定细胞命运所需的 TFs 数量却出人意料地少。外胚层分为神经外胚层和表面外胚层，后者产生表皮角质形成细胞和角膜上皮细胞（CECs）。与此同时，神经外胚层细胞产生眼睛的其他部分，如角膜内皮细胞和视网膜。为了研究 TFs 在 CECs 中的调控作用，我们在人成纤维细胞中过表达了“核心 TFs”（PAX6、OVOL2 和 KLF4），发现细胞获得了 CEC 样的特性。OVOL2 的过表达甚至能够直接诱导具有神经外胚层命运的细胞向表面外胚层命运转变，称为“直接重编程”。相反，抑制 OVOL2 或 PAX6 的表达会诱导 CECs 表现出与神经谱系细胞或表皮角质形成细胞一致的特性。这表明这些核心 TFs 可以通过相互调节基因来维持 CEC 表型。直接重编程对细胞治疗具有重要意义。与诱导多能干细胞相比，直接重编程获得的细胞具有一些潜在的优势，例如，它需要的时间比将细胞重新编程回多能状态然后再编程为另一种细胞类型所需的时间要少。进一步了解核心 TFs 的相互抑制作用机制可能会为不需要细胞移植的再生医学提供替代治疗方法。
