Edith J. Crawley Vision Research Center/Department of Ophthalmology, College of Medicine, University of Cincinnati, Cincinnati, OH 45267, USA.
Development. 2013 Feb 1;140(3):594-605. doi: 10.1242/dev.082842.
Conjunctival goblet cells primarily synthesize mucins to lubricate the ocular surface, which is essential for normal vision. Notch signaling has been known to associate with goblet cell differentiation in intestinal and respiratory tracts, but its function in ocular surface has yet to be fully characterized. Herein, we demonstrate that conditional inhibition of canonical Notch signaling by expressing dominant negative mastermind-like 1 (dnMaml1) in ocular surface epithelia resulted in complete suppression of goblet cell differentiation during and subsequent to development. When compared with the ocular surface of wild-type mice (OS(Wt)), expression of dnMaml1 at the ocular surface (OS(dnMaml1)) caused conjunctival epithelial hyperplasia, aberrant desquamation, failure of Mucin 5ac (Muc5ac) synthesis, subconjunctival inflammation and epidermal metaplasia in cornea. In addition, conditional deletion of Notch1 from the ocular surface epithelia partially recapitulated OS(dnMaml1) phenotypes. We have demonstrated that N1-ICD (Notch1 intracellular domain) transactivated the mouse Krüppel-like factor 4 (Klf) promoter and that Klf4 directly bound to and significantly potentiated the Muc5ac promoter. By contrast, OS(dnMaml1) dampened Klf4 and Klf5 expression, and diminished Muc5ac synthesis. Collectively, these findings indicated that Maml-mediated Notch signaling plays a pivotal role in the initiation and maintenance of goblet cell differentiation for normal ocular surface morphogenesis and homeostasis through regulation of Klf4 and Klf5.
结膜杯状细胞主要合成黏液以润滑眼表面，这对于正常视力至关重要。 Notch 信号通路已被证实与肠道和呼吸道中的杯状细胞分化有关，但它在眼表面的功能尚未完全阐明。在此，我们证明在眼表面上皮细胞中表达显性负性的主调控样蛋白 1（dnMaml1）来抑制经典 Notch 信号通路，会导致在发育过程中和发育后完全抑制杯状细胞分化。与野生型小鼠的眼表面（OS（Wt））相比，在眼表面表达 dnMaml1（OS（dnMaml1））会导致结膜上皮增生、异常脱落、Mucin 5ac（Muc5ac）合成失败、结膜下炎症和角膜表皮化生。此外，从眼表面上皮细胞中条件性缺失 Notch1 部分再现了 OS（dnMaml1）的表型。我们已经证明 N1-ICD（Notch1 细胞内结构域）可反式激活小鼠 Krüppel 样因子 4（Klf）启动子，并且 Klf4 直接结合并显著增强 Muc5ac 启动子的活性。相比之下，OS（dnMaml1）降低了 Klf4 和 Klf5 的表达，并减少了 Muc5ac 的合成。总之，这些发现表明，Maml 介导的 Notch 信号通路通过调节 Klf4 和 Klf5 在启动和维持杯状细胞分化以维持正常眼表面形态发生和稳态方面发挥关键作用。
