Zhang Jinglin, Upadhya Dinesh, Lu Lin, Reneker Lixing W
State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-Sen University, Guangzhou, China.
Dept. of Ophthalmology, Mason Eye Institute, University of Missouri, Columbia, Missouri, United States of America.
PLoS One. 2015 Jan 23;10(1):e0117089. doi: 10.1371/journal.pone.0117089. eCollection 2015.
Fibroblast growth factors (FGFs) play important roles in many aspects of embryonic development. During eye development, the lens and corneal epithelium are derived from the same surface ectodermal tissue. FGF receptor (FGFR)-signaling is essential for lens cell differentiation and survival, but its role in corneal development has not been fully investigated. In this study, we examined the corneal defects in Fgfr2 conditional knockout mice in which Cre expression is activated at lens induction stage by Pax6 P0 promoter. The cornea in LeCre, Fgfr2(loxP/loxP) mice (referred as Fgfr2(CKO)) was analyzed to assess changes in cell proliferation, differentiation and survival. We found that Fgfr2(CKO) cornea was much thinner in epithelial and stromal layer when compared to WT cornea. At embryonic day 12.5-13.5 (E12.5-13.5) shortly after the lens vesicle detaches from the overlying surface ectoderm, cell proliferation (judged by labeling indices of Ki-67, BrdU and phospho-histone H3) was significantly reduced in corneal epithelium in Fgfr2(CKO) mice. At later stage, cell differentiation markers for corneal epithelium and underlying stromal mesenchyme, keratin-12 and keratocan respectively, were not expressed in Fgfr2(CKO) cornea. Furthermore, Pax6, a transcription factor essential for eye development, was not present in the Fgfr2(CKO) mutant corneal epithelial at E16.5 but was expressed normally at E12.5, suggesting that FGFR2-signaling is required for maintaining Pax6 expression in this tissue. Interestingly, the role of FGFR2 in corneal epithelial development is independent of ERK1/2-signaling. In contrast to the lens, FGFR2 is not required for cell survival in cornea. This study demonstrates for the first time that FGFR2 plays an essential role in controlling cell proliferation and differentiation, and maintaining Pax6 levels in corneal epithelium via ERK-independent pathways during embryonic development.
成纤维细胞生长因子（FGFs）在胚胎发育的许多方面发挥着重要作用。在眼睛发育过程中，晶状体和角膜上皮均源自同一表面外胚层组织。FGF受体（FGFR）信号传导对于晶状体细胞的分化和存活至关重要，但其在角膜发育中的作用尚未得到充分研究。在本研究中，我们检查了Fgfr2条件性敲除小鼠的角膜缺陷，其中Cre表达在晶状体诱导阶段由Pax6 P0启动子激活。分析LeCre、Fgfr2（loxP/loxP）小鼠（称为Fgfr2（CKO））的角膜，以评估细胞增殖、分化和存活的变化。我们发现，与野生型角膜相比，Fgfr2（CKO）角膜的上皮层和基质层要薄得多。在晶状体泡从上方表面外胚层分离后不久的胚胎第12.5 - 13.5天（E12.5 - 13.5），Fgfr2（CKO）小鼠角膜上皮中的细胞增殖（通过Ki - 67、BrdU和磷酸化组蛋白H3的标记指数判断）显著降低。在后期，角膜上皮和下方基质间充质的细胞分化标志物，即角蛋白 - 12和角蛋白聚糖，在Fgfr2（CKO）角膜中均未表达。此外，Pax6是眼睛发育所必需的转录因子，在E16.5时Fgfr2（CKO）突变体角膜上皮中不存在，但在E12.5时正常表达，这表明FGFR2信号传导是维持该组织中Pax6表达所必需的。有趣的是，FGFR2在角膜上皮发育中的作用独立于ERK1/2信号传导。与晶状体不同，FGFR2对角膜细胞存活不是必需的。本研究首次证明，在胚胎发育过程中，FGFR2通过不依赖ERK的途径在控制角膜上皮细胞增殖和分化以及维持Pax6水平方面发挥着重要作用。
