Ramaesh Thaya, Ramaesh Kanna, Martin Collinson J, Chanas Simon A, Dhillon Baljean, West John D
Division of Reproductive and Developmental Sciences, Genes and Development Group, University of Edinburgh, Hugh Robson Building, George Square, Edinburgh EH8 9XD, UK.
Exp Eye Res. 2005 Aug;81(2):224-35. doi: 10.1016/j.exer.2005.02.002.
Heterozygosity for a PAX6 deficiency (PAX6+/-) results in low levels of the PAX6 transcription factor and causes aniridia. Corneal changes in aniridia-related keratopathy (ARK) include peripheral pannus and epithelial abnormalities, which eventually result in corneal opacity and contribute to visual loss. The corneal abnormalities of Pax6+/- mice provide an excellent model for the corneal changes seen in PAX6+/- humans. The aim of the present study was to investigate the contributions of different factors (including altered cell proliferation, abnormal epithelial differentiation and incursion of the conjunctival epithelium) that may underlie the pathogenesis of the corneal changes caused by low levels of Pax6 in heterozygous Pax6+/Sey-Neu (Pax6+/-) mice. BrdU incorporation showed enhanced proliferation of Pax6+/- corneal epithelium compared to wild-type controls and analysis of p63 (a marker of high proliferative potential) revealed a slight increase in frequency of p63-positive basal corneal epithelial cells in Pax6+/- mice. Immunohistochemical investigation of K12 (a Pax6-regulated marker of corneal epithelial differentiation) in 2-52-week-old mice showed that K12 expression was delayed and down-regulated in the Pax6+/- corneal epithelium, implying that differentiation of the Pax6+/- corneal epithelium was delayed and abnormal. Goblet cells were identified within the peripheral corneal epithelium of the Pax6+/- eyes, but some were surrounded by cells expressing K12, suggesting they may have arisen in situ in the corneal epithelium. These findings suggest that low levels of Pax6 may be directly responsible for failure or delay of proper differentiation of the corneal epithelial cells, but the proliferative component of the mutant epithelium is probably not impaired. This abnormal differentiation suggests that ARK is not entirely attributable to a limbal stem cell deficiency.
PAX6基因缺陷杂合子（PAX6+/-）会导致PAX6转录因子水平降低，并引发无虹膜症。无虹膜相关角膜病变（ARK）的角膜变化包括周边血管翳和上皮异常，最终导致角膜混浊并造成视力丧失。Pax6+/-小鼠的角膜异常为PAX6+/-人类患者所出现的角膜变化提供了一个极佳的模型。本研究的目的是探究不同因素（包括细胞增殖改变、上皮分化异常以及结膜上皮侵入）在杂合子Pax6+/Sey-Neu（Pax6+/-）小鼠中，因Pax6水平降低所引起的角膜病变发病机制中可能发挥的作用。与野生型对照相比，BrdU掺入显示Pax6+/-角膜上皮细胞增殖增强，并且对p63（高增殖潜能标志物）的分析表明，Pax6+/-小鼠中p63阳性角膜基底上皮细胞的频率略有增加。对2至52周龄小鼠角膜上皮分化的Pax6调控标志物K12进行免疫组织化学研究表明，K12在Pax6+/-角膜上皮中的表达延迟且下调，这意味着Pax6+/-角膜上皮的分化延迟且异常。在Pax6+/-眼睛的周边角膜上皮中发现了杯状细胞，但有些杯状细胞被表达K12的细胞所包围，这表明它们可能是在角膜上皮中原位产生的。这些发现表明，低水平的Pax6可能直接导致角膜上皮细胞正常分化失败或延迟，但突变上皮的增殖成分可能并未受损。这种异常分化表明，ARK并不完全归因于角膜缘干细胞缺陷。
