Schermer A, Galvin S, Sun T T
J Cell Biol. 1986 Jul;103(1):49-62. doi: 10.1083/jcb.103.1.49.
In this paper we present keratin expression data that lend strong support to a model of corneal epithelial maturation in which the stem cells are located in the limbus, the transitional zone between cornea and conjunctiva. Using a new monoclonal antibody, AE5, which is highly specific for a 64,000-mol-wt corneal keratin, designated RK3, we demonstrate that this keratin is localized in all cell layers of rabbit corneal epithelium, but only in the suprabasal layers of the limbal epithelium. Analysis of cultured corneal keratinocytes showed that they express sequentially three major keratin pairs. Early cultures consisting of a monolayer of "basal" cells express mainly the 50/58K keratins, exponentially growing cells synthesize additional 48/56K keratins, and postconfluent, heavily stratified cultures begin to express the 55/64K corneal keratins. Cell separation experiments showed that basal cells isolated from postconfluent cultures contain predominantly the 50/58K pair, whereas suprabasal cells contain additional 55/64K and 48/56K pairs. Basal cells of the older, postconfluent cultures, however, can become AE5 positive, indicating that suprabasal location is not a prerequisite for the expression of the 64K keratin. Taken together, these results suggest that the acidic 55K and basic 64K keratins represent markers for an advanced stage of corneal epithelial differentiation. The fact that epithelial basal cells of central cornea but not those of the limbus possess the 64K keratin therefore indicates that corneal basal cells are in a more differentiated state than limbal basal cells. These findings, coupled with the known centripetal migration of corneal epithelial cells, strongly suggest that corneal epithelial stem cells are located in the limbus, and that corneal basal cells correspond to "transient amplifying cells" in the scheme of "stem cells----transient amplifying cells----terminally differentiated cells."
在本文中，我们展示了角蛋白表达数据，这些数据有力地支持了一种角膜上皮成熟模型，即干细胞位于角膜缘，也就是角膜与结膜之间的过渡区域。我们使用一种新的单克隆抗体AE5，它对一种分子量为64,000的角膜角蛋白（命名为RK3）具有高度特异性，证明这种角蛋白定位于兔角膜上皮的所有细胞层，但仅定位于角膜缘上皮的基底上层。对培养的角膜角质形成细胞的分析表明，它们依次表达三对主要的角蛋白。由单层“基底”细胞组成的早期培养物主要表达50/58K角蛋白，指数生长的细胞合成额外的48/56K角蛋白，汇合后、高度分层的培养物开始表达55/64K角膜角蛋白。细胞分离实验表明，从汇合后培养物中分离出的基底细胞主要含有50/58K这对角蛋白，而基底上层细胞含有额外的55/64K和48/56K这对角蛋白。然而，较老的、汇合后培养物中的基底细胞可以变为AE5阳性，这表明基底上层位置并非表达64K角蛋白的必要条件。综上所述，这些结果表明酸性的55K和碱性的64K角蛋白代表角膜上皮分化晚期的标志物。中央角膜的上皮基底细胞而非角膜缘的上皮基底细胞拥有64K角蛋白这一事实因此表明角膜基底细胞比角膜缘基底细胞处于更分化的状态。这些发现，再加上已知的角膜上皮细胞向心迁移，有力地表明角膜上皮干细胞位于角膜缘，并且在“干细胞→短暂扩增细胞→终末分化细胞”的模式中，角膜基底细胞相当于“短暂扩增细胞”。
