Bard J B, Bansal M K, Ross A S
MRC Clinical and Population Cytogenetics Unit, Western General Hospital, Edinburgh, UK.
Development. 1988;103 Suppl:195-205. doi: 10.1242/dev.103.Supplement.195.
This paper examines the role of the extracellular matrix (ECM) in the development of the cornea. After a brief summary of the corneal structure and ECM, we describe evidence suggesting that the differentiation of neural crest (NC) cells into endothelium and fibroblasts is under the control of ocular ECM. We then examine the role of collagen I in stromal morphogenesis by comparing normal corneas with those of homozygous Mov 13 mice which do not make collagen I. We report that, in spite of this absence, the cellular morphology of the Mov13 eye is indistinguishable from that of the wild type. In the 16-day mutant stroma, however, the remaining collagens form small amounts of disorganized, thin fibrils rather than orthogonally organized 20 nm-diameter fibrils; a result implying that collagen I plays only a structural role and that its absence is not compensated for. It also suggests that, because these remaining collagens will not form the normal fibrils that they will in vitro, fibrillogenesis in the corneal stroma differs from that elsewhere. The latter part of the paper describes our current work on chick stromal deposition using corneal epithelia isolated with an intact basal lamina that lay down in vitro approximately 3 microns-thick stromas of organized fibrils similar to that seen in vivo. This experimental system has yielded two unexpected results. First, the amount of collagen and proteoglycans produced by such epithelia is not dependent on whether its substratum is collagenous and we therefore conclude that stromal production by the intact epithelium is more autonomous than hitherto thought. Second, chondroitin sulphate (CS), the predominant proteoglycan, appears to play no role in stromal morphogenesis: epithelia cultured in testicular hyaluronidase, which degrades CS, lay down stromas whose organization and fibril-diameter distribution are indistinguishable from controls. One possible role for CS, however, is as a lubricant which facilitates corneal growth: it could allow fibrils to move over one another without deforming their orthogonal organization. Finally, we have examined the processes of fibrillogenesis in the corneal stroma and conclude that they are different from those elsewhere in the embryo and in vitro, perhaps because there is in the primary stroma an unidentified, highly hydrated ECM macromolecule that embeds the fibrils and that may mediate their morphogenesis.
本文探讨了细胞外基质（ECM）在角膜发育中的作用。在简要概述角膜结构和ECM之后，我们描述了一些证据，这些证据表明神经嵴（NC）细胞向内皮细胞和成纤维细胞的分化受眼部ECM的控制。然后，我们通过将正常角膜与不产生胶原蛋白I的纯合Mov 13小鼠的角膜进行比较，研究了胶原蛋白I在基质形态发生中的作用。我们报告称，尽管缺乏胶原蛋白I，但Mov13眼的细胞形态与野生型并无差异。然而，在16天龄的突变体基质中，剩余的胶原蛋白形成了少量无序的细纤维，而不是直径为20纳米的正交排列的纤维；这一结果表明胶原蛋白I仅起结构作用，其缺失无法得到补偿。这也表明，由于这些剩余的胶原蛋白在体外无法形成正常的纤维，角膜基质中的纤维形成过程与其他地方不同。本文的后半部分描述了我们目前关于鸡角膜基质沉积的研究工作，我们使用分离出完整基膜的角膜上皮细胞，这些上皮细胞在体外形成了约3微米厚的、有组织的纤维基质，类似于体内所见。这个实验系统产生了两个意外的结果。第一，这种上皮细胞产生的胶原蛋白和蛋白聚糖的量并不取决于其底物是否为胶原质，因此我们得出结论，完整上皮细胞产生基质的过程比以往认为的更具自主性。第二，硫酸软骨素（CS）作为主要的蛋白聚糖，似乎在基质形态发生中不起作用：在睾丸透明质酸酶中培养的上皮细胞（该酶可降解CS）形成的基质，其组织结构和纤维直径分布与对照组无明显差异。然而，CS的一个可能作用是作为一种润滑剂，促进角膜生长：它可以使纤维相互移动而不改变其正交排列。最后，我们研究了角膜基质中的纤维形成过程，并得出结论，这些过程与胚胎其他部位及体外的过程不同，这可能是因为在初级基质中存在一种未确定的、高度水合的ECM大分子，它包裹着纤维并可能介导其形态发生。
