Changes in extracellular matrix proteins and actin during corneal endothelial growth

Basement membranes influence growth, shape and differentiation of cells and tissues. However, the role and influence of Descemet's membrane during corneal development is not understood. To address this question, the relationships between cell growth and fibronectin, laminin and actin distribution in the developing rat corneal endothelium in vivo has been examined. During fetal development, rat corneal endothelial cells undergo DNA synthesis and mitosis. However, at day 14 of gestation both processes begin to decline and neither can be detected in endothelium of 1-month-old animals. By this time cell number has increased to approximately 100,000 and tissue area has increased 25-fold. However, as the tissue area increased, cell density decreased, indicating that cell spreading occurred in order to maintain tissue integrity. Changes in endothelial growth were accompanied by changes in the distribution of laminin, fibronectin and actin. Laminin and fibronectin were diffusely localized within endothelial cells in newborn animals. By 4 weeks of age, no proliferation was demonstrated and both extracellular matrix proteins were localized in pericellular patterns. Actin, on the other hand, which appeared diffuse at 16 days in utero, was distributed at or near the cell membrane by 19 days in utero. Thus, the reorganization of extracellular matrix glycoproteins and actin may indicate important roles for these components in regulating the growth and formation of the corneal endothelium in vivo.