Figure 4: Trends in relative gene expression of corneal genes in differentiating corneal orbs (n=3 independent orbs) vs. adult human cornea (n=2 independent corneas) show that the differentiating orbs express many normal corneal genes. Data are expressed as mean and bars are standard deviation. (Statistics not performed because of low n and high S.D.) A. Importin 13 may be expressed by a resident limbal stem cell population in both differentiating and normal adult corneas, but the limbal stem cell population was not assayed with other markers. Integrin alpha 9, connexin-43, and enolase-α are normally expressed in corneal epithelium, B. Connexin-43 and ZO-1 are both important for cell-cell communication in the cornea, and combined with immunohistochemistry (Figure 3) these results suggest maturation of subcellular structures involved in intercellular communication by 120 days of differentiation. C. Differential expression of cytokeratins suggests relatively high expression of CK8 and CK19 in the stem cell-derived differentiating corneal orbs relative to mature adult cornea. D. The most striking pattern in the gene expression studies was the high expression of various extracellular matrix proteins in the differentiating orbs compared to the lower level expression in mature adult cornea. At the protein level these ECM genes are low abundance in normal cornea compared to the relatively large collagen content of cornea.