Epigenetic signals resulting from either cell-matrix or cell-cell interactions are critical to the regulation of cell differentiation and development. This is particularly true in the complex differentiation process that enables a lens epithelial cell to become a differentiated lens fiber cell and in the developmental events that direct a region of head ectoderm to invaginate, pinch off, and begin to form the lens. In this chapter we discuss the role of cell adhesion molecules in lens differentiation and development.

Extracellular Matrix

The molecular organization of the basement membrane can profoundly influence cellular behavior by providing information that can affect the genetic program of a cell. Its major components include proteins such as laminin, collagen type IV, fibronectin, and proteoglycans. These extracellular matrix (ECM) proteins direct differentiation-specific gene expression in most cell and tissue types (Bissell and Barcellos-Hoff, 1987; Bissell et al., 1982; Streuli et al., 1991). Their ability to orchestrate both cell differentiation and tissue development requires interaction with cell surface receptors (e.g., the integrins), by which they initiate specific intracellular signaling pathways (Giancotti and Ruoslahti, 1999). The expression and distribution of ECM proteins in the lens is well characterized, both throughout development and in the mature lens. The knowledge that has been gained, in combination with mutational and inhibitor studies, provides insight into the role of ECM molecules in the process of lens development.