The embryonic lens contains two populations of cells, lens epithelial cells and lens fiber cells. As the growth of the human lens is linear from the age of 10 to 90, lens epithelial cells divide and differentiate into fiber cells at a uniform rate during adulthood. Any defects that arise during fiber formation will remain in the lens. We postulate that regulation of early lens growth is critical for the onset of cataracts that usually occur later in life. Slowing the growth of the lens could therefore provide a strategy to suppress the formation of cataracts. However, the factor(s) that control lens growth in vivo have not been identified.

We have identified 18 receptor and cytoplasmic kinases present in lens epithelial cells. Using these as potential targets for factors controlling growth, we tested corresponding ligands in a lens epithelial cell proliferation assay. Platelet-derived growth factor (PDGF) proved to promote a growth activity similar to, but distinct from, that of embryo serum.