The control of lens growth: relationship to secondary cataract

A lens growth factor was identified that is present in the anterior chamber of the embryonic chicken eye. The mitogen is similar to an embryo-specific activity found in embryo serum. Several purified growth factors, applied singly or in combination, did not stimulate cell division in embryonic lens cells. The serum mitogen is a protein which does not bind to heparin-Sepharose. The possibility is presented that the lens epithelium contains two distinct cell types, the proliferating cells of the germinative zone and the mitotically quiescent central epithelial cells. It is proposed that only cells in the germinative zone are capable of responding to normal lens growth factors. It is likely, therefore, that these cells present the greatest risk for secondary cataract formation.