Biochemical investigation of lens induction in vitro. II. Demonstration of the induction substance.

An organ culture method to study the process of lens induction in the chick is described. To see whether or not a direct contact between the participating tissues is required for lens formation, agar slices (0.5 mm thickness) were cultured between the eye cup and the ectoderm. New lenses were formed in 43% of the transplants. Both the eye cup and the ectoderm originated from 72 hours old embryos (stage 18). By culturing agar slices on the eye cups during 2--24 hours and afterwards culturing these slices separately in combination with ectoderm, it was proved that lens inducing substance (s) penetrate into the agar slices. 3-4 hours of culturing on the eye cup is sufficient to obtain "inducing" agar slices. The same eye cups were shown to be able to induce a lens for more than one time. By using millipore filters with a 0.65 mu pore size, induction occurs in 36% of the cultures. The possibility of a restraining influence of the formed lens on the induction capacity of the eye cup was noticed.