The inductive capacity of proteins secreted by cells of corneal epithelium

Two classes of proteins play a leading role in the mechanisms of differentiation. The first class presents structural proteins that are fundamental for the structure and function of organs. Proteins of the second class are less understood; they exist in minor quantities and realize their action only in determining the accomplishment by structural proteins of their terminal functional state. Here we try to clarify the role of peptides synthesized by the corneal epithelium in determining the fate of differentiating cells. The acting protein fractions were obtained from isolated corneas of adult pigs, cows and carps. Their inducing activities were tested by a standard method, i. e. by checking their action on the early gastrula ectoderm of Xenopus laevis. To study a possibility of cornea conservation, we used preferentially lyophilizing drying of the obtained substances. With some differences in frequency, the protein mixtures obtained from all corneas induced the appearance of neural tissue (brain), but in the case of lyophilized cow corneas lenses, ear vesicles and somites also appeared. The results of this work clearly show the absence of homology between the sources of inducing factors and the specificity of their action. The cornea is an ectodermal derivative, but its products induce neural derivatives and, moreover, after lyophilization they change their induction specificity and induce also mesodermal cell types due, presumably, to changes in the tertiary structure of protein molecules after lyophilization.