Analysis of corneal development with monoclonal antibodies. II. Tissue autonomy in cornea-skin recombinants

Developmental autonomy of corneal epithelial and stromal components was assessed by their subsequent differentiation after recombination with feather-forming thigh dermis and epidermis, respectively. Work by others has shown that feather-forming dermis exhibits strong inductive ability when used in such epithelial-mesenchymal recombinations. After culture of the recombinants on the chorioallantoic membrane (CAM) of host embryos, differentiation as "cornea" was assessed immunohistochemically using the anti-corneal stromal matrix and anti-corneal epithelial antibodies described previously (Zak and Linsenmayer, Dev. Biol. 99, 373-381, 1983). Feather initiation and outgrowth and keratin synthesis served as markers for differentiation as skin. It has been found that corneal epithelia from 5-day embryos, when grown in association with feather-forming dermis from the thigh, will participate in feather formation. In such recombinants, when the corneal epithelium became incorporated into feathers it failed to express the corneal epithelial antigen, but in regions of the recombinant where feathers did not form, de novo expression of the antigen was sometimes detected. The limited liability of the epithelium is not present in corneal epithelia taken from embryos a day or two older. When such epithelia were used for making the recombinants, no feathers were formed and the corneal epithelial antigen was extensively produced. Thus epithelial determination occurs long before the epithelium would begin to overtly differentiate and express the epithelial antigen in vivo (about 12 days of development). In reciprocal recombinations of corneal stromas with feather-forming epidermis, the stromas proceeded to express the corneal stromal matrix specific antigen de novo after culture on the CAM. They did not, however, redirect differentiation of the epidermis which never expressed the corneal epithelial antigen and in some cases went on to keratinize. These results indicate that development of both the corneal epithelial and stromal components becomes autonomous at least several days before these tissues overtly differentiate. This suggests that the component tissues of the cornea may not interact in a manner typical of those of other organs which, in general, are thought to require continual interaction of their epithelial and mesenchymal components for normal development.