Specificity in the differentiation and morphogenesis of neural crest-derived scleral ossicles and of epithelial scleral papillae in the eye of the embryonic chick.

Enzymatic digestion followed by recombination of epithelia and ectomesenchyme from embryonic sclera and mandibles has been used to demonstrate that isolated scleral ectomesenchyme is only able to form scleral ossicles if in prior contact with scleral epithelium until H.H. stage 36 (10 days of incubation); that this induction by epithelial scleral papillae is a prolonged one, commencing as early as H.H. stage 30 (6.5-7 days); that scleral ectomesenchyme can respond to mandibular epithelium by forming bony ossicles and that mandibular ectomesenchyme can respond to scleral epithelium by forming bony rods, i.e. these interactions are not site, time or tissue specific. Scleral epithelia did not form scleral papillae when maintained alone in vitro or when recombined with scleral ectomesenchyme and maintained in vitro. Nor did papillae form when mandibular epithelia were cultured with scleral ectomesenchyme. These results, coupled with data from the literature, are used to argue that papillae will only form when scleral epithelia are under the tension generated by normal intraocular pressure of the growing eye.