Mechanisms of repression and derepression of artificial transformation of pigmented epithelium into retina inXenopus laevis.

The present study shows that pigmented epithelium of tadpoles and adult frogs ofXenopus laevis, like that of the other Anurans and the Cyprinid fishes, cannot transform into retina without the action of retinal factors. Transformation of pigmented epithelium into retina occurs when a sheet of it is implanted into the lensless eye. Transformation of pigmented epithelium also occurs when a sheet of it is wrapped in Bruch's membrane of the adult frog and afterwards implanted into a lensless eye, thus suggesting that Bruch's membrane is permeable to the inducing factors. Bruch's membrane was shown to play a polarizing role in the newly formed retina. Artificial transformation is based on a mechanism involving both the elimination of the repressive action of membranes adjacent to pigmented epithelium and the influence of retinal factors.