Regeneration of neural retina from the pigmented epithelium in the chick embryo

The neural retina and lens were removed from the eyes of 4-day chick embryos, which were then divided into six groups: (a) 6 eyes were fixed immediately; (b) in 17 animals a 4-day lens alone was replaced; (c) in 32 cases both a 4-day lens and a piece of 4-day neural retina were reintroduced into the eye; (d) in 14 cases a 4-day otocyst was implanted; (e) in 13 cases a 4-day lens and a piece of 4-day optic tectum were implanted; (f) in 4 specimens a piece of 4-day neural retina alone was reintroduced into the eye. Analysis of the subsequent development of these groups led to the following observations and conclusions: 1. 1. Neural retina can regenerate from the pigmented epithelium of the chick embryo at least as late as stage 24. 2. 2. Regeneration occurs in two ways: (a) from the cup margin; (b) in patches of pigmented epithelium some distance from the margin. 3. 3. Both types of regeneration require that the neural retina be physically separated from the pigmented epithelium without being removed from the immediate environment. 4. 4. The 4-day otocyst can elicit neural retinal regeneration from the embryonic pigmented epithelium. 5. 5. The 4-day optic tectum does not elicit neural retinal regeneration from the pigmented epithelium. 6. 6. The presence of the lens is not necessary for regeneration of the neural retina. 7. 7. Regenerating neural retina differentiates more rapidly than normally developing neural retina. 8. 8. The polarity of the regenerating neural retina with respect to the eye is normal if it arises from the cup margin, and reversed if it arises in patches from the pigmented epithelium. 9. 9. The axons of the ganglion cells of the regenerating neural retina fasciculate to form a single “optic nerve” which leaves the eye at its posterior pole.