Artificial neural induction in amphibia

Summary

The initial steps of neuralization by denatured embryonic tissue were studied in single and double layer Triturus ectoderm explants.

• 1. In single layer explants only part of the responding ectoderm is neuralized. A vesicle with continuous epidermoid envelope develops, from which neuralized spindle-shaped cell groups retract into the interior. Several neural cell groups fuse with each other and form a cushion of neural tissue between implant and vesicle wall. Neural tissue thus never comes into contact with the culture medium but is always protected by an epidermoid envelope.

• 2. In double layer explants the inner layer is completely neuralized. No epidermoid tissue remains. The inhibitory effect of single layer ectoderm is unblocked by the second envelope, which now furnishes the epidermoid protective vesicle. A thick layer of neural tissue encloses and faces the dead implant. The retinal character of this tissue soon becomes apparent by elimination of micropigment away from the implant (transparence).

• 3. Three to four days after the operation a process of self-organization begins in this thick layer of retinal tissue. It splits parallel to the surface and forms several retinal vesicles. The inner vesicle walls continue histo-and morphodifferentiation in the original direction, while in the outer walls this direction is reversed: micropigment now is eliminated toward the ventricle-like cavity and retina fronts (eyecups) face the outer epidermoid envelope.

• 4. The discussion deals with the inhibition of total neuralization in single layer explants and its unblocking by a second envelope, and with the process of splitting and self-organization of induced retinal tissue. Retina induction in explants is compared with normal and artificial neural and retina induction in embryos.