Plasticity and reprogramming of differentiated ocular tissue of tadpoles of the frog, Euphlyctis cyanophlyctis under the influence of vitamin A.

Present study has shown that differentiated cell types may loose their definitive characteristics and acquire features of another specialized cell type. Young (3 toe stage) and mature (5 toe stage) tadpoles of the frog, Euphylictis cyanophlyctis were employed as experimental animals. Experiments were completed in two phases: in the first part of experiment, lenses were extracted from right eye balls of tadpoles and treated with vitamin A; in the second part of the experiment, meshed lentectomized eye ball tissues were implanted into the pit made on mid lateral position of the tail of young and mature tadpoles and were treated with vitamin A. The results obtained gave clear evidence of plasticity and reprogramming of terminally differentiated ocular tissue into lens, retina and even complete eye. Vitamin A was found to be good model for accelerating the reprogramming of differentiated ocular tissue in anuran frog tadpoles.

Trans-differentiation of iris pigmented epithelial cells of Euphlyctis cyanophlyctis tadpoles into lens in vitro.

Meshed pigmented iris epithelium along with neural retina of tadpoles of the frog Euphlyctis cyanophlyctis were found to undergo dedifferentiation and subsequently transdifferentiate into lens in culture medium. During lag period, depigmentation (dedifferentiation) occurred in many cells. When culture became confluent 3-4 weeks after seeding tiny lens like structures differentiated from foci of cultured pigmented iris epithelium cells. The percentage of lens formation was higher in vitamin A treated cases. The culture system appears to be a suitable for investigating the changes occurred during trans-differentiation of pigmented epithelial cells into lens.

Effect of Emblica officinalis (Gaertn) on lens regeneration in the frog, Rana cyanophlyctis (Schneider).

Emblica officinalis (Amla) accelerated cell proliferation and dedifferentiation of pigmented epithelial cells of dorsal iris and consequently induced lens regeneration in R. cyanophlyctis. Further it enhanced the percentage of lens regeneration not only in young tadpoles but also is adult frogs. Lens regeneration ability declined with the age of animals in both control as well as treated groups.

The "third eye"-- a new concept of trans-differentiation of pineal gland into median eye in amphibian tadpoles of Bufo melanostictus.

Median third eye was found to develop from transplanted pineal gland of external gill stage tadpoles in the recipient 5 toe stage tadpoles of Bufo melanostictus. Pineal gland along with a bit part of brain tissue of the donor external gill stage tadpole was cut out and transplanted into a pit made between two lateral eyes of 5 toe stage recipient tadpoles. Half of the operated tadpoles were treated with vitamin A (15 IU/ml.) for 15 days. Median "third eye" was found to develop in the both untreated and vitamin A treated tadpoles. However, vitamin A increased the percentage of the development of median eyes. Morphological and histological study revealed that newly transformed median eyes were similar to that of normal functional eyes. A stalk like structure developed which connects the median eye to the brain. The median third eye could not develop when pineal gland of 5 toe stage mature tadpole was transplanted into the tadpole of the same age.

Effect of vitamin A on lens regeneration in pigs.

Intraperitoneal injections of vitamin A (0.5 ml of 1500 IU/ml) to lentectomized pigs on alternate days up to 60 th day after lentectomy induced lens regeneration in not only 10 days old young ones but also in 40 and 100 days old pigs. Lens regeneration did not occur even in a single case of control groups. In shape, size, transparency and histological features regenerated lenses were similar to normal intact lenses. The experimental model is the first to show that mitogenic and dedifferentiate activity of vitamin A can induce iris pigmented epithelial cells to trans-differentiate into new lens in pigs.

Homeotic regeneration of eye in amphibian tadpoles and its enhancement by vitamin A.

After removal of both the lateral eyes of external gill stage tadpoles of the toad Bufo melanostictus, the pineal organ gets transformed into a median eye. This type of transformation occurs in tadpoles of both control and vitamin A treated groups. However, vitamin A increases the likelihood of homeotic regeneration (57% in the control group and 71% in the vitamin A treated group). Histological studies showed that the newly transformed median eye developed from the pineal organ. The pineal eye so developed possessed all components of a normal eye such as a retina, sensory cells and lens.

Lens regeneration in mice under the influence of vitamin A.

The effect of vitamin A has been studied on lens regeneration in young (7 days old) as well as adult mice. A longitudinal slit was made under local anesthesia in the cornea over the lens. The lens was extracted intact through the incision. Intraperitonial injection of vitamin A (0.05 ml of 30 IU/ml in young and 0.05 ml of 50 IU/ml in adult) was given to the operated animals. Vitamin A was found to induce lens regeneration in not only young but also in adult mice. Regenerated lenses were similar in shape, size, transparency and histological features to normal intact lenses.

Effect of vitamin A excess on oral armature in tadpoles of toad, Bufo melanostictus (Schneider) and frog, Rana cyanophlyctis (Schneider).

Tadpoles of B. melanostictus and R. cyanophlyctis were reared in vitamin A solution. Rearing of the tadpoles of B. melanostictus in solutions containing 15, 20 and 30 IU/ml vitamin A palmitate resulted in complete disappearance of the keratinized epidermal material over the jaws and horny labial teeth. However tadpoles of the frog R. cyanophlyctis, were not affected in this way.