Role of the neural retina in newt (Notophthalmus viridescens) lens regeneration in vitro.

Removal of the lens from the eye of an adult newt (Notophthalmus viridescens) is followed by regeneration of a new lens from the dorsal iris epithelial cells at the pupillary margin. This process is dependent upon the neural retina for its normal completion in vivo and in vitro. To examine the relationship between the retina and lens regeneration, we have conducted experiments that delimit the time period during which the retinal presence is critical (in vivo) and have investigated the influence of extracts of the retina on the progress of regeneration (in vitro). In vivo, removal of the retina at day 11 seriously retards further progression of regeneration while removal of the retina at day 15 does not retard regeneration significantly. This defines a "critical period" in regeneration of the lens during which the retina is required. Explantation of regenerates 11 or 12 days after lentectomy to organ culture medium enriched with either crude retinal homogenate or extracts prepared from chick or bovine retinas according to Courty et al. ('85, Biochimie, 67:265-269) reveals that the progress of regeneration can be supported in culture by the crude extract. This is the first demonstration of complete iris-lens transformation in culture in the presence of retinal extract. It is possible that the retina acts indirectly by promoting passage of the iris epithelial cells through the critical number of mitoses required before redifferentiation into lens cells can occur (as proposed by Yamada, '77, Monogr. Dev. Biol., 13:126). It is also possible that the retina acts by directly instructing the iris cells to redifferentiate.(ABSTRACT TRUNCATED AT 250 WORDS)

Microdensitometric analysis of denervation effects on newt limb blastema cells.

This report examines the fate of cycling cells in normal and denervated blastemas of adult newts. Cells are found to accumulate in G1 in blastemas which are nerve independent. No stage specific accumulation different from controls is found in limbs with nerve-dependent blastemas.

DNA synthesis and mitosis in adult newt limbs following amputation and insertion into the body cavity.

Experiments were designed to investigate the roles of injury, nerves, and wound epidermis in regeneration. By immediate insertion of amputated limbs into the body cavity, the wound epidermis was prevented from forming. Through 3 weeks post amputation, these inserted limbs showed lower 3H-thymidine labeling indices and mitotic indices than control normally regenerating limbs. No blastema formed and regeneration did not occur. When denervation preceded insertion, some labeling with 3H-thymidine was seen but essentially no mitoses were observed. When insertion of innervated limbs was delayed for 48 hr to allow the wound epidermis to form, regeneration occurred in a normal fashion. These results emphasize the importance of injury, nerves, and wound epidermis in controlling cell cycle events during regeneration.