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.