Determination of the Blastema Cell Cycle in Regenerating Limbs of the Larval Axolotl, Ambystoma Mexicanum

Total cell cycle time as well as time of S phase, G2+K> M phase, and Gi+/^ M phase was determined for blastema cells of 9 day nerve-dependent forelimb regenerates of larval axolotls. Nine days post-amputation the limbs had early cone blastemas which continued regeneration (on those larvae not fixed for histology) and by day 23 had 4 digit regenerates. The mean mitotic index for 9 day blastemas was 2.65% with 79.5% of the mitotic figures labeled 8 hrs post 3H-thymidine injection and 96% at 16 hours. Mean cycle time, as determined from the time from the 1st 50% intercept to the 3rd 50% intercept, was 40 hrs. The S phase, G2+K M, and G1+//2 M were 32 hrs, 5.6 hrs, and 2.4 hrs respectively.