Neurotrophic and x-ray blocks in the blastemal cell cycle

Using microdensitometry techniques the points in the cycle where blastemal cells become blocked after X-irradiation or denervation of the regenerating amphibian limb have been identified. X-irradiation blocks the cells in both G1 and G2 and those cells that were in S at the time of irradiation presumably proceed to G2. After denervation, however, cells accumulate only in G1 and those that were in S or G2 continue through the cycle to the next G1. The latter results are clearly contradictory to a recent theory proposing a G2 neurotrophic control of blastemal cells and a solution to the contradiction is presented in the light of recent results.