Control of the blastemal cell cycle by the peripheral nervous system during newt limb regeneration; continuous labeling analysis

Forty-eight and 96 hr 3H-thymidine continuous labeling was analyzed on denervated mid-bud limb blastemas of Pleurodeles waltlii M. In innervated blastemas, 92 to 95% of mesenchymal cells are cycling; denervation provokes an early exiting from the cycle in G0-1(+ 15% of non-cycling cells for a 6-day denervation, + 20% for an 8 day denervation) and an elongation of the G1 phase. For epidermis only 25% (48 hr labeling) to 53% (96 hr labeling) of cells are cycling in innervated blastemas; denervation strongly decreases this percentage (+ 40% of non-cycling cells for a 6-day denervation, + 60% for an 8-day denervation). As for mesenchyme, denervation also lengthens the G1 phase of epidermal cells. So our results contradict the conclusion of other authors claiming a G2 blockage. They account for the fall in proliferation indices and the arrest of regeneration after denervation. Finally, they show that the cell cycle of regeneration cells is controlled by the neurotrophic factor.