Planarian regeneration: DNA metabolism in adults

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Abstract
For the first time, a study of DNA synthesis during planarian regeneration is presented. DNA content per animal was measured at different times after sectioning. It reached a first maximum at 18 h after sectioning, then diminished slowly until day 7. This DNA content was further compared to RNA and protein contents. It is suddenly after 10 h of regeneration that DNA is synthesized as shown by the variations of the rate of DNA labelling. As planarian cells are totally impervious to exogenous thymidine, 32P was used to establish these variations. Cells showing DNA polymerase activity were then detected in situ by a histoenzymological method; they were localized in a crown just behind the blastema. Measurements of the pool of adenylic nucleotides showed that ATP and ADP concentrations increased immediately after sectioning until 18 h, then they decreased until day 7. After a transitory diminution following sectioning, AMP concentration rose slightly up to 48 h and then decreased. The effect of the changes of adenylic nucleotide concentrations on DNA synthesis and labelling was considered. Acid and alkaline DNase activities were also studied during planarian regeneration as these activities are known to be stimulated in proliferating cellular systems; their variations presented a significant correlation with DNA synthesis. Comparison of the time course of DNA synthesis with those of other biochemical modifications induced by sectioning, and those previously described, such as cAMP and serotonin concentrations and RNA synthesis, supports the hypothesis that stem cells are the main source of regeneration in planarians.