[A radioautographic study of the dynamics of 3H-thymidine incorporation into the limb tissues of anuran amphibians during the process of loss of regenerating capacity].

DNA synthesis was studied by 3H-thymidine incorporation in limb tissues of mesodermal origin in metamorphosing common frog (Rana temporaria) tadpoles in the process of loss of regenerative ability. During metamorphosis of tadpoles, the process of histodifferentiation is accompanied by the decrease in the number of nuclei incorporating 3H-thymidine. In tadpoles capable of regeneration, during the first days after limb amputation the index of labelled nuclei decreases, as compared with that in intact tissues, and then, as the regenerate forms, increases. In tadpoles uncapable of regeneration, the index of labelled nuclei after limb amputation decreases in the stump tissues during the whole experiment but is high enough in the scar connective tissue cells. Thus, the loss of regenerative ability of anuran limbs appears to be related with the decrease in the number of DNA-synthesizing cells in tissues of mesodermal origin, due apparently to the progress of their differentiation