Cyclic nucleotide metabolism during amphibian forelimb regeneration : II. The protein kinases.

The hypothesis that cAMP mediates neural and endocrine influences on limb regeneration was examined by studying the protein kinases in regenerating limb tissues. Since these enzymes are the vehicles through which cAMP acts intracellularly, an understanding of changes in their concentrations and behaviors during regeneration can be instrumental in elucidating the role of cAMP in this process. Mean activities oscillated throughout regeneration with maximal activities being observed during the mid-late bud stage. The phosphorylation of histone, added to the assay, varied with the stage of regeneration-greatest activity occurring during the early bud stage and very weak activity during the palette and early digital stages. Histone actually appeared to inhibit endogenous phosphorylation during dedifferentiation. In addition, cAMP demonstrated different degrees of enhancement of histone phosphorylation during regeneration-producing its greatest effect at the palette stage and having the least effect at the early bud stage. The results of this study suggest that changes in the absolute amounts of protein kinase are probably not significant in the regulation of regeneration. In addition, the variable acceptability of histone as an exogenous substrate and the variations in the cAMP effects on phosphorylation suggest that physiological changes are occurring in which cAMP might play a significant role. In particular, these data suggest that cAMP might be instrumental in influencing events associated with differentiation and morphogenesis.