CYTOCHEMICAL-LOCALIZATION OF ADENYLATE-CYCLASE IN THE LIMB BUDS OF BUFO-BUFO

The importance of cyclic nucleotides in the regulation of the processe s of differentiation and embryonic development is known. The possible role that cyclic adenosine monophosphate (cAMP) plays during the devel opment of the posterior limb of Bufo bufo is studied by the cytochemic al localization of adenylate cyclase (AC), an enzyme that catalyzes th e synthesis of the cyclic nucleotide. The method is based on the react ion between the enzyme AC and its specific substrate AMP-PNP (5'-adeny lylimidodiphosphate) in the presence of lead. The lead precipitates th at form as secondary reaction products are evidence of enzymatic activ ity. Reaction products are present only at the epithelial level in the limb bud; initially, such products are visible only at the base of th e bud, particularly on the epithelial fascia located at the boundary w ith the body. During successive elongation and toe formation, AC activ ity is only present on the cells of the proximal portion of each new s egment. Enzymatic activity is never present in correspondence to the e ctodermal apical crest. cAMP is probably not involved in the processes of cellular proliferation but, rather, in the processes of inducing d ifferentiation of the internal mesenchymal cells. (C) 1998 Wiley-Liss, Inc.