Differentiation induced by cyclic AMP in undifferentiated cells of early chick embryo in vitro

Abstract

THE undifferentiated cells of the chick embryo in the post-nodal piece (PNP), obtained by a transverse cut at 0.5 mm posterior to Hensen's node of stage 4 blastoderm, remain incapable of differentiation when grown in a variety of media or by chorioallontoic grafting technique. When combined with the region anterior to the streak, including Hensen's node, however, the PNP would undergo normal differentiation similar to the embryonic axial structures^1–3, suggesting that information might have been transferred from one tissue to another. Later studies by Butros² and Niu and coworkers^4,5 have shown that the PNP explants could be induced to develop into specific tissues, such as pulsating cardiac muscle tissues, when the explants were cultured in the presence of RNA isolated from the embryonic heart. The development was organ specific since RNA from kidney or thymus was incapable of inducing the heart formation⁵. To confirm this mode of differentiation in the PNP and to provide a meaningful biochemical interpretation to the phenomenon, we have begun studies examining the precise nature of the competent RNA and the sequence of events that leads to the formation of highly organised myofibrils. In a parallel study, we asked whether addition of exogenous cyclic AMP, which seems to be involved in control of morphological differentiation and biochemical changes in both normal and neoplastic cells (for review see ref. 6 and subsequent papers 7–15) would affect the development of the PNP in culture. Here we report that cyclic AMP, in the absence of exogenous RNA, can indeed produce specific morphological transformations, including the formation of heart-like pulsating tissues.