Action of Heart and Liver Rna on the Differentiation of Segments of Chick Blastoderms.

T H E posterior segment isolated from definitive streak or head process blastoderms by a transverse cut 0 • 5-0 • 2 mm. posterior to Hensen's node seems to be a suitable experimental object for the study of differentiation. Its limited prospective significance and potency in chorioallantoic transplantation or in vitro compared with the versatile node has been the subject of several studies (Hunt, 1931; Willier & Rawles, 1931; Rawles, 1936; Rudnick, 1938a, b; Waddington 1933; Spratt, 1952). The present author has shown that rooster testis DNA and 5-day chick embryo DNA (0-25-0-50 mg./ml.) induce neural tubes and somitelike aggregations of the mesoderm in post-nodal explants cultured on albuminagar (Butros, 1960). When axial structures were grafted on the explants, the latter were induced to develop nephrotomes, ducts, neural folds and notochords (Butros, 1962). Improved procedures for culturing post-nodal explants, which circumvent the tendency of these pieces to form hollow vesicles, were reported recently (Butros, 1963a). A programme was then initiated for the study of the action of nucleic acids extracted from chick embryo organs on these fragments. As a first approach to the problem, the fragments were cultuted in a proteindeficient medium containing the RNA for 2 days and were then grafted on to the chorioallantoic membrane for a second period of about 9 days. Embryonic brain RNA produced in the treated tissues papillomatous epidermis with giant epidermal cysts that were keratinized and highly fibrillar. Adult heart RNA caused hyperplasia of the epidermis with some keratinized, papillary projections. In the control fragments there was no keratinization nor papillary formation of the epidermis, the cysts were very small and devoid of fibrillar organizations. Adult pancreatic RNA enhanced the development of the entodermal layer (Butros, 19636). It is the purpose of this report to describe the