"In vitro" expression of the cardiogenic potentiality of chick embryo heart-forming cells.

Chick embryos between final presomitic and 4 somites stage were studied. The subcephalic fold was handly severed from the embryos and cultivated in liquid medium for 7 days. Because of the embryo age, no heart anlage was observed at the moment of dissection. After 4 hours of culture the cells began to migrate from the explants. After 20 hours a very extended migration ring was observed in all of the cultures; in the explants, one or more newformed tubular or spherical masses of cells throbbed rhythmically. Their size and shape were related to the embryos age: from presomitic embryos, irregular clusters appeared, while starting from two somites embryos tubular, vascular-like structures were formed. The cells of the throbbing areas at submicroscopic observation showed organizing myofibrillar apparatus into the cytoplasm; junctional complexes between the cells and gap junctions in course of organization were present in the vascular-like structures. This suggests that very early, in the lateral mesoderm are the presumptive cardiac cells which can develop "in vitro" as myocardic elements even in absence of the interactions that occur during the development "in vitro"; the observed vascular-like structures may be considered as an attempt to form a sort of cardiac primordium "in vitro", and a further step in the expression of the cardiogenic potentiality, involving cell-cell communications. The serial sections of the embryos enhanced that into the cultivated areas, vessels from yolk sac are always present; this suggests that the vascular structures, i.e. the endothelium may be involved in the determination of the myocardic elements.