Metabolic Characteristics of the Heart-forming Areas of the Early Chick Embryo

OU R knowledge of the sequence of events that culminate in the onset of contracility in the heart of the early chick embryo has been evaluated by Ebert, Tolman, Mun, & Albright (1955). Immunochemical analyses made during the initial phases of cardiogenesis, which precede the appearance of recognizable cardiac primordia, indicate that in the embryo at the head-process stage the distribution of the proteins, cardiac myosin (Ebert, 1953), and cardiac actin (Ebert et ah, 1955), coincides with the heart-forming areas as defined by isolation methods (Rawles, 1943). In earlier stages detectable quantities of cardiac actin are absent, and cardiac myosin is distributed throughout the epiblast in the embryo at the definitive primitive streak stage. Present concepts of the synthesis and distribution of the cardiac contractile proteins are based on the sensitivity of the immunochemical methods. The progress of the research makes it appear likely that the extension of these studies through the application of precise quantitative techniques may lead to an understanding of the mechanisms underlying the loss of myosin from regions of the embryo adjacent to the heart-forming areas; in addition, however, the need to continue to search for patterns of intermediary metabolic differentiation underlying the initial phases of heart development has been emphasized. The provocative observation by Spratt (1950) that critical concentrations of sodium fluoride specifically inhibit the formation of the heart suggested that this inhibitor might be used to determine in part the degree of metabolic differentiation in the chick embryo during the initial phases of cardiogenesis and might provide