The origins of cardiac tissue in the amphibian, Xenopus laevis.

Understanding the mechanisms that regulate cardiogenesis is of fundamental importance if we are to determine the origins of congenital heart disease or devise effective new therapies for the regeneration of healthy cardiac tissue. Amphibian embryos provide a useful model for such studies because embryos are relatively large, available in large numbers, and robust enough to survive simple microsurgery. Because eggs are shed from the adult prior to fertilization, all stages of embryo development are readily accessible. Furthermore, until swimming tadpole stages, development occurs without growth, using nutrients stored in each cell. These features have three significant experimental consequences: all stages of heart development are readily accessible, explants of embryonic tissue will continue to differentiate in simple salts solution, and the function of individual gene products can be studied by microinjection into embryonic cells. Additionally, because heart function is entirely unnecessary until tadpoles begin feeding, even treatments that cause severe disruption of cardiogenesis are readily amenable to study. This article reviews how the combination of simple embryologic manipulation and direct assays of gene function have been used to investigate the cell interactions necessary for heart formation in Xenopus embryos.