Heart shape carefully arranged, as described in Nature, vol 427, p309, 22 January 2004. During embryonic development mammal and human hearts, with their four chambers and complex arrangement of vessels and valves, develop from a simple tube. In order to understand how this process happened, Sigolene Meilhac and colleagues labelled cells in the heart tube of a mouse with genetic markers that were only inherited by cells descended from the original marked cells. This enabled them to identify the progeny of each cell. They found the new generations of cells arranged themselves in highly specific ways depending on what type of structure they were growing into. Cells that formed the heart ventricles, (large rounded chambers that pump the blood), arranged themselves like spokes of a wheel, whilst cells forming the tube-shaped outflow tract lined up in vertical rows. It was previously believed that the precise shapes of internal organs were formed by variations in the rate of cell division, and by the death of cells that had spread out randomly.

Editorial Comment: Making a non-living pump designed by a human engineer, involves the same level of, random or chance activities as building a living pump such as a human heart. The more we study embryonic development the more precise the organisation and evidence of forward planning we see. (Ref. heart, embryo, design)


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