Cardiac semilunar valves, which stop blood leaking back into the heart, contain an elastic fibre network that is essential for their physiological function. Histochemical studies suggest that this network, which contains elastin, fibrillins, linking proteins such as fibulins, and fibronectin, is not crucial for early human cardiac valve development. Here (p. ), Katja Schenke-Layland and colleagues challenge this assumption by systematically analysing elastogenesis in human semilunar valves. The researchers report that the transcription of genes essential for elastic fibre formation starts early within the first trimester of pregnancy. Using immunohistochemistry, they show that fibronectin, fibrillins and linking proteins are present at the onset of cardiac cushion formation (about week 4 of development) and that tropoelastin/elastin protein expression is first detectable in the valves at about week 7 of pregnancy, the stage of development when the embryo's blood pressure and heartbeat increase. Together, these findings suggest that elastogenesis is important for the development of functional semilunar valves.
