Xenopus Hand2 expression marks anterior vascular progenitors but not the developing heart

We have isolated cDNAs encoding the bHLH protein Hand2 in the amphibian Xen opus laevis and analysed Hand2 expression in early development from the ons et of gastrulation to feeding tadpole stages. XHand2 is expressed in the br anchial arch mesenchyme and also in small bilateral populations of cells in the anterior, ventrolateral region of early tailbud embryos. At later stag es, these punctate Hand2-expressing cells are located at the sites of the f orming common cardinal veins, suggesting that they may constitute progenito rs of vascular smooth muscle cells. Other Hand2-expressing cells are also a ssociated with further components of the forming anterior vasculature but a re not detected in mature blood vessels. Interestingly, no myocardial expre ssion of XHand2 can be detected in the developing tadpole heart, in marked contrast to results obtained with chick and mouse embryos. (C) 2000 Wiley-L iss, Inc.