FGF8 functions in the specification of the right body side of the chick

Left-right asymmetry in vertebrate embryos is first recognisable using mole cular markers that encode secreted proteins or transcription factors. The a symmetry becomes morphologically obvious in the turning of the embryo and i n the development of the heart, the gut and other visceral organs. In the c hick embryo, a signalling pathway for the specification of the left body si de was demonstrated. Here, Sonic hedgehog (Shh) protein is the first asymme tric signal identified in the node [1,2]. Further downstream in this pathwa y are the left-specific genes nodal, lefty-1, lefty-2 and Pitx2 [1,3-5]. On the right body side, a function of the activin pathway is indicated by the right-sided expression of cActRIIa [1,6]. We detected that another key mol ecule in vertebrate development, fibroblast growth factor 8 (FGF8) [7,8], i s expressed asymmetrically on the right side of the posterior node. We demo nstrate that transcription of FGF8 is induced by activin and the FGF8 prote in inhibits the expression of nodal and Pitx2 and leads to expression of th e chicken snail related gene (cSnR) [9]. Left-sided application of FGF8 ran domises the direction of heart looping. (C) Elsevier Science Ltd ISSN 0960- 9822.