Hepatocyte growth factor/scatter factor (HGF/SF) in early development: evidence for a role in neural induction

Since the pioneering work of Spemann and Mangold, who found that transplantation of the dorsal lip of the frog blastopore produces a secondary neural axis, embryologists have been intrigued by the process of neural induction. However, the molecular nature of the inducer(s) has remained obscure, largely due to the complication that neural induction often occurs as a secondary consequence of mesodermal induction. In the past few years, candidate molecules have been identified that are able to induce neural tissue in the absence of mesodenn in the frog. These include noggin and follistatin (reviewed in Ref. 1), which are thought to function by inhibiting activin. In the chick, recent experiments have implicated hepatocyte growth factor/scatter factor (HGF/SF) as a neural inducer based on it5 expression in the primitive streak and Hensen's node of the early chick embryo, and its ability to induce neural tissue in naive epiblast. This review describes the evidence supporting the possible function of HGF/SF as an early embryonic inducer.