Head in the WNT - the molecular nature of Spemann's head organizer

Formation of the head during vertebrate embryogenesis has been one of the m ost-studied topics in development, probably because we are such cephalized beings ourselves. Early experimenters found that the head is induced during gastrulation by Spemann's organizer. In 1999 we celebrate the 75th anniver sary of the discovery of the organizer by Spemann and Mangold, a group of c ells in amphibia that secretes powerful signalling molecules. Recently, adv ances have been made in identifying candidate head inducers. Not surprising ly, these inducers act in familiar molecular pathways, namely transforming growth factor beta (TGF-beta) and WNT signalling.