Xenopusembryos provide a powerful model system to investigate the complex molecular mechanisms, which are controlled by or control the activity of the Hedgehog (Hh) signaling pathway. The use of synthetic mRNA or antisense oligonucleotide (morpholino) microinjection into blastomeres of early embryos or by simply treating the embryos with small organic inhibitors, has already led to an idea of the network in which the Hh pathway is embedded. More needs to be done in order to achieve a detailed understanding of how the different players of the Hh signaling pathway are integrated to control different genetic programs, such as axis formation in early embryos or cell differentiation during retinogenesis.
