Wnt signaling in oncogenesis and embryogenesis-a look outside the nucleus

The Wnt cell-cell signaling pathway plays a critical and evolutionarily conserved role in directing cell fates during embryogenesis. In addition, inappropriate activation of the Wnt signal transduction pathway plays a role in a variety of human cancers. Many recent studies of Wnt signaling have provided mechanistic insight into these dual roles. Here we focus on two areas of rapid advance: (i) the machinery that regulates the stability of the key signal transducer, b-catenin, and (ii) the effect of Wnt signaling on cellular targets outside the nucleus, the actin and microtubule cytoskeletons. Some of the most profound questions inbiology were first asked by ordinarypeople confronting events in their ev-eryday lives. The miracle of a newborn baby raises questions about how an egg assembles itself into an animal. The tragedy of a cancer diagnosis leads to questions about how nor-mal cells go wrong. Although seemingly dis-tinct, biological processes like embryogene-sis and carcinogenesis both rely on cell com