Fig. 1. Wnt/β-catenin signalling as a tale of four multiprotein complexes. Two snapshots of the dynamic processes in the Wnt/β-catenin signal transduction cascade that involve multiprotein complexes. (A) In the presence of extracellular Wnt signalling, Wnt receptor complexes assemble in the cell membrane (Complex 1); as a consequence, β-catenin is able to form transcription activation complexes with TCF/LEFs in the nucleus (Complex 3). (B) In the absence of extracellular Wnt signalling, β-catenin destruction complexes assemble (Complex 2), leaving TCF/LEF to form transcription-repressing complexes with transcriptional co-repressors (Complex 4). A, Axin protein; β, β-catenin protein; TCF, TCF or LEF protein; W, extracellular Wnt signal. For further details, see main text, recent reviews (e.g. Cadigan and Liu, 2006; Willert and Jones, 2006) and the Wnt homepage (http://www.stanford.edu/~rnusse/wntwindow.html).