Wnt mediated signal transduction is considered to regulate activity of target genes. In Xenopus embryos, ectopic Wnt1 and Wnt8 expression induces gap-junctional communication. During murine brain formation, Wnt1 and the gap-junctional protein connexin43 (Cx43) are coexpressed at the mid/hindbrain border, while interference with Wnt1 or Cx43 expression during embryogenesis leads to severe brain defects in the mid/hindbrain region. In PC12 cells, Wnt1 expression leads to an apparent increase in cell-cell adhesion. We investigated the effects of Wnt1 overexpression on gap-junctional communication in PC12 cells. Wnt1 expressing clones displayed an increased electrical and chemical coupling. This coincides with an increased expression of Cx43 mRNA and protein, while other connexins, Cx26, Cx32, Cx37, Cx40 and Cx45, were not up-regulated. Also, induction of Wnt1 expression in a mammary epithelial cell line leads to an increase in gapjunctional communication and Cx43 protein expression. In transient transactivation assays in P19 EC cells we found that Wnt1 and Li+, an ion that mimics Wnt signalling, increased transcription from the rat Cx43 promoter, potentially via TCF/LEF binding elements, in a pathway separate from cAMP-induced Cx43 transactivation. The results demonstrate that Cx43 acts as a functional target of Wnt1 signalling, and Cx43 expression can be regulated by Wnt1 at the transcriptional level. Our data suggest that Wnt1-induced cell fate determination is likely to involve regulation of gap-junctional communication.