The symbol for a group of homologous genes which encode proteins that regulate cell-to-cell interactions during development. The Drosophila gene wingless (wg) controls the segmental pattern of the embryo, and the mouse was later shown to have a homologous gene called integration (int). Once it became clear that these genes were conserved in both invertebrates and vertebrates, the symbol Wnt was chosen, w from wg and nt from int, to reflect the widespread evolutionary distribution of this family. The proteins encoded by Wnt genes are cysteine-rich, secreted glycoproteins which interact with specific cell-surface receptors that in turn initiate a signaling cascade which turns on specific genes in target cells. In the mouse embryo the timing of Wnt expression in the central nervous system indicates that Wnt genes regulate the differentiation of forebrain and spinal cord. In Xenopus embryos the ectopic expression of Wnt can cause a second neural axis to develop, and a two-headed larva will be produced. See cellular signal transduction.