Wnt proteins constitute a large family of secreted molecules that are involved in intercellular signalling during development. The name derives from the first 2 members of the family to be discovered: int-1 (mouse) and wingless (Drosophila) (PUBMED:9891778). It is now recognised that Wnt signalling controls many cell fate decisions in a variety of different organisms, including mammals (PUBMED:10508601). Wnt signalling has been implicated in tumorigenesis, early mesodermal patterning of the embryo, morphogenesis of the brain and kidneys, regulation of mammary gland proliferation and Alzheimer's disease (PUBMED:10967351), (PUBMED:9192851).

Wnt-mediated signalling is believed to proceed initially through binding to cell surface receptors of the frizzled family; the signal is subsequently transduced through several cytoplasmic components to B-catenin, which enters the nucleus and activates the transcription of several genes important in development (PUBMED:10733430). More recently, however, several non-canonical Wnt signalling pathways have been elucidated that act independently of B-catenin. Members of the Wnt gene family are defined by their sequence similarity to mouse Wnt-1 and Wingless in Drosophila. They encode proteins of ~350-400 residues in length, with orthologues identified in several, mostly vertebrate, species. Very little is known about the structure of Wnts as they are notoriously insoluble; but they share the following features characteristics of secretory proteins: a signal peptide, several potential N-glycosylation sites and 22 conserved cysteines (PUBMED:9891778) that are probably involved in disulphide bonds. The Wnt proteins seem to adhere to the plasma membrane of the secreting cells and are therefore likely to signal over only few cell diameters. Fifteen major Wnt gene families have been identified in vertebrates, with multiple subtypes within some classes.

This entry represents Wnt-1 (previously known as int-1) is a proto-oncogene induced by the integration of the mouse mammary tumor virus. It is thought to play a role in intercellular communication and seems to be a signalling molecule important in the development of the central nervous system (CNS). The sequence of wnt-1 is highly conserved in mammals, fish, and amphibians. Wnt-1 is a member of a large family of related proteins that are all thought to be developmental regulators. These proteins are known as wnt-2 (also known as irp), wnt-3 up to wnt-15. At least four members of this family are present in Drosophila, one of them, wingless (wg), is implicated in segmentation polarity.