Wnt signaling refers to a form of communication between nearby cells. It can be divided conceptually into two main branches or biochemical pathways.
Wnt/b-catenin pathway: regulates levels of b-catenin, a protein that controls gene expression (i.e. whether a gene is "on" or "off") inside the cell nucleus. This pathway helps determine crucial biological decisions such as how many times an immature cell divides, when it stops dividing, and what kind of mature cell it becomes. Because it was the first Wnt pathway to be scientifically described, it is sometimes referred to as the 'canonical' Wnt signaling pathway.
b-catenin-independent Wnt pathway: by definition this is any Wnt pathway that does not regulate b-catenin levels.
Multiple b-catenin-independent ('non-canonical') Wnt pathways have been described in different cell types. One common output of these pathways is cytoskeletal dynamics, which controls cell shape and movements.
Two well-defined b-catenin-independent pathways are the:
Planar Cell Polarity (PCP) pathway, which determines the transverse orientation of cells in many epithelial tissues. The PCP pathway also regulates some types of cell migration during development.
Wnt/Ca++ pathway, which transiently increases calcium levels inside the cell by opening channels in the cell membrane and from intracellular storage sites. This brief spike in calcium can activate several downstream biochemical cascades within the cell.
Each of these signaling pathways can intersect with biochemical processes that determine adhesive properties between neighboring cells, such as the cadherin/catenin complex (partly composed of the b-catenin protein in a structural role). Relationships between these pathways and related biochemistry and cell biology are a focus of investigation in many laboratories, including ours.