Wnt signaling pathway
Wnt glycoproteins are signaling molecules that control a wide range of developmental processes and is a conserved feature of metazoan development. In C. elegans Wnt signaling has been shown to play a role in cell fate specification and determination of cell polarity, cell migration, and axis determination during axon outgrowth. A 'canonical' Wnt signaling pathway has been elucidated in vertebrate and invertebrate model systems where Wnt binding leads to the stabilization of the transcription factor beta-catenin, which then enters the nucleus to regulate Wnt pathway target genes. Like other species, the C. elegans genome encodes multiple genes for Wnt ligands, EGL-20, LIN-44, MOM-2, CWN-1, CWN-2) and Wnt receptors (LIN-17, MOM-5, MIG-1, CFZ-2, LIN-18). Canonical Wnt signaling in C. elegans, utilizes the beta-catenin BAR-1 to convert POP-1 into an activator and controls the expression of several homeobox genes. However, unlike vertebrates or Drosophila, the C. elegans genome encodes multiple beta-catenin genes (HMP-2, BAR-1, SYS-1, WRM-1), which give rise to noncanonical Wnt signalling pathways: for example, the endoderm induction pathway requires the beta-catenin WRM-1 and parallel input from a mitogen-activated kinase (MAPK) pathway to downregulate POP-1.