C-elegans POP-1/TCF functions in a canonical Wnt pathway that controls cell migration acid in a noncanonical Wnt pathway that controls cell polarity

In Caenorhabditis elegans, Wnt signaling pathways are important in controll ing cell polarity and cell migrations. In the embryo, a novel Wnt pathway f unctions through a beta -catenin homolog, WRM-1, to downregulate the levels of POP-1/Tcf in the posterior daughter of the EMS blastomere, The level of POP-1 is also lower in the posterior daughters of many anteroposterior asy mmetric cell divisions during development. I have found that this is the ca se for of a pair of postembryonic blast cells in the tail. In wild-type ani mals, the level of POP-1 is lower in the posterior daughters of the two T c ells, TL and TR, Furthermore, in lin-44/Wnt mutants, in which the polaritie s of the T cell divisions are frequently reversed, the level of POP-1 is fr equently lower in the anterior daughters of the T cells. I have used a nove l RNA-mediated interference technique to interfere specifically with pop-1 zygotic function and have determined that pop-1 is required for wild-type T cell polarity. Surprisingly, none of the three C. elegans beta -catenin ho mologs appeared to function with POP-1 to control T cell polarity. Wnt sign aling by EGL-20/Wnt controls the migration of the descendants of the QL neu roblast by regulating the expression the Hox gene mab-5, Interfering with p op-1 zygotic function caused defects in the migration of the QL descendants that mimicked the defects in egl-20/Wnt mutants and blocked the expression of mab-5, This suggests that POP-1 functions in the canonical Wnt pathway to control QL descendant migration and in novel Wnt pathways to control EMS and T cell polarities.