Two βs or not two βs: regulation of asymmetric division by β-catenin

Wnt signaling through T-cell factor phosphorylation

“…While this pathway is similar to the Wnt/NLK/POP-1 pathway proposed for C. elegans [45,47] (Figure 1), the upstream regulators of both pathways are largely unknown. A priori, HIPK2 may be constitutively required for this phosphorylation, or it may be activated in response to a Wnt signal, as has been proposed for c-Myb regulation [100].…”

“…Asymmetric division of the EMS progenitor generates the MS (mesodermal) cell and the E (endodermal) cell [44][45][46]. Both cells produce endoderm in pop-1 mutants, indicating that POP-1 normally suppresses endodermal fate in the MS cell lineage [26].…”

“…This POP-1 asymmetry requires LIT-1, a protein kinase that regulates asymmetric cell divisions [50] and promotes the nuclear export of POP-1 [49,51,52]. Paradoxically, the small amount of POP-1 that remains in the E-cell nucleus is required, together with SYS-1, a distant member of the β-catenin family [53,54], for Wnt-dependent activation of endoderm-specific end-1 and end-3 target genes [44,45,47,[55][56][57]. POP-1 also functions as a transcriptional activator in T neuroblasts and somatic gonadal precursors, in which POP-1 and SYS-1 directly activate the ceh-22/tinman gene [47,53,54,58].…”

-Catenin-Dependent Wnt Signaling in C. elegans: Teaching an Old Dog a New Trick

“…Signaling regulated by Wnt ligand binding plays an important and often essential role in an astounding number of processes during invertebrate and vertebrate development, as well as functioning in the maintenance of adult stem cell populations in vertebrates and Drosophila (reviewed in Clevers 2006;Cadigan and Peifer 2009;MacDonald et al 2009). In the nematode Caenorhabditis elegans, Wnt signaling is necessary for many events during both embryonic and larval development, and regulates many processes including cell migration, cell polarity, fate specification, axon guidance, synaptogenesis, and stem cell-like renewal (see Eisenmann 2005;Mizumoto and Sawa 2007b;Van Hoffelen and Herman 2008). Intriguingly, although C. elegans uses a Wnt/b-catenin or "canonical" signaling pathway similar to that in other metazoans, it also has a second, novel Wnt signaling pathway that uses additional b-catenins to effect transcriptional up-regulation of target genes by a mechanism distinct from that in the common Wnt pathway (Mizumoto and Sawa 2007b;Phillips and Kimble 2009).…”

“…In the nematode Caenorhabditis elegans, Wnt signaling is necessary for many events during both embryonic and larval development, and regulates many processes including cell migration, cell polarity, fate specification, axon guidance, synaptogenesis, and stem cell-like renewal (see Eisenmann 2005;Mizumoto and Sawa 2007b;Van Hoffelen and Herman 2008). Intriguingly, although C. elegans uses a Wnt/b-catenin or "canonical" signaling pathway similar to that in other metazoans, it also has a second, novel Wnt signaling pathway that uses additional b-catenins to effect transcriptional up-regulation of target genes by a mechanism distinct from that in the common Wnt pathway (Mizumoto and Sawa 2007b;Phillips and Kimble 2009). Here we summarize our current understanding of these two C. elegans signaling pathways and the ways they are similar to, and diverge from, Wnt signaling pathways in other species.…”