Wnt and CDK-1 regulate cortical release of WRM-1/β-catenin to control cell division orientation in early Caenorhabditis elegans embryos

Abstract

In early Caenorhabditis elegans embryos, the Wingless/int (Wnt)-and Src-signaling pathways function in parallel to induce both the division orientation of the endomesoderm (EMS) blastomere and the endoderm fate of the posterior EMS daughter cell, called E. Here, we show that, in addition to its role in endoderm specification, the β-catenin-related protein Worm armadillo 1 (WRM-1) also plays a role in controlling EMS division orientation. WRM-1 localizes to the cortex of cells in both embryos and larvae and is released from the cortex in a Wnt-responsive manner. We show that WRM-1 cortical release is disrupted in a hypomorphic cyclindependent protein kinase 1 (cdk-1) mutant and that WRM-1 lacking potential CDK-1 phosphoacceptor sites is retained at the cortex. In both cases, cortical WRM-1 interferes with EMS spindle rotation without affecting endoderm specification. Finally, we show that removal of WRM-1 from the cortex can restore WT division orientation, even when both Wnt-and Src-signaling pathways are compromised. Our findings are consistent with a model in which Wnt signaling and CDK-1 modify WRM-1 in a temporal and spatial manner to unmask an intrinsic polarity cue required for proper orientation of the EMS cell division axis.cell polarity | embryogenesis | asymmetric cell division | Src signaling

Divide and differentiate

“…At the onset of M-phase, in response to P2-EMS signaling, WRM-1 disappears from the posterior cortex of EMS proximal to P2. After division, WRM-1 accumulates asymmetrically to higher levels in the nucleus of the posterior daughter cell E relative to the anterior daughter MS. 37,38 This asymmetric nuclear localization of WRM-1 depends on both Wnt signaling and Src-signaling. On the other hand, the asymmetric cortical disappearance of WRM-1 depends primarily on Wnt signaling, suggesting that these 2 localizations of WRM-1 are regulated independently.…”

“…On the other hand, the asymmetric cortical disappearance of WRM-1 depends primarily on Wnt signaling, suggesting that these 2 localizations of WRM-1 are regulated independently. 38 In genetic backgrounds where WRM-1 remains cortical, such as in Wnt signaling mutants, removal of the parallel Src-signaling pathway results in a highly penetrant defect in aligning the EMS mitotic spindle to the anterior-posterior axis. Significantly, removal of WRM-1 activity from these mutant backgrounds was found to rescue the spindle orientation defect, supporting a negative role for cortical WRM-1 in regulating spindle rotation in EMS.…”

“…These observations lead to a model in which removal of cortical WRM-1 exposes an intrinsic cue on the posterior cortex that captures astral microtubules and rotates the EMS mitotic spindle onto the anterior-posterior axis of the embryo. 38 Interestingly, in early embryos harboring hypomorphic alleles of cdk-1 (ne236 and ne2257), the EMS cell fails to orient its division axis properly and, instead, divides left-right, suggesting a link between cdk-1 and regulation of spindle rotation by the P2-EMS signal. 38 Moreover, at non-permissive temperature cdk-1(ne2257) mutant embryos retain cortical WRM-1 throughout the EMS cell cycle just as in Wnt signaling mutants, suggesting that CDK-1 acts together with Wnt signaling to dissociate WRM-1 from the posterior cortex.…”

“…38 Interestingly, in early embryos harboring hypomorphic alleles of cdk-1 (ne236 and ne2257), the EMS cell fails to orient its division axis properly and, instead, divides left-right, suggesting a link between cdk-1 and regulation of spindle rotation by the P2-EMS signal. 38 Moreover, at non-permissive temperature cdk-1(ne2257) mutant embryos retain cortical WRM-1 throughout the EMS cell cycle just as in Wnt signaling mutants, suggesting that CDK-1 acts together with Wnt signaling to dissociate WRM-1 from the posterior cortex. 38 In addition, biochemical studies have shown that CDK-1 directly phosphorylates 2 CDK-1 target sites in the N terminus of WRM-1 in vitro.…”

Connections between cadherin-catenin proteins, spindle misorientation, and cancer

“…56 As a final example, it has also been observed that the ortholog of b-catenin in C.elegans controls cell division orientation in early embryos. 57 In mammals, a connection between AJ proteins and intracellular asymmetry during cell division and cell fate has been observed in certain tissues, but mostly characterized in stratified epithelia. For example, in embryonic neural stem cells, it has been documented that AJs are organized into different microdomains that are split unequally during asymmetric cell divisions by the cleavage plane.…”