Aurora A and cortical flows promote polarization and cytokinesis by inducing asymmetric ECT-2 accumulation

Abstract

In the early C. elegans embryo, cell polarization and cytokinesis are interrelated yet distinct processes. Here, we sought to understand a poorly understood aspect of cleavage furrow positioning. Early C. elegans embryos deficient in the cytokinetic regulator centralspindlin form furrows, due to an inhibitory activity that depends on aster positioning relative to the polar cortices. Here, we show polar relaxation is associated with depletion of cortical ECT-2, a RhoGEF, specifically at the posterior cortex. Asymmetric ECT-2 accumulation requires intact centrosomes, Aurora A (AIR-1), and myosin-dependent cortical flows. Within a localization competent ECT-2 fragment, we identified three putative phospho-acceptor sites in the PH domain of ECT-2 that render ECT-2 responsive to inhibition by AIR-1. During both polarization and cytokinesis, our results suggest that centrosomal AIR-1 breaks symmetry via ECT-2 phosphorylation; this local inhibition of ECT-2 is amplified by myosin-driven flows that generate regional ECT-2 asymmetry. Together, these mechanisms cooperate to induce polarized assembly of cortical myosin, contributing to both embryo polarization and cytokinesis.

Temporally distinct roles of Aurora A in polarization of theC. eleganszygote

“…However, we found that in embryos treated with PLK-1 inhibitors, PAR-2 retained its ability to bind the membrane and showed weak bipolar and extended domains phenotypes, similar to those observed in plk-1(RNAi) (Calvi et al, 2022;Noatynska et al, 2010;Reich et al, 2019). Because AIR-1 has multiple functions and substrates during the different stages of the cell cycle (Kettenbach et al, 2011;Magnaghi-Jaulin et al, 2019;Sardon et al, 2010;Tien et al, 2004), it is possible that AIR-1 works in concert with PLK-1 early in meiosis I to prevent microtubule-binding dependent PAR-2 cortical recruitment whereas, in meiosis II, AIR-1 acts through a novel target that is yet to be identified (Figure 4F). In summary, our work has demonstrated temporally distinct roles of Aurora A kinase in regulating C. elegans anterior-posterior polarization.…”

“…AIR-1 is a conserved serine/threonine kinase that has multiple functions during cell division including centrosome maturation, spindle assembly, and spindle alignment (Hannak et al, 2001; Magnaghi-Jaulin et al, 2019; Reboutier et al, 2013; Sumiyoshi et al, 2015). During polarity establishment, recent evidence suggests that AIR-1 may act locally through a RhoA Guanine Nucleotide Exchange Factor, ECT-2, to inhibit actomyosin contractility at the posterior end of the zygote (Gan and Motegi, 2021; Kapoor and Kotak, 2019; Klinkert et al, 2019; Longhini and Glotzer, 2022; Zhao et al, 2019). The resulting anterior-directed cortical flows then sweep membrane-bound aPARs to the anterior (Chang and Dickinson, 2022; Illukkumbura et al, 2023; Munro et al, 2004).…”

Cleavage furrow-directed cortical flows bias mechanochemical pathways for PAR polarization in theC. elegansgerm lineage

“…Given the ubiquity of furrow-directed flows in dividing cells (Bray and White, 1988; Cao and Wang, 1990; Chen et al, 2008; Yumura, 2001), it would be surprising that they are not used as a general mechanism for spatial patterning during development, either to concentrate molecules that may help promote cytokinesis (Khaliullin et al, 2018; Longhini and Glotzer, 2022), or as seen here to induce asymmetry in daughter cells.…”

Cleavage furrow positioning in dividing Dictyostelium cells

“…Furthermore, our previous results indicate that relaxation induced by laser ablation at the polar cortex neither triggers blebs nor impacts furrowing (Tanvir & Yumura, 2023). Consequently, Another proposed mechanism for aster-dependent polar relaxation involves the inhibition of ECT2 by Aurora A kinase (Longhini & Glotzer, 2022). However, it is important to note that Dictyostelium cells lack homologs of ECT2 and Rho and possess only a single Aurora kinase with properties resembling both Aurora A and Aurora B kinases.…”

“…elegans embryos, dynein plays a role in removing myosin at the polar regions, leading to polar relaxation and subsequent cortical flow toward the equator (Chapa‐Y‐Lazo et al, 2020). Another proposed mechanism for aster‐dependent polar relaxation involves the inhibition of ECT2 by Aurora A kinase (Longhini & Glotzer, 2022). However, it is important to note that Dictyostelium cells lack homologs of ECT2 and Rho and possess only a single Aurora kinase with properties resembling both Aurora A and Aurora B kinases.…”