Regulation and functions of cell division in the intestinal tissue.

In multicellular organisms, epithelial cells are key elements of tissue organization. In developing epithelial tissues, cellular proliferation and differentiation are under the tight regulation of morphogenetic programs to ensure correct organ formation and functioning. In these processes, proliferation rates and division orientation regulate the speed, timing and direction of tissue expansion but also its proper patterning. Moreover, tissue homeostasis relies on spatio-temporal modulations of daughter cell behavior and arrangement. These aspects are particularly crucial in the intestine, which is one of the most proliferative tissues in adults, making it a very attractive adult organ system to study the role of cell division on epithelial morphogenesis and organ function. Although epithelial cell division has been the subject of intense research for many years in multiple models, it still remains in its infancy in the context of the intestinal tissue. In this review, we focus on the current knowledge on cell division and regulatory mechanisms at play in the intestinal epithelial tissue, as well as their importance in developmental biology and physiopathology.

LAT1 supports mitotic progression through Golgi unlinking in an amino acid transport activity-independent manner.

Amino acid transporters play a vital role in cellular homeostasis by maintaining protein synthesis. L-type amino acid transporter 1 (LAT1/SLC7A5/CD98lc) is a major transporter of large neutral amino acids in cancer cells because of its predominant expression. Although amino acid restriction with various amino acid analog treatments is known to induce mitotic defects, the involvement of amino acid transporters in cell division remains unclear. In this study, we identified that LAT1 is responsible for mitotic progression in a transport activity-independent manner. LAT1 knockdown activates the spindle assembly checkpoint, leading to a delay in metaphase. LAT1 maintains proper spindle orientation with confinement of the lateral cortex localization of the NuMA protein, which mediates the pulling force against the mitotic spindle toward the lateral cortex. Unexpectedly, JPH203, an inhibitor of LAT1 amino acid transport activity, does not affect mitotic progression. Moreover, the transport activity-deficient LAT1 mutant maintains the proper spindle orientation and mitotic progression. LAT1 forms a heterodimer with CD98 (SLC3A2/CD98hc) both in interphase and mitosis. Although CD98 knockdown decreases the plasma membrane localization of LAT1, it does not affect mitotic progression. LAT1 is localized to the Golgi and ER not only at the plasma membrane in interphase, and promotes Golgi unlinking during the mitotic entry, leading to centrosome maturation. These results suggest that LAT1 supports mitotic progression in an amino acid transport activity-independent manner and that Golgi-localized LAT1 is important for mitotic progression through the acceleration of Golgi unlinking and centrosome maturation. These findings reveal a novel LAT1 function in mitosis.

The Drosophila mitotic spindle orientation machinery requires activation, not just localization.

The orientation of the mitotic spindle at metaphase determines the placement of the daughter cells. Spindle orientation in animals typically relies on an evolutionarily conserved biological machine comprised of at least four proteins - called Pins, Gαi, Mud, and Dynein in flies - that exerts a pulling force on astral microtubules and reels the spindle into alignment. The canonical model for spindle orientation holds that the direction of pulling is determined by asymmetric placement of this machinery at the cell cortex. In most cell types, this placement is thought to be mediated by Pins, and a substantial body of literature is therefore devoted to identifying polarized cues that govern localized cortical enrichment of Pins. In this study we revisit the canonical model and find that it is incomplete. Spindle orientation in the Drosophila follicular epithelium and embryonic ectoderm requires not only Pins localization but also direct interaction between Pins and the multifunctional protein Discs large. This requirement can be over-ridden by interaction with another Pins interacting protein, Inscuteable.

Rassf7a promotes spinal cord regeneration and controls spindle orientation in neural progenitor cells.

Spinal cord injury (SCI) can cause long-lasting disability in mammals due to the lack of axonal regrowth together with the inability to reinitiate spinal neurogenesis at the injury site. Deciphering the mechanisms that regulate the proliferation and differentiation of neural progenitor cells is critical for understanding spinal neurogenesis after injury. Compared with mammals, zebrafish show a remarkable capability of spinal cord regeneration. Here, we show that Rassf7a, a member of the Ras-association domain family, promotes spinal cord regeneration after injury. Zebrafish larvae harboring a rassf7a mutation show spinal cord regeneration and spinal neurogenesis defects. Live imaging shows abnormal asymmetric neurogenic divisions and spindle orientation defects in mutant neural progenitor cells. In line with this, the expression of rassf7a is enriched in neural progenitor cells. Subcellular analysis shows that Rassf7a localizes to the centrosome and is essential for cell cycle progression. Our data indicate a role for Rassf7a in modulating spindle orientation and the proliferation of neural progenitor cells after spinal cord injury.

Cell division-dependent dissemination following E-cadherin loss underlies initiation of diffuse-type gastric cancer.

Loss of the cell-cell adhesion protein E-cadherin underlies the development of diffuse-type gastric cancer (DGC), which is characterized by the gradual accumulation of tumor cells originating from the gastric epithelium in the surrounding stroma. How E-cadherin deficiency drives DGC formation remains elusive. Therefore, we investigated the consequences of E-cadherin loss on gastric epithelial organization utilizing a human gastric organoid model and histological analyses of early-stage DGC lesions. E-cadherin depletion from gastric organoids recapitulates DGC initiation, with progressive loss of a single-layered architecture and detachment of individual cells. We found that E-cadherin deficiency in gastric epithelia does not lead to a general loss of epithelial cohesion but disrupts the spindle orientation machinery. This leads to a loss of planar cell division orientation and, consequently, daughter cells are positioned outside of the gastric epithelial layer. Although basally delaminated cells fail to detach and instead reintegrate into the epithelium, apically mispositioned daughter cells can trigger the gradual loss of the single-layered epithelial architecture. This impaired architecture hampers reintegration of mispositioned daughter cells and enables basally delaminated cells to disseminate into the surrounding matrix. Taken together, our findings describe how E-cadherin deficiency disrupts gastric epithelial architecture through displacement of dividing cells and provide new insights in the onset of DGC. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Spindle reorientation in response to mechanical stress is an emergent property of the spindle positioning mechanisms.

Proper orientation of the mitotic spindle plays a crucial role in embryos, during tissue development, and in adults, where it functions to dissipate mechanical stress to maintain tissue integrity and homeostasis. While mitotic spindles have been shown to reorient in response to external mechanical stresses, the subcellular cues that mediate spindle reorientation remain unclear. Here, we used a combination of optogenetics and computational modeling to investigate how mitotic spindles respond to inhomogeneous tension within the actomyosin cortex. Strikingly, we found that the optogenetic activation of RhoA only influences spindle orientation when it is induced at both poles of the cell. Under these conditions, the sudden local increase in cortical tension induced by RhoA activation reduces pulling forces exerted by cortical regulators on astral microtubules. This leads to a perturbation of the balance of torques exerted on the spindle, which causes it to rotate. Thus, spindle rotation in response to mechanical stress is an emergent phenomenon arising from the interaction between the spindle positioning machinery and the cell cortex.

Tension at intercellular junctions is necessary for accurate orientation of cell division in the epithelium plane.

The direction in which a cell divides is set by the orientation of its mitotic spindle and is important for determining cell fate, controlling tissue shape, and maintaining tissue architecture. Divisions parallel to the epithelial plane sustain tissue expansion. By contrast, divisions perpendicular to the plane promote tissue stratification and lead to the loss of epithelial cells from the tissue-an event that has been suggested to promote metastasis. Much is known about the molecular machinery involved in orienting the spindle, but less is known about the contribution of mechanical factors, such as tissue tension, in ensuring spindle orientation in the plane of the epithelium. This is important as epithelia are continuously subjected to mechanical stresses. To explore this further, we subjected suspended epithelial monolayers devoid of extracellular matrix to varying levels of tissue tension to study the orientation of cell divisions relative to the tissue plane. This analysis revealed that lowering tissue tension by compressing epithelial monolayers or by inhibiting myosin contractility increased the frequency of out-of-plane divisions. Reciprocally, increasing tissue tension by elevating cell contractility or by tissue stretching restored accurate in-plane cell divisions. Moreover, a characterization of the geometry of cells within these epithelia suggested that spindles can sense tissue tension through its impact on tension at subcellular surfaces, independently of their shape. Overall, these data suggest that accurate spindle orientation in the plane of the epithelium relies on a threshold level of tension at intercellular junctions.

Annexin A2 and Ahnak control cortical NuMA-dynein localization and mitotic spindle orientation.

Proper mitotic spindle orientation depends on the correct anchorage of astral microtubules to the cortex. It relies on the remodeling of the cell cortex, a process not fully understood. Annexin A2 (Anx2; also known as ANXA2) is a protein known to be involved in cortical domain remodeling. Here, we report that in HeLa cell early mitosis, Anx2 recruits the scaffold protein Ahnak at the cell cortex facing spindle poles, and the distribution of both proteins is controlled by cell adhesion. Depletion of either protein or impaired cortical Ahnak localization result in delayed anaphase onset and unstable spindle anchoring, which leads to altered spindle orientation. We find that Ahnak is present in a complex with dynein-dynactin. Furthermore, Ahnak and Anx2 are required for correct dynein and NuMA (also known as NUMA1) cortical localization and dynamics. We propose that the Ahnak-Anx2 complex influences the cortical organization of the astral microtubule-anchoring complex, and thereby mitotic spindle positioning in human cells. This article has an associated First Person interview with the first author of the paper.

Impairment of α-tubulin and F-actin interactions of GJB3 induces aneuploidy in urothelial cells and promotes bladder cancer cell invasion.

BACKGROUND: We have previously identified an unsuspected role for GJB3 showing that the deficiency of this connexin protein induces aneuploidy in human and murine cells and accelerates cell transformation as well as tumor formation in xenograft models. The molecular mechanisms by which loss of GJB3 leads to aneuploidy and cancer initiation and progression remain unsolved. METHODS: GJB3 expression levels were determined by RT-qPCR and Western blot. The consequences of GJB3 knockdown on genome instability were assessed by metaphase chromosome counting, multinucleation of cells, by micronuclei formation and by the determination of spindle orientation. Interactions of GJB3 with α-tubulin and F-actin was analyzed by immunoprecipitation and immunocytochemistry. Consequences of GJB3 deficiency on microtubule and actin dynamics were measured by live cell imaging and fluorescence recovery after photobleaching experiments, respectively. Immunohistochemistry was used to determine GJB3 levels on human and murine bladder cancer tissue sections. Bladder cancer in mice was chemically induced by BBN-treatment. RESULTS: We find that GJB3 is highly expressed in the ureter and bladder epithelium, but it is downregulated in invasive bladder cancer cell lines and during tumor progression in both human and mouse bladder cancer. Downregulation of GJB3 expression leads to aneuploidy and genomic instability in karyotypically stable urothelial cells and experimental modulation of GJB3 levels alters the migration and invasive capacity of bladder cancer cell lines. Importantly, GJB3 interacts both with α-tubulin and F-actin. The impairment of these interactions alters the dynamics of these cytoskeletal components and leads to defective spindle orientation. CONCLUSION: We conclude that deregulated microtubule and actin dynamics have an impact on proper chromosome separation and tumor cell invasion and migration. Consequently, these observations indicate a possible role for GJB3 in the onset and spreading of bladder cancer and demonstrate a molecular link between enhanced aneuploidy and invasive capacity cancer cells during tumor cell dissemination.

Loss of ORP3 induces aneuploidy and promotes bladder cancer cell invasion through deregulated microtubule and actin dynamics.

We have recently shown that loss of ORP3 leads to aneuploidy induction and promotes tumor formation. However, the specific mechanisms by which ORP3 contributes to ploidy-control and cancer initiation and progression is still unknown. Here, we report that ORP3 is highly expressed in ureter and bladder epithelium while its expression is downregulated in invasive bladder cancer cell lines and during tumor progression, both in human and in mouse bladder cancer. Moreover, we observed an increase in the incidence of N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN)-induced invasive bladder carcinoma in the tissue-specific Orp3 knockout mice. Experimental data demonstrate that ORP3 protein interacts with γ-tubulin at the centrosomes and with components of actin cytoskeleton. Altering the expression of ORP3 induces aneuploidy and genomic instability in telomerase-immortalized urothelial cells with a stable karyotype and influences the migration and invasive capacity of bladder cancer cell lines. These findings demonstrate a crucial role of ORP3 in ploidy-control and indicate that ORP3 is a bona fide tumor suppressor protein. Of note, the presented data indicate that ORP3 affects both cell invasion and migration as well as genome stability through interactions with cytoskeletal components, providing a molecular link between aneuploidy and cell invasion and migration, two crucial characteristics of metastatic cells.

GPR125 (ADGRA3) is an autocleavable adhesion GPCR that traffics with Dlg1 to the basolateral membrane and regulates epithelial apicobasal polarity.

The adhesion family of G protein-coupled receptors (GPCRs) is defined by an N-terminal large extracellular region that contains various adhesion-related domains and a highly-conserved GPCR-autoproteolysis-inducing (GAIN) domain, the latter of which is located immediately before a canonical seven-transmembrane domain. These receptors are expressed widely and involved in various functions including development, angiogenesis, synapse formation, and tumorigenesis. GPR125 (ADGRA3), an orphan adhesion GPCR, has been shown to modulate planar cell polarity in gastrulating zebrafish, but its biochemical properties and role in mammalian cells have remained largely unknown. Here, we show that human GPR125 likely undergoes cis-autoproteolysis when expressed in canine kidney epithelial MDCK cells and human embryonic kidney HEK293 cells. The cleavage appears to occur at an atypical GPCR proteolysis site within the GAIN domain during an early stage of receptor biosynthesis. The products, i.e., the N-terminal and C-terminal fragments, seem to remain associated after self-proteolysis, as observed in other adhesion GPCRs. Furthermore, in polarized MDCK cells, GPR125 is exclusively recruited to the basolateral domain of the plasma membrane. The recruitment likely requires the C-terminal PDZ-domain-binding motif of GPR125 and its interaction with the cell polarity protein Dlg1. Knockdown of GPR125 as well as that of Dlg1 results in formation of aberrant cysts with multiple lumens in Matrigel 3D culture of MDCK cells. Consistent with the multilumen phenotype, mitotic spindles are incorrectly oriented during cystogenesis in GPR125-KO MDCK cells. Thus, the basolateral protein GPR125, an autocleavable adhesion GPCR, appears to play a crucial role in apicobasal polarization in epithelial cells.

Tissue tension and not interphase cell shape determines cell division orientation in the Drosophila follicular epithelium.

We investigated the cell behaviors that drive morphogenesis of the Drosophila follicular epithelium during expansion and elongation of early-stage egg chambers. We found that cell division is not required for elongation of the early follicular epithelium, but drives the tissue toward optimal geometric packing. We examined the orientation of cell divisions with respect to the planar tissue axis and found a bias toward the primary direction of tissue expansion. However, interphase cell shapes demonstrate the opposite bias. Hertwig's rule, which holds that cell elongation determines division orientation, is therefore broken in this tissue. This observation cannot be explained by the anisotropic activity of the conserved Pins/Mud spindle-orienting machinery, which controls division orientation in the apical-basal axis and planar division orientation in other epithelial tissues. Rather, cortical tension at the apical surface translates into planar division orientation in a manner dependent on Canoe/Afadin, which links actomyosin to adherens junctions. These findings demonstrate that division orientation in different axes-apical-basal and planar-is controlled by distinct, independent mechanisms in a proliferating epithelium.

Importin α phosphorylation promotes TPX2 activation by GM130 to control astral microtubules and spindle orientation.

Spindle orientation is important in multiple developmental processes as it determines cell fate and function. The orientation of the spindle depends on the assembly of a proper astral microtubule network. Here, we report that the spindle assembly factor TPX2 regulates astral microtubules. TPX2 in the spindle pole area is activated by GM130 (GOLGA2) on Golgi membranes to promote astral microtubule growth. GM130 relieves TPX2 inhibition by competing for importin α1 (KPNA2) binding. Mitotic phosphorylation of importin α at serine 62 (S62) by CDK1 switches its substrate preference from TPX2 to GM130, thereby enabling competition-based activation. Importin α S62A mutation impedes local TPX2 activation and compromises astral microtubule formation, ultimately resulting in misoriented spindles. Blocking the GM130-importin α-TPX2 pathway impairs astral microtubule growth. Our results reveal a novel role for TPX2 in the organization of astral microtubules. Furthermore, we show that the substrate preference of the important mitotic modulator importin α is regulated by CDK1-mediated phosphorylation.

RGCC balances self-renewal and neuronal differentiation of neural stem cells in the developing mammalian neocortex.

During neocortical development, neural stem cells (NSCs) divide symmetrically to self-renew at the early stage and then divide asymmetrically to generate post-mitotic neurons. The molecular mechanisms regulating the balance between NSC self-renewal and neurogenesis are not fully understood. Using mouse in utero electroporation (IUE) technique and in vitro human NSC differentiation models including cerebral organoids (hCOs), we show here that regulator of cell cycle (RGCC) modulates NSC self-renewal and neuronal differentiation by affecting cell cycle regulation and spindle orientation. RGCC deficiency hampers normal cell cycle process and dysregulates the mitotic spindle, thus driving more cells to divide asymmetrically. These modulations diminish the NSC population and cause NSC pre-differentiation that eventually leads to brain developmental malformation in hCOs. We further show that RGCC might regulate NSC spindle orientation by affecting the organization of centrosome and microtubules. Our results demonstrate that RGCC is essential to maintain the NSC pool during cortical development and suggest that RGCC defects could have etiological roles in human brain malformations.

Understanding the underlying mechanisms governing spindle orientation: How far are we from there?

Proper spindle orientation is essential for cell fate determination and tissue morphogenesis. Recently, accumulating studies have elucidated several factors that regulate spindle orientation, including geometric, internal and external cues. Abnormality in these factors generally leads to defects in the physiological functions of various organs and the development of severe diseases. Herein, we first review models that are commonly used for studying spindle orientation. We then review a conservative heterotrimeric complex critically involved in spindle orientation regulation in different models. Finally, we summarize some cues that affect spindle orientation and explore whether we can establish a model that precisely elucidates the effects of spindle orientation without interfusing other spindle functions. We aim to summarize current models used in spindle orientation studies and discuss whether we can build a model that disturbs spindle orientation alone. This can substantially improve our understanding of how spindle orientation is regulated and provide insights to investigate this complex event.

Multifunctional protein 4.1R regulates the asymmetric segregation of Numb during terminal erythroid maturation.

The asymmetric cell division of stem or progenitor cells generates daughter cells with distinct fates that balance proliferation and differentiation. Asymmetric segregation of Notch signaling regulatory protein Numb plays a crucial role in cell diversification. However, the molecular mechanism remains unclear. Here, we examined the unequal distribution of Numb in the daughter cells of murine erythroleukemia cells (MELCs) that undergo DMSO-induced erythroid differentiation. In contrast to the cytoplasmic localization of Numb during uninduced cell division, Numb is concentrated at the cell boundary in interphase, near the one-spindle pole in metaphase, and is unequally distributed to one daughter cell in anaphase in induced cells. The inheritance of Numb guides this daughter cell toward erythroid differentiation while the other cell remains a progenitor cell. Mitotic spindle orientation, critical for distribution of cell fate determinants, requires complex communication between the spindle microtubules and the cell cortex mediated by the NuMA-LGN-dynein/dynactin complex. Depletion of each individual member of the complex randomizes the position of Numb relative to the mitotic spindle. Gene replacement confirms that multifunctional erythrocyte protein 4.1R (4.1R) functions as a member of the NuMA-LGN-dynein/dynactin complex and is necessary for regulating spindle orientation, in which interaction between 4.1R and NuMA plays an important role. These results suggest that mispositioning of Numb is the result of spindle misorientation. Finally, disruption of the 4.1R-NuMA-LGN complex increases Notch signaling and decreases the erythroblast population. Together, our results identify a critical role for 4.1R in regulating the asymmetric segregation of Numb to mediate erythropoiesis.

Centrosomal ALIX regulates mitotic spindle orientation by modulating astral microtubule dynamics.

The orientation of the mitotic spindle (MS) is tightly regulated, but the molecular mechanisms are incompletely understood. Here we report a novel role for the multifunctional adaptor protein ALG-2-interacting protein X (ALIX) in regulating MS orientation in addition to its well-established role in cytokinesis. We show that ALIX is recruited to the pericentriolar material (PCM) of the centrosomes and promotes correct orientation of the MS in asymmetrically dividing Drosophila stem cells and epithelial cells, and symmetrically dividing Drosophila and human epithelial cells. ALIX-deprived cells display defective formation of astral microtubules (MTs), which results in abnormal MS orientation. Specifically, ALIX is recruited to the PCM via Drosophila Spindle defective 2 (DSpd-2)/Cep192, where ALIX promotes accumulation of γ-tubulin and thus facilitates efficient nucleation of astral MTs. In addition, ALIX promotes MT stability by recruiting microtubule-associated protein 1S (MAP1S), which stabilizes newly formed MTs. Altogether, our results demonstrate a novel evolutionarily conserved role of ALIX in providing robustness to the orientation of the MS by promoting astral MT formation during asymmetric and symmetric cell division.

Transgelin-2 and phosphoregulation of the LIC2 subunit of dynein govern mitotic spindle orientation.

The molecular motor dynein is essential for mitotic spindle orientation, which defines the axis of cell division. The light intermediate chain subunits, LIC1 and LIC2, define biochemically and functionally distinct vertebrate dynein complexes, with LIC2-dynein playing a crucial role in ensuring spindle orientation. We reveal a novel, mitosis-specific interaction of LIC2-dynein with the cortical actin-bundling protein transgelin-2. Transgelin-2 is required for maintaining proper spindle length, equatorial metaphase chromosome alignment, spindle orientation and timely anaphase onset. We show that transgelin-2 stabilizes the cortical recruitment of LGN-NuMA, which together with dynein is required for spindle orientation. The opposing actions of transgelin-2 and LIC2-dynein maintain optimal cortical levels of LGN-NuMA. In addition, we show that the highly conserved serine 194 phosphorylation of LIC2 is required for proper spindle orientation, by maintaining mitotic centrosome integrity to ensure optimal astral microtubule nucleation. The work reveals two specific mechanisms through which LIC2-dynein regulates mitotic spindle orientation; namely, through a new interactor transgelin-2, which is required for engagement of LGN-NuMA with the actin cortex, and through mitotic phosphoregulation of LIC2 to control microtubule nucleation from the poles.This article has an associated First Person interview with the first author of the paper.

RAS-mediated suppression of PAR3 and its effects on SCC initiation and tissue architecture occur independently of hyperplasia.

Proper epithelial development and homeostasis depends on strict control of oriented cell division. Current evidence shows that this process is regulated by intrinsic polarity factors and external spatial cues. Owing to the lack of an appropriate model system that can recapitulate the architecture of the skin, deregulation of spindle orientation in human epithelial carcinoma has never been investigated. Here, using an inducible model of human squamous cell carcinoma (SCC), we demonstrate that RAS-dependent suppression of PAR3 (encoded by PARD3) accelerates epithelial disorganization during early tumorigenesis. Diminished PAR3 led to loss of E-cadherin-mediated cell adhesion, which in turn contributed to misoriented cell division. Pharmacological inhibition of the MAPK pathway downstream of RAS activation reversed the defects in PAR3 expression, E-cadherin-mediated cell adhesion and mitotic spindle orientation. Thus, temporal analysis of human neoplasia provides a powerful approach to study cellular and molecular transformations during early oncogenesis, which allowed identification of PAR3 as a critical regulator of tissue architecture during initial human SCC development.

PP2A--B55γ counteracts Cdk1 and regulates proper spindle orientation through the cortical dynein adaptor NuMA.

Proper orientation of the mitotic spindle is critical for accurate development and morphogenesis. In human cells, spindle orientation is regulated by the evolutionarily conserved protein NuMA, which interacts with dynein and enriches it at the cell cortex. Pulling forces generated by cortical dynein orient the mitotic spindle. Cdk1-mediated phosphorylation of NuMA at threonine 2055 (T2055) negatively regulates its cortical localization. Thus, only NuMA not phosphorylated at T2055 localizes at the cell cortex. However, the identity and the mechanism of action of the phosphatase complex involved in T2055 dephosphorylation remains elusive. Here, we characterized the PPP2CA-B55γ (PPP2R2C)-PPP2R1B complex that counteracts Cdk1 to orchestrate cortical NuMA for proper spindle orientation. In vitro reconstitution experiments revealed that this complex is sufficient for T2055 dephosphorylation. Importantly, we identified polybasic residues in NuMA that are critical for T2055 dephosphorylation, and for maintaining appropriate cortical NuMA levels for accurate spindle elongation. Furthermore, we found that Cdk1-mediated phosphorylation and PP2A-B55γ-mediated dephosphorylation at T2055 are reversible events. Altogether, this study uncovers a novel mechanism by which Cdk1 and its counteracting PP2A-B55γ complex orchestrate spatiotemporal levels of cortical force generators for flawless mitosis.