Dictyostelium Aurora kinase has properties of both Aurora A and Aurora B kinases

Dynamic Mitotic Localization of the Centrosomal Kinases CDK1, Plk, AurK, and Nek2 in Dictyostelium amoebae

The centrosome of the amoebozoan model Dictyostelium discoideum provides the best-established model for an acentriolar centrosome outside the Opisthokonta. Dictyostelium exhibits an unusual centrosome cycle, in which duplication is initiated only at the G2/M transition and occurs entirely during the M phase. Little is known about the role of conserved centrosomal kinases in this process. Therefore, we have generated knock-in strains for Aurora (AurK), CDK1, cyclin B, Nek2, and Plk, replacing the endogenous genes with constructs expressing the respective green fluorescent Neon fusion proteins, driven by the endogenous promoters, and studied their behavior in living cells. Our results show that CDK1 and cyclin B arrive at the centrosome first, already during G2, followed by Plk, Nek2, and AurK. Furthermore, CDK1/cyclin B and AurK were dynamically localized at kinetochores, and AurK in addition at nucleoli. The putative roles of all four kinases in centrosome duplication, mitosis, cytokinesis, and nucleolar dynamics are discussed.

Functional specialization of Aurora kinase homologs during oogenic meiosis in the tunicate Oikopleura dioica

A single Aurora kinase found in non-vertebrate deuterostomes is assumed to represent the ancestor of vertebrate Auroras A/B/C. However, the tunicate Oikopleura dioica, a member of the sister group to vertebrates, possesses two Aurora kinases (Aurora1 and Aurora2) that are expressed in proliferative cells and reproductive organs. Previously, we have shown that Aurora kinases relocate from organizing centers to meiotic nuclei and were enriched on centromeric regions as meiosis proceeds to metaphase I. Here, we assessed their respective functions in oogenic meiosis using dsRNA interferences. We found that Aurora1 (Aur1) was involved in meiotic spindle organization and chromosome congression, probably through the regulation of microtubule dynamics, whereas Aurora2 (Aur2) was crucial for chromosome condensation and meiotic spindle assembly. In vitro kinase assays showed that Aur1 and Aur2 had comparable levels of kinase activities. Using yeast two-hybrid library screening, we identified a few novel interaction proteins for Aur1, including c-Jun-amino-terminal kinase-interacting protein 4, cohesin loader Scc2, and mitochondrial carrier homolog 2, suggesting that Aur1 may have an altered interaction network and participate in the regulation of microtubule motors and cohesin complexes in O. dioica.

Cleavage furrow positioning in dividing Dictyostelium cells

Accurate placement of the cleavage furrow is crucial for successful cell division. Recent advancements have revealed that diverse mechanisms have evolved across different branches of the phylogenetic tree. Here, we employed Dictyostelium cells to validate previous models. We observed that during metaphase and early anaphase, mitotic spindles exhibited random rotary movements which ceased when the spindle elongated by approximately 7 μm. At this point, astral microtubules reached the polar cell cortex and fixed the spindle axis, causing cells to elongate by extending polar pseudopods and divide along the spindle axis. Therefore, the position of the furrow is determined when the spindle orientation is fixed. The distal ends of astral microtubules stimulate the extension of pseudopods at the polar cortex. One signal for pseudopod extension may be phosphatidylinositol trisphosphate in the cell membrane, but there appears to be another unknown signal. At the onset of polar pseudopod extension, cortical flow began from both poles toward the equator. We suggest that polar stimulation by astral microtubules determines the furrow position, induces polar pseudopod extension and cortical flow, and accumulates the elements necessary for the construction of the contractile ring.

An altered transcriptome underlies cln5-deficiency phenotypes in Dictyostelium discoideum

Mutations in CLN5 cause a subtype of neuronal ceroid lipofuscinosis (NCL) called CLN5 disease. The NCLs, commonly referred to as Batten disease, are a family of neurodegenerative lysosomal storage diseases that affect all ages and ethnicities globally. Previous research showed that CLN5 participates in a variety of cellular processes. However, the precise function of CLN5 in the cell and the pathway(s) regulating its function are not well understood. In the model organism Dictyostelium discoideum, loss of the CLN5 homolog, cln5, impacts various cellular and developmental processes including cell proliferation, cytokinesis, aggregation, cell adhesion, and terminal differentiation. In this study, we used comparative transcriptomics to identify differentially expressed genes underlying cln5-deficiency phenotypes during growth and the early stages of multicellular development. During growth, genes associated with protein ubiquitination/deubiquitination, cell cycle progression, and proteasomal degradation were affected, while genes linked to protein and carbohydrate catabolism were affected during early development. We followed up this analysis by showing that loss of cln5 alters the intracellular and extracellular amounts of proliferation repressors during growth and increases the extracellular amount of conditioned medium factor, which regulates cAMP signalling during the early stages of development. Additionally, cln5- cells displayed increased intracellular and extracellular amounts of discoidin, which is involved in cell-substrate adhesion and migration. Previous work in mammalian models reported altered lysosomal enzyme activity due to mutation or loss of CLN5. Here, we detected altered intracellular activities of various carbohydrate enzymes and cathepsins during cln5- growth and starvation. Notably, cln5- cells displayed reduced β-hexosaminidase activity, which aligns with previous work showing that D. discoideum Cln5 and human CLN5 can cleave the substrate acted upon by β-hexosaminidase. Finally, consistent with the differential expression of genes associated with proteasomal degradation in cln5- cells, we also observed elevated amounts of a proteasome subunit and reduced proteasome 20S activity during cln5- growth and starvation. Overall, this study reveals the impact of cln5-deficiency on gene expression in D. discoideum, provides insight on the genes and proteins that play a role in regulating Cln5-dependent processes, and sheds light on the molecular mechanisms underlying CLN5 disease.

The Dictyostelium Centrosome

The centrosome of Dictyostelium amoebae contains no centrioles and consists of a cylindrical layered core structure surrounded by a corona harboring microtubule-nucleating γ-tubulin complexes. It is the major centrosomal model beyond animals and yeasts. Proteomics, protein interaction studies by BioID and superresolution microscopy methods led to considerable progress in our understanding of the composition, structure and function of this centrosome type. We discuss all currently known components of the Dictyostelium centrosome in comparison to other centrosomes of animals and yeasts.

Ancient origins of allosteric activation in a Ser-Thr kinase

A myriad of cellular events are regulated by allostery; therefore, evolution of this process is of fundamental interest. Here, we use ancestral sequence reconstruction to resurrect ancestors of two colocalizing proteins, Aurora A kinase and its allosteric activator TPX2 (targeting protein for Xklp2), to experimentally characterize the evolutionary path of allosteric activation. Autophosphorylation of the activation loop is the most ancient activation mechanism; it is fully developed in the oldest kinase ancestor and has remained stable over 1 billion years of evolution. As the microtubule-associated protein TPX2 appeared, efficient kinase binding to TPX2 evolved, likely owing to increased fitness by virtue of colocalization. Subsequently, TPX2-mediated allosteric kinase regulation gradually evolved. Surprisingly, evolution of this regulation is encoded in the kinase and did not arise by a dominating mechanism of coevolution.

Force balances between interphase centrosomes as revealed by laser ablation

Numerous studies have highlighted the self-centering activities of individual microtubule (MT) arrays in animal cells, but relatively few works address the behavior of multiple arrays that coexist in a common cytoplasm. In multinucleated Dictyostelium discoideum cells, each centrosome organizes a radial MT network, and these networks remain separate from one another. This feature offers an opportunity to reveal the mechanism(s) responsible for the positioning of multiple centrosomes. Using a laser microbeam to eliminate one of the two centrosomes in binucleate cells, we show that the unaltered array is rapidly repositioned at the cell center. This result demonstrates that each MT array is constantly subject to centering forces and infers a mechanism to balance the positions of multiple arrays. Our results address the limited actions of three kinesins and a cross-linking MAP that are known to have effects in maintaining MT organization and suggest a simple means used to keep the arrays separated.

Aurora-PLK1 cascades as key signaling modules in the regulation of mitosis

Mitosis is controlled by reversible protein phosphorylation involving specific kinases and phosphatases. A handful of major mitotic protein kinases, such as the cyclin B-CDK1 complex, the Aurora kinases, and Polo-like kinase 1 (PLK1), cooperatively regulate distinct mitotic processes. Research has identified proteins and mechanisms that integrate these kinases into signaling cascades that guide essential mitotic events. These findings have important implications for our understanding of the mechanisms of mitotic regulation and may advance the development of novel antimitotic drugs. We review collected evidence that in vertebrates, the Aurora kinases serve as catalytic subunits of distinct complexes formed with the four scaffold proteins Bora, CEP192, INCENP, and TPX2, which we deem "core" Aurora cofactors. These complexes and the Aurora-PLK1 cascades organized by Bora, CEP192, and INCENP control crucial aspects of mitosis and all pathways of spindle assembly. We compare the mechanisms of Aurora activation in relation to the different spindle assembly pathways and draw a functional analogy between the CEP192 complex and the chromosomal passenger complex that may reflect the coevolution of centrosomes, kinetochores, and the actomyosin cleavage apparatus. We also analyze the roles and mechanisms of Aurora-PLK1 signaling in the cell and centrosome cycles and in the DNA damage response.

Cytokinesis: Robust cell shape regulation

Cytokinesis, the final step of cell division, is a great example of robust cell shape regulation. A wide variety of cells ranging from the unicellular Dictyostelium to human cells in tissues proceed through highly similar, stereotypical cell shape changes during cell division. Typically, cells first round up forming a cleavage furrow in the middle, which constricts resulting in the formation of two daughter cells. Tight control of cytokinesis is essential for proper segregation of genetic and cellular materials, and its failure is deleterious to cell viability. Thus, biological systems have developed elaborate mechanisms to ensure high fidelity of cytokinesis, including the existence of multiple biochemical and mechanical pathways regulated through feedback. In this review, we focus on the built-in redundancy of the cytoskeletal machinery that allows cells to divide successfully in a variety of biological and mechanical contexts. Using Dictyostelium cytokinesis as an example, we demonstrate that the crosstalk between biochemical and mechanical signaling through feedback ensures correct assembly and function of the cell division machinery.

Spatial Compartmentalization Specializes the Function of Aurora A and Aurora B

Aurora kinase A and B share great similarity in sequences, structures, and phosphorylation motif, yet they show different localizations and play distinct crucial roles. The factors that determine such differences are largely unknown. Here we targeted Aurora A to the localization of Aurora B and found that Aurora A phosphorylates the substrate of Aurora B and substitutes its function in spindle checkpoint. In return, the centrosome targeting of Aurora B substitutes the function of Aurora A in the mitotic entry. Expressing the chimera proteins of the Auroras with exchanged N termini in cells indicates that the divergent N termini are also important for their spatiotemporal localizations and functions. Collectively, we demonstrate that functional divergence of Aurora kinases is determined by spatial compartmentalization, and their divergent N termini also contribute to their spatial and functional differentiation.

Genetic suppression of a phosphomimic myosin II identifies system-level factors that promote myosin II cleavage furrow accumulation

How myosin II localizes to the cleavage furrow in Dictyostelium and metazoan cells remains largely unknown despite significant advances in understanding its regulation. We designed a genetic selection using cDNA library suppression of 3xAsp myosin II to identify factors involved in myosin cleavage furrow accumulation. The 3xAsp mutant is deficient in bipolar thick filament assembly, fails to accumulate at the cleavage furrow, cannot rescue myoII-null cytokinesis, and has impaired mechanosensitive accumulation. Eleven genes suppressed this dominant cytokinesis deficiency when 3xAsp was expressed in wild-type cells. 3xAsp myosin II's localization to the cleavage furrow was rescued by constructs encoding rcdBB, mmsdh, RMD1, actin, one novel protein, and a 14-3-3 hairpin. Further characterization showed that RMD1 is required for myosin II cleavage furrow accumulation, acting in parallel with mechanical stress. Analysis of several mutant strains revealed that different thresholds of myosin II activity are required for daughter cell symmetry than for furrow ingression dynamics. Finally, an engineered myosin II with a longer lever arm (2xELC), producing a highly mechanosensitive motor, could also partially suppress the intragenic 3xAsp. Overall, myosin II accumulation is the result of multiple parallel and partially redundant pathways that comprise a cellular contractility control system.

Nucleocytoplasmic protein translocation during mitosis in the social amoebozoan Dictyostelium discoideum

Mitosis is a fundamental and essential life process. It underlies the duplication and survival of all cells and, as a result, all eukaryotic organisms. Since uncontrolled mitosis is a dreaded component of many cancers, a full understanding of the process is critical. Evolution has led to the existence of three types of mitosis: closed, open, and semi-open. The significance of these different mitotic species, how they can lead to a full understanding of the critical events that underlie the asexual duplication of all cells, and how they may generate new insights into controlling unregulated cell division remains to be determined. The eukaryotic microbe Dictyostelium discoideum has proved to be a valuable biomedical model organism. While it appears to utilize closed mitosis, a review of the literature suggests that it possesses a form of mitosis that lies in the middle between truly open and fully closed mitosis-it utilizes a form of semi-open mitosis. Here, the nucleocytoplasmic translocation patterns of the proteins that have been studied during mitosis in the social amoebozoan D. discoideum are detailed followed by a discussion of how some of them provide support for the hypothesis of semi-open mitosis.

Aurora at the pole and equator: overlapping functions of Aurora kinases in the mitotic spindle

The correct assembly and timely disassembly of the mitotic spindle is crucial for the propagation of the genome during cell division. Aurora kinases play a central role in orchestrating bipolar spindle establishment, chromosome alignment and segregation. In most eukaryotes, ranging from amoebas to humans, Aurora activity appears to be required both at the spindle pole and the kinetochore, and these activities are often split between two different Aurora paralogues, termed Aurora A and B. Polar and equatorial functions of Aurora kinases have generally been considered separately, with Aurora A being mostly involved in centrosome dynamics, whereas Aurora B coordinates kinetochore attachment and cytokinesis. However, double inactivation of both Aurora A and B results in a dramatic synergy that abolishes chromosome segregation. This suggests that these two activities jointly coordinate mitotic progression. Accordingly, recent evidence suggests that Aurora A and B work together in both spindle assembly in metaphase and disassembly in anaphase. Here, we provide an outlook on these shared functions of the Auroras, discuss the evolution of this family of mitotic kinases and speculate why Aurora kinase activity may be required at both ends of the spindle microtubules.

Urochordate ascidians possess a single isoform of Aurora kinase that localizes to the midbody via TPX2 in eggs and cleavage stage embryos

Aurora kinases are key proteins found throughout the eukaryotes that control mitotic progression. Vertebrate Aurora-A and B kinases are thought to have evolved from a single Aurora-kinase isoform closest to that found in present day urochordates. In urochordate ascidians Aurora binds both TPX2 (a vertebrate AURKA partner) and INCENP (a vertebrate AURKB partner) and localizes to centrosomes and spindle microtubules as well as chromosomes and midbody during both meiosis and mitosis. Ascidian Aurora also displays this localization pattern during mitosis in echinoderms, strengthening the idea that non-vertebrate deuterostomes such as the urochordates and echinoderms possess a single form of Aurora kinase that has properties of vertebrate Aurora-kinase A and B. In the ascidian, TPX2 localizes to the centrosome and the spindle poles also as in vertebrates. However, we were surprised to find that TPX2 also localized strongly to the midbody in ascidian eggs and embryos. We thus examined more closely Aurora localization to the midbody by creating two separate point mutations of ascidian Aurora predicted to perturb binding to TPX2. Both forms of mutated Aurora behaved as predicted: neither localized to spindle poles where TPX2 is enriched. Interestingly, neither form of mutated Aurora localized to the midbody where TPX2 is also enriched, suggesting that ascidian Aurora midbody localization required TPX2 binding in ascidians. Functional analysis revealed that inhibition of Aurora kinase with a pharmacological inhibitor or with a dominant negative kinase dead form of Aurora caused cytokinesis failure and perturbed midbody formation during polar body extrusion. Our data support the view that vertebrate Aurora-A and B kinases evolved from a single non-vertebrate deuterostome ancestor. Moreover, since TPX2 localizes to the midbody in ascidian eggs and cleavage stage embryos it may be worthwhile re-assessing whether Aurora A kinase or TPX2 localize to the midbody in eggs and cleavage stage embryos.

Cytokinesis mechanics and mechanosensing

Cytokinesis shape change occurs through the interfacing of three modules, cell mechanics, myosin II-mediated contractile stress generation and sensing, and a control system of regulatory proteins, which together ensure flexibility and robustness. This integrated system then defines the stereotypical shape changes of successful cytokinesis, which occurs under a diversity of mechanical contexts and environmental conditions.

A retinoblastoma orthologue is a major regulator of S-phase, mitotic, and developmental gene expression in Dictyostelium

Background

The retinoblastoma tumour suppressor, Rb, has two major functions. First, it represses genes whose products are required for S-phase entry and progression thus stabilizing cells in G1. Second, Rb interacts with factors that induce cell-cycle exit and terminal differentiation. Dictyostelium lacks a G1 phase in its cell cycle but it has a retinoblastoma orthologue, rblA.

Methodology/Principal Findings

Using microarray analysis and mRNA-Seq transcriptional profiling, we show that RblA strongly represses genes whose products are involved in S phase and mitosis. Both S-phase and mitotic genes are upregulated at a single point in late G2 and again in mid-development, near the time when cell cycling is reactivated. RblA also activates a set of genes unique to slime moulds that function in terminal differentiation.

Conclusions

Like its mammalian counterpart Dictyostelium, RblA plays a dual role, regulating cell-cycle progression and transcriptional events leading to terminal differentiation. In the absence of a G1 phase, however, RblA functions in late G2 controlling the expression of both S-phase and mitotic genes.

A mechanosensory system governs myosin II accumulation in dividing cells

The mitotic spindle is generally considered the initiator of furrow ingression. However, recent studies suggest that furrows can form without spindles, particularly during asymmetric cell division. In Dictyostelium, the mechanoenzyme myosin II and the actin cross-linker cortexillin I form a mechanosensor that responds to mechanical stress, which could account for spindle-independent contractile protein recruitment. Here we show that the regulatory and contractility network composed of myosin II, cortexillin I, IQGAP2, kinesin-6 (kif12), and inner centromeric protein (INCENP) is a mechanical stress-responsive system. Myosin II and cortexillin I form the core mechanosensor, and mechanotransduction is mediated by IQGAP2 to kif12 and INCENP. In addition, IQGAP2 is antagonized by IQGAP1 to modulate the mechanoresponsiveness of the system, suggesting a possible mechanism for discriminating between mechanical and biochemical inputs. Furthermore, IQGAP2 is important for maintaining spindle morphology and kif12 and myosin II cleavage furrow recruitment. Cortexillin II is not directly involved in myosin II mechanosensitive accumulation, but without cortexillin I, cortexillin II's role in membrane-cortex attachment is revealed. Finally, the mitotic spindle is dispensable for the system. Overall, this mechanosensory system is structured like a control system characterized by mechanochemical feedback loops that regulate myosin II localization at sites of mechanical stress and the cleavage furrow.

Plant Aurora kinases play a role in maintenance of primary meristems and control of endoreduplication

• The conserved family of Aurora kinases has multiple functions during mitosis. The roles of plant Aurora kinases have been characterized using inhibitor treatments. • We down-regulated Aurora kinases in Arabidopsis thaliana using RNA interference (RNAi). We carried out a detailed phenotypic analysis of Aurora RNAi plants, biochemical and microscopic studies of AtAurora1 kinase together with AtTPX2 (targeting protein for Xklp2) and γ-tubulin. • Cell division defects were observed in plants with reduced expression of Aurora kinases. Furthermore, the maintenance of primary meristems was compromised and RNAi seedlings entered endoreduplication prematurely. AtAurora1, its activator AtTPX2, and γ-tubulin were associated with microtubules in vitro; they were attached to regrowing kinetochore microtubules and colocalized on spindle microtubules and with a subset of early phragmoplast microtubules. Only the AtAurora1 kinase was translocated to the area of the cell plate. • RNAi silencing of Aurora kinases showed that, in addition to their function in regulating mitosis, the kinases are required for maintaining meristematic activity and controlling the switch from meristematic cell proliferation to differentiation and endoreduplication. The colocalization and co-fractionation of AtAurora1 with AtTPX2, and γ-tubulin on microtubules in a cell cycle-specific manner suggests that AtAurora1 kinase may function to phosphorylate substrates that are critical to the spatiotemporal regulation of acentrosomal microtubule formation and organization.

Arabidopsis α Aurora kinases function in formative cell division plane orientation

To establish three-dimensional structures/organs, plant cells continuously have to adapt the orientation of their division plane in a highly regulated manner. However, mechanisms underlying switches in division plane orientation remain elusive. Here, we characterize a viable double knockdown mutant in Arabidopsis thaliana group α Aurora (AUR) kinases, AUR1 and AUR2, (aur1-2 aur2-2), with a primary defect in lateral root formation and outgrowth. Mutant analysis revealed that aur1-2 aur2-2 lateral root primordia are built from randomly oriented cell divisions instead of distinct cell layers. This phenotype could be traced back to cytokinesis defects and misoriented cell plates during the initial anticlinal pericycle cell divisions that give rise to lateral root primordia. Complementation assays showed that the Arabidopsis α group Aurora kinases are functionally divergent from the single β group member AUR3 and that AUR1 functions in division plane orientation prior to cytokinesis. In addition to defective lateral root patterning, aur1-2 aur2-2 plants also show defects in orienting formative divisions during embryogenesis, divisions surrounding the main root stem cell niche, and divisions surrounding stomata formation. Taken together, our results put forward a central role for α Aurora kinases in regulating formative division plane orientation throughout development.

A single starfish Aurora kinase performs the combined functions of Aurora-A and Aurora-B in human cells

Aurora, an essential mitotic kinase, is highly conserved during evolution. Most vertebrates have at least two Aurora kinases, Aurora-A and Aurora-B, which have distinct functions in the centrosome–spindle and inner centromere–midbody, respectively. However, some non-vertebrate deuterostomes have only a single Aurora. It remains to be verified whether the single Aurora performs the same functions as vertebrate Auroras A and B combined. We have isolated a cDNA of a single Aurora (ApAurora) from the echinoderm starfish, Asterina pectinifera, and show that ApAurora displays most features of both Aurora-A and Aurora-B in starfish oocytes and early embryos. Furthermore, ApAurora that is stably expressed in HeLa cells can substitute for both human Aurora-A and Aurora-B when either is reduced by RNAi. A single ApAurora thus has properties of both Aurora-A and Aurora-B in starfish eggs and HeLa cells. Together with phylogenetic analysis indicating that ApAurora forms a clade with all types of vertebrate Auroras and single Auroras of non-vertebrate deuterostomes, our observations support the idea that the single Aurora found in non-vertebrate deuterostomes represents the ancestor that gave rise to various types of vertebrate Auroras. This study thus provides functional evidence for phylogenetic considerations.

14-3-3 coordinates microtubules, Rac, and myosin II to control cell mechanics and cytokinesis

BACKGROUND

During cytokinesis, regulatory signals are presumed to emanate from the mitotic spindle. However, what these signals are and how they lead to the spatiotemporal changes in the cortex structure, mechanics, and regional contractility are not well understood in any system.

RESULTS

To investigate pathways that link the microtubule network to the cortical changes that promote cytokinesis, we used chemical genetics in Dictyostelium to identify genetic suppressors of nocodazole, a microtubule depolymerizer. We identified 14-3-3 and found that it is enriched in the cortex, helps maintain steady-state microtubule length, contributes to normal cortical tension, modulates actin wave formation, and controls the symmetry and kinetics of cleavage furrow contractility during cytokinesis. Furthermore, 14-3-3 acts downstream of a Rac small GTPase (RacE), associates with myosin II heavy chain, and is needed to promote myosin II bipolar thick filament remodeling.

CONCLUSIONS

14-3-3 connects microtubules, Rac, and myosin II to control several aspects of cortical dynamics, mechanics, and cytokinesis cell shape change. Furthermore, 14-3-3 interacts directly with myosin II heavy chain to promote bipolar thick filament remodeling and distribution. Overall, 14-3-3 appears to integrate several critical cytoskeletal elements that drive two important processes-cytokinesis cell shape change and cell mechanics.

Cytokinesis through biochemical-mechanical feedback loops

Cytokinesis is emerging as a control system defined by interacting biochemical and mechanical modules, which form a system of feedback loops. This integrated system accounts for the regulation and kinetics of cytokinesis furrowing and demonstrates that cytokinesis is a whole-cell process in which the global and equatorial cortices and cytoplasm are active players in the system. Though originally defined in Dictyostelium, features of the control system are recognizable in other organisms, suggesting a universal mechanism for cytokinesis regulation and contractility.

Aurora kinases orchestrate mitosis; who are the players?

The Aurora are a conserved family of serine/threonine kinases with essential functions in cell division. In mitosis, Aurora kinases are required for chromosome segregation, condensation and orientation in the metaphase plate, spindle assembly, and the completion of cytokinesis. This review presents the Aurora kinases, their partners and how their interactions impact on the different mitotic functions.

A single amino acid change converts Aurora-A into Aurora-B-like kinase in terms of partner specificity and cellular function

Aurora kinase-A and -B are key regulators of the cell cycle and tumorigenesis. It has remained a mystery why these 2 Aurora kinases, although highly similar in protein sequence and structure, are distinct in subcellular localization and function. Here, we report the striking finding that a single amino acid residue is responsible for these differences. We replaced the Gly-198 of Aurora-A with the equivalent residue Asn-142 of Aurora-B and found that in HeLa cells, Aurora-A(G198N) was recruited to the inner centromere in metaphase and the midzone in anaphase, reminiscent of the Aurora-B localization. Moreover, Aurora-A(G198N) compensated for the loss of Aurora-B in chromosome misalignment and cell premature exit from mitosis. Furthermore, Aurora-A(G198N) formed a complex with the Aurora-B partners, INCENP and Survivin, and its localization depended on this interaction. Aurora-A(G198N) phosphorylated the Aurora-B substrates INCENP and Survivin in vitro. Therefore, we propose that the presence of Gly or Asn at a single site assigns Aurora-A and -B to their respective partners and thus to their distinctive subcellular localizations and functions.