TPX2 phosphorylation maintains metaphase spindle length by regulating microtubule flux

Diverse microtubule-binding repeats regulate TPX2 activities at distinct locations within the spindle

TPX2 is an elongated molecule containing multiple α-helical repeats. It stabilizes microtubules (MTs), promotes MT nucleation, and is essential for spindle assembly. However, the molecular basis of how TPX2 performs these functions remains elusive. Here, we systematically characterized the MT-binding activities of all TPX2 modules individually and in combinations and investigated their respective contributions both in vitro and in cells. We show that TPX2 contains α-helical repeats with opposite preferences for "extended" and "compacted" tubulin dimer spacing, and their distinct combinations produce divergent outcomes, making TPX2 activity highly robust yet tunable. Importantly, a repeat group at the C terminus, R8-9, is the key determinant of the TPX2 function. It stabilizes MTs by promoting rescues in vitro and is critical in spindle assembly. We propose a model where TPX2 activities are spatially regulated via its diverse MT-binding repeats to accommodate its varied functions in distinct locations within the spindle. Furthermore, we reveal a synergy between TPX2 and HURP in stabilizing spindle MTs.

NKX6.3 modulation of mitotic dynamics and genomic stability in gastric carcinogenesis

BACKGROUND

Gastric cancer remains a significant global health challenge, characterized by poor prognosis and high mortality rates. Mitotic integrity and genomic stability are crucial in maintaining cellular homeostasis and preventing tumorigenesis. The transcription factor NKX6.3 has emerged as a potential regulator of these processes in gastric epithelial cells, prompting an investigation into its role in gastric cancer development.

METHODS

We employed a combination of in vitro and in vivo techniques to elucidate the impact of NKX6.3 depletion on mitotic dynamics and genomic stability in gastric epithelial cells. Quantitative real-time PCR and Western blot analyses were conducted to assess the expression of mitosis-related genes and proteins. Flow cytometry was utilized to evaluate cell cycle distribution, while immunofluorescence microscopy enabled the visualization of mitotic abnormalities. Statistical analyses, including Student's t-test and ANOVA, were performed to determine the significance of our findings.

RESULTS

Our results demonstrate that NKX6.3 depletion leads to significant mitotic defects, characterized by increased chromosome misalignment and lagging chromosomes during anaphase. These abnormalities corresponded with elevated levels of genomic instability markers, indicating compromised genomic integrity. Furthermore, the loss of NKX6.3 resulted in altered expression of key regulatory proteins involved in mitosis and DNA repair pathways, suggesting a mechanistic link between NKX6.3 and the maintenance of genomic stability in gastric epithelial cells. Depletion of NKX6.3 resulted in accelerated cell cycle progression and the formation of abnormal mitotic figures, leading to genomic instability characterized by increased DNA content and structural abnormalities. In both in vitro and xenograft models, the depletion of NKX6.3 significantly upregulated AurkA and TPX2, which correlated with gains in DNA copy number. An inverse relationship was observed between NKX6.3 expression and the levels of AurkA and TPX2 in human gastric cancer tissues.

CONCLUSIONS

This study highlights the essential role of NKX6.3 in regulating mitotic integrity and genomic stability in gastric carcinogenesis. The findings suggest that targeting NKX6.3 may offer a novel therapeutic strategy for improving treatment outcomes in gastric cancer by restoring mitotic fidelity and genomic stability.

TRIAL REGISTRATION

This study was not registered.

Centrosome age breaks spindle size symmetry even in cells thought to divide symmetrically

Centrosomes are the main microtubule-organizing centers in animal cells. Due to the semiconservative nature of centrosome duplication, the two centrosomes differ in age. In asymmetric stem cell divisions, centrosome age can induce an asymmetry in half-spindle lengths. However, whether centrosome age affects the symmetry of the two half-spindles in tissue culture cells thought to divide symmetrically is unknown. Here, we show that in human epithelial and fibroblastic cell lines centrosome age imposes a mild spindle asymmetry that leads to asymmetric cell daughter sizes. At the mechanistic level, we show that this asymmetry depends on a cenexin-bound pool of the mitotic kinase Plk1, which favors the preferential accumulation on old centrosomes of the microtubule nucleation-organizing proteins pericentrin, γ-tubulin, and Cdk5Rap2, and microtubule regulators TPX2 and ch-TOG. Consistently, we find that old centrosomes have a higher microtubule nucleation capacity. We postulate that centrosome age breaks spindle size symmetry via microtubule nucleation even in cells thought to divide symmetrically.

NuSAP regulates microtubule flux and Kif2A localization to ensure accurate chromosome congression

Precise chromosome congression and segregation requires the proper assembly of a steady-state metaphase spindle, which is dynamic and maintained by continuous microtubule flux. NuSAP is a microtubule-stabilizing and -bundling protein that promotes chromosome-dependent spindle assembly. However, its function in spindle dynamics remains unclear. Here, we demonstrate that NuSAP regulates the metaphase spindle length control. Mechanistically, NuSAP facilitates kinetochore capture and spindle assembly by promoting Eg5 binding to microtubules. It also prevents excessive microtubule depolymerization through interaction with Kif2A, which reduces Kif2A spindle-pole localization. NuSAP is phosphorylated by Aurora A at Ser-240 during mitosis, and this phosphorylation promotes its interaction with Kif2A on the spindle body and reduces its localization with the spindle poles, thus maintaining proper spindle microtubule flux. NuSAP knockout resulted in the formation of shorter spindles with faster microtubule flux and chromosome misalignment. Taken together, we uncover that NuSAP participates in spindle assembly, dynamics, and metaphase spindle length control through the regulation of microtubule flux and Kif2A localization.

Chromosomal Instability in Gastric Cancer: Role in Tumor Development, Progression, and Therapy

According to the Cancer Genome Atlas (TCGA), gastric cancers are classified into four molecular subtypes: Epstein-Barr virus-positive (EBV+), tumors with microsatellite instability (MSI), tumors with chromosomal instability (CIN), and genomically stable (GS) tumors. However, the gastric cancer (GC) with chromosomal instability remains insufficiently described and does not have effective markers for molecular and histological verification and diagnosis. The CIN subtype of GC is characterized by chromosomal instability, which is manifested by an increased frequency of aneuploidies and/or structural chromosomal rearrangements in tumor cells. Structural rearrangements in the CIN subtype of GC are not accidental and are commonly detected in chromosomal loci, being abnormal because of specific structural organization. The causes of CIN are still being discussed; however, according to recent data, aberrations in the TP53 gene may cause CIN development or worsen its phenotype. Clinically, patients with the CIN subtype of GC demonstrate poor survival, but receive the maximum benefit from adjuvant chemotherapy. In the review, we consider the molecular mechanisms and possible causes of chromosomal instability in GC, the common rearrangements of chromosomal loci and their impact on the development and clinical course of the disease, as well as the driver genes, their functions, and perspectives on their targeting in the CIN subtype of GC.

PP6 regulation of Aurora A-TPX2 limits NDC80 phosphorylation and mitotic spindle size

Amplification of the mitotic kinase Aurora A or loss of its regulator protein phosphatase 6 (PP6) have emerged as drivers of genome instability. Cells lacking PPP6C, the catalytic subunit of PP6, have amplified Aurora A activity, and as we show here, enlarged mitotic spindles which fail to hold chromosomes tightly together in anaphase, causing defective nuclear structure. Using functional genomics to shed light on the processes underpinning these changes, we discover synthetic lethality between PPP6C and the kinetochore protein NDC80. We find that NDC80 is phosphorylated on multiple N-terminal sites during spindle formation by Aurora A-TPX2, exclusively at checkpoint-silenced, microtubule-attached kinetochores. NDC80 phosphorylation persists until spindle disassembly in telophase, is increased in PPP6C knockout cells, and is Aurora B-independent. An Aurora-phosphorylation-deficient NDC80-9A mutant reduces spindle size and suppresses defective nuclear structure in PPP6C knockout cells. In regulating NDC80 phosphorylation by Aurora A-TPX2, PP6 plays an important role in mitotic spindle formation and size control and thus the fidelity of cell division.

NuMA regulates mitotic spindle assembly, structural dynamics and function via phase separation

A functional mitotic spindle is essential for accurate chromosome congression and segregation during cell proliferation; however, the underlying mechanisms of its assembly remain unclear. Here we show that NuMA regulates this assembly process via phase separation regulated by Aurora A. NuMA undergoes liquid-liquid phase separation during mitotic entry and KifC1 facilitates NuMA condensates concentrating on spindle poles. Phase separation of NuMA is mediated by its C-terminus, whereas its dynein-dynactin binding motif also facilitates this process. Phase-separated NuMA droplets concentrate tubulins, bind microtubules, and enrich crucial regulators, including Kif2A, at the spindle poles, which then depolymerizes spindle microtubules and promotes poleward spindle microtubule flux for spindle assembly and structural dynamics. In this work, we show that NuMA orchestrates mitotic spindle assembly, structural dynamics and function via liquid-liquid phase separation regulated by Aurora A phosphorylation.

Corosolic acid reduces A549 and PC9 cell proliferation, invasion, and chemoresistance in NSCLC via inducing mitochondrial and liposomal oxidative stress

Corosolic acid is a pentacyclic triterpenoid isolated from Lagerstroemia speciosa, which is known to inhibit cancer cell proliferations. Whereas, the role of this compound on non-small cell lung cancer (NSCLC) cells still largely unclear. So, the aim of this study was to reveal the regulatory mechanism of corosolic acid to NSCLC. Here, we cultured A549 and PC9 cells in increasing corosolic acid concentrations, as well as treated mice with a physiologically relevant concentration of the compound, and used metabolomics analysis and high-throughput sequencing to examine its influences on cell invasion and proliferation, chemoresistance, and metastasis. We found that corosolic acid inhibited cell invasion and proliferation in vivo and in vitro, as well as increase the chemosensitivity of both cell types to cisplatin. Furthermore, we found that corosolic acid destabilized the glutathione peroxidase 2-mediated redox system, which increased mitochondrial and liposomal oxidative stress. Corosolic acid also decreased the targeting protein for TPX2 level, which inhibited PI3K/AKT signaling and induced apoptosis. In addition, the accumulation of reactive oxygen species dissociated the CCNB1/CDK1 complex and induced G2/M cell cycle arrest. Taken collectively, the data indicate that corosolic acid reduces NSCLC cell invasion and proliferation, as well as chemoresistance, by inducing mitochondrial and liposomal oxidative stress.

Loss of acentriolar MTOCs disrupts spindle pole Aurora A and assembly of the liquid-like meiotic spindle domain in oocytes

Oocyte-specific knockdown of pericentrin (PCNT) in transgenic (Tg) mice disrupts acentriolar microtubule-organizing center (aMTOC) formation, leading to spindle instability and error-prone meiotic division. Here, we show that PCNT-depleted oocytes lack phosphorylated Aurora A (pAURKA) at spindle poles, while overall levels are unaltered. To test aMTOC-associated AURKA function, metaphase II (MII) control (WT) and Tg oocytes were briefly exposed to a specific AURKA inhibitor (MLN8237). Similar defects were observed in Tg and MLN8237-treated WT oocytes, including altered spindle structure, increased chromosome misalignment and impaired microtubule regrowth. Yet, AURKA inhibition had a limited effect on Tg oocytes, revealing a critical role for aMTOC-associated AURKA in regulating spindle stability. Notably, spindle instability was associated with disrupted γ-tubulin and lack of the liquid-like meiotic spindle domain (LISD) in Tg oocytes. Analysis of this Tg model provides the first evidence that LISD assembly depends expressly on aMTOC-associated AURKA, and that Ran-mediated spindle formation ensues without the LISD. These data support that loss of aMTOC-associated AURKA and failure of LISD assembly contribute to error-prone meiotic division in PCNT-depleted oocytes, underscoring the essential role of aMTOCs for spindle stability.

Mitotic poleward flux: Finding balance between microtubule dynamics and sliding

Continuous poleward motion of microtubules in metazoan mitotic spindles has been fascinating generations of cell biologists over the last several decades. In human cells, this so-called poleward flux was recently shown to be driven by the coordinated action of four mitotic kinesins. The sliding activities of kinesin-5/EG5 and kinesin-12/KIF15 are sequentially supported by kinesin-7/CENP-E at kinetochores and kinesin-4/KIF4A on chromosome arms, with the individual contributions peaking during prometaphase and metaphase, respectively. Although recent data elucidate the molecular mechanism underlying this cellular phenomenon, the functional roles of microtubule poleward flux during cell division remain largely elusive. Here, we discuss potential contribution of microtubule flux engine to various essential processes at different stages of mitosis.

The metaphase spindle at steady state - Mechanism and functions of microtubule poleward flux

The mitotic spindle is a bipolar cellular structure, built from tubulin polymers, called microtubules, and interacting proteins. This macromolecular machine orchestrates chromosome segregation, thereby ensuring accurate distribution of genetic material into the two daughter cells during cell division. Powered by GTP hydrolysis upon tubulin polymerization, the microtubule ends exhibit a metastable behavior known as the dynamic instability, during which they stochastically switch between the growth and shrinkage phases. In the context of the mitotic spindle, dynamic instability is furthermore regulated by microtubule-associated proteins and motor proteins, which enables the spindle to undergo profound changes during mitosis. This highly dynamic behavior is essential for chromosome capture and congression in prometaphase, as well as for chromosome alignment to the spindle equator in metaphase and their segregation in anaphase. In this review we focus on the mechanisms underlying microtubule dynamics and sliding and their importance for the maintenance of shape, structure and dynamics of the metaphase spindle. We discuss how these spindle properties are related to the phenomenon of microtubule poleward flux, highlighting its highly cooperative molecular basis and role in keeping the metaphase spindle at a steady state.

CEP215 and AURKA regulate spindle pole focusing and aMTOC organization in mouse oocytes

Acentriolar microtubule-organizing centers (aMTOCs) play a critical role in stable meiotic spindle assembly in oocytes, necessary for accurate chromosome segregation. Yet, there is a limited understanding of the essential regulatory components of these unique MTOCs. In somatic cells, CEP215 (Centrosomal Protein 215) serves as an important regulator of centrosome maturation and spindle organization. Here, we assessed whether it has a similar function in mouse oocytes. CEP215 was detected in oocyte lysates and specifically localized to aMTOCs throughout the progression of meiosis in a pericentrin-dependent manner. Super-resolution microscopy revealed CEP215 co-localization with pericentrin and a unique pore/ring-like structural organization of aMTOCs. Interestingly, inhibition of Aurora Kinase A in either MI or MII-stage oocytes resulted in a striking loss of the ring-like aMTOC organization and pronounced CEP215 clustering at spindle poles, as well as shorter spindles with highly focused poles. In vitro siRNA-mediated transcript knockdown effectively reduced CEP215 in approximately 85% of the oocytes. Maturation rates to MII were similar in the Cep215 siRNA and injected controls; however, a high percentage (~40%) of the Cep215-knockdown oocytes showed notable variations in spindle pole focusing. Surprisingly, pericentrin and γ-tubulin localization and fluorescence intensity at aMTOCs were unaltered in knockdown oocytes, contrasting with mitotic cells where CEP215 depletion reduced γ-tubulin at centrosomes. Our results demonstrate that CEP215 is a functional component of oocyte aMTOCs and participates in the regulation of meiotic spindle pole focusing. Moreover, these studies reveal a vital role for Aurora Kinase A activity in the maintenance of aMTOC organization in oocytes.

Aurora kinase A is essential for meiosis in mouse oocytes

The Aurora protein kinases are well-established regulators of spindle building and chromosome segregation in mitotic and meiotic cells. In mouse oocytes, there is significant Aurora kinase A (AURKA) compensatory abilities when the other Aurora kinase homologs are deleted. Whether the other homologs, AURKB or AURKC can compensate for loss of AURKA is not known. Using a conditional mouse oocyte knockout model, we demonstrate that this compensation is not reciprocal because female oocyte-specific knockout mice are sterile, and their oocytes fail to complete meiosis I. In determining AURKA-specific functions, we demonstrate that its first meiotic requirement is to activate Polo-like kinase 1 at acentriolar microtubule organizing centers (aMTOCs; meiotic spindle poles). This activation induces fragmentation of the aMTOCs, a step essential for building a bipolar spindle. We also show that AURKA is required for regulating localization of TACC3, another protein required for spindle building. We conclude that AURKA has multiple functions essential to completing MI that are distinct from AURKB and AURKC.

Spindle scaling mechanisms

The mitotic spindle robustly scales with cell size in a plethora of different organisms. During development and throughout evolution, the spindle adjusts to cell size in metazoans and yeast in order to ensure faithful chromosome separation. Spindle adjustment to cell size occurs by the scaling of spindle length, spindle shape and the velocity of spindle assembly and elongation. Different mechanisms, depending on spindle structure and organism, account for these scaling relationships. The limited availability of critical spindle components, protein gradients, sequestration of spindle components, or post-translational modification and differential expression levels have been implicated in the regulation of spindle length and the spindle assembly/elongation velocity in a cell size-dependent manner. In this review, we will discuss the phenomenon and mechanisms of spindle length, spindle shape and spindle elongation velocity scaling with cell size.

Reciprocal regulation of Aurora kinase A and ATIP3 in the control of metaphase spindle length

Maintaining the integrity of the mitotic spindle in metaphase is essential to ensure normal cell division. We show here that depletion of microtubule-associated protein ATIP3 reduces metaphase spindle length. Mass spectrometry analyses identified the microtubule minus-end depolymerizing kinesin Kif2A as an ATIP3 binding protein. We show that ATIP3 controls metaphase spindle length by interacting with Kif2A and its partner Dda3 in an Aurora kinase A-dependent manner. In the absence of ATIP3, Kif2A and Dda3 accumulate at spindle poles, which is consistent with reduced poleward microtubule flux and shortening of the spindle. ATIP3 silencing also limits Aurora A localization to the poles. Transfection of GFP-Aurora A, but not kinase-dead mutant, rescues the phenotype, indicating that ATIP3 maintains Aurora A activity on the poles to control Kif2A targeting and spindle size. Collectively, these data emphasize the pivotal role of Aurora kinase A and its mutual regulation with ATIP3 in controlling spindle length.

Targeting AURKA in Cancer: molecular mechanisms and opportunities for Cancer therapy

Aurora kinase A (AURKA) belongs to the family of serine/threonine kinases, whose activation is necessary for cell division processes via regulation of mitosis. AURKA shows significantly higher expression in cancer tissues than in normal control tissues for multiple tumor types according to the TCGA database. Activation of AURKA has been demonstrated to play an important role in a wide range of cancers, and numerous AURKA substrates have been identified. AURKA-mediated phosphorylation can regulate the functions of AURKA substrates, some of which are mitosis regulators, tumor suppressors or oncogenes. In addition, enrichment of AURKA-interacting proteins with KEGG pathway and GO analysis have demonstrated that these proteins are involved in classic oncogenic pathways. All of this evidence favors the idea of AURKA as a target for cancer therapy, and some small molecules targeting AURKA have been discovered. These AURKA inhibitors (AKIs) have been tested in preclinical studies, and some of them have been subjected to clinical trials as monotherapies or in combination with classic chemotherapy or other targeted therapies.

Phospho-regulation of mitotic spindle assembly

The assembly of the bipolar mitotic spindle requires the careful orchestration of a myriad of enzyme activities like protein posttranslational modifications. Among these, phosphorylation has arisen as the principle mode for spatially and temporally activating the proteins involved in early mitotic spindle assembly processes. Here, we review key kinases, phosphatases, and phosphorylation events that regulate critical aspects of these processes. We highlight key phosphorylation substrates that are important for ensuring the fidelity of centriole duplication, centrosome maturation, and the establishment of the bipolar spindle. We also highlight techniques used to understand kinase-substrate relationships and to study phosphorylation events. We conclude with perspectives on the field of posttranslational modifications in early mitotic spindle assembly.

Microtubule poleward flux in human cells is driven by the coordinated action of four kinesins

Mitotic spindle microtubules (MTs) undergo continuous poleward flux, whose driving force and function in humans remain unclear. Here, we combined loss-of-function screenings with analysis of MT-dynamics in human cells to investigate the molecular mechanisms underlying MT-flux. We report that kinesin-7/CENP-E at kinetochores (KTs) is the predominant driver of MT-flux in early prometaphase, while kinesin-4/KIF4A on chromosome arms facilitates MT-flux during late prometaphase and metaphase. Both these activities work in coordination with kinesin-5/EG5 and kinesin-12/KIF15, and our data suggest that the MT-flux driving force is transmitted from non-KT-MTs to KT-MTs by the MT couplers HSET and NuMA. Additionally, we found that the MT-flux rate correlates with spindle length, and this correlation depends on the establishment of stable end-on KT-MT attachments. Strikingly, we find that MT-flux is required to regulate spindle length by counteracting kinesin 13/MCAK-dependent MT-depolymerization. Thus, our study unveils the long-sought mechanism of MT-flux in human cells as relying on the coordinated action of four kinesins to compensate for MT-depolymerization and regulate spindle length.

Mechanisms of spindle assembly and size control

The spindle is crucial for cell division by allowing the faithful segregation of replicated chromosomes to daughter cells. Proper segregation is ensured only if microtubules (MTs) and hundreds of other associated factors interact to assemble this complex structure with the appropriate architecture and size. In this review, we describe the latest view of spindle organisation as well as the molecular gradients and mechanisms underlying MT nucleation and spindle assembly. We then discuss the overlapping physical and molecular constraints that dictate spindle morphology, concluding with a focus on spindle size regulation.

CircPOSTN/miR-361-5p/TPX2 axis regulates cell growth, apoptosis and aerobic glycolysis in glioma cells

Background

Glioma is the most primary central nervous system tumor in adults. The 5 year survival rate for glioma patients remains poor, although treatment strategies had improved in the past few decades. The cumulative studies have shown that circular RNA (circRNA) is associated with glioma process, so the purpose of this study is to clarify the function of circPOSTN in glioma.

Methods

The expression levels of circPOSTN, miR-361-5p, and targeting protein for Xenopus kinesin-like protein 2 (TPX2) were assessed with real-time quantitative polymerase chain reaction (RT-qPCR). The 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl-2H-tetrazol-3-ium bromide (MTT) and flow cytometry assays were executed to examine proliferation and apoptosis of glioma cells, respectively. Western blot was applied to assess protein expression. The glucose metabolism of glioma cells was analyzed by testing the glucose consumption, lactate production, ATP level, reactive oxygen species (ROS) accumulation and performing Seahorse XF assay. The interaction relationship between miR-361-5p and circPOSTN or TPX2 was analyzed by bioinformatics database and dual-luciferase reporter assay. The influences of circPOSTN silencing in vivo were observed by a xenograft experiment.

Results

CircPOSTN was overexpressed in glioma tissues and cells. Absence of circPOSTN in glioma cells promoted apoptosis while impeded proliferation and aerobic glycolysis, which were mitigated by silencing miR-361-5p. What’s more, loss-of-functional experiment suggested that knockdown of TPX2 repressed proliferation and aerobic glycolysis, while induced apoptosis in glioma cells. In addition, circPOSTN targetedly regulated TPX2 expression in glioma cells via sponging miR-361-5p. In vivo study revealed that deficiency of circPOSTN restrained tumor growth.

Conclusion

Mechanistically, circPOSTN regulated cell growth, apoptosis, and aerobic glycolysis in glioma through miR-361-5p/TPX2 axis.

Identification of early stage recurrence endometrial cancer biomarkers using bioinformatics tools

Endometrial cancer (EC) is the sixth most common cancer in women worldwide. Early diagnosis is critical in recurrent EC management. The present study aimed to identify biomarkers of EC early recurrence using a workflow that combined text and data mining databases (DisGeNET, Gene Expression Omnibus), a prioritization algorithm to select a set of putative candidates (ToppGene), protein-protein interaction network analyses (Search Tool for the Retrieval of Interacting Genes, cytoHubba), association analysis of selected genes with clinicopathological parameters, and survival analysis (Kaplan-Meier and Cox proportional hazard ratio analyses) using a The Cancer Genome Atlas cohort. A total of 10 genes were identified, among which the targeting protein for Xklp2 (TPX2) was the most promising independent prognostic biomarker in stage I EC. TPX2 expression (mRNA and protein) was higher (P<0.0001 and P<0.001, respectively) in ETS variant transcription factor 5-overexpressing Hec1a and Ishikawa cells, a previously reported cell model of aggressive stage I EC. In EC biopsies, TPX2 mRNA expression levels were higher (P<0.05) in high grade tumors (grade 3) compared with grade 1–2 tumors (P<0.05), in tumors with deep myometrial invasion (>50% compared with <50%; P<0.01), and in intermediate-high recurrence risk tumors compared with low-risk tumors (P<0.05). Further validation studies in larger and independent EC cohorts will contribute to confirm the prognostic value of TPX2.

Nocodazole-Induced Expression and Phosphorylation of Anillin and Other Mitotic Proteins Are Decreased in DNA-Dependent Protein Kinase Catalytic Subunit-Deficient Cells and Rescued by Inhibition of the Anaphase-Promoting Complex/Cyclosome with proTAME but Not Apcin

The DNA-dependent protein kinase catalytic subunit (DNA-PKcs) has well-established roles in DNA double-strand break repair, and recently, nonrepair functions have also been reported. To better understand its cellular functions, we deleted DNA-PKcs from HeLa and A549 cells using CRISPR/Cas9. The resulting cells were radiation sensitive, had reduced expression of ataxia-telangiectasia mutated (ATM), and exhibited multiple mitotic defects. Mechanistically, nocodazole-induced upregulation of cyclin B1, anillin, and securin was decreased in DNA-PKcs-deficient cells, as were phosphorylation of Aurora A on threonine 288, phosphorylation of Polo-like kinase 1 (PLK1) on threonine 210, and phosphorylation of targeting protein for Xenopus Klp2 (TPX2) on serine 121. Moreover, reduced nocodazole-induced expression of anillin, securin, and cyclin B1 and phosphorylation of PLK1, Aurora A, and TPX2 were rescued by inhibition of the anaphase-promoting complex/cyclosome (APC/C) by proTAME, which prevents binding of the APC/C-activating proteins Cdc20 and Cdh1 to the APC/C. Altogether, our studies suggest that loss of DNA-PKcs prevents inactivation of the APC/C in nocodazole-treated cells.

Mitotic kinase anchoring proteins: the navigators of cell division

The coordinated activities of many protein kinases, acting on multiple protein substrates, ensures the error-free progression through mitosis of eukaryotic cells. Enormous research effort has thus been devoted to studying the roles and regulation of these mitotic kinases, and to the identification of their physiological substrates. Central for the timely deployment of specific protein kinases to their appropriate substrates during the cell division cycle are the many anchoring proteins, which serve critical regulatory roles. Through direct association, anchoring proteins are capable of modulating the catalytic activity and/or sub-cellular distribution of the mitotic kinases they associate with. The key roles of some anchoring proteins in cell division are well-established, whilst others are still being unearthed. Here, we review the current knowledge on anchoring proteins for some mitotic kinases, and highlight how targeting anchoring proteins for inhibition, instead of the mitotic kinases themselves, could be advantageous for disrupting the cell division cycle.

Phosphorylation of importin-α1 by CDK1-cyclin B1 controls mitotic spindle assembly

Importin-α serves as an adaptor linking importin-β to proteins carrying a nuclear localization sequence (NLS). During interphase, this interaction enables nuclear protein import, while in mitosis it regulates spindle assembly factors (SAFs) and controls microtubule nucleation, stabilization and spindle function. Here, we show that human importin-α1 is regulated during the cell cycle and is phosphorylated at two sites (threonine 9 and serine 62) during mitosis by the major mitotic protein kinase CDK1-cyclin B. Mutational analysis indicates that the mitotic phosphorylation of importin-α1 inhibits its binding to importin-β and promotes the release of TPX2 and KIFC1, which are then targeted like importin-β to the spindle. Loss of importin-α1 or expression of a non-phosphorylated mutant of importin-α1 results in the formation of shortened spindles with reduced microtubule density and induces a prolonged metaphase, whereas phosphorylation-mimicking mutants are functional in mitosis. We propose that phosphorylation of importin-α1 is a general mechanism for the spatial and temporal control of mitotic spindle assembly by CDK1-cyclin B1 that acts through the release of SAFs such as TPX2 and KIFC1 from inhibitory complexes that restrict spindle assembly.

Prognostic significance of TOP2A in non-small cell lung cancer revealed by bioinformatic analysis

Background

Lung cancer has been a common malignant tumor with a leading cause of morbidity and mortality, current molecular targets are woefully lacking comparing to the highly progressive cancer. The study is designed to identify new prognostic predictors and potential gene targets based on bioinformatic analysis of Gene Expression Omnibus (GEO) database.

Methods

Four cDNA expression profiles GSE19188, GSE101929, GSE18842 and GSE33532 were chosen from GEO database to analyze the differently expressed genes (DEGs) between non-small cell lung cancer (NSCLC) and normal lung tissues. After the DEGs functions were analyzed, the protein-protein interaction network (PPI) of DEGs were constructed, and the core gene in the network which has high connectivity degree with other genes was identified. We analyzed the association of the gene with the development of NSCLC as well as its prognosis. Lastly we explored the conceivable signaling mechanism of the gene regulation during the development of NSCLC.

Results

A total of 92 up regulated and 214 down regulated DEGs were shared in four cDNA expression profiles. Based on their PPI network, TOP2A was connected with most of other genes and was selected for further analysis. Kaplan-Meier overall survival analysis (OS) revealed that TOP2A was associated with worse NSCLC patients survival. And both GEPIA analysis and immunohistochemistry experiment (IHC) confirmed that TOP2A was aberrant gain of expression in cancer comparing to normal tissues. The clinical significance of TOP2A and probable signaling pathways it involved in were further explored, and a positive correlation between TOP2A and TPX2 expression was found in lung cancer tissues.

Conclusion

Using bioinformatic analysis, we revealed that TOP2A could be adopted as a prognostic indicator of NSCLC and it potentially regulate cancer development through co-work with TPX2. However, more detailed experiments are needed to clarify its drug target role in clinical medical use.

A Transcriptomic Insight into the Impact of Colon Cancer Cells on Mast Cells

Mast cells (MCs) are one of the first immune cells recruited to a tumor. It is well recognized that MCs accumulate in colon cancer lesion and their density is associated with the clinical outcomes. However, the molecular mechanism of how colon cancer cells may modify MC function is still unclear. In this study, primary human MCs were generated from CD34⁺ progenitor cells and a 3D coculture model was developed to study the interplay between colon cancer cells and MCs. By comparing the transcriptomic profile of colon cancer-cocultured MCs versus control MCs, we identified a number of deregulated genes, such as MMP-2, VEGF-A, PDGF-A, COX2, NOTCH1 and ISG15, which contribute to the enrichment of cancer-related pathways. Intriguingly, pre-stimulation with a TLR2 agonist prior to colon cancer coculture induced upregulation of multiple interferon-inducible genes as well as MHC molecules in MCs. Our study provides an alternative approach to study the influence of colon cancer on MCs. The transcriptome signature of colon cancer-cocultured MCs may potentially reflect the mechanism of how colon cancer cells educate MCs to become pro-tumorigenic in the initial phase and how a subsequent inflammatory signal—e.g., TLR2 ligands—may modify their responses in the cancer milieu.

Lysine-specific demethylase 2A enhances binding of various nuclear factors to CpG-rich genomic DNAs by action of its CXXC-PHD domain

The lysine-specific demethylase 2A gene (KDM2A) is ubiquitously expressed and its transcripts consist of several alternatively spliced forms, including KDM2A and the shorter form N782 that lacks the 3' end encoding F-box and LRR. KDM2A binds to numerous CpG-rich genomic loci and regulates various cellular activities; however, the mechanism of the pleiotropic function is unknown. Here, we identify the mechanism of KDM2A played by its CXXC-PHD domain. KDM2A is necessary for a rapid proliferation of post-natal keratinocytes while its 3' end eclipses the stimulatory effect. EGFP-N782 binds to chromatin together with the XRCC5/6 complex, and the CXXC-PHD domain regulates the CpG-rich IGFBPL1 promoter. In vitro, CXXC-PHD enhances binding of nuclear extract ORC3 to the CpG-rich promoter, but not to the AT-rich DIP2B promoter to which ORC3 binds constitutively. Furthermore, CXXC-PHD recruits 94 nuclear factors involved in replication, ribosome synthesis, and mitosis, including POLR1A to the IGFBPL1 promoter. This recruitment is unprecedented; however, the result suggests that these nuclear factors bind to their cognate loci, as substantiated by the result that CXXC-PHD recruits POLR1A to the rDNA promoter. We propose that CXXC-PHD promotes permissiveness for nuclear factors to interact, but involvement of the XRCC5/6 complex in the recruitment is undetermined.

A rapid computational approach identifies SPICE1 as an Aurora kinase substrate

Aurora kinases play a major role in mitosis by regulating diverse substrates. Defining their critical downstream targets is important in understanding Aurora kinase function. Here we have developed an unbiased computational approach to identify new Aurora kinase substrates based on phosphorylation site clustering, protein localization, protein structure, and species conservation. We validate the microtubule-associated proteins Clasp2, Elys, tubulin tyrosine ligase-like polyglutamylase residues 330-624 and spindle and centriole associated protein 1, residues 549-855 (SPICE1), as Aurora A and B kinases substrates in vitro. We also demonstrate that SPICE1 localization is regulated by Aurora kinases during mitosis. In the absence of Aurora kinase activity, SPICE1 remains at centrioles but does not target to the spindle. Similarly, a nonphosphorylatable SPICE1 mutant no longer localizes to the spindle. Finally, we show that misregulating SPICE1 phosphorylation results in abnormal centriole number, spindle multipolarity, and chromosome alignment defects. Overall, our work indicates that temporal and spatial Aurora kinase-mediated regulation of SPICE1 is important for correct chromosome segregation. In addition, our work provides a database-search tool that enables rapid identification of Aurora kinase substrates.

Overexpression of TPX2 is associated with progression and prognosis of prostate cancer

Targeting protein for Xenopus kinesin-like protein 2 (TPX2) activates Aurora kinase A during mitosis and targets its activity to the mitotic spindle, serving an important role in mitosis. It has been associated with different types of cancer and is considered to promote tumor growth. The aim of the present study was to explore the role of TPX2 in diagnosing prostate cancer (PCa). It was identified that TPX2 expression in PCa tissues was increased compared with benign prostate tissues. Microarray analysis demonstrated that TPX2 was positively associated with the Gleason score, tumor-node-metastasis (TNM) stage, clinicopathological stage, metastasis, overall survival and biochemical relapse-free survival. In vitro studies revealed that the high expression of TPX2 in PCa cells improved proliferative, invasive and migratory abilities, and repressed apoptosis of the PCa cells, without affecting tolerance to docetaxel. The results suggested that TPX2 serves as a tumorigenesis-promoting gene in PCa, and a potential therapeutic target for patients with PCa.

Adducin-1 is essential for spindle pole integrity through its interaction with TPX2

Bipolar spindle assembly is necessary to ensure the proper progression of cell division. Loss of spindle pole integrity leads to multipolar spindles and aberrant chromosomal segregation. However, the mechanism underlying the maintenance of spindle pole integrity remains unclear. In this study, we show that the actin‐binding protein adducin‐1 (ADD1) is phosphorylated at S726 during mitosis. S726‐phosphorylated ADD1 localizes to centrosomes, wherein it organizes into a rosette‐like structure at the pericentriolar material. ADD1 depletion causes centriole splitting and therefore results in multipolar spindles during mitosis, which can be restored by re‐expression of ADD1 and the phosphomimetic S726D mutant but not by the S726A mutant. Moreover, the phosphorylation of ADD1 at S726 is crucial for its interaction with TPX2, which is essential for spindle pole integrity. Together, our findings unveil a novel function of ADD1 in maintaining spindle pole integrity through its interaction with TPX2.

Spindle assembly in egg extracts of the Marsabit clawed frog, Xenopus borealis

Egg extracts of the African clawed frog Xenopus laevis have provided a cell-free system instrumental in elucidating events of the cell cycle, including mechanisms of spindle assembly. Comparison with extracts from the diploid Western clawed frog, Xenopus tropicalis, which is smaller at the organism, cellular and subcellular levels, has enabled the identification of spindle size scaling factors. We set out to characterize the Marsabit clawed frog, Xenopus borealis, which is intermediate in size between the two species, but more recently diverged in evolution from X. laevis than X. tropicalis. X. borealis eggs were slightly smaller than those of X. laevis, and slightly smaller spindles were assembled in egg extracts. Interestingly, microtubule distribution across the length of the X. borealis spindles differed from both X. laevis and X. tropicalis. Extract mixing experiments revealed common scaling phenomena among Xenopus species, while characterization of spindle factors katanin, TPX2, and Ran indicate that X. borealis spindles possess both X. laevis and X. tropicalis features. Thus, X. borealis egg extract provides a third in vitro system to investigate interspecies scaling and spindle morphometric variation.

A guide to classifying mitotic stages and mitotic defects in fixed cells

Cell division is fundamental to life and its perturbation can disrupt organismal development, alter tissue homeostasis, and cause disease. Analysis of mitotic abnormalities provides insight into how certain perturbations affect the fidelity of cell division and how specific cellular structures, molecules, and enzymatic activities contribute to the accuracy of this process. However, accurate classification of mitotic defects is instrumental for correct interpretation of data and formulation of new hypotheses. In this article, we provide guidelines for identifying specific mitotic stages and for classifying normal and deviant mitotic phenotypes. We hope this will clarify confusion about how certain defects are classified and help investigators avoid misnomers, misclassification, and/or misinterpretation, thus leading to a unified and standardized system to classify mitotic defects.

MicroRNA-1294 inhibits the proliferation and enhances the chemosensitivity of glioma to temozolomide via the direct targeting of TPX2

MicroRNA-1294 (miR-1294) has been reported to be involved in the progression of esophageal squamous cell carcinoma. However, the function and the mechanisms of miR-1294 in glioma remain unclear. In this study, we explore the potential biological roles of miR-1294 in glioma cell lines. First, we detected the aberrant down-regulation of miR-1294 in glioma tissues and cell lines. Second, we determined that miR-1294 suppresses the proliferation, migration and invasiveness and enhances the chemosensitivity of glioma cells lines to temozolomide. Third, we found that the targeting protein for Xenopus kinesin-like protein 2 (TPX2) is the functional target of miR-1294; miR-1294 acts through TPX2 to exert an important biological effect in glioma. Importantly, TPX2 knockdown had the same effect on glioma cell lines as miR-1294 overexpression. In addition, when TPX2 was up-regulated in these cells, the effects of miR-1294 on glioma cell lines were suppressed. Moreover, the effect of miR-1294 on glioma was verified using a xenograft model. These findings demonstrated that miR-1294 inhibits the development of glioma by targeting TPX2. These findings provide a new potential therapeutic target for glioma treatment.

Eml1 loss impairs apical progenitor spindle length and soma shape in the developing cerebral cortex

The ventricular zone (VZ) of the developing cerebral cortex is a pseudostratified epithelium that contains progenitors undergoing precisely regulated divisions at its most apical side, the ventricular lining (VL). Mitotic perturbations can contribute to pathological mechanisms leading to cortical malformations. The HeCo mutant mouse exhibits subcortical band heterotopia (SBH), likely to be initiated by progenitor delamination from the VZ early during corticogenesis. The causes for this are however, currently unknown. Eml1, a microtubule (MT)-associated protein of the EMAP family, is impaired in these mice. We first show that MT dynamics are perturbed in mutant progenitor cells in vitro. These may influence interphase and mitotic MT mechanisms and indeed, centrosome and primary cilia were altered and spindles were found to be abnormally long in HeCo progenitors. Consistently, MT and spindle length regulators were identified in EML1 pulldowns from embryonic brain extracts. Finally, we found that mitotic cell shape is also abnormal in the mutant VZ. These previously unidentified VZ characteristics suggest altered cell constraints which may contribute to cell delamination.

Aurora A activation in mitosis promoted by BuGZ

Mitotic spindle component BuGZ is known to undergo phase separation. Huang et al. show that BuGZ promotes Aurora A phosphorylation and activation and that this is inhibited when BuGZ phase separation is disrupted.

Protein phase separation or coacervation has emerged as a potential mechanism to regulate biological functions. We have shown that coacervation of a mostly unstructured protein, BuGZ, promotes assembly of spindle and its matrix. BuGZ in the spindle matrix binds and concentrates tubulin to promote microtubule (MT) assembly. It remains unclear, however, whether BuGZ could regulate additional proteins to promote spindle assembly. In this study, we report that BuGZ promotes Aurora A (AurA) activation in vitro. Depletion of BuGZ in cells reduces the amount of phosphorylated AurA on spindle MTs. BuGZ also enhances MCAK phosphorylation. The two zinc fingers in BuGZ directly bind to the kinase domain of AurA, which allows AurA to incorporate into the coacervates formed by BuGZ in vitro. Importantly, mutant BuGZ that disrupts the coacervation activity in vitro fails to promote AurA phosphorylation in Xenopus laevis egg extracts. These results suggest that BuGZ coacervation promotes AurA activation in mitosis.

Mitotic Spindle Assembly and Genomic Stability in Breast Cancer Require PI3K-C2α Scaffolding Function

Proper organization of the mitotic spindle is key to genetic stability, but molecular components of inter-microtubule bridges that crosslink kinetochore fibers (K-fibers) are still largely unknown. Here we identify a kinase-independent function of class II phosphoinositide 3-OH kinase α (PI3K-C2α) acting as limiting scaffold protein organizing clathrin and TACC3 complex crosslinking K-fibers. Downregulation of PI3K-C2α causes spindle alterations, delayed anaphase onset, and aneuploidy, indicating that PI3K-C2α expression is required for genomic stability. Reduced abundance of PI3K-C2α in breast cancer models initially impairs tumor growth but later leads to the convergent evolution of fast-growing clones with mitotic checkpoint defects. As a consequence of altered spindle, loss of PI3K-C2α increases sensitivity to taxane-based therapy in pre-clinical models and in neoadjuvant settings.

FAM83D, a microtubule-associated protein, promotes tumor growth and progression of human gastric cancer

FAM83D, a microtubule-associated protein (MAP), is overexpressed in diverse types of human cancer. The expression and critical role of FAM83D in human gastric cancer (GC), however, remains largely unknown. Here, we conducted molecular, cellular and clinical analyses to evaluate the functional link of FAM83D to GC. FAM83D expression was elevated in gastric tumors, and its expression strongly correlated with lymph node metastasis and TNM stage. In addition, over-expression of FAM83D in GC cell lines enhanced cell proliferation, cycle progression, migration, invasion, as well as tumor growth and metastatic dissemination in vivo. Furthermore, FAM83D exhibited a strong cell cycle correlated expression. The knockdown of FAM83D inhibited the regrowth of microtubules in GC cells. FAM83D was co-immunoprecipitated with HMMR, TPX2, and AURKA, a set of drivers of mitosis progression. Taken together, our results demonstrate FAM83D as an important player in the development of human gastric cancer, and as a potential therapeutic target for the treatment of cancer.

AURKA, DLGAP5, TPX2, KIF11 and CKAP5: Five specific mitosis-associated genes correlate with poor prognosis for non-small cell lung cancer patients

The growth of a tumor depends to a certain extent on an increase in mitotic events. Key steps during mitosis are the regulated assembly of the spindle apparatus and the separation of the sister chromatids. The microtubule-associated protein Aurora kinase A phosphorylates DLGAP5 in order to correctly segregate the chromatids. Its activity and recruitment to the spindle apparatus is regulated by TPX2. KIF11 and CKAP5 control the correct arrangement of the microtubules and prevent their degradation. In the present study, we investigated the role of these five molecules in non-small cell lung cancer (NSCLC). We analyzed the expression of the five genes in a large cohort of NSCLC patients (n=362) by quantitative real-time PCR. Each of the genes was highly overexpressed in the tumor tissues compared to corresponding normal lung tissue. The correlation of the expression of the individual genes depended on the histology. An increased expression of AURKA, DLGAP5, TPX2, KIF11 and CKAP5 was associated with poor overall survival (P=0.001–0.065). AURKA was a significant prognostic marker using multivariate analyses (P=0.006). Immunofluorescence studies demonstrated that the five mitosis-associated proteins co-localized with the spindle apparatus during cell division. Taken together, our data demonstrate that the expression of the mitosis-associated genes AURKA, DLGAP5, TPX2, KIF11 and CKAP5 is associated with the prognosis of NSCLC patients.

Regulation of Kif15 localization and motility by the C-terminus of TPX2 and microtubule dynamics

Mitotic motor proteins generate force to establish and maintain spindle bipolarity, but how they are temporally and spatially regulated in vivo is unclear. Prior work demonstrated that a microtubule-associated protein, TPX2, targets kinesin-5 and kinesin-12 motors to spindle microtubules. The C-terminal domain of TPX2 contributes to the localization and motility of the kinesin-5, Eg5, but it is not known whether this domain regulates kinesin-12, Kif15. We found that the C-terminal domain of TPX2 contributes to the localization of Kif15 to spindle microtubules in cells and suppresses motor walking in vitro. Kif15 and Eg5 are partially redundant motors, and overexpressed Kif15 can drive spindle formation in the absence of Eg5 activity. Kif15-dependent bipolar spindle formation in vivo requires the C-terminal domain of TPX2. In the spindle, fluorescent puncta of GFP-Kif15 move toward the equatorial region at a rate equivalent to microtubule growth. Reduction of microtubule growth with paclitaxel suppresses GFP-Kif15 motility, demonstrating that dynamic microtubules contribute to Kif15 behavior. Our results show that the C-terminal region of TPX2 regulates Kif15 in vitro, contributes to motor localization in cells, and is required for Kif15 force generation in vivo and further reveal that dynamic microtubules contribute to Kif15 behavior in vivo.

Accurate measurement of poleward microtubule flux in the spindle of Drosophila S2 cells

The spindle microtubule (MT) flux is the continuous translocation of MTs toward the spindle poles caused by MT polymerization at plus ends coupled to depolymerization at minus ends. Poleward flux is observed in both mitotic and meiotic spindles; it is evolutionarily conserved and contributes to the regulation of spindle length and anaphase chromosome movement. MT photobleaching is a tool frequently used to measure poleward flux. Spindles containing fluorescently tagged tubulin are photobleached to generate a non-fluorescent stripe, which moves toward the spindle poles allowing a measure of the flux. However, this method only permits rapid measurements of the flux, because the fluorescence of the bleached stripe recovers rapidly due to the spindle MT turnover. Here, we describe a modification of the current photobleaching-based method for flux measurement. We photobleached two large areas at the opposite sides of the metaphase plate in spindles of Drosophila S2 cells expressing Cherry-tagged tubulin, leaving unbleached only the area near the chromosomes. We then measured the speed with which the fluorescent MTs move toward the poles. We found that this method allows a measure of the flux over a two- to threefold longer time than the "single stripe" method, providing a reliable evaluation of the flux rate.

Non-centrosomal TPX2-Dependent Regulation of the Aurora A Kinase: Functional Implications for Healthy and Pathological Cell Division

Aurora A has been extensively characterized as a centrosomal kinase with essential functions during cell division including centrosome maturation and separation and spindle assembly. However, Aurora A localization is not restricted to the centrosomes and compelling evidence support the existence of specific mechanisms of activation and functions for non-centrosomal Aurora A in the dividing cell. It has been now well established that spindle assembly involves an acentrosomal RanGTP-dependent pathway that triggers microtubule assembly and organization in the proximity of the chromosomes whether centrosomes are present or not. The mechanism involves the regulation of a number of NLS-containing proteins, generically called SAFS (Spindle Assembly Factors) that exert their functions upon release from karyopherins by RanGTP. One of them, the nuclear protein TPX2 interacts with and activates Aurora A upon release from importins by RanGTP. This basic mechanism triggers the activation of Aurora A in the proximity of the chromosomes potentially translating the RanGTP signaling gradient centered on the chromosome into an Aurora A phosphorylation network. Here, we will review our current knowledge on the RanGTP-dependent TPX2 activation of Aurora A away from centrosomes: from the mechanism of activation and its functional consequences on the kinase stability and regulation to its roles in spindle assembly and cell division. We will then focus on the substrates of the TPX2-activated Aurora A having a role in microtubule nucleation, stabilization, and organization. Finally, we will briefly discuss the implications of the use of Aurora A inhibitors in anti-tumor therapies in the light of its functional interaction with TPX2.

A Balance between Nuclear and Cytoplasmic Volumes Controls Spindle Length

Proper assembly of the spindle apparatus is crucially important for faithful chromosome segregation during anaphase. Thanks to the effort over the last decades, we have very detailed information about many events leading to spindle assembly and chromosome segregation, however we still do not understand certain aspects, including, for example, spindle length control. When tight regulation of spindle size is lost, chromosome segregation errors emerge. Currently, there are several hypotheses trying to explain the molecular mechanism of spindle length control. The number of kinetochores, activity of molecular rulers, intracellular gradients, cell size, limiting spindle components, and the balance of the spindle forces seem to contribute to spindle size regulation, however some of these mechanisms are likely specific to a particular cell type. In search for a general regulatory mechanism, in our study we focused on the role of cell size and nuclear to cytoplasmic ratio in this process. To this end, we used relatively large cells isolated from 2-cell mouse embryos. Our results showed that the spindle size upper limit is not reached in these cells and suggest that accurate control of spindle length requires balanced ratio between nuclear and cytoplasmic volumes.

The Ran Pathway in Drosophila melanogaster Mitosis

Over the last two decades, the small GTPase Ran has emerged as a central regulator of both mitosis and meiosis, particularly in the generation, maintenance, and regulation of the microtubule (MT)-based bipolar spindle. Ran-regulated pathways in mitosis bear many similarities to the well-characterized functions of Ran in nuclear transport and, as with transport, the majority of these mitotic effects are mediated through affecting the physical interaction between karyopherins and Spindle Assembly Factors (SAFs)—a loose term describing proteins or protein complexes involved in spindle assembly through promoting nucleation, stabilization, and/or depolymerization of MTs, through anchoring MTs to specific structures such as centrosomes, chromatin or kinetochores, or through sliding MTs along each other to generate the force required to achieve bipolarity. As such, the Ran-mediated pathway represents a crucial functional module within the wider spindle assembly landscape. Research into mitosis using the model organism Drosophila melanogaster has contributed substantially to our understanding of centrosome and spindle function. However, in comparison to mammalian systems, very little is known about the contribution of Ran-mediated pathways in Drosophila mitosis. This article sets out to summarize our understanding of the roles of the Ran pathway components in Drosophila mitosis, focusing on the syncytial blastoderm embryo, arguing that it can provide important insights into the conserved functions on Ran during spindle formation.