Proper Chromosome Segregation Research Articles

Fdo1, Fkh1, Fkh2 and the Swi6-Mbp1 MBF complex regulate Mcd1 levels to impact eco1 rad61 cell growth in Saccharomyces cerevisiae.

Cohesins promote proper chromosome segregation, gene transcription, genomic architecture, DNA condensation, and DNA damage repair. Mutations in either cohesin subunits or regulatory genes can give rise to severe developmental abnormalities (such as Robert Syndrome and Cornelia de Lange Syndrome) and also are highly correlated with cancer. Despite this, little is known about cohesin regulation. Eco1 (ESCO2/EFO2 in humans) and Rad61 (WAPL in humans) represent two such regulators but perform opposing roles. Eco1 acetylation of cohesin during S phase, for instance, stabilizes cohesin-DNA binding to promote sister chromatid cohesion. On the other hand, Rad61 promotes the dissociation of cohesin from DNA. While Eco1 is essential, ECO1 and RAD61 co-deletion results in yeast cell viability, but only within a limited temperature range. Here, we report that eco1 rad61 cell lethality is due to reduced levels of the cohesin subunit Mcd1. Results from a suppressor screen further reveals that FDO1 deletion rescues the temperature sensitive (ts) growth defects exhibited by eco1 rad61 double mutant cells by increasing Mcd1 levels. Regulation of MCD1 expression, however, appears more complex. Elevated expression of MBP1, which encodes a subunit of the MBF transcription complex, also rescues eco1 rad61 cell growth defects. Elevated expression of SWI6, however, which encodes the Mbp1-binding partner of MBF, exacerbates eco1 rad61 cell growth and also abrogates the Mpb1-dependent rescue. Finally, we identify two additional transcription factors, Fkh1 and Fkh2, that impact MCD1 expression. In combination, these findings provide new insights into the nuanced and multi-faceted transcriptional pathways that impact MCD1 expression.

Argonaute CSR-1 restricts holocentromere protein CENP-A/HCP-3 localization.

Chromosome segregation errors caused by centromere malfunction can lead to chromosome instability and aneuploidy. In Caenorhabditis elegans, the Argonaute protein CSR-1 is essential for proper chromosome segregation, though the specific mechanisms are not fully understood. Here we investigated how CSR-1 regulates centromere and kinetochore function in C. elegans embryos. We found that the depletion of CSR-1 results in defects in mitotic progression and chromosome positioning relative to the spindle pole. CSR-1 knockdown does not affect centromeric histone H3 variant CENP-A/HCP-3 mRNA and protein levels, but increases the localization of HCP-3 and some kinetochore proteins onto the mitotic chromosomes. Such elevation of chromatin HCP-3 localization depends on the CSR-1 RNAi pathway upstream factor EGO-1 and CSR-1's PIWI domain activity. Our results suggest that CSR-1 restricts HCP-3 level at the holocentromeres, prevents erroneous kinetochore assembly, and thereby promotes accurate chromosome segregation. Our work sheds light on CSR-1's role in regulating deposition of HCP-3 on chromatin and centromere function in the embryos.

P-705 Telomere length of white blood cells is a non-invasive marker of reproductive aging in women

Abstract Study question Can leukocyte telomere length be a marker of ovarian decline? Summary answer The significant correlation found between leukocyte and cumulus cell telomere lengths supports the use of leukocyte telomere length (TL) as a marker of ovarian aging. What is known already The telomere-based theory of reproductive aging proposes that age-related ovarian dysfunction is a consequence of progressive telomere shortening from fetal oogenesis to the adult ovary, compromising genome stability and proper chromosome segregation. Telomere length in cumulus cells (CCTL) is known to be a biomarker of oocyte and embryo quality, but its assessment is not practical. Hence, we previously proposed leukocyte telomere length (LTL) as an alternative to directly measuring telomere length in follicular cells, but so far it has only been assessed in samples of moderate size and homogeneous populations without consistent results. Study design, size, duration This prospective, non-interventional cohort study involved 300 women aged 18 to 46 years undergoing controlled ovarian stimulation over a 24-month period. The cohort included 169 egg donors and 131 IVF patients. Oocyte retrieval was performed 36 hours after maturation induction, with cumulus cells collected during oocyte stripping and blood samples taken via peripheral venous access. Participants/materials, setting, methods Genomic DNA was isolated from leukocytes and cumulus cells of all subjects for TL measurements. Relative TL was determined using a SYBR-Green quantitative real-time PCR protocol. A Taqman assay for the multicopy gene Alu was used to normalize the measurements. A Pearson’s correlation test was used to analyze the correlation between CCTL and LTL, as well as between TL and age, antral follicle count, Anti-Müllerian hormone, and number of mature oocytes retrieved. Main results and the role of chance Mean age of the subjects was 30.70±7.61 years. Anti-Müllerian hormone (AMH) mean level was 2.60±1.87 ng/ml, antral follicle count (AFC) was 17.8±7.4 and the number of mature oocytes was 14.3±9.3. A significant correlation was observed between CCTL and LTL (R = 0.6, p-value=2.2E-16). Notably, the relationship between leukocyte and cumulus cell telomere lengths was stronger in the 97 participants over 35 years (R = 0.67, p-value=1.55E-13), especially those between 39 to 46 years (R = 0.70, p-value=1.19E-12). Telomere length was inversely correlated with age in both leukocytes and cumulus cells (R=-0.23, p-value=6.98E-05; R=-0.4, p-value=2.38E-05), meaning the older the subject, the shorter the telomeres in both cells. Furthermore, longer telomeres in leukocytes and cumulus cells were significantly correlated with higher AFC (R = 0.20, p-value=0.0006; R = 0.25, p-value=1.83E-05), and more mature oocytes retrieved (R = 0.16, p-value=0.0043; R = 0.27, p-value=2.83E-06). However, we did not find any association between AMH levels and LTL or CCTL (R = 0.07, p-value=0.2666; R = 0.07, p-value=0.2747). Limitations, reasons for caution The method used to measure the average telomere length from pooled leukocyte samples may not reflect individual cell variability. Additionally, it allows for relative but not absolute telomere length comparisons. Wider implications of the findings This study is the first to demonstrate in a large and heterogeneous population that LTL could be a viable marker for ovarian aging by reflecting follicular cell telomere length. This finding may provide a valuable tool for assessing and monitoring the reproductive health of IVF patients. Trial registration number Not applicable

Understanding the Genetic Basis of Variation in Meiotic Recombination: Past, Present, and Future.

Meiotic recombination is a fundamental feature of sexually reproducing species. It is often required for proper chromosome segregation and plays important role in adaptation and the maintenance of genetic diversity. The molecular mechanisms of recombination are remarkably conserved across eukaryotes, yet meiotic genes and proteins show substantial variation in their sequence and function, even between closely related species. Furthermore, the rate and distribution of recombination shows a huge diversity within and between chromosomes, individuals, sexes, populations, and species. This variation has implications for many molecular and evolutionary processes, yet how and why this diversity has evolved is not well understood. A key step in understanding trait evolution is to determine its genetic basis-that is, the number, effect sizes, and distribution of loci underpinning variation. In this perspective, I discuss past and current knowledge on the genetic basis of variation in recombination rate and distribution, explore its evolutionary implications, and present open questions for future research.

P-558 Characterization of the morphology of the outer-kinetochore expandable module, aka fibrous corona, and its role in ensuring proper chromosome segregation in human and bovine oocytes

Abstract Study question How does the Fibrous Corona (FC) behave in human and bovine oocyte meiosis and what is its function in chromosome segregation during meiosis I? Summary answer In human and bovine oocytes, FC shows extreme plasticity expanding beyond the centromeric region of the chromosomes. Pharmacological inhibition of FC’s expansion induces chromosome mis-segregation. What is known already Embryonic aneuploidy of meiotic origin is one of the major causes of implantation failure and early pregnancy loss. Erroneous microtubule (MT)-kinetochore attachments in human meiosis are the main cause of meiotic chromosome segregation errors. In somatic cells, the FC, a multiprotein complex, assembles on kinetochores and expands around the centromere during prometaphase to facilitate MT interactions and stimulate correct MT-kinetochore attachment. We have shown that in bovine oocytes FC expand beyond the centrosomes and is a potent MTs nucleator (10.1016/j.cub.2023.01.010). However, it is still unknown how FC behaves and what are its functions in MT-kinetochore interactions in human oocytes. Study design, size, duration FC morphology was studied in immature human oocytes discarded during ICSI procedures and donated (informed consent) by the patients for research (Ethical permit TCBio.21-754) during the years 2021-2024. Because of ethical concerns and reduced availability of human oocytes, functional studies on FC were performed on bovine oocytes collected from slaughterhouse ovaries. Participants/materials, setting, methods 180 immature human oocytes were matured in vitro and either fixed at different meiosis I stages or treated 2h with colcemid, a MT depolymerizing drug, to induce maximum FC expansion and fixed. The oocytes were then immuno-stained for chromatin(DAPI), FC(ZW10), MT(alpha tubulin) and kinetochores(CREST) and imaged with super-resolution confocal microscopy. Bovine immature oocytes were matured in vitro with or without lonafarnib (inhibitor of FC expansion). After maturation chromosome spreads were performed to evaluate oocyte ploidy. Main results and the role of chance In human oocytes, after nuclear envelope breakdown, before microtubule appearance when the chromosomes appear compacted, FCs are visible on the top of the kinetochores. During MT nucleation, FCs form thick mesh in the center of the compacted chromosomes. During prometaphase I, FCs expand beyond the centromeric region of the chromosomes forming a cup around the sister kinetochores of the paired homologous chromosomes. When the chromosomes starts to align at the metaphase plate, FCs start to be stripped from the kinetochores and colocalize to the MTs. At metaphase I and II, only kinetochore localization is visible. When oocytes are treated with colcemid, FCs extend to partially cover chromosome arms. We observed a wide variability in FCs expansion between and within patients. Inhibition of FC expansion in bovine oocytes increase the incidence of oocyte aneuploidy (90% in lonafarnib treated vs 37% in control oocytes). Altogether, our data reveal that in human oocytes FCs expand more compared to human somatic cells. Considering that inhibition of FC expansion induces chromosome segregation errors, we propose that the large FC size in human oocytes may play a role in achieving correct chromosome-MT attachments within their extremely large cytoplasm thus ensuring proper chromosome segregation. Limitations, reasons for caution The limited availability of human oocytes requires the use of an animal model for in depth mechanistic studies. Although bovine oocytes have similar aneuploidy rate and spindle assembly mechanisms as human oocytes, they show morphological differences in FC expansion which could underlie intrinsic functional discrepancies between the two organisms. Wider implications of the findings A better understanding of the chromosome segregation mechanisms in human meiosis will help understanding what causes the high incidence of aneuploidies in human oocytes and possibly contribute to the development of interventions or of oocyte selection procedures to reduce the incidence of oocyte aneuploidy during in vitro maturation. Trial registration number Not applicable

Metformin augments major cytoplasmic organization except for spindle organization in oocytes cultured under hyperglycemic and hyperlipidemic conditions: An in vitro study

The present study aimed to investigate the role of antidiabetic drug metformin on the cytoplasmic organization of oocytes. Germinal vesicle (GV) stage oocytes were collected from adult female Swiss albino mice and subjected to in vitro maturation (IVM) in various experimental groups- control, vehicle control (0.3% ethanol), metformin (50 μg/mL), high glucose and high lipid (HGHL, 10 mM glucose; 150 μM palmitic acid; 75 μM stearic acid and 200 μM oleic acid in ethanol), and HGHL supplemented with metformin. The metaphase II (MII) oocytes were analyzed for lipid accumulation, mitochondrial and endoplasmic reticulum (ER) distribution pattern, oxidative and ER stress, actin filament organization, cortical granule distribution pattern, spindle organization and chromosome alignment. An early polar body extrusion was observed in the HGHL group. However, the maturation rate at 24 h did not differ significantly among the experimental groups compared to the control. The HGHL conditions exhibited significantly higher levels of oxidative stress, ER stress, poor actin filament organization, increased lipid accumulation, altered mitochondrial distribution, spindle abnormalities, and chromosome misalignment compared to the control. Except for spindle organization, supplementation of metformin to the HGHL conditions improved all the parameters (non-significant for ER and actin distribution pattern). These results show that metformin exposure in the culture media helped to improve the hyperglycemia and hyperlipidemia-induced cytoplasmic anomalies except for spindle organization. Given the crucial role of spindle organization in proper chromosome segregation during oocyte maturation and meiotic resumption, the implications of metformin's limitations in this aspect warrant careful evaluation and further investigation.

Proximity-based activation of AURORA A by MPS1 potentiates error correction.

Faithfull cell division relies on mitotic chromosomes becoming bioriented with each pair of sister kinetochores bound to microtubules oriented toward opposing spindle poles. Erroneous kinetochore-microtubule attachments often form during early mitosis, but are destabilized through the phosphorylation of outer kinetochore proteins by centromeric AURORA B kinase (ABK) and centrosomal AURORA A kinase (AAK), thus allowing for re-establishment of attachments until biorientation is achieved. MPS1-mediated phosphorylation of NDC80 has also been shown to directly weaken the kinetochore-microtubule interface in yeast. In human cells, MPS1 has been proposed to transiently accumulate at end-on attached kinetochores and phosphorylate SKA3 to promote microtubule release. Whether MPS1 directly targets NDC80 and/or promotes the activity of AURORA kinases in metazoans remains unclear. Here, we report a novel mechanism involving communication between kinetochores and centrosomes, wherein MPS1 acts upstream of AAK to promote error correction. MPS1 on pole-proximal kinetochores phosphorylates the C-lobe of AAK thereby increasing its activation at centrosomes. This proximity-based activation ensures the establishment of a robust AAK activity gradient that locally destabilizes mal-oriented kinetochores near spindle poles. Accordingly, MPS1 depletion from Drosophila cells causes severe chromosome misalignment and erroneous kinetochore-microtubule attachments, which can be rescued by tethering either MPS1 or constitutively active AAK mutants to centrosomes. Proximity-based activation of AAK by MPS1 also occurs in human cells to promote AAK-mediated phosphorylation of the NDC80 N-terminal tail. These findings uncover an MPS1-AAK cross-talk that is required for efficient error correction, showcasing the ability of kinetochores to modulate centrosome outputs to ensure proper chromosome segregation.

Chromosome segregation: Mps1 and Dam1 battle to bind a shared interaction site at the kinetochore

The attachment of kinetochores to spindle microtubules is highly regulated to ensure proper chromosome segregation. Three new studies identify an interaction hub at the kinetochore that integrates kinetochore attachment state with spindle checkpoint activity and kinetochore assembly.

Molecular interplay between HURP and Kif18A in mitotic spindle regulation.

During mitosis, microtubule dynamics are regulated to ensure proper alignment and segregation of chromosomes. The dynamics of kinetochore-attached microtubules are regulated by hepatoma-upregulated protein (HURP) and the mitotic kinesin-8 Kif18A, but the underlying mechanism remains elusive. Using single-molecule imaging in vitro, we demonstrate that Kif18A motility is regulated by HURP. While sparse decoration of HURP activates the motor, higher concentrations hinder processive motility. To shed light on this behavior, we determined the binding mode of HURP to microtubules using Cryo-EM. The structure reveals that one HURP motif spans laterally across β-tubulin, while a second motif binds between adjacent protofilaments. HURP partially overlaps with the microtubule-binding site of the Kif18A motor domain, indicating that excess HURP inhibits Kif18A motility by steric exclusion. We also observed that HURP and Kif18A function together to suppress dynamics of the microtubule plus-end, providing a mechanistic basis for how they collectively serve in spindle length control.

Contribution of CENP-F to FOXM1-Mediated Discordant Centromere and Kinetochore Transcriptional Regulation.

Proper chromosome segregation is required to ensure chromosomal stability. The centromere (CEN) is a unique chromatin domain defined by CENP-A and is responsible for recruiting the kinetochore (KT) during mitosis, ultimately regulating microtubule spindle attachment and mitotic checkpoint function. Upregulation of many CEN/KT genes is commonly observed in cancer. Here, we show that although FOXM1 occupies promoters of many CEN/KT genes with MYBL2, FOXM1 overexpression alone is insufficient to drive the FOXM1-correlated transcriptional program. CENP-F is canonically an outer kinetochore component; however, it functions with FOXM1 to coregulate G2/M transcription and proper chromosome segregation. Loss of CENP-F results in altered chromatin accessibility at G2/M genes and reduced FOXM1-MBB complex formation. We show that coordinated CENP-FFOXM1 transcriptional regulation is a cancer-specific function. We observe a small subset of CEN/KT genes including CENP-C, that are not regulated by FOXM1. Upregulation of CENP-C in the context of CENP-A overexpression leads to increased chromosome missegregation and cell death suggesting that escape of CENP-C from FOXM1 regulation is a cancer survival mechanism. Together, we show that FOXM1 and CENP-F coordinately regulate G2/M genes, and this coordination is specific to a subset of genes to allow for maintenance of chromosome instability levels and subsequent cell survival.

SKA3 Expression as a Prognostic Factor for Patients with Pancreatic Adenocarcinoma.

The spindle and kinetochore-associated complex subunit 3 (SKA3) is a protein essential for proper chromosome segregation during mitosis and thus responsible for maintaining genome stability. Although its involvement in the pathogenesis of various cancer types has been reported, the potential clinicopathological significance of SKA3 in pancreatic ductal adenocarcinoma (PDAC) has not been fully elucidated. Therefore, this study aimed to assess clinicopathological associations and prognostic value of SKA3 in PDAC. For this purpose, in-house immunohistochemical analysis on tissue macroarrays (TMAs), as well as a bioinformatic examination using publicly available RNA-Seq dataset, were performed. It was demonstrated that SKA3 expression at both mRNA and protein levels was significantly elevated in PDAC compared to control tissues. Upregulated mRNA expression constituted an independent unfavorable prognostic factor for the overall survival of PDAC patients, whereas altered SKA3 protein levels were associated with significantly better clinical outcomes. The last observation was particularly clear in the early-stage tumors. These findings render SKA3 a promising prognostic biomarker for patients with pancreatic ductal adenocarcinoma. However, further studies are needed to confirm this conclusion.

Centromere pairing enables correct segregation of meiotic chromosomes

Proper chromosome segregation in meiosis I relies on the formation of connections between homologous chromosomes. Crossovers between homologs provide a connection that allows them to attach correctly to the meiosis I spindle. Tension is transmitted across the crossover when the partners attach to microtubules from opposing poles of the spindle. Tension stabilizes microtubule attachments that will pull the partners toward opposite poles at anaphase. Paradoxically, in many organisms, non-crossover partners segregate correctly. The mechanism by which non-crossover partners become bioriented on the meiotic spindle is unknown. Both crossover and non-crossover partners pair their centromeres early in meiosis (prophase). In budding yeast, centromere pairing is correlated with subsequent correct segregation of the partners. The mechanism by which centromere pairing, in prophase, promotes later correct attachment of the partners to the metaphase spindle is unknown. We used live cell imaging to track the biorientation process of non-crossover chromosomes. We find that centromere pairing allows the establishment of connections between the partners that allows their later interdependent attachment to the meiotic spindle using tension-sensing biorientation machinery. Because all chromosome pairs experience centromere pairing, our findings suggest that crossover chromosomes also utilize this mechanism to achieve maximal segregation fidelity.

Medaka Terb1 Mutant Displays Defects of Synaptonemal Complex Formation and Sexual Difference in Gametogenesis.

Formation of the synaptonemal complex (SC) is a prerequisite for proper recombination and chromosomal segregation during meiotic prophase I. One mechanism that ensures SC formation is chromosomal movement, which is driven by the force derived from cytoskeletal motors. Here, we report the phenotype of medaka mutants lacking the telomere repeat binding bouquet formation protein 1 (TERB1), which, in combination with the SUN/KASH protein, mediates chromosomal movement by connecting telomeres and cytoskeletal motors. Mutations in the terb1 gene exhibit defects in SC formation in medaka. Although SC formation was initiated, as seen by the punctate lateral elements and fragmented transverse filaments, it was not completed in the terb1 mutant meiocytes. The mutant phenotype further revealed that the introduction of double strand breaks was independent of synapsis completion. In association with these phenotypes, meiocytes in both the ovaries and testes exhibited an aberrant arrangement of homologous chromosomes. Interestingly, although oogenesis halted at the zygotene-like stage in terb1 mutant, testes continued to produce sperm-like cells with aberrant DNA content. This indicates that the mechanism of meiotic checkpoint is sexually different in medaka, similar to the mammalian checkpoint in which oogenesis proceeds while spermatogenesis is arrested. Moreover, our results suggest that spermatogenesis is mechanistically dissociable from meiosis.

SKA3 targeted therapies in cancer precision surgery: bridging bench discoveries to clinical applications-review article.

Spindle and kinetochore-associated complex subunit 3 (SKA3) is a microtubule-binding subcomplex of the outer kinetochore which plays a vital role in proper chromosomal segregation and cell division. Recently, SKA3 have been demonstrated its oncogenic role of tumorigenesis and development in cancers. In this review, we comprehensively deciphered SKA3 in human cancer from various aspects, including bibliometrics, pan-cancer analysis and narrative summary. We also provided top 10 predicted drugs targeting SKA3. We proposed that SKA3 was a potential target and brought new therapeutic opportunities for cancer patients.

Abstract 1638: Regulation of spindle pole integrity by the MASTL-ENSA-aurora a pathway during mitosis

Abstract The preservation of spindle pole integrity is crucial for proper spindle assembly and chromosome segregation in mitosis, yet the precise mechanisms governing spindle pole integrity remain elusive. During mitosis, phosphorylated Ensa (p-ENSA) localizes to spindle poles, and the inhibition of ENSA leads to a range of mitotic defects, including misaligned chromosomes, multipolar spindles, asymmetric bipolar spindles, and centrosome aberrations, resulting in a delayed mitotic progression. Remarkably, the mitotic delay induced by ENSA inhibition is alleviated upon depletion of PP2A-B55α, but spindle pole defects persist. Significantly, we have observed an interaction between ENSA and Aurora A during mitosis, and the inhibition of ENSA diminishes Aurora A expression at the mitotic spindle poles. Intriguingly, the injection of MKI-2-sensitized tumors is associated with heightened chromosomal instability and downregulation of the MASTL-ENSA-Aurora A pathway in an orthotopic breast cancer mouse model. These findings offer new insights into the regulation of spindle pole integrity through the MASTL-ENSA-Aurora A pathway during mitosis, emphasizing the pivotal role of ENSA in recruiting Aurora A to the spindle pole, independently of PP2A-B55α. Citation Format: Seul Kim, Kyoungho Jun, Ye-Hyun Kim, Jae Sung Kim. Regulation of spindle pole integrity by the MASTL-ENSA-aurora a pathway during mitosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1638.

Abstract 628: RNA binding protein Matrin3 acts as a tumor suppressor by inhibiting microtubule nucleation

Abstract Introduction: Microtubule-associated proteins (MAPs) regulate microtubule dynamics, which is critical for controlling cell division, proliferation, migration, and intracellular transport. Due to their critical role in maintaining cellular integrity, microtubules have served as potent therapeutic targets for cancer treatment. Here, we report “Matrin 3 (MATR3)” as a novel MAP that interacts with β- tubulin and γ-tubulin, which constitutes microtubule organizing center (MTOC) essential for proper spindle formation and chromosomal segregation. Methods: Breast cancer cell lines (MDA-MB-231, MDA-MB-468, SKBR3, MCF7, BT549, HMEC, and MCF10A) were purchased from the American Type Culture Collection and cultured in standard medium. Breast cancer cells were transfected either with MATR3 overexpression plasmid or siRNA specific to MATR3. These overexpression/knockdown breast cancer cells were analyzed for cell viability, migration, invasion, colony formation, cell cycle, apoptosis assays, RNA sequencing, RT-qPCR, western blotting, RNA immunoprecipitation, and in vivo tumor xenograft study. Results: Our findings show that MATR3 binds to RNA encoding MAPs including β-tubulin and γ-tubulin, and regulate their stabilization. MATR3 also interacted with β-tubulin protein. Our data demonstrate that MATR3 functions as a tumor suppressor, as its overexpression inhibits cancer growth, while its depletion increased tumor growth in vivo. Mechanistic studies confirmed that MATR3 mediates its tumor suppressor role by regulating the expression of the MTOC-associated protein-encoding gene MZT2B (Mitotic Spindle Organizing Protein 2B), which is overexpressed in cancers and promotes cancer growth. Further, loss of MATR3 expression or function results in dysregulated microtubule dynamics and uncontrolled expression of the oncogenic proteins including MZT2B. Conclusions: In conclusion, our data strongly suggests that MATR3 serves as a novel RNA-binding protein with tumor suppressor properties. This discovery holds significant importance as MATR3 becomes the second protein, following Adenomatous Polyposis Coli (APC), to be identified for its binding to both MAP RNA and protein. Citation Format: Panneerdoss Subbarayalu, Subapriya Rajamanickam, Santosh Timilsina, Saif Nirzhor, Daisy Medina, Shahad Abdulsahib, Pitta V Prabhakar, Deepika Singh, Fu-Yang Li, Pooja Yadav, Esha Reddy, Krishna Evani, Vijay Eedunuri, Trong Phat Do, Benjamin C. Onyeagucha, Tabrez A. Mohammad, Jae-Hoon Ji, Yidong Chen, Nourhan Abdelfattah, Nicholas Dybdal-Hargreaves, Li-Ju Wang, Yu-Chiao Chiu, Suryavathi Viswanadhapalli, Ratna K. Vadlamudi, Manjeet K. Rao. RNA binding protein Matrin3 acts as a tumor suppressor by inhibiting microtubule nucleation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 628.

Abstract 4757: Combining PARP inhibitor with TACC3 inhibition overcomes PARP inhibitor resistance in ovarian cancer

Abstract The treatment of ovarian cancer (OC) presents a significant challenge due to the emergence of resistance to poly (ADP-ribose) polymerase inhibitors (PARPi). Transforming acidic coiled coil containing protein 3 (TACC3) belongs to the TACC family, characterized by its coiled-coil domains. TACC3 plays a crucial role in cell division, particularly in the formation and stability of the mitotic spindle, which is essential for proper chromosome segregation. Mutations or changes in TACC3 have been associated with various cancers, making it an increasingly attractive target for anticancer therapy in recent years. Here, we demonstrated a significant upregulation of TACC3 in OC, correlating with adverse clinical outcomes. Notably, PARPi-resistant OC cells exhibited a marked sensitivity to TACC3 inhibition. This was evidenced by the induction of spindle defects and mitotic catastrophe in PARPi-resistant cells upon TACC3 suppression, achieved either genetically or pharmacologically. Moreover, we explored the therapeutic efficacy of combining TACC3 inhibitor with PARPi, specifically BO-264 with olaparib or niraparib. This combination exhibited a synergistic effect, markedly reducing cell viability in vitro and tumor growth in PARPi-resistant tumor xenograft models. Our study suggests a promising new method for treating ovarian cancer, especially for those resistant to current PARPi treatments, by simultaneously targeting TACC3 and PARPi, enhancing treatment efficacy and potentially improving patient outcomes. Citation Format: Yu Wu, Qilong Wang, Chaolin Deng, Mo Li, Yinan Xiao. Combining PARP inhibitor with TACC3 inhibition overcomes PARP inhibitor resistance in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4757.

Induction of somatic cell haploidy by premature cell division.

Canonical mitotic and meiotic cell divisions commence with replicated chromosomes consisting of two sister chromatids. Here, we developed and explored a model of premature cell division, where nonreplicated, G0/G1-stage somatic cell nuclei are transplanted to the metaphase cytoplasm of mouse oocytes. Subsequent cell division generates daughter cells with reduced ploidy. Unexpectedly, genome sequencing analysis revealed proper segregation of homologous chromosomes, resulting in complete haploid genomes. We observed a high occurrence of somatic genome haploidization in nuclei from inbred genetic backgrounds but not in hybrids, emphasizing the importance of sequence homology between homologs. These findings suggest that premature cell division relies on mechanisms similar to meiosis I, where genome haploidization is facilitated by homologous chromosome interactions, recognition, and pairing. Unlike meiosis, no evidence of recombination between somatic cell homologs was detected. Our study offers an alternative in vitro gametogenesis approach by directly reprogramming diploid somatic cells into haploid oocytes.

The noncanonical function of borealin, a component of chromosome passenger complex, promotes glycolysis via stabilization of survivin in squamous cell carcinoma cells

The chromosome passenger complex (CPC) is a kinase complex formed by Aurora B, borealin, survivin and inner centromere protein (INCENP). The CPC is active during mitosis and contributes to proper chromosome segregation via the phosphorylation of various substrates. Overexpression of each CPC component has been reported in most cancers. However, its significance remains unclear, as only survivin is known to confer chemoresistance. This study showed that the overexpression of borealin, a CPC component, stabilized survivin protein depending on its interaction with survivin. Unexpectedly, the accumulation of survivin by borealin overexpression did not affect the well-characterized functions of survivin, such as chemoresistance and cell proliferation. Interestingly, the overexpression of borealin promoted lactate production but not the overexpression of the deletion mutant that lacks the ability to bind to survivin. Consistent with these findings, the expression levels of glycolysis-related genes were enhanced in borealin-overexpressing cancer cells. Meanwhile, the overexpression of survivin alone did not promote lactate production. Overall, the accumulation of the borealin–survivin complex promoted glycolysis in squamous cell carcinoma cells. This mechanism may contribute to cancer progression via excessive lactate production.

Physical interaction with Spo11 mediates the localisation of Mre11 to chromatin in meiosis and promotes its nuclease activity.

Meiotic recombination is of central importance for the proper segregation of homologous chromosomes, but also for creating genetic diversity. It is initiated by the formation of double-strand breaks (DSBs) in DNA catalysed by evolutionarily conserved Spo11, together with additional protein partners. Difficulties in purifying the Spo11 protein have limited the characterization of its biochemical properties and of its interactions with other DSB proteins. In this study, we have purified fragments of Spo11 and show for the first time that Spo11 can physically interact with Mre11 and modulates its DNA binding, bridging, and nuclease activities. The interaction of Mre11 with Spo11 requires its far C-terminal region, which is in line with the severe meiotic phenotypes of various mre11 mutations located at the C-terminus. Moreover, calibrated ChIP for Mre11 shows that Spo11 promotes Mre11 recruitment to chromatin, independent of DSB formation. A mutant deficient in Spo11 interaction severely reduces the association of Mre11 with meiotic chromatin. Consistent with the reduction of Mre11 foci in this mutant, it strongly impedes DSB formation, leading to spore death. Our data provide evidence that physical interaction between Spo11 and Mre11, together with end-bridging, promote normal recruitment of Mre11 to hotspots and DSB formation.