Duplication and Segregation of Centrosomes during Cell Division

Developmental and tissue-specific roles of mammalian centrosomes

Centrosomes are dominant microtubule organizing centers in animal cells with a pair of centrioles at their core. They template cilia during interphase and help organize the mitotic spindle for a more efficient cell division. Here, we review the roles of centrosomes in the early developing mouse and during organ formation. Mammalian cells respond to centrosome loss-of-function by activating the mitotic surveillance pathway, a timing mechanism that, when a defined mitotic duration is exceeded, leads to p53-dependent cell death in the descendants. Mouse embryos without centrioles are highly susceptible to this pathway and undergo embryonic arrest at mid-gestation. The complete loss of the centriolar core results in earlier and more severe phenotypes than that of other centrosomal proteins. Finally, different developing tissues possess varying thresholds and mount graded responses to the loss of centrioles that go beyond the germ layer of origin.

Investigation of artificial cells containing the Par system for bacterial plasmid segregation and inheritance mimicry

A crucial step in life processes is the transfer of accurate and correct genetic material to offspring. During the construction of autonomous artificial cells, a very important step is the inheritance of genetic information in divided artificial cells. The ParMRC system, as one of the most representative systems for DNA segregation in bacteria, can be purified and reconstituted into GUVs to form artificial cells. In this study, we demonstrate that the eGFP gene is segregated into two poles by a ParM filament with ParR as the intermediate linker to bind ParM and parC-eGFP DNA in artificial cells. After the ParM filament splits, the cells are externally induced to divide into two daughter cells that contain parC-eGFP DNA by osmotic pressure and laser irradiation. Using a PURE system, we translate eGFP DNA into enhanced green fluorescent proteins in daughter cells, and bacterial plasmid segregation and inheritance are successfully mimicked in artificial cells. Our results could lead to the construction of more sophisticated artificial cells that can reproduce with genetic information.

Loss of ninein interferes with osteoclast formation and causes premature ossification

Ninein is a centrosome protein that has been implicated in microtubule anchorage and centrosome cohesion. Mutations in the human NINEIN gene have been linked to Seckel syndrome and to a rare form of skeletal dysplasia. However, the role of ninein in skeletal development remains unknown. Here, we describe a ninein knockout mouse with advanced endochondral ossification during embryonic development. Although the long bones maintain a regular size, the absence of ninein delays the formation of the bone marrow cavity in the prenatal tibia. Likewise, intramembranous ossification in the skull is more developed, leading to a premature closure of the interfrontal suture. We demonstrate that ninein is strongly expressed in osteoclasts of control mice, and that its absence reduces the fusion of precursor cells into syncytial osteoclasts, whereas the number of osteoblasts remains unaffected. As a consequence, ninein-deficient osteoclasts have a reduced capacity to resorb bone. At the cellular level, the absence of ninein interferes with centrosomal microtubule organization, reduces centrosome cohesion, and provokes the loss of centrosome clustering in multinucleated mature osteoclasts. We propose that centrosomal ninein is important for osteoclast fusion, to enable a functional balance between bone-forming osteoblasts and bone-resorbing osteoclasts during skeletal development.

Mechanism of chromosomal mosaicism in preimplantation embryos and its effect on embryo development

Aneuploidy is one of the main causes of miscarriage and in vitro fertilization failure. Mitotic abnormalities in preimplantation embryos are the main cause of mosaicism, which may be influenced by several endogenous factors such as relaxation of cell cycle control mechanisms, defects in chromosome cohesion, centrosome aberrations and abnormal spindle assembly, and DNA replication stress. In addition, incomplete trisomy rescue is a rare cause of mosaicism. However, there may be a self-correcting mechanism in mosaic embryos, which allows some mosaicisms to potentially develop into normal embryos. At present, it is difficult to accurately diagnose mosaicism using preimplantation genetic testing for aneuploidy. Therefore, in clinical practice, embryos diagnosed as mosaic should be considered comprehensively based on the specific situation of the patient.

The two sides of chromosomal instability: drivers and brakes in cancer

Chromosomal instability (CIN) is a hallmark of cancer and is associated with tumor cell malignancy. CIN triggers a chain reaction in cells leading to chromosomal abnormalities, including deviations from the normal chromosome number or structural changes in chromosomes. CIN arises from errors in DNA replication and chromosome segregation during cell division, leading to the formation of cells with abnormal number and/or structure of chromosomes. Errors in DNA replication result from abnormal replication licensing as well as replication stress, such as double-strand breaks and stalled replication forks; meanwhile, errors in chromosome segregation stem from defects in chromosome segregation machinery, including centrosome amplification, erroneous microtubule-kinetochore attachments, spindle assembly checkpoint, or defective sister chromatids cohesion. In normal cells, CIN is deleterious and is associated with DNA damage, proteotoxic stress, metabolic alteration, cell cycle arrest, and senescence. Paradoxically, despite these negative consequences, CIN is one of the hallmarks of cancer found in over 90% of solid tumors and in blood cancers. Furthermore, CIN could endow tumors with enhanced adaptation capabilities due to increased intratumor heterogeneity, thereby facilitating adaptive resistance to therapies; however, excessive CIN could induce tumor cells death, leading to the "just-right" model for CIN in tumors. Elucidating the complex nature of CIN is crucial for understanding the dynamics of tumorigenesis and for developing effective anti-tumor treatments. This review provides an overview of causes and consequences of CIN, as well as the paradox of CIN, a phenomenon that continues to perplex researchers. Finally, this review explores the potential of CIN-based anti-tumor therapy.

DIS3 depletion in multiple myeloma causes extensive perturbation in cell cycle progression and centrosome amplification

DIS3 gene mutations occur in approximately 10% of patients with multiple myeloma (MM); furthermore, DIS3 expression can be affected by monosomy 13 and del(13q), found in roughly 40% of MM cases. Despite the high incidence of DIS3 mutations and deletions, the biological significance of DIS3 and its contribution to MM pathogenesis remain poorly understood. In this study we investigated the functional role of DIS3 in MM, by exploiting a loss-of-function approach in human MM cell lines. We found that DIS3 knockdown inhibits proliferation in MM cell lines and largely affects cell cycle progression of MM plasma cells, ultimately inducing a significant increase in the percentage of cells in the G0/G1 phase and a decrease in the S and G2/M phases. DIS3 plays an important role not only in the control of the MM plasma cell cycle, but also in the centrosome duplication cycle, which are strictly co-regulated in physiological conditions in the G1 phase. Indeed, DIS3 silencing leads to the formation of supernumerary centrosomes accompanied by the assembly of multipolar spindles during mitosis. In MM, centrosome amplification is present in about a third of patients and may represent a mechanism leading to genomic instability. These findings strongly prompt further studies investigating the relevance of DIS3 in the centrosome duplication process. Indeed, a combination of DIS3 defects and deficient spindle-assembly checkpoint can allow cells to progress through the cell cycle without proper chromosome segregation, generating aneuploid cells which ultimately lead to the development of MM.

Site-specific phosphorylation of ZYG-1 regulates ZYG-1 stability and centrosome number

Spindle bipolarity is critical for genomic integrity. As centrosome number often dictates bipolarity, tight control of centrosome assembly is vital for faithful cell division. The master centrosome regulator ZYG-1/Plk4 plays a pivotal role in this process. In C. elegans, casein kinase II (CK2) negatively regulates centrosome duplication by controlling centrosome-associated ZYG-1 levels. Here, we investigated CK2 as a regulator of ZYG-1 and its impact on centrosome assembly. We show that CK2 phosphorylates ZYG-1 in vitro and physically interacts with ZYG-1 in vivo. Depleting CK2 or blocking ZYG-1 phosphorylation at CK2 target sites leads to centrosome amplification. Non-phosphorylatable ZYG-1 mutants exhibit elevated ZYG-1 levels, leading to increased ZYG-1 and downstream factors at centrosomes, thus driving centrosome amplification. Moreover, inhibiting the 26S proteasome prevents degradation of the phospho-mimetic ZYG-1. Our findings suggest that CK2-dependent phosphorylation of ZYG-1 controls ZYG-1 levels via proteasomal degradation to limit centrosome number.

KIFC1 promotes proliferation and pseudo-bipolar division of ESCC through the transportation of Aurora B kinase

Esophageal squamous cell carcinoma (ESCC) accounts for over 90% of total in China, and the five-year survival rate for patients is less than 30%. Accordingly, the identification of novel, effective early diagnosis markers and therapeutic targets for ESCC is of paramount importance. KIFC1 has been identified as highly expressed in several types of cancer, although its prognostic value is inconsistent, and no research has been conducted specifically on its effect on ESCC. To investigate the expression and function of KIFC1 in ESCC, we conducted immunohistochemical staining on 30 pairs of para-carcinoma tissue and cancerous tissues, revealing a significant increase in KIFC1 expression in ESCC tissues. Using siRNA to knock down KIFC1 significantly reduced the proliferation of EC109 ESCC cells both in vitro and in vivo. Bioinformatics analysis revealed a highly significant positive correlation between KIFC1 overexpression and signaling pathways associated with tumor proliferation pathways. In EC109 cells, overexpression of KIFC1 significantly increased the rate of centrosome amplification and the likelihood of pseudo-bipolar division. Furthermore, the expression of KIFC1 and the rate of centrosome amplification in ESCC tissues were also positively correlated. In order to explore the underline molecular mechanisms, we identified, through proteomics, that KIFC1 binds to the protein Aurora B. The knockdown of KIFC1 significantly reduced the distribution of Aurora B on the metaphase plate and substantially inhibited the phosphorylation of its classical substrate, Histone H3. In conclusion, these findings indicate the potential utility of KIFC1 as both a tumor marker and a promising target for therapeutic interventions.

Site-Specific Phosphorylation of ZYG-1 Regulates ZYG-1 Stability and Centrosome Number

Spindle bipolarity is critical for genomic integrity. Given that centrosome number often dictates mitotic bipolarity, tight control of centrosome assembly is vital for the fidelity of cell division. The kinase ZYG-1/Plk4 is a master centrosome factor that is integral for controlling centrosome number and is modulated by protein phosphorylation. While autophosphorylation of Plk4 has been extensively studied in other systems, the mechanism of ZYG-1 phosphorylation in C. elegans remains largely unexplored. In C. elegans, Casein Kinase II (CK2) negatively regulates centrosome duplication by controlling centrosome-associated ZYG-1 levels. In this study, we investigated ZYG-1 as a potential substrate of CK2 and the functional impact of ZYG-1 phosphorylation on centrosome assembly. First, we show that CK2 directly phosphorylates ZYG-1 in vitro and physically interacts with ZYG-1 in vivo. Intriguingly, depleting CK2 or blocking ZYG-1 phosphorylation at putative CK2 target sites leads to centrosome amplification. In the non-phosphorylatable (NP)-ZYG-1 mutant embryo, the overall levels of ZYG-1 are elevated, leading to an increase in centrosomal ZYG-1 and downstream factors, providing a possible mechanism of the NP-ZYG-1 mutation to drive centrosome amplification. Moreover, inhibiting the 26S proteasome blocks degradation of the phospho-mimetic (PM)-ZYG-1, while the NP-ZYG-1 mutant shows partial resistance to proteasomal degradation. Our findings suggest that site-specific phosphorylation of ZYG-1, partly mediated by CK2, controls ZYG-1 levels via proteasomal degradation, limiting centrosome number. We provide a mechanism linking CK2 kinase activity to centrosome duplication through direct phosphorylation of ZYG-1, which is critical for the integrity of centrosome number.

Identification of a centrosome-related prognostic signature for breast cancer

Background

As the major microtubule organizing center in animal cells, the centrosome is implicated with human breast tumor in multiple ways, such as promotion of tumor cell immune evasion. Here, we aimed to detect the expression of centrosome-related genes (CRGs) in normal and malignant breast tissues, and construct a novel centrosome-related prognostic model to discover new biomarkers and screen drugs for breast cancer.

Methods

We collected CRGs from the public databases and literature. The differentially expressed CRGs between normal and malignant breast tissues were identified by the DESeq2. Univariate Cox and LASSO regression analyses were conducted to screen candidate prognostic CRGs and develop a centrosome-related signature (CRS) to score breast cancer patients. We further manipulated and visualized data from TCGA, GEO, IMvigor210, TCIA and TIMER to explore the correlation between CRS and patient outcomes, clinical manifestations, mutational landscapes, tumor immune microenvironments, and responses to diverse therapies. Single cell analyses were performed to investigate the difference of immune cell landscape between high- and low-risk group patients. In addition, we constructed a nomogram to guide clinicians in precise treatment.

Results

A total of 726 CRGs were collected from the public databases and literature. PSME2, MAPK10, EIF4EBP1 were screened as the prognostic genes in breast cancer. Next, we constructed a centrosome-related prognostic signature and validated its efficacy based on the genes for predicting the survival of breast cancer patients. The high-risk group patients had poor prognoses, the area under the ROC curve for 1-, 3-, and 5-year overall survival (OS) was 0.77, 0.67, and 0.65, respectively. The predictive capacity of CRS was validated by other datasets from GEO dataset. In addition, high-risk group patients exhibited elevated level of mutational landscapes and decreased level of immune infiltration, especially T and B lymphocytes. In terms of treatment responses, patients in the high-risk group were found to be resistant to immunotherapy but sensitive to chemotherapy. Moreover, we screened a series of candidate anticancer drugs with high sensitivity in the high-risk group.

Conclusion

Our work exploited a centrosome-related prognostic signature and developed a predictive nomogram capable of accurately predicting breast cancer OS. The above discoveries provide deeper insights into the vital roles of the centrosome and contribute to the development of personalized treatment for breast cancer.

The second half of mitosis and its implications in cancer biology

The nucleus undergoes dramatic structural and functional changes during cell division. With the entry into mitosis, in human cells the nuclear envelope breaks down, chromosomes rearrange into rod-like structures which are collected and segregated by the spindle apparatus. While these processes in the first half of mitosis have been intensively studied, much less is known about the second half of mitosis, when a functional nucleus reforms in each of the emerging cells. Here we review our current understanding of mitotic exit and nuclear reformation with spotlights on the links to cancer biology.