A theoretical model of anaphase.

This paper develops a theory for anaphase in cells. After a brief description of microtubules, the mitotic spindle and the centrosome, a mathematical model for anaphase is introduced and developed in the context of the cell cytoplasm and liquid crystalline structures. Prophase, prometaphase and metaphase are then briefly described in order to focus on anaphase, which is the main study of this paper. The entities involved are modelled in terms of liquid crystal defects and microtubules are represented as defect flux lines. The mathematical techniques employed make extensive use of energy considerations based on the work that was developed by Dafermos (1970) from the classical Frank-Oseen nematic liquid crystal energy (Frank, 1958; Oseen, 1933). With regard to liquid crystal theory we introduce the concept of regions of influence for defects which it is believed have important implications beyond the subject of this paper. The results of this paper align with observed biochemical phenomena and are explored in application to HeLa cells and Caenorhabditis elegans. This unified approach offers the possibility of gaining insight into various consequences of mitotic abnormalities which may result in Down syndrome, Hodgkin lymphoma, breast, prostate and various other types of cancer.

The Impact of Centrosome Pathologies on Ovarian Cancer Development and Progression with a Focus on Centrosomes as Therapeutic Target.

The impact of centrosome abnormalities on cancer cell proliferation has been recognized as early as 1914 (Boveri, Zur Frage der Entstehung maligner Tumoren. Jena: G. Fisher, 1914), but vigorous research on molecular levels has only recently started when it became fully apparent that centrosomes can be targeted for new cancer therapies. While best known for their microtubule-organizing capabilities as MTOC (microtubule organizing center) in interphase and mitosis, centrosomes are now further well known for a variety of different functions, some of which are related to microtubule organization and consequential activities such as cell division, migration, maintenance of cell shape, and vesicle transport powered by motor proteins, while other functions include essential roles in cell cycle regulation, metabolic activities, signal transduction, proteolytic activity, and several others that are now heavily being investigated for their role in diseases and disorders (reviewed in Schatten and Sun, Histochem Cell Biol 150:303-325, 2018; Schatten, Adv Anat Embryol Cell Biol 235:43-50, 2022a; Schatten, Adv Anat Embryol Cell Biol 235:17-35, 2022b).Cancer cell centrosomes differ from centrosomes in noncancer cells in displaying specific abnormalities that include phosphorylation abnormalities, overexpression of specific centrosomal proteins, abnormalities in centriole and centrosome duplication, formation of multipolar spindles that play a role in aneuploidy and genomic instability, and several others that are highlighted in the present review on ovarian cancer. Ovarian cancer cell centrosomes, like those in other cancers, display complex abnormalities that in part are based on the heterogeneity of cells in the cancer tissues resulting from different etiologies of individual cancer cells that will be discussed in more detail in this chapter.Because of the critical role of centrosomes in cancer cell proliferation, several lines of research are being pursued to target centrosomes for therapeutic intervention to inhibit abnormal cancer cell proliferation and control tumor progression. Specific centrosome abnormalities observed in ovarian cancer will be addressed in this chapter with a focus on targeting such aberrations for ovarian cancer-specific therapies.

Centrosome Movements Are TUBG1-Dependent.

The centrosome of mammalian cells is in constant movement and its motion plays a part in cell differentiation and cell division. The purpose of this study was to establish the involvement of the TUBG meshwork in centrosomal motility. In live cells, we used a monomeric red-fluorescence-protein-tagged centrin 2 gene and a green-fluorescence-protein-tagged TUBG1 gene for labeling the centrosome and the TUBG1 meshwork, respectively. We found that centrosome movements occurred in cellular sites rich in GTPase TUBG1 and single-guide RNA mediated a reduction in the expression of TUBG1, altering the motility pattern of centrosomes. We propose that the TUBG1 meshwork enables the centrosomes to move by providing them with an interacting platform that mediates positional changes. These findings uncover a novel regulatory mechanism that controls the behavior of centrosomes.

Sperm centriolar factors and genetic defects that can predict pregnancy.

The human sperm centrosome, comprising the two morphologically distinct centrioles and associated pericentriolar materials, plays a crucial role in fertilization and early embryonic development after fertilization. Once inside the oocyte, the sperm centrosome serves as a microtubule-organizing center, orchestrating mitotic spindle formation, chromosome segregation, and syngamy. Abnormalities of the sperm centrosome can lead to abnormal embryonic development and embryonic chromosomal instability, and are associated with pregnancy loss. Recent research has shed light on the molecular composition, regulation, and function of this vital organelle. Understanding the intricacies of the sperm centrosome is crucial for elucidating the mechanisms underlying successful fertilization and early embryonic development, as well as addressing infertility and developmental disorders associated with centrosomal defects.

Stable expression and multi-site location of Odf2 in mouse oocytes, sperm and early embryos.

In mammals, centriole is degenerated during early oogenesis, but it is still not known about the expression and function of centriolar structural components in oocyte meiosis. Here we found that Odf2 (outer dense fiber of sperm tails 2), a key centriolar appendage protein, was stably expressed in mouse oocytes during meiotic progression. Distinct from its single location at centrosomes in somatic mitosis, Odf2 was multiply located at microtubule organizing centers (MTOCs), chromosome centromeres and vesicles in oocyte meiosis. In addition, the vesicle-associated Odf2 disappeared in oocytes treated with the vesicle inhibitor Brefeldin A. Odf2 was mainly co-localized with the mitochondrial sheath in the sperm tail and presented as double spots, similar to γ-tubulin, in the sperm neck region. After fertilization, Odf2 remained on vesicles in embryos from 1-cell to 4-cell stage but was only detected on centrosomes at blastocyst stage. Taken together, Odf2 is expressed precisely in mouse oocytes even in the absence of intact centriole structure, and may regulate oocyte spindle assembly and positioning, additionally, the sperm motility and early embryo development.

Kinesin-1 promotes centrosome clustering and nuclear migration in the Drosophila oocyte.

Microtubules and their associated motors are important players in nucleus positioning. Although nuclear migration in Drosophila oocytes is controlled by microtubules, a precise role for microtubule-associated molecular motors in nuclear migration has yet to be reported. We characterize novel landmarks that allow a precise description of the pre-migratory stages. Using these newly defined stages, we report that, before migration, the nucleus moves from the oocyte anterior side toward the center and concomitantly the centrosomes cluster at the posterior of the nucleus. In the absence of Kinesin-1, centrosome clustering is impaired and the nucleus fails to position and migrate properly. The maintenance of a high level of Polo-kinase at centrosomes prevents centrosome clustering and impairs nuclear positioning. In the absence of Kinesin-1, SPD-2, an essential component of the pericentriolar material, is increased at the centrosomes, suggesting that Kinesin-1-associated defects result from a failure to reduce centrosome activity. Consistently, depleting centrosomes rescues the nuclear migration defects induced by Kinesin-1 inactivation. Our results suggest that Kinesin-1 controls nuclear migration in the oocyte by modulating centrosome activity.

Cell and Molecular Biology of Centrosome Structure and Function.

The centrosome field has seen enormous progress during the past few decades which spans the large areas of cell biology with new information on cell cycle controls and cellular health; immunology with centrosomes being essential for the formation of the immunological synapse; neurobiology with new insights into centrosome dysfunctions leading to disorders and disease; stem cell biology with fate-determining distribution of centrosomal material during asymmetric cell division; cancer biology with huge insights into the role of centrosomes in disease initiation, progression, and manifestation; reproductive biology with essential centrosome functions in oocytes, during fertilization and embryo development in which centrosome dysfunctions can be related back to abnormal centrosomal material in the meiotic spindle of oocytes; and several others that will be highlighted in the specific chapters of this book.

Centrosomes in Reproduction.

Centrosome functions are vitally important for all aspects of reproduction with essential functions during meiosis, fertilization, cell division, centrosome remodeling during cellular polarization for tissue formation, and all stages of subsequent embryo development. Any defects in centrosome organization and dynamics can result in meiotic spindle formation errors, meiotic division errors, infertility, subfertility, arrested or failed development, and predisposition to various diseases including cancer. These aspects of reproduction will be addressed in more detail in the following sections.

Beyond the centrosome: The mystery of microtubule organising centres across mammalian preimplantation embryos.

Mammalian preimplantation embryogenesis depends on the spatio-temporal dynamics of the microtubule cytoskeleton to enable exceptionally fast changes in cell number, function, architecture, and fate. Microtubule organising centres (MTOCs), which coordinate the remodelling of microtubules, are therefore of fundamental significance during the first days of a new life. Despite its indispensable role during early mammalian embryogenesis, the origin of microtubule growth remains poorly understood. In this review, we summarise the most recent discoveries on microtubule organisation and function during early human embryogenesis and compare these to innovative studies conducted in alternative mammalian models. We emphasise the differences and analogies of centriole inheritance and their role during the first cleavage. Furthermore, we highlight the significance of non-centrosomal MTOCs for embryo viability and discuss the potential of novel in vitro models and light-inducible approaches towards unravelling microtubule formation in research and assisted reproductive technologies.

KIF24 depletion induces clustering of supernumerary centrosomes in PDAC cells.

Clustering of supernumerary centrosomes, which potentially leads to cell survival and chromosomal instability, is frequently observed in cancers. However, the molecular mechanisms that control centrosome clustering remain largely unknown. The centrosomal kinesin KIF24 was previously shown to restrain the assembly of primary cilia in mammalian cells. Here, we revealed that KIF24 depletion suppresses multipolar spindle formation by clustering centrosomes in pancreatic ductal adenocarcinoma (PDAC) cells harboring supernumerary centrosomes. KIF24 depletion also induced hyper-proliferation and improved mitotic progression in PDAC cells. In contrast, disruption of primary cilia failed to affect the proliferation and spindle formation in KIF24-depleted cells. These results suggest a novel role for KIF24 in suppressing centrosome clustering independent of primary ciliation in centrosome-amplified PDAC cells.

Estrogens-Origin of Centrosome Defects in Human Cancer?

Estrogens are associated with a variety of diseases and play important roles in tumor development and progression. Centrosome defects are hallmarks of human cancers and contribute to ongoing chromosome missegragation and aneuploidy that manifest in genomic instability and tumor progression. Although several mechanisms underlie the etiology of centrosome aberrations in human cancer, upstream regulators are hardly known. Accumulating experimental and clinical evidence points to an important role of estrogens in deregulating centrosome homeostasis and promoting karyotype instability. Here, we will summarize existing literature of how natural and synthetic estrogens might contribute to structural and numerical centrosome defects, genomic instability and human carcinogenesis.

Control of the Hedgehog pathway by compartmentalized PKA in the primary cilium.

The Hedgehog (Hh) signaling is one of the essential signaling pathways during embryogenesis and in adults. Hh signal transduction relies on primary cilium, a specialized cell surface organelle viewed as the hub of cell signaling. Protein kinase A (PKA) has been recognized as a potent negative regulator of the Hh pathway, raising the question of how such a ubiquitous kinase specifically regulates one signaling pathway. We reviewed recent genetic, molecular and biochemical studies that have advanced our mechanistic understanding of PKA's role in Hh signaling in vertebrates, focusing on the compartmentalized PKA at the centrosome and in the primary cilium. We outlined the recently developed genetic and optical tools that can be harvested to study PKA activities during the course of Hh signal transduction.

Centrosome dysfunction associated with somatic expression of the synaptonemal complex protein TEX12.

The synaptonemal complex (SC) is a supramolecular protein scaffold that mediates chromosome synapsis and facilitates crossing over during meiosis. In mammals, SC proteins are generally assumed to have no other function. Here, we show that SC protein TEX12 also localises to centrosomes during meiosis independently of chromosome synapsis. In somatic cells, ectopically expressed TEX12 similarly localises to centrosomes, where it is associated with centrosome amplification, a pathology correlated with cancer development. Indeed, TEX12 is identified as a cancer-testis antigen and proliferation of some cancer cells is TEX12-dependent. Moreover, somatic expression of TEX12 is aberrantly activated via retinoic acid signalling, which is commonly disregulated in cancer. Structure-function analysis reveals that phosphorylation of TEX12 on tyrosine 48 is important for centrosome amplification but not for recruitment of TEX12 to centrosomes. We conclude that TEX12 normally localises to meiotic centrosomes, but its misexpression in somatic cells can contribute to pathological amplification and dysfunction of centrosomes in cancers.

Centrosome Aberrations as Drivers of Chromosomal Instability in Breast Cancer.

Chromosomal instability (CIN), or the dynamic change in chromosome number and composition, has been observed in cancer for decades. Recently, this phenomenon has been implicated as facilitating the acquisition of cancer hallmarks and enabling the formation of aggressive disease. Hence, CIN has the potential to serve as a therapeutic target for a wide range of cancers. CIN in cancer often occurs as a result of disrupting key regulators of mitotic fidelity and faithful chromosome segregation. As a consequence of their essential roles in mitosis, dysfunctional centrosomes can induce and maintain CIN. Centrosome defects are common in breast cancer, a heterogeneous disease characterized by high CIN. These defects include amplification, structural defects, and loss of primary cilium nucleation. Recent studies have begun to illuminate the ability of centrosome aberrations to instigate genomic flux in breast cancer cells and the tumor evolution associated with aggressive disease and poor patient outcomes. Here, we review the role of CIN in breast cancer, the processes by which centrosome defects contribute to CIN in this disease, and the emerging therapeutic approaches that are being developed to capitalize upon such aberrations.

Centrosome instability: when good centrosomes go bad.

The centrosome is a tiny cytoplasmic organelle that organizes and constructs massive molecular machines to coordinate diverse cellular processes. Due to its many roles during both interphase and mitosis, maintaining centrosome homeostasis is essential to normal health and development. Centrosome instability, divergence from normal centrosome number and structure, is a common pathognomonic cellular state tightly associated with cancers and other genetic diseases. As novel connections are investigated linking the centrosome to disease, it is critical to understand the breadth of centrosome functions to inspire discovery. In this review, we provide an introduction to normal centrosome function and highlight recent discoveries that link centrosome instability to specific disease states.

An extended DNA-free intranuclear compartment organizes centrosome microtubules in malaria parasites.

Proliferation of Plasmodium falciparum in red blood cells is the cause of malaria and is underpinned by an unconventional cell division mode, called schizogony. Contrary to model organisms, P. falciparum replicates by multiple rounds of nuclear divisions that are not interrupted by cytokinesis. Organization and dynamics of critical nuclear division factors remain poorly understood. Centriolar plaques, the centrosomes of P. falciparum, serve as microtubule organizing centers and have an acentriolar, amorphous structure. The small size of parasite nuclei has precluded detailed analysis of intranuclear microtubule organization by classical fluorescence microscopy. We apply recently developed super-resolution and time-lapse imaging protocols to describe microtubule reconfiguration during schizogony. Analysis of centrin, nuclear pore, and microtubule positioning reveals two distinct compartments of the centriolar plaque. Whereas centrin is extranuclear, we confirm by correlative light and electron tomography that microtubules are nucleated in a previously unknown and extended intranuclear compartment, which is devoid of chromatin but protein-dense. This study generates a working model for an unconventional centrosome and enables a better understanding about the diversity of eukaryotic cell division.

Dual spindles assemble in bovine zygotes despite the presence of paternal centrosomes.

The first mitosis of the mammalian embryo must partition the parental genomes contained in two pronuclei. In rodent zygotes, sperm centrosomes are degraded, and instead, acentriolar microtubule organizing centers and microtubule self-organization guide the assembly of two separate spindles around the genomes. In nonrodent mammals, including human or bovine, centrosomes are inherited from the sperm and have been widely assumed to be active. Whether nonrodent zygotes assemble a single centrosomal spindle around both genomes or follow the dual spindle self-assembly pathway is unclear. To address this, we investigated spindle assembly in bovine zygotes by systematic immunofluorescence and real-time light-sheet microscopy. We show that two independent spindles form despite the presence of centrosomes, which had little effect on spindle structure and were only loosely connected to the two spindles. We conclude that the dual spindle assembly pathway is conserved in nonrodent mammals. This could explain whole parental genome loss frequently observed in blastomeres of human IVF embryos.

Live imaging of the Drosophila ovarian niche shows spectrosome and centrosome dynamics during asymmetric germline stem cell division.

Drosophila female germline stem cells (GSCs) are found inside the cellular niche at the tip of the ovary. They undergo asymmetric divisions to renew the stem cell lineage and to produce sibling cystoblasts that will in turn enter differentiation. GSCs and cystoblasts contain spectrosomes, membranous structures essential for orientation of the mitotic spindle and that, particularly in GSCs, change shape depending on the cell cycle phase. Using live imaging and a fusion protein of GFP and the spectrosome component Par-1, we follow the complete spectrosome cycle throughout GSC division and quantify the relative duration of the different spectrosome shapes. We also determine that the Par-1 kinase shuttles between the spectrosome and the cytoplasm during mitosis and observe the continuous addition of new material to the GSC and cystoblast spectrosomes. Next, we use the Fly-FUCCI tool to define, in live and fixed tissues, that GSCs have a shorter G1 compared with the G2 phase. The observation of centrosomes in dividing GSCs allowed us to determine that centrosomes separate very early in G1, before centriole duplication. Furthermore, we show that the anterior centrosome associates with the spectrosome only during mitosis and that, upon mitotic spindle assembly, it translocates to the cell cortex, where it remains anchored until centrosome separation. Finally, we demonstrate that the asymmetric division of GSCs is not an intrinsic property of these cells, as the spectrosome of GSC-like cells located outside of the niche can divide symmetrically. Thus, GSCs display unique properties during division, a behaviour influenced by the surrounding niche.

Cosegregation of asymmetric features during cell division.

Cellular asymmetry plays a major role in the ageing and evolution of multicellular organisms. However, it remains unknown how the cell distinguishes 'old' from 'new' and whether asymmetry is an attribute of highly specialized cells or a feature inherent in all cells. Here, we investigate the segregation of three asymmetric features: old and new DNA, the spindle pole body (SPB, the centrosome analogue) and the old and new cell ends, using a simple unicellular eukaryote, Schizosaccharomyces pombe. To our knowledge, this is the first study exploring three asymmetric features in the same cells. We show that of the three chromosomes of S. pombe, chromosome I containing the new parental strand, preferentially segregated to the cells inheriting the old cell end. Furthermore, the new SPB also preferentially segregated to the cells inheriting the old end. Our results suggest that the ability to distinguish 'old' from 'new' and to segregate DNA asymmetrically are inherent features even in simple unicellular eukaryotes.

The SON RNA splicing factor is required for intracellular trafficking structures that promote centriole assembly and ciliogenesis.

Control of centrosome assembly is critical for cell division, intracellular trafficking, and cilia. Regulation of centrosome number occurs through the precise duplication of centrioles that reside in centrosomes. Here we explored transcriptional control of centriole assembly and find that the RNA splicing factor SON is specifically required for completing procentriole assembly. Whole genome mRNA sequencing identified genes whose splicing and expression are affected by the reduction of SON, with an enrichment in genes involved in the microtubule (MT) cytoskeleton, centrosome, and centriolar satellites. SON is required for the proper splicing and expression of CEP131, which encodes a major centriolar satellite protein and is required to organize the trafficking and MT network around the centrosomes. This study highlights the importance of the distinct MT trafficking network that is intimately associated with nascent centrioles and is responsible for procentriole development and efficient ciliogenesis.