Depletion of the LINC complex disrupts cytoskeleton dynamics and meiotic resumption in mouse oocytes

A cooperative network at the nuclear envelope counteracts LINC-mediated forces during oogenesis in C. elegans

Oogenesis involves transduction of mechanical forces from the cytoskeleton to the nuclear envelope (NE). In Caenorhabditis elegans, oocyte nuclei lacking the single lamin protein LMN-1 are vulnerable to collapse under forces mediated through LINC (linker of nucleoskeleton and cytoskeleton) complexes. Here, we use cytological analysis and in vivo imaging to investigate the balance of forces that drive this collapse and protect oocyte nuclei. We also use a mechano-node-pore sensing device to directly measure the effect of genetic mutations on oocyte nuclear stiffness. We find that nuclear collapse is not a consequence of apoptosis. It is promoted by dynein, which induces polarization of a LINC complex composed of Sad1 and UNC-84 homology 1 (SUN-1) and ZYGote defective 12 (ZYG-12). Lamins contribute to oocyte nuclear stiffness and cooperate with other inner nuclear membrane proteins to distribute LINC complexes and protect nuclei from collapse. We speculate that a similar network may protect oocyte integrity during extended oocyte arrest in mammals.

Homozygous Variant in KASH5 Causes Premature Ovarian Insufficiency by Disordered Meiotic Homologous Pairing

CONTEXT

Premature ovarian insufficiency (POI) affects 1% to 3.7% of women at reproductive age, and its etiology is heterogeneous. The linker of nucleoskeleton and cytoskeleton (LINC) complex, consisting of KASH5 and SUN1, plays an indispensable role in meiotic homolog pairing, determining the ovarian reserve. However, their roles in the pathogenesis of POI are unknown.

OBJECTIVE

To investigate the role of KASH5 variation in the pathogenesis of POI.

DESIGN

Whole-exome sequencing was performed in a pedigree with 2 POI patients. The pathogenicity of identified variant was illustrated by in vitro functional studies, and its effect on ovarian function and meiosis was confirmed by histological analysis and oocyte spreads with Kash5 C-terminal deleted mice model.

RESULTS

A homozygous splicing site variant in KASH5 (c.747G > A) was identified. In vitro studies found the variant disturbed the nuclear membrane localization of KASH5 and its binding with SUN1. Moreover, the Kash5 C-terminal deleted mice revealed defective meiotic homolog pairing and accelerated depletion of oocytes.

CONCLUSIONS

The splicing site variant in KASH5 is responsible for POI due to defective meiotic homolog pairing and accelerated depletion of oocytes. Our study is the first to report disorganized LINC complex participating in POI pathogenesis, potentially suggesting the essential roles of meiotic telomere attachment and dynein-driven proteins for chromosome movement in ovarian function maintenance.

Homozygous missense mutation in CCDC155 disrupts the transmembrane distribution of CCDC155 and SUN1, resulting in non-obstructive azoospermia and premature ovarian insufficiency in humans

Non-obstructive azoospermia (NOA) and premature ovarian insufficiency (POI) represent the most serious forms of human infertility caused by gametogenic failure. Although whole-exome sequencing (WES) has uncovered multiple monogenic causes of human infertility, our knowledge of the genetic basis of human gametogenesis defects remains at a rudimentary stage. Coiled-coil-domain-containing protein 155 (CCDC155) encodes a core component of the linker of the nucleoskeleton and cytoskeleton complex that is essential for modulating telomere-led chromosome movements during the meiotic prophase of mice. Additionally, Ccdc155 deficiency in mice causes infertility in both sexes with meiotic arrest. In this study, we applied WES to identify the pathogenic genes for 15 NOA and POI patients whose parents were consanguineous and identified a novel homozygous missense mutation in CCDC155 [c.590T>C (p.Leu197Pro)] in a pair of familial NOA and POI patients whose parents were first cousins. The affected spermatocytes were unable to complete meiotic division coupled with unresolved repair of the DNA double-strand break. This rare missense mutation with lesions in the conserved CC domain of CCDC155 blocked nuclear envelope (NE) distribution and subsequently prevented NE-specific enrichment of Sad1- and UNC84-domain-containing 1 either ex vivo or in vitro, eventually leading to disruptive NE anchoring of chromosome-induced meiotic arrest in both sexes. This study presents the first evidence of the necessity of the SUN1-CCDC155 complex during human meiosis and provides insight into the CCDC155 CC domain, thereby expanding the genetic spectrum of human NOA and POI and promoting adequate genetic counselling and appropriate fertility guidance for these patients.

Nuclear envelope mechanobiology: linking the nuclear structure and function

The nucleus, central to cellular activity, relies on both direct mechanical input as well as its molecular transducers to sense external stimuli and respond by regulating intra-nuclear chromatin organization that determines cell function and fate. In mesenchymal stem cells of musculoskeletal tissues, changes in nuclear structures are emerging as a key modulator of their differentiation and proliferation programs. In this review we will first introduce the structural elements of the nucleoskeleton and discuss the current literature on how nuclear structure and signaling are altered in relation to environmental and tissue level mechanical cues. We will focus on state-of-the-art techniques to apply mechanical force and methods to measure nuclear mechanics in conjunction with DNA, RNA, and protein visualization in living cells. Ultimately, combining real-time nuclear deformations and chromatin dynamics can be a powerful tool to study mechanisms of how forces affect the dynamics of genome function.

Molecular mimicry between SARS-CoV-2 and the female reproductive system

Introduction

Oogenesis, the process of egg production by the ovary, involves a complex differentiation program leading to the production of functional oocytes. This process comprises a sequential pathway of steps that are finely regulated. The question related to SARS‐CoV‐2 infection and fertility has been evoked for several reasons, including the mechanism of molecular mimicry, which may contribute to female infertility by leading to the generation of deleterious autoantibodies, possibly contributing to the onset of an autoimmune disease in infected patients.

Objective

The immunological potential of the peptides shared between SARS‐CoV‐2 spike glycoprotein and oogenesis‐related proteins; Thus we planned a systematic study to improve our understanding of the possible effects of SARS‐CoV‐2 infection on female fertility using the angle of molecular mimicry as a starting point.

Methods

A library of 82 human proteins linked to oogenesis was assembled at random from UniProtKB database using oogenesis, uterine receptivity, decidualization, and placentation as a key words. For the analyses, an artificial polyprotein was built by joining the 82 a sequences of the oogenesis‐associated proteins. These were analyzed by searching the Immune Epitope DataBase for immunoreactive SARS‐CoV‐2 spike glycoprotein epitopes hosting the shared pentapeptides.

Results

SARS‐CoV‐2 spike glycoprotein was found to share 41 minimal immune determinants, that is, pentapeptides, with 27 human proteins that relate to oogenesis, uterine receptivity, decidualization, and placentation. All the shared pentapeptides that we identified, with the exception of four, are also present in SARS‐CoV‐2 spike glycoprotein–derived epitopes that have been experimentally validated as immunoreactive.

Diverse roles for CDK-associated activity during spermatogenesis

The primary function of cyclin-dependent kinases (CDKs) in complex with their activating cyclin partners is to promote mitotic division in somatic cells. This canonical cell cycle-associated activity is also crucial for fertility as it allows the proliferation and differentiation of stem cells within the reproductive organs to generate meiotically competent cells. Intriguingly, several CDKs exhibit meiosis-specific functions and are essential for the completion of the two reductional meiotic divisions required to generate haploid gametes. These meiosis-specific functions are mediated by both known CDK/cyclin complexes and meiosis-specific CDK-regulators and are important for a variety of processes during meiotic prophase. The majority of meiotic defects observed upon deletion of these proteins occur during the extended prophase I of the first meiotic division. Importantly a lack of redundancy is seen within the meiotic arrest phenotypes described for many of these proteins, suggesting intricate layers of cell cycle control are required for normal meiotic progression. Using the process of male germ cell development (spermatogenesis) as a reference, this review seeks to highlight the diverse roles of selected CDKs their activators, and their regulators during gametogenesis.

Molecular-Level Interactions between Engineered Materials and Cells

Various recent experimental observations indicate that growing cells on engineered materials can alter their physiology, function, and fate. This finding suggests that better molecular-level understanding of the interactions between cells and materials may guide the design and construction of sophisticated artificial substrates, potentially enabling control of cells for use in various biomedical applications. In this review, we introduce recent research results that shed light on molecular events and mechanisms involved in the interactions between cells and materials. We discuss the development of materials with distinct physical, chemical, and biological features, cellular sensing of the engineered materials, transfer of the sensing information to the cell nucleus, subsequent changes in physical and chemical states of genomic DNA, and finally the resulting cellular behavior changes. Ongoing efforts to advance materials engineering and the cell-material interface will eventually expand the cell-based applications in therapies and tissue regenerations.

Microtubules Deform the Nuclear Membrane and Disrupt Nucleocytoplasmic Transport in Tau-Mediated Frontotemporal Dementia

The neuronal microtubule-associated protein tau, MAPT, is central to the pathogenesis of many dementias. Autosomal-dominant mutations in MAPT cause inherited frontotemporal dementia (FTD), but the underlying pathogenic mechanisms are unclear. Using human stem cell models of FTD due to MAPT mutations, we find that tau becomes hyperphosphorylated and mislocalizes to cell bodies and dendrites in cortical neurons, recapitulating a key early event in FTD. Mislocalized tau in the cell body leads to abnormal microtubule movements in FTD-MAPT neurons that grossly deform the nuclear membrane. This results in defective nucleocytoplasmic transport, which is corrected by microtubule depolymerization. Neurons in the post-mortem human FTD-MAPT cortex have a high incidence of nuclear invaginations, indicating that tau-mediated nuclear membrane dysfunction is an important pathogenic process in FTD. Defects in nucleocytoplasmic transport in FTD point to important commonalities in the pathogenic mechanisms of tau-mediated dementias and ALS-FTD due to TDP-43 and C9orf72 mutations.

Loss and Rebirth of the Animal Microtubule Organizing Center: How Maternal Expression of Centrosomal Proteins Cooperates with the Sperm Centriole in Zygotic Centrosome Reformation

Centrosomes are the main microtubule organizing centers in animal cells. In particular during embryogenesis, they ensure faithful spindle formation and proper cell divisions. As metazoan centrosomes are eliminated during oogenesis, they have to be reassembled upon fertilization. Most metazoans use the sperm centrioles as templates for new centrosome biogenesis while the egg's cytoplasm re-prepares all components for on-going centrosome duplication in rapidly dividing embryonic cells. We discuss our knowledge and the experimental challenges to analyze zygotic centrosome reformation, which requires genetic experiments to enable scrutinizing respective male and female contributions. Male and female knockout animals and mRNA injection to mimic maternal expression of centrosomal proteins could point a way to the systematic molecular dissection of the process. The most recent data suggest that timely expression of centrosome components in oocytes is the key to zygotic centrosome reformation that uses male sperm as coordinators for de novo centrosome production.

Autoantibodies against HSF1 and CCDC155 as Biomarkers of Early-Stage, High-Grade Serous Ovarian Cancer

Background: Tumor-directed circulating autoantibodies (AAb) are a well-established feature of many solid tumor types, and are often observed prior to clinical disease manifestation. As such, they may provide a good indicator of early disease development. We have conducted a pilot study to identify novel AAbs as markers of early-stage HGSOCs.Methods: A rare cohort of patients with early (FIGO stage Ia-c) HGSOCs for IgG, IgA, and IgM-mediated AAb reactivity using high-content protein arrays (containing 9,184 individual proteins). AAb reactivity against selected antigens was validated by ELISA in a second, independent cohort of individual patients.Results: A total of 184 antigens were differentially detected in early-stage HGSOC patients compared with all other patient groups assessed. Among the six most highly detected "early-stage" antigens, anti-IgA AAbs against HSF1 and anti-IgG AAbs CCDC155 (KASH5; nesprin 5) were significantly elevated in patients with early-stage malignancy. Receiver operating characteristic (ROC) analysis suggested that AAbs against HSF1 provided better detection of early-stage malignancy than CA125 alone. Combined measurement of anti-HSF1, anti-CCDC155, and CA125 also improved efficacy at higher sensitivity.Conclusions: The combined measurement of anti-HSF1, anti-CCDC155, and CA125 may be useful for early-stage HGSOC detection.Impact: This is the first study to specifically identify AAbs associated with early-stage HGSOC. The presence and high frequency of specific AAbs in early-stage cancer patients warrants a larger scale examination to define their value for early disease detection at primary diagnosis and/or recurrence. Cancer Epidemiol Biomarkers Prev; 27(2); 183-92. ©2017 AACR.

Mechano-adaptation of the stem cell nucleus

Exogenous mechanical forces are transmitted through the cell and to the nucleus, initiating mechanotransductive signaling cascades with profound effects on cellular function and stem cell fate. A growing body of evidence has shown that the force sensing and force-responsive elements of the nucleus adapt to these mechanotransductive events, tuning their response to future mechanical input. The mechanisms underlying this “mechano-adaptation” are only just beginning to be elucidated, and it remains poorly understood how these components act and adapt in tandem to drive stem cell differentiation. Here, we review the evidence on how the stem cell nucleus responds and adapts to physical forces, and provide a perspective on how this mechano-adaptation may function to drive and enforce stem cell differentiation.

Function and regulation mechanism of Chk1 during meiotic maturation in porcine oocytes

Checkpoint 1 (Chk1), as an important member of DNA replication checkpoint and DNA damage response, has an important role during the G2/M stage of mitosis. In this study, we used porcine oocyte as a model to investigate the function of Chk1 during porcine oocyte maturation. Chk1 was expressed from germinal vesicle (GV) to metaphase II (MII) stages, mainly localized in the cytoplasm at GV stage and moved to the spindle after germinal vesicle breakdown (GVBD). Chk1 depletion not only induced oocytes to be arrested at MI stage with abnormal chromosomes arrangement, but also inhibited the degradation of Cyclin B1 and decreased the expression of Mitotic Arrest Deficient 2-Like 1 (Mad2L1), one of spindle assembly checkpoint (SAC) proteins, and cadherin 1 (Cdh1), one of coactivation for anaphase-promoting complex/cyclosome (APC/C). Moreover, Chk1 overexpression delayed GVBD. These results demonstrated that Chk1 facilitated the timely degradation of Cyclin B1 at anaphase I (AI) and maintained the expression of Mad2L1 and Cdh1, which ensured that all chromosomes were accurately located in a line, and then oocytes passed metaphase I (MI) and AI and exited from the first meiotic division successfully. In addition, we proved that Chk1 had not function on GVBD of porcine oocytes, which suggested that maturation of porcine oocytes did not need the DNA damage checkpoint, which was different from the mouse oocyte maturation.

Regulation of GVBD in mouse oocytes by miR-125a-3p and Fyn kinase through modulation of actin filaments

Meiotically arrested oocytes are characterized by the presence of the nuclear structure known as germinal-vesicle (GV), the breakdown of which (GVBD) is associated with resumption of meiosis. Fyn is a pivotal factor in resumption of the first meiotic division; its inhibition markedly decreases the fraction of oocytes undergoing GVBD. Here, we reveal that in mouse oocytes Fyn is post-transcriptionally regulated by miR-125a-3p. We demonstrate that in oocytes resuming meiosis miR-125a-3p and Fyn exhibit a reciprocal expression pattern; miR-125a-3p decreases alongside with an increase in Fyn expression. Microinjection of miR-125a-3p inhibits GVBD, an effect that is markedly reduced by Fyn over-expression, and impairs the organization of the actin rim surrounding the nucleus. Lower rate of GVBD is also observed in oocytes exposed to cytochalasin-D or blebbistatin, which interfere with actin polymerization and contractility of actin bundles, respectively. By down-regulating Fyn in HEK-293T cells, miR-125a-3p reduces the interaction between actin and A-type lamins, which constitute the nuclear-lamina. Our findings suggest a mechanism, by which a decrease in miR-125a-3p during oocyte maturation facilitates GVBD by allowing Fyn up-regulation and the resulting stabilization of the interaction between actin and A-type lamins.