Defective folliculogenesis in female mice lacking Vaccinia-related kinase 1

Nuclear functions regulated by the VRK1 kinase

In the nucleus, the VRK1 Ser-Thr kinase is distributed in nucleoplasm and chromatin, where it has different roles. VRK1 expression increases in response to mitogenic signals. VRK1 regulates cyclin D1 expression at G0 exit and facilitates chromosome condensation at the end of G2 and G2/M progression to mitosis. These effects are mediated by the phosphorylation of histone H3 at Thr3 by VRK1, and later in mitosis by haspin. VRK1 regulates the apigenetic patterns of histones in processes requiring chromating remodeling, such as transcription, replication and DNA repair. VRK1 is overexpressed in tumors, facilitating tumor progression and resistance to genotoxic treatments. VRK1 also regulates the organization of Cajal bodies assembled on coilin, which are necessary for the assembly of different types of RNP complexes. VRK1 pathogenic variants cuase defects in Cajal bodies, functionally altering neurons with long axons and leading to neurological diseases, such as amyotrophic laterla sclerosis, spinal muscular atrophy, distal hereditay motor neuropathies and Charcot-Marie-Tooth.

VRK1 variants at the cross road of Cajal body neuropathogenic mechanisms in distal neuropathies and motor neuron diseases

Distal hereditary neuropathies and neuro motor diseases are complex neurological phenotypes associated with pathogenic variants in a large number of genes, but in some the origin is unknown. Recently, rare pathogenic variants of the human VRK1 gene have been associated with these neurological phenotypes. All VRK1 pathogenic variants are recessive, and their clinical presentation occurs in either homozygous or compound heterozygous patients. The pathogenic VRK1 gene pathogenic variants are located in three clusters within the protein sequence. The main, and initial, shared clinical phenotype among VRK1 pathogenic variants is a distal progressive loss of motor and/or sensory function, which includes diseases such as spinal muscular atrophy, Charcot-Marie-Tooth, amyotrophic lateral sclerosis and hereditary spastic paraplegia. In most cases, symptoms start early in infancy, or in utero, and are slowly progressive. Additional neurological symptoms vary among non-related patients, probably because of their different VRK1 variants and their genetic background. The underlying common pathogenic mechanism, by its functional impairment, is a likely consequence of the roles that the VRK1 protein plays in the regulation on the stability and assembly of Cajal bodies, which affect RNA maturation and processing, neuronal migration of RNPs along axons, and DNA-damage responses. Alterations of these processes are associated with several neuro sensory or motor syndromes. The clinical heterogeneity of the neurological phenotypes associated with VRK1 is a likely consequence of the protein complexes in which VRK1 is integrated, which include several proteins known to be associated with Cajal bodies and DNA damage responses. Several hereditary distal neurological diseases are a consequence of pathogenic variants in genes that alter these cellular functions. We conclude that VRK1-related distal hereditary neuropathies and motor neuron diseases represent a novel subgroup of Cajal body related neurological syndromes.

Three-dimensional reconstruction of testis cords/seminiferous tubules

BACKGROUND

Due to the development of novel equipment for the acquisition of two-dimensional serial images and software capable of displaying three-dimensional (3D) images from serial images, the accurate 3D reconstruction of organs and tissues has become possible.

METHODS

Based on published studies, this review summarizes techniques for the 3D reconstruction of the testis cords/seminiferous tubules, with special reference to our method using serial paraffin sections and 3D visualization software.

MAIN FINDINGS

The testes of mice, rats, and hamsters of various ages were 3D reconstructed and species and age differences in the structures of the testis cords/seminiferous tubules were analyzed. Our method is advantageous because conventional paraffin-embedded normal and pathological specimens may be utilized for the 3D analysis without the need for complicated and expensive equipment.

CONCLUSION

By further decreasing the time and labor required for the procedure and adding information on molecular localization, the technique for 3D reconstruction will contribute to the elucidation of not only the structures, but also the functions of various organs, including the testis.

Recent updates on animal models for understanding the etiopathogenesis of polycystic ovarian syndrome

Polycystic ovarian syndrome (PCOS) is the primary cause of female infertility affecting several women worldwide. Changes in hormonal functions such as hyperandrogenism are considered a significant factor in developing PCOS in women. In addition, many molecular pathways are involved in the pathogenesis of PCOS in women. To have better insights about PCOS, it is data from clinical studies carried on women suffering from PCOS should be collected. However, this approach has several implications, including ethical considerations, cost involved and availability of subject. Moreover, during the early drug development process, it is always advisable to use non-human models mimicking human physiology as they are less expensive, readily available, have a shorter gestation period and less risk involved. Many animal models have been reported that resemble the PCOS pathways in human subjects. However, the models developed on rats and mice are more preferred over other rodent/non-rodent models due to their closer resemblance with human PCOS development mechanism. The most extensively reported PCOS models for rats and mice include those induced by using testosterone, letrozole and estradiol valerate. As the pathophysiology of PCOS is complex, none of the explored models completely surrogates the PCOS related conditions occurring in women. Hence, there is a need to develop an animal model that can resemble the pathophysiology of PCOS in women. The review focuses on various animal models explored to understand the pathophysiology of PCOS. The article also highlights some environmental and food-related models that have been used to induce PCOS.

Three-dimensional imaging and reconstruction of the whole ovary and testis: a new frontier for the reproductive scientist

The 3D functional reconstruction of a whole organ or organism down to the single cell level and to the subcellular components and molecules is a major future scientific challenge. The recent convergence of advanced imaging techniques with an impressively increased computing power allowed early attempts to translate and combine 2D images and functional data to obtain in-silico organ 3D models. This review first describes the experimental pipeline required for organ 3D reconstruction: from the collection of 2D serial images obtained with light, confocal, light-sheet microscopy or tomography, followed by their registration, segmentation and subsequent 3D rendering. Then, we summarise the results of investigations performed so far by applying these 3D image analyses to the study of the female and male mammalian gonads. These studies highlight the importance of working towards a 3D in-silico model of the ovary and testis as a tool to gain insights into their biology during the phases of differentiation or adulthood, in normal or pathological conditions. Furthermore, the use of 3D imaging approaches opens to key technical improvements, ranging from image acquisition to optimisation and development of new processing tools, and unfolds novel possibilities for multidisciplinary research.

Three-Dimensional Micro-Computed Tomography of the Adult Mouse Ovary

In the mouse ovary, folliculogenesis proceeds through eight main growth stages, from small primordial type 1 (T1) to fully grown antral T8 follicles. Most of our understanding of this process was obtained with approaches that disrupted the ovary three-dimensional (3D) integrity. Micro-Computed Tomography (microCT) allows the maintenance of the organ structure and a true in-silico 3D reconstruction, with cubic voxels and isotropic resolution, giving a precise spatial mapping of its functional units. Here, we developed a robust method that, by combining an optimized contrast procedure with microCT imaging of the tiny adult mouse ovary, allowed 3D mapping and counting of follicles, from pre-antral secondary T4 (53.2 ± 12.7 μm in diameter) to antral T8 (321.0 ± 21.3 μm) and corpora lutea, together with the major vasculature branches. Primordial and primary follicles (T1–T3) could not be observed. Our procedure highlighted, with unprecedent details, the main functional compartments of the growing follicle: granulosa, antrum, cumulus cells, zona pellucida, and oocyte with its nucleus. The results describe a homogeneous distribution of all follicle types between the ovary dorsal and ventral regions. Also, they show that each of the eight sectors, virtually segmented along the dorsal-ventral axis, houses an equal number of each follicle type. Altogether, these data suggest that follicle recruitment is homogeneously distributed all-over the ovarian surface. This topographic reconstruction builds sound bases for modeling follicles position and, prospectively, could contribute to our understanding of folliculogenesis dynamics, not only under normal conditions, but, importantly, during aging, in the presence of pathologies or after hormones or drugs administration.

Hard and soft X-ray imaging to resolve human ovarian cortical structures

Laboratory and synchrotron X-ray tomography are powerful tools for non-invasive studies of biological samples at micrometric resolution. In particular, the development of phase contrast imaging is enabling the visualization of sample details with a small range of attenuation coefficients, thus allowing in-depth analyses of anatomical and histological structures. Reproductive medicine is starting to profit from these techniques, mainly applied to animal models. This study reports the first imaging of human ovarian tissue where the samples consisted of surgically obtained millimetre fragments, properly fixed, stained with osmium tetroxide and included in epoxydic resin. Samples were imaged by the use of propagation phase contrast synchrotron radiation micro-computed tomography (microCT), obtained at the SYRMEP beamline of Elettra light source (Trieste, Italy), and X-ray absorption microCT at the Theoretical Biology MicroCT Imaging Laboratory in Vienna, Austria. The reconstructed microCT images were compared with the soft X-ray absorption and phase contrast images acquired at the TwinMic beamline of Elettra in order to help with the identification of structures. The resulting images allow the regions of the cortex and medulla of the ovary to be distinguished, identifying early-stage follicles and visualizing the distribution of blood vessels. The study opens to further application of micro-resolved 3D imaging to improve the understanding of human ovary's structure and support diagnostics as well as advances in reproductive technologies.

Vrk1 partial Knockdown in Mice Results in Reduced Brain Weight and Mild Motor Dysfunction, and Indicates Neuronal VRK1 Target Pathways

Mutations in Vaccinia-related kinase 1 (VRK1) have emerged as a cause of severe neuronal phenotypes in human, including brain developmental defects and degeneration of spinal motor neurons, leading to Spinal Muscular Atrophy (SMA) or early onset Amyotrophic Lateral Sclerosis (ALS). Vrk1 gene-trap partial Knockout (KO) mice (Vrk1GT3/GT3), which express decreased levels of Vrk1, are sterile due to impaired gamete production. Here, we examined whether this mouse model also presents neuronal phenotypes. We found a 20-50% reduction in Vrk1 expression in neuronal tissues of the Vrk1GT3/GT3 mice, leading to mild neuronal phenotypes including significant but small reduction in brain mass and motor (rotarod) impairment. Analysis of gene expression in the Vrk1GT3/GT3 cortex predicts novel roles for VRK1 in neuronal pathways including neurotrophin signaling, axon guidance and pathways implicated in the pathogenesis of ALS. Together, our studies of the partial KO Vrk1 mice reveal that even moderately reduced levels of Vrk1 expression result in minor neurological impairment and indicate new neuronal pathways likely involving VRK1.

Implication of the VRK1 chromatin kinase in the signaling responses to DNA damage: a therapeutic target?

DNA damage causes a local distortion of chromatin that triggers the sequential processes that participate in specific DNA repair mechanisms. This initiation of the repair response requires the involvement of a protein whose activity can be regulated by histones. Kinases are candidates to regulate and coordinate the connection between a locally altered chromatin and the response initiating signals that lead to identification of the type of lesion and the sequential steps required in specific DNA damage responses (DDR). This initiating kinase must be located in chromatin, and be activated independently of the type of DNA damage. We review the contribution of the Ser-Thr vaccinia-related kinase 1 (VRK1) chromatin kinase as a new player in the signaling of DNA damage responses, at chromatin and cellular levels, and its potential as a new therapeutic target in oncology. VRK1 is involved in the regulation of histone modifications, such as histone phosphorylation and acetylation, and in the formation of γH2AX, NBS1 and 53BP1 foci induced in DDR. Induction of DNA damage by chemotherapy or radiation is a mainstay of cancer treatment. Therefore, novel treatments can be targeted to proteins implicated in the regulation of DDR, rather than by directly causing DNA damage.

Imaging the ovary

During each reproductive cycle, the ovary exhibits tissue remodelling and cyclic vasculature changes associated with hormonally regulated folliculogenesis, follicle rupture, luteal formation and regression. However, the relationships among different types of follicles and corpora lutea are unclear, and the role of ovarian vasculature in folliculogenesis and luteal dynamics has not been extensively investigated. Understanding of ovarian physiology and pathophysiology relies upon elucidation of ovarian morphology and architecture. This paper summarizes the literature on traditional approaches to the imaging of ovarian structures and discusses recent advances in ovarian imaging. Traditional in-vivo ultrasound, together with histological and electron microscopic approaches provide detailed views of the ovary at organ, tissue and molecular levels. However, in-vivo imaging is limited to antral and larger follicles whereas histological imaging is mainly two-dimensional in nature. Also discussed are emerging approaches in the use of near-infrared fluorophores to image follicles in live animals to detect preantral follicles as well as visualizing ovarian structures using CLARITY in fixed whole ovaries to elucidate three-dimensional interrelationships among follicles, corpora lutea and ovarian vasculature. Advances in ovarian imaging techniques provide new understanding of ovarian physiology and allow for the development of better tools to diagnose ovarian pathophysiology.

CLARITY reveals dynamics of ovarian follicular architecture and vasculature in three-dimensions

Optimal distribution of heterogeneous organelles and cell types within an organ is essential for physiological processes. Unique for the ovary, hormonally regulated folliculogenesis, ovulation, luteal formation/regression and associated vasculature changes lead to tissue remodeling during each reproductive cycle. Using the CLARITY approach and marker immunostaining, we identified individual follicles and corpora lutea in intact ovaries. Monitoring lifetime changes in follicle populations showed age-dependent decreases in total follicles and percentages of advanced follicles. Follicle development from primordial to preovulatory stage was characterized by 3 × 10⁵-fold increases in volume, decreases in roundness, and decreased clustering of same stage follicles. Construction of follicle-vasculature relationship maps indicated age- and gonadotropin-dependent increases in vasculature and branching surrounding follicles. Heterozygous mutant mice with deletion of hypoxia-response element in the vascular endothelial growth factor A (VEGFA) promoter showed defective ovarian vasculature and decreased ovulatory responses. Unilateral intrabursal injection of axitinib, an inhibitor of VEGF receptors, retarded neo-angiogenesis that was associated with defective ovulation in treated ovaries. Our approach uncovers unique features of ovarian architecture and essential roles of vasculature in organizing follicles to allow future studies on normal and diseased human ovaries. Similar approaches could also reveal roles of neo-angiogenesis during embryonic development and tumorigenesis.

Ursolic acid exerts anti-cancer activity by suppressing vaccinia-related kinase 1-mediated damage repair in lung cancer cells

Many mitotic kinases have been targeted for the development of anti-cancer drugs, and inhibitors of these kinases have been expected to perform well for cancer therapy. Efforts focused on selecting good targets and finding specific drugs to target are especially needed, largely due to the increased frequency of anti-cancer drugs used in the treatment of lung cancer. Vaccinia-related kinase 1 (VRK1) is a master regulator in lung adenocarcinoma and is considered a key molecule in the adaptive pathway, which mainly controls cell survival. We found that ursolic acid (UA) inhibits the catalytic activity of VRK1 via direct binding to the catalytic domain of VRK1. UA weakens surveillance mechanisms by blocking 53BP1 foci formation induced by VRK1 in lung cancer cells, and possesses synergistic anti-cancer effects with DNA damaging drugs. Taken together, UA can be a good anti-cancer agent for targeted therapy or combination therapy with DNA damaging drugs for lung cancer patients.

VRK1 regulates Cajal body dynamics and protects coilin from proteasomal degradation in cell cycle

Cajal bodies (CBs) are nuclear organelles associated with ribonucleoprotein functions and RNA maturation. CBs are assembled on coilin, its main scaffold protein, in a cell cycle dependent manner. The Ser-Thr VRK1 (vaccinia-related kinase 1) kinase, whose activity is also cell cycle regulated, interacts with and phosphorylates coilin regulating assembly of CBs. Coilin phosphorylation is not necessary for its interaction with VRK1, but it occurs in mitosis and regulates coilin stability. Knockdown of VRK1 or VRK1 inactivation by serum deprivation causes a loss of coilin phosphorylation in Ser184 and of CBs formation, which are rescued with an active VRK1, but not by kinase-dead VRK1. The phosphorylation of coilin in Ser184 occurs during mitosis before assembly of CBs. Loss of coilin phosphorylation results in disintegration of CBs, and of coilin degradation that is prevented by proteasome inhibitors. After depletion of VRK1, coilin is ubiquitinated in nuclei, which is partly mediated by mdm2, but its proteasomal degradation occurs in cytosol and is prevented by blocking its nuclear export. We conclude that VRK1 is a novel regulator of CBs dynamics and stability in cell cycle by protecting coilin from ubiquitination and degradation in the proteasome, and propose a model of CB dynamics.

Synchrotron X-ray imaging of pulmonary alveoli in respiration in live intact mice

Despite nearly a half century of studies, it has not been fully understood how pulmonary alveoli, the elementary gas exchange units in mammalian lungs, inflate and deflate during respiration. Understanding alveolar dynamics is crucial for treating patients with pulmonary diseases. In-vivo, real-time visualization of the alveoli during respiration has been hampered by active lung movement. Previous studies have been therefore limited to alveoli at lung apices or subpleural alveoli under open thorax conditions. Here we report direct and real-time visualization of alveoli of live intact mice during respiration using tracking X-ray microscopy. Our studies, for the first time, determine the alveolar size of normal mice in respiration without positive end expiratory pressure as 58 ± 14 (mean ± s.d.) μm on average, accurately measured in the lung bases as well as the apices. Individual alveoli of normal lungs clearly show heterogeneous inflation from zero to ~25% (6.7 ± 4.7% (mean ± s.d.)) in size. The degree of inflation is higher in the lung bases (8.7 ± 4.3% (mean ± s.d.)) than in the apices (5.7 ± 3.2% (mean ± s.d.)). The fraction of the total tidal volume allocated for alveolar inflation is 34 ± 3.8% (mean ± s.e.m). This study contributes to the better understanding of alveolar dynamics and helps to develop potential treatment options for pulmonary diseases.

Luteolin suppresses cancer cell proliferation by targeting vaccinia-related kinase 1

Uncontrolled proliferation, a major feature of cancer cells, is often triggered by the malfunction of cell cycle regulators such as protein kinases. Recently, cell cycle-related protein kinases have become attractive targets for anti-cancer therapy, because they play fundamental roles in cellular proliferation. However, the protein kinase-targeted drugs that have been developed so far do not show impressive clinical results and also display severe side effects; therefore, there is undoubtedly a need to investigate new drugs targeting other protein kinases that are critical in cell cycle progression. Vaccinia-related kinase 1 (VRK1) is a mitotic kinase that functions in cell cycle regulation by phosphorylating cell cycle-related substrates such as barrier-to-autointegration factor (BAF), histone H3, and the cAMP response element (CRE)-binding protein (CREB). In our study, we identified luteolin as the inhibitor of VRK1 by screening a small-molecule natural compound library. Here, we evaluated the efficacy of luteolin as a VRK1-targeted inhibitor for developing an effective anti-cancer strategy. We confirmed that luteolin significantly reduces VRK1-mediated phosphorylation of the cell cycle-related substrates BAF and histone H3, and directly interacts with the catalytic domain of VRK1. In addition, luteolin regulates cell cycle progression by modulating VRK1 activity, leading to the suppression of cancer cell proliferation and the induction of apoptosis. Therefore, our study suggests that luteolin-induced VRK1 inhibition may contribute to establish a novel cell cycle-targeted strategy for anti-cancer therapy.

Dendritic planarity of Purkinje cells is independent of Reelin signaling

The dendritic planarity of Purkinje cells is critical for cerebellar circuit formation. In the absence of Crk and CrkL, the Reelin pathway does not function resulting in partial Purkinje cell migration and defective dendritogenesis. However, the relationships among Purkinje cell migration, dendritic development and Reelin signaling have not been clearly delineated. Here, we use synchrotron X-ray microscopy to obtain 3-D images of Golgi-stained Purkinje cell dendrites. Purkinje cells that failed to migrate completely exhibited conical dendrites with abnormal 3-D arborization and reduced dendritic complexity. Furthermore, their spines were fewer in number with a distorted morphology. In contrast, Purkinje cells that migrated successfully displayed planar dendritic and spine morphologies similar to normal cells, despite reduced dendritic complexity. These results indicate that, during cerebellar formation, Purkinje cells migrate into an environment that supports development of dendritic planarity and spine formation. While Reelin signaling is important for the migration process, it does not make a direct major contribution to dendrite formation.

Mutations in VRK1 associated with complex motor and sensory axonal neuropathy plus microcephaly

IMPORTANCE

Patients with rare diseases and complex clinical presentations represent a challenge for clinical diagnostics. Genomic approaches are allowing the identification of novel variants in genes for very rare disorders, enabling a molecular diagnosis. Genomics is also revealing a phenotypic expansion whereby the full spectrum of clinical expression conveyed by mutant alleles at a locus can be better appreciated.

OBJECTIVE

To elucidate the molecular cause of a complex neuropathy phenotype in 3 patients by applying genomic sequencing strategies.

DESIGN, SETTING, AND PARTICIPANTS

Three affected individuals from 2 unrelated families presented with a complex neuropathy phenotype characterized by axonal sensorimotor neuropathy and microcephaly. They were recruited into the Centers for Mendelian Genomics research program to identify the molecular cause of their phenotype. Whole-genome, targeted whole-exome sequencing, and high-resolution single-nucleotide polymorphism arrays were performed in genetics clinics of tertiary care pediatric hospitals and biomedical research institutions.

MAIN OUTCOMES AND MEASURES

Whole-genome and whole-exome sequencing identified the variants responsible for the patients' clinical phenotype.

RESULTS

We identified compound heterozygous alleles in 2 affected siblings from 1 family and a homozygous nonsense variant in the third unrelated patient in the vaccinia-related kinase 1 gene (VRK1). In the latter subject, we found a common haplotype on which the nonsense mutation occurred and that segregates in the Ashkenazi Jewish population.

CONCLUSIONS AND RELEVANCE

We report the identification of disease-causing alleles in 3 children from 2 unrelated families with a previously uncharacterized complex axonal motor and sensory neuropathy accompanied by severe nonprogressive microcephaly and cerebral dysgenesis. Our data raise the question of whether VRK1 mutations disturb cell cycle progression and may result in apoptosis of cells in the nervous system. The application of unbiased genomic approaches allows the identification of potentially pathogenic mutations in unsuspected genes in highly genetically heterogeneous and uncharacterized neurological diseases.

VRK1 interacts with p53 forming a basal complex that is activated by UV-induced DNA damage

DNA damage immediate cellular response requires the activation of p53 by kinases. We found that p53 forms a basal stable complex with VRK1, a Ser-Thr kinase that responds to UV-induced DNA damage by specifically phosphorylating p53. This interaction takes place through the p53 DNA binding domain, and frequent DNA-contact mutants of p53, such as R273H, R248H or R280K, do not disrupt the complex. UV-induced DNA damage activates VRK1, and is accompanied by phosphorylation of p53 at Thr-18 before it accumulates. We propose that the VRK1-p53 basal complex is an early-warning system for immediate cellular responses to DNA damage.

Growth patterns for acervuli in human pineal gland

Acervuli are calcified concretions in the pineal gland (PG). Particularly interesting are their incidence and size, which are believed to affect neurological disorders and many physiological functions of PG such as regulating circadian rhythm. Despite long investigations for a century, detailed growth mechanism of acervuli has yet to be studied. Here we study the growth morphology of acervuli in human PGs by a direct visualization in 3-dimension (3-D) using a synchrotron X-ray imaging method. For an entire PG, non-aggregated acervuli show Gaussian distribution in size with 47±28 µm. The 3-D volume rendered images of acervuli reveal that the bumpy surfaces developed by lamination result in the mulberry-like structure. In addition, coalescence of multiple acervuli leads to large-scale lamination on the whole aggregate. We suggest a novel hypothesis on the growth patterns of acervuli by their nucleation density (N_d): i) mulberry-like structure at low N_d, and ii) large-scale lamination on an aggregate at high N_d.

Fast microtomography using bright monochromatic x-rays

A fast microtomography system for high-resolution high-speed imaging has been developed using bright monochromatic x-rays at the BL29XU beamline of SPring-8. The shortest scan time for microtomography we attained was 0.25 s in 1.25 μm effective pixel size by combining the bright monochromatic x-rays, a fast rotating sample stage, and a high performance x-ray imaging detector. The feasibility of the tomography system was successfully demonstrated by visualization of rising bubbles in a viscous liquid, an interesting issue in multiphase flow physics. This system also provides a high spatial (a measurable feature size of 300 nm) or a very high temporal (9.8 μs) resolution in radiographs.