The lamin CxxM motif promotes nuclear membrane growth

Maintenance of germline stem cell homeostasis despite severe nuclear distortion

Stem cell loss in aging and disease is associated with nuclear deformation. Yet, how nuclear shape influences stem cell homeostasis is poorly understood. We investigated this connection using Drosophila germline stem cells, as survival of these stem cells is compromised by dysfunction of the nuclear lamina, the extensive protein network that lines the inner nuclear membrane and gives shape to the nucleus. To induce nuclear distortion in germline stem cells, we used the GAL4-UAS system to increase expression of the permanently farnesylated nuclear lamina protein, Kugelkern, a rate limiting factor for nuclear growth. We show that elevated Kugelkern levels cause severe nuclear distortion in germline stem cells, including extensive thickening and lobulation of the nuclear envelope and nuclear lamina, as well as alteration of internal nuclear compartments. Despite these changes, germline stem cell number, proliferation, and female fertility are preserved, even as females age. Collectively, these data demonstrate that disruption of nuclear architecture does not cause a failure of germline stem cell survival or homeostasis, revealing that nuclear deformation does not invariably promote stem cell loss.

Dynamic changes in the proximitome of neutral sphingomyelinase-2 (nSMase2) in TNFα stimulated Jurkat cells

Ceramides generated by the activity of the neutral sphingomyelinase 2 (nSMase2) play a pivotal role in stress responses in mammalian cells. Dysregulation of sphingolipid metabolism has been implicated in numerous inflammation-related pathologies. However, its influence on inflammatory cytokine-induced signaling is yet incompletely understood. Here, we used proximity labeling to explore the plasma membrane proximal protein network of nSMase2 and TNFα-induced changes thereof. We established Jurkat cells stably expressing nSMase2 C-terminally fused to the engineered ascorbate peroxidase 2 (APEX2). Removal of excess biotin phenol substantially improved streptavidin-based affinity purification of biotinylated proteins. Using our optimized protocol, we determined nSMase2-proximal biotinylated proteins and their changes within the first 5 min of TNFα stimulation by quantitative mass spectrometry. We observed significant dynamic changes in the nSMase2 microenvironment in response to TNFα stimulation consistent with rapid remodeling of protein networks. Our data confirmed known nSMase2 interactors and revealed that the recruitment of most proteins depended on nSMase2 enzymatic activity. We measured significant enrichment of proteins related to vesicle-mediated transport, including proteins of recycling endosomes, trans-Golgi network, and exocytic vesicles in the proximitome of enzymatically active nSMase2 within the first minutes of TNFα stimulation. Hence, the nSMase2 proximal network and its TNFα-induced changes provide a valuable resource for further investigations into the involvement of nSMase2 in the early signaling pathways triggered by TNFα.

The Role of Neutral Sphingomyelinase-2 (NSM2) in the Control of Neutral Lipid Storage in T Cells

The accumulation of lipid droplets (LDs) and ceramides (Cer) is linked to non-alcoholic fatty liver disease (NAFLD), regularly co-existing with type 2 diabetes and decreased immune function. Chronic inflammation and increased disease severity in viral infections are the hallmarks of the obesity-related immunopathology. The upregulation of neutral sphingomyelinase-2 (NSM2) has shown to be associated with the pathology of obesity in tissues. Nevertheless, the role of sphingolipids and specifically of NSM2 in the regulation of immune cell response to a fatty acid (FA) rich environment is poorly studied. Here, we identified the presence of the LD marker protein perilipin 3 (PLIN3) in the intracellular nano-environment of NSM2 using the ascorbate peroxidase APEX2-catalyzed proximity-dependent biotin labeling method. In line with this, super-resolution structured illumination microscopy (SIM) shows NSM2 and PLIN3 co-localization in LD organelles in the presence of increased extracellular concentrations of oleic acid (OA). Furthermore, the association of enzymatically active NSM2 with isolated LDs correlates with increased Cer levels in these lipid storage organelles. NSM2 enzymatic activity is not required for NSM2 association with LDs, but negatively affects the LD numbers and cellular accumulation of long-chain unsaturated triacylglycerol (TAG) species. Concurrently, NSM2 expression promotes mitochondrial respiration and fatty acid oxidation (FAO) in response to increased OA levels, thereby shifting cells to a high energetic state. Importantly, endogenous NSM2 activity is crucial for primary human CD4+ T cell survival and proliferation in a FA rich environment. To conclude, our study shows a novel NSM2 intracellular localization to LDs and the role of enzymatically active NSM2 in metabolic response to enhanced FA concentrations in T cells.

Nuclear lamin facilitates collective border cell invasion into confined spaces in vivo

Cells migrate collectively through confined environments during development and cancer metastasis. The nucleus, a stiff organelle, impedes single cells from squeezing into narrow channels within artificial environments. However, how nuclei affect collective migration into compact tissues is unknown. Here, we use border cells in the fly ovary to study nuclear dynamics in collective, confined in vivo migration. Border cells delaminate from the follicular epithelium and squeeze into tiny spaces between cells called nurse cells. The lead cell nucleus transiently deforms within the lead cell protrusion, which then widens. The nuclei of follower cells deform less. Depletion of the Drosophila B-type lamin, Lam, compromises nuclear integrity, hinders expansion of leading protrusions, and impedes border cell movement. In wildtype, cortical myosin II accumulates behind the nucleus and pushes it into the protrusion, whereas in Lam-depleted cells, myosin accumulates but does not move the nucleus. These data suggest that the nucleus stabilizes lead cell protrusions, helping to wedge open spaces between nurse cells.

Use of Farnesyl Transferase Inhibitors in an Ageing Model in Drosophila

The presence of farnesylated proteins at the inner nuclear membrane (INM), such as the Lamins or Kugelkern in Drosophila, leads to specific changes in the nuclear morphology and accelerated ageing on the organismal level reminiscent of the Hutchinson-Gilford progeria syndrome (HGPS). Farnesyl transferase inhibitors (FTIs) can suppress the phenotypes of the nuclear morphology in cultured fibroblasts from HGPS patients and cultured cells overexpressing farnesylated INM proteins. Similarly, FTIs have been reported to suppress the shortened lifespan in model organisms. Here, we report an experimental system combining cell culture and Drosophila flies for testing the activity of substances on the HGPS-like nuclear morphology and lifespan, with FTIs as an experimental example. Consistent with previous reports, we show that FTIs were able to ameliorate the nuclear phenotypes induced by the farnesylated nuclear proteins Progerin, Kugelkern, or truncated Lamin B in cultured cells. The subsequent validation in Drosophila lifespan assays demonstrated the applicability of the experimental system: treating adult Drosophila with the FTI ABT-100 reversed the nuclear phenotypes and extended the lifespan of experimentally induced short-lived flies. Since kugelkern-expressing flies have a significantly shorter average lifespan, half the time is needed for testing substances in the lifespan assay.

The role of Lamin B2 in human diseases

Lamin B2 (LMNB2), on the inner side of the nuclear envelope, constitutes the nuclear skeleton by connecting with other nuclear proteins. LMNB2 is involved in a wide range of nuclear functions, including DNA replication and stability, regulation of chromatin, and nuclear stiffness. Moreover, LMNB2 regulates several cellular processes, such as tissue development, cell cycle, cellular proliferation and apoptosis, chromatin localization and stability, and DNA methylation. Besides, the influence of abnormal expression and mutations of LMNB2 has been gradually discovered in cancers and laminopathies. Therefore, this review summarizes the recent advances of LMNB2-associated biological roles in physiological or pathological conditions, with a particular emphasis on cancers and laminopathies, as well as the potential mechanism of LMNB2 in related cancers.

The epigenetic landscape of oligodendrocyte lineage cells

The epigenetic landscape of oligodendrocyte lineage cells refers to the cell-specific modifications of DNA, chromatin, and RNA that define a unique gene expression pattern of functionally specialized cells. Here, we focus on the epigenetic changes occurring as progenitors differentiate into myelin-forming cells and respond to the local environment. First, modifications of DNA, RNA, nucleosomal histones, key principles of chromatin organization, topologically associating domains, and local remodeling will be reviewed. Then, the relationship between epigenetic modulators and RNA processing will be explored. Finally, the reciprocal relationship between the epigenome as a determinant of the mechanical properties of cell nuclei and the target of mechanotransduction will be discussed. The overall goal is to provide an interpretative key on how epigenetic changes may account for the heterogeneity of the transcriptional profiles identified in this lineage.

Development of a multicellular in vitro model of the meningeal blood-CSF barrier to study Neisseria meningitidis infection

Background

Bacterial meningitis is a life-threatening disease that occurs when pathogens such as Neisseria meningitidis cross the meningeal blood cerebrospinal fluid barrier (mBCSFB) and infect the meninges. Due to the human-specific nature of N. meningitidis, previous research investigating this complex host–pathogen interaction has mostly been done in vitro using immortalized brain endothelial cells (BECs) alone, which often do not retain relevant barrier properties in culture. Here, we developed physiologically relevant mBCSFB models using BECs in co-culture with leptomeningeal cells (LMCs) to examine N. meningitidis interaction.

Methods

We used BEC-like cells derived from induced pluripotent stem cells (iBECs) or hCMEC/D3 cells in co-culture with LMCs derived from tumor biopsies. We employed TEM and structured illumination microscopy to characterize the models as well as bacterial interaction. We measured TEER and sodium fluorescein (NaF) permeability to determine barrier tightness and integrity. We then analyzed bacterial adherence and penetration of the cell barrier and examined changes in host gene expression of tight junctions as well as chemokines and cytokines in response to infection.

Results

Both cell types remained distinct in co-culture and iBECs showed characteristic expression of BEC markers including tight junction proteins and endothelial markers. iBEC barrier function as determined by TEER and NaF permeability was improved by LMC co-culture and remained stable for seven days. BEC response to N. meningitidis infection was not affected by LMC co-culture. We detected considerable amounts of BEC-adherent meningococci and a relatively small number of intracellular bacteria. Interestingly, we discovered bacteria traversing the BEC-LMC barrier within the first 24 h post-infection, when barrier integrity was still high, suggesting a transcellular route for N. meningitidis into the CNS. Finally, we observed deterioration of barrier properties including loss of TEER and reduced expression of cell-junction components at late time points of infection.

Conclusions

Here, we report, for the first time, on co-culture of human iPSC derived BECs or hCMEC/D3 with meningioma derived LMCs and find that LMC co-culture improves barrier properties of iBECs. These novel models allow for a better understanding of N. meningitidis interaction at the mBCSFB in a physiologically relevant setting.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-022-00379-z.

Tumour cell characteristics and microenvironment composition correspond to clinical presentation in newly diagnosed nodular lymphocyte-predominant Hodgkin lymphoma

Different studies have characterized the microenvironment and its prognostic impact in classic Hodgkin lymphoma whereas such analyses are pending for nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL). We thus investigated characteristics of tumour cells and microenvironment in NLPHL and evaluated possible correlations with the clinical presentation. Lymph node samples from 152 NLPHL patients who had first-line treatment within the randomized German Hodgkin Study Group HD16-HD18 trials were available and analysed with regard to IgD status and nuclear size of the tumour cells as well as presence of PD1-positive follicular T helper cells and CD163-positive macrophages in the microenvironment. While large tumour cell nuclei and high numbers of PD1-positive follicular T helper cells in the microenvironment were more common in patients presenting with early/intermediate stages than in patients with advanced-stage disease (p < 0.0001, unpaired t-test; p = 0.0022, Mann-Whitney test), no differences between risk groups were observed in terms of the IgD status of the tumour cells and the content of CD163-positive macrophages in the microenvironment. PD1-positive follicular T helper cells were present in both cases with typical and variant growth patterns and rosetting around the tumour cells was observed in 96% of patients, indicating an important role of PD1-positive follicular T helper cells in NLPHL.

The Role of Lamins in the Nucleoplasmic Reticulum, a Pleiomorphic Organelle That Enhances Nucleo-Cytoplasmic Interplay

Invaginations of the nuclear membrane occur in different shapes, sizes, and compositions. Part of these pleiomorphic invaginations make up the nucleoplasmic reticulum (NR), while others are merely nuclear folds. We define the NR as tubular invaginations consisting of either both the inner and outer nuclear membrane, or only the inner nuclear membrane. Specifically, invaginations of both the inner and outer nuclear membrane are also called type II NR, while those of only the inner nuclear membrane are defined as type I NR. The formation and structure of the NR is determined by proteins associated to the nuclear membrane, which induce a high membrane curvature leading to tubular invaginations. Here we review and discuss the current knowledge of nuclear invaginations and the NR in particular. An increase in tubular invaginations of the nuclear envelope is associated with several pathologies, such as laminopathies, cancer, (reversible) heart failure, and Alzheimer’s disease. Furthermore, viruses can induce both type I and II NR. In laminopathies, the amount of A-type lamins throughout the nucleus is generally decreased or the organization of lamins or lamin-associated proteins is disturbed. Also, lamin overexpression or modulation of lamin farnesylation status impacts NR formation, confirming the importance of lamin processing in NR formation. Virus infections reorganize the nuclear lamina via (de)phosphorylation of lamins, leading to an uneven thickness of the nuclear lamina and in turn lobulation of the nuclear membrane and the formation of invaginations of the inner nuclear membrane. Since most studies on the NR have been performed with cell cultures, we present additional proof for the existence of these structures in vivo, focusing on a variety of differentiated cardiovascular and hematopoietic cells. Furthermore, we substantiate the knowledge of the lamin composition of the NR by super-resolution images of the lamin A/C and B1 organization. Finally, we further highlight the essential role of lamins in NR formation by demonstrating that (over)expression of lamins can induce aberrant NR structures.

Susceptibility of Human Airway Tissue Models Derived From Different Anatomical Sites to Bordetella pertussis and Its Virulence Factor Adenylate Cyclase Toxin

To study the interaction of human pathogens with their host target structures, human tissue models based on primary cells are considered suitable. Complex tissue models of the human airways have been used as infection models for various viral and bacterial pathogens. The Gram-negative bacterium Bordetella pertussis is of relevant clinical interest since whooping cough has developed into a resurgent infectious disease. In the present study, we created three-dimensional tissue models of the human ciliated nasal and tracheo-bronchial mucosa. We compared the innate immune response of these models towards the B. pertussis virulence factor adenylate cyclase toxin (CyaA) and its enzymatically inactive but fully pore-forming toxoid CyaA-AC^-. Applying molecular biological, histological, and microbiological assays, we found that 1 µg/ml CyaA elevated the intracellular cAMP level but did not disturb the epithelial barrier integrity of nasal and tracheo-bronchial airway mucosa tissue models. Interestingly, CyaA significantly increased interleukin 6, interleukin 8, and human beta defensin 2 secretion in nasal tissue models, whereas tracheo-bronchial tissue models were not significantly affected compared to the controls. Subsequently, we investigated the interaction of B. pertussis with both differentiated primary nasal and tracheo-bronchial tissue models and demonstrated bacterial adherence and invasion without observing host cell type-specific significant differences. Even though the nasal and the tracheo-bronchial mucosa appear similar from a histological perspective, they are differentially susceptible to B. pertussis CyaA in vitro. Our finding that nasal tissue models showed an increased innate immune response towards the B. pertussis virulence factor CyaA compared to tracheo-bronchial tissue models may reflect the key role of the nasal airway mucosa as the first line of defense against airborne pathogens.

Inducible Resistance to β-Lactams in Oxacillin-Susceptible mecA1-Positive Staphylococcus sciuri Isolated From Retail Pork

Most isolated strains of Staphylococcus sciuri contain mecA1, the evolutionary origin of mecA, but are sensitive to β-lactams (OS-MRSS, oxacillin-susceptible mecA1-positive S. sciuri). In order to improve the efficacy of antibiotic treatment, it is important to clarify whether the resistance of OS-MRSS to β-lactams is an inducible phenotype. In this study, three OS-MRSS strains with oxacillin MIC = 1 μg/ml were isolated from 29 retail pork samples. The resistance of OS-MRSS to β-lactams (MIC > 256 μg/ml) was found to be induced by oxacillin, and the induced resistance was observed to remain stable within a certain period of time. Interestingly, the induced β-lactam resistance was not caused by mecA1, heterogeneous resistance, or any genetic mutation, but mainly due to increased wall teichoic acid (WTA) synthesis that thickened the cell wall. The induced strains also showed slower growth rate, as well as decreased adhesion ability and biofilm thickness. These phenotypes were found to be achieved through altered gene expression in associated pathways, such as the citrate cycle and pentose phosphate pathway. The results challenge the traditional antibiotic sensitivity test. In the presence of β-lactam antibiotics, OS-MRSS that was initially sensitive to β-lactams was observed to gradually develop β-lactam resistance in several days. This often-neglected phenomenon in antibiotic sensitivity tests requires further research attention.

Nuclear Morphological Remodeling in Human Granulocytes Is Linked to Prenylation Independently from Cytoskeleton

Nuclear shape modulates cell behavior and function, while aberrant nuclear morphologies correlate with pathological phenotype severity. Nevertheless, functions of specific nuclear morphological features and underlying molecular mechanisms remain poorly understood. Here, we investigate a nucleus-intrinsic mechanism driving nuclear lobulation and segmentation concurrent with granulocyte specification, independently from extracellular forces and cytosolic cytoskeleton contributions. Transcriptomic regulation of cholesterol biosynthesis is equally concurrent with nuclear remodeling. Its putative role as a regulatory element is supported by morphological aberrations observed upon pharmacological impairment of several enzymatic steps of the pathway, most prominently the sterol ∆14-reductase activity of laminB-receptor and protein prenylation. Thus, we support the hypothesis of a nuclear-intrinsic mechanism for nuclear shape control with the putative involvement of the recently discovered GGTase III complex. Such process could be independent from or complementary to the better studied cytoskeleton-based nuclear remodeling essential for cell migration in both physiological and pathological contexts such as immune system function and cancer metastasis.

ESCRT-III controls nuclear envelope deformation induced by progerin

Hutchinson-Gilford progeria syndrome (HGPS) is a premature aging disorder, caused by mutation in the gene encoding lamin A/C, which produces a truncated protein called progerin. In cells from HGPS patients, progerin accumulates at the nuclear membrane (NM), where it causes NM deformations. In this study, we investigated whether progerin-induced NM deformation involved ESCRT-III, a protein complex that remodels nuclear and cytoplasmic membranes. The ESCRT-III protein CHMP4B was recruited to sites of aberrant NM proliferation in human cells ectopically expressing progerin and in patient-derived HGPS fibroblasts. Derepression of NM deformation in these cells was observed following depletion of CHMP4B or an ESCRT-III adaptor, ALIX. Treatment with rapamycin (which induce autophagic clearance of progerin and reverse progerin-induced cellular phenotypes) down-regulated progerin-induced NM deformation, whereas treatment with bafilomycin A1 (an inhibitor of autophagy and lysosome-based degradation) or CHMP4B depletion antagonized the effects of rapamycin. These results indicate that the ALIX-mediated ESCRT-III pathway plays a suppressive role in progerin-induced NM deformation and suggest that autophagy down-regulates progerin-induced NM deformation in a manner dependent on ESCRT-III machinery.

Qualitative and Quantitative Study of the Changes in the Ultrastructure of Mammalian Adrenal Cortex Caused by the Venezuelan Tigra Mariposa (Bothrops venezuelensis) Snake Venom

The damage of the adrenal gland by snake venoms needs to be clarified. Lethality (LD50) of Bothrops venezuelensis (Bv) venom was established by intraperitoneally mice injections. Preparation of specimens for transmission electron microscopy samples from cortex adrenal gland biopsies at 3, 6, and 24 h was processed. The quantitative description by the principal component analysis (PCA) of the adrenal gland was as follows: thickening of the capillary endothelium, area of the capillary lumen, cell nucleus area, enlargement of the perinuclear space, number of mitochondria, area of the mitochondria, number of mitochondrial cristae, number of cristae per mitochondrial unit, and tubular diameter of the smooth endoplasmic reticulum (SER). Sections of the adrenal cortex, after 3 h postinjection with Bv venom showed in the cortical cells: mitochondria with tubular cristae and slightly swollen SER cisternae, nucleus with variable heterochromatin content, irregular edges, and swollen nuclear envelope. After 6 h, cells with swollen nucleus envelope, electron dense lipids and mitochondria with loss of their cristae were observed. Myelin figures, close to the microvilli of the cortical cell, multivesicular bodies, swollen profiles of the SER, and electron dense lipid drops were noticed. After 24 h, thickening of the endothelial wall, fenestrae and projections into the capillary lumen, loss of the mitochondrial cristae, destruction of the capillary and the plasma membrane of the cortical cell, multivesicular body, SER loss, and an enlargement of the perinuclear space were detected. In the quantitative PCA, there were significant changes after the venom treatments.

An improved growth medium for enhanced inoculum production of the plant growth-promoting fungus Serendipita indica

BACKGROUND

The plant endophytic fungus Serendipita indica colonizes roots of a wide range of plant species and can enhance growth and stress resistance of these plants. Due to its ease of axenic cultivation and its broad host plant range including the model plant Arabidopsis thaliana and numerous crop plants, it is widely used as a model fungus to study beneficial fungus-root interactions. In addition, it was suggested to be utilized for commercial applications, e.g. to enhance yield in barley and other species. To produce inoculum, S. indica is mostly cultivated in a complex Hill-Käfer medium (CM medium), however, growth in this medium is slow, and yield of chlamydospores, which are often used for plant root inoculation, is relatively low.

RESULTS

We tested and optimized a simple vegetable juice-based medium for an enhanced yield of fungal inoculum. The described vegetable juice (VJ) medium is based on commercially available vegetable juice and is easy to prepare. VJ medium was superior to the currently used CM medium with respect to biomass production in liquid medium and hyphal growth on agar plates. Using solid VJ medium supplemented with sucrose (VJS), a high amount of chlamydospores developed already after 8 days of cultivation, producing significantly more spores than on CM medium. Use of VJ medium is not restricted to S. indica, as it also supported growth of two pathogenic fungi often used in plant pathology experiments: the ascomycete Fusarium graminearum, the causal agent of Fusarium head blight disease on wheat and barley, and Verticillium longisporum, the causal agent of verticillium wilt.

CONCLUSIONS

The described VJ medium is recommended for streamlined and efficient production of inoculum for the plant endophytic fungus Serendipita indica and might prove superior for the propagation of other fungi for research purposes.

Investigation on Ciliary Functionality of Different Airway Epithelial Cell Lines in Three-Dimensional Cell Culture

Three-dimensional respiratory tissue models have been generated using, for example, human primary airway epithelial cells (hAEC) or respective cell lines. To investigate ciliopathies, such as primary ciliary dyskinesia, the presence of functional kinocilia in vitro is an essential prerequisite. Since access to hAEC of healthy donors is limited, we aimed to identify a respiratory epithelial cell line that is capable to display functional kinocilia on at least 60% of the apical surface. Thus, we cultured four different human respiratory cell lines with human primary airway fibroblasts under airlift conditions, characterized the morphology, and analyzed ciliary function. Only one of the tested cell lines showed beating kinocilia; however, <10% of the whole surface was covered and ciliary beating was undirected. Positive control tissue models using hAEC and fibroblasts displayed expected directed ciliary beating pattern around 11 Hz. Our data show that the available cell lines are not suitable for basic and applied research questions whenever functional kinocilia are required and that, rather, hAEC- or human induced pluripotent stem cell-derived tissue models need to be generated.

Expression of lamina proteins Lamin and Kugelkern suppresses stem cell proliferation

The nuclear lamina is involved in numerous cellular functions, such as gene expression, nuclear organization, nuclear stability, and cell proliferation. The mechanism underlying the involvement of lamina is often not clear, especially in physiological or developmental contexts. Here we investigate the role and activity of farnesylated lamina proteins Lamin (Lam) and Kugelkern (Kuk) in proliferation control of intestinal stem cells (ISCs) in adult Drosophila flies. We found that ISCs mutant for Lam or kuk proliferate, whereas overexpression of Lam or Kuk strongly suppressed proliferation. The anti-proliferative activity is, at least in part, due to suppression of Jak/Stat but not Delta/Notch signaling. Lam expression suppresses Jak/Stat signaling by normalization of about 50% of the Stat target genes in ISCs.

Allele-specific silencing as treatment for gene duplication disorders: proof-of-principle in autosomal dominant leukodystrophy

Allele-specific silencing by RNA interference (ASP-siRNA) holds promise as a therapeutic strategy for downregulating a single mutant allele with minimal suppression of the corresponding wild-type allele. This approach has been effectively used to target autosomal dominant mutations and single nucleotide polymorphisms linked with aberrantly expanded trinucleotide repeats. Here, we propose ASP-siRNA as a preferable choice to target duplicated disease genes, avoiding potentially harmful excessive downregulation. As a proof-of-concept, we studied autosomal dominant adult-onset demyelinating leukodystrophy (ADLD) due to lamin B1 (LMNB1) duplication, a hereditary, progressive and fatal disorder affecting myelin in the CNS. Using a reporter system, we screened the most efficient ASP-siRNAs preferentially targeting one of the alleles at rs1051644 (average minor allele frequency: 0.45) located in the 3' untranslated region of the gene. We identified four siRNAs with a high efficacy and allele-specificity, which were tested in ADLD patient-derived fibroblasts. Three of the small interfering RNAs were highly selective for the target allele and restored both LMNB1 mRNA and protein levels close to control levels. Furthermore, small interfering RNA treatment abrogates the ADLD-specific phenotypes in fibroblasts and in two disease-relevant cellular models: murine oligodendrocytes overexpressing human LMNB1, and neurons directly reprogrammed from patients' fibroblasts. In conclusion, we demonstrated that ASP-silencing by RNA interference is a suitable and promising therapeutic option for ADLD. Moreover, our results have a broad translational value extending to several pathological conditions linked to gene-gain in copy number variations.

Mitochondrial distribution violation and nuclear indentations in neurons differentiated from iPSCs of Huntington's disease patients

AIM: Huntington’s disease (HD) is an inherited disease caused by an expansion of cytosine-adenine-guanine (CAG) repeats in the huntingtin gene (HTT) that ultimately leads to neurodegeneration. To study the molecular basis of this disease, induced pluripotent stem cells (iPSCs) generated from patients’ fibroblasts were used to investigate axonal mitochondrial trafficking and the nature of nuclear indentations.

METHODS: Pathological and control iPSCs generated from patients with a low number of repeats were differentiated in striatal neurons of the brain. Mitochondrial density was measured along the axon using tubulin beta 3 co-staining in pathological and control neurons. To investigate the connection of nuclear roundness with calcium dysregulation, several calcium inhibitors were used. Proteasome system inhibition was applied to mimic premature neuronal ageing.

RESULTS: We found that the mitochondrial density was approximately 7.6 ± 0.2 in neurites in control neurons but was only 5.3 ± 0.2 in mutant neurons with 40-44 CAG repeats (p-value <0.005). Neuronal ageing induced by proteasome inhibitor MG132 significantly decreased the mitochondrial density by 15% and 25% in control and mutant neurons to 6.5 ± 0.1 (p-value < 0.005) and 4.0 ± 0.3 (p-value < 0.005), respectively. Thus, for the first time, an impairment of mitochondrial trafficking in pathological neurons with endogenous mutant huntingtin was demonstrated. We found that inhibiting the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA), the ryanodine-receptor (RyR) or the inositol 1,4,5-trisphosphate receptor (IP3R) by specific inhibitors did not specifically affect the nuclear roundness or survival of pathological neurons differentiated from patient iPSCs. Therefore, nuclear calcium homeostasis is not directly associated with HD pathology.

CONCLUSION: Identifying HD iPSCs and differentiating from them neurons provide a unique system for modelling the disease in vitro. Impairments of mitochondrial trafficking and nuclear roundness manifest long before the disease onset, while premature neuronal ageing enhances differences in mitochondrial distribution.

Single-molecule imaging correlates decreasing nuclear volume with increasing TF-chromatin associations during zebrafish development

Zygotic genome activation (ZGA), the onset of transcription after initial quiescence, is a major developmental step in many species, which occurs after ten cell divisions in zebrafish embryos. How transcription factor (TF)-chromatin interactions evolve during early development to support ZGA is largely unknown. We establish single molecule tracking in live developing zebrafish embryos using reflected light-sheet microscopy to visualize two fluorescently labeled TF species, mEos2-TBP and mEos2-Sox19b. We further develop a data acquisition and analysis scheme to extract quantitative information on binding kinetics and bound fractions during fast cell cycles. The chromatin-bound fraction of both TFs increases during early development, as expected from a physical model of TF-chromatin interactions including a decreasing nuclear volume and increasing DNA accessibility. For Sox19b, data suggests the increase is mainly due to the shrinking nucleus. Our single molecule approach provides quantitative insight into changes of TF-chromatin associations during the developmental period embracing ZGA.

The serine/threonine kinase Stk and the phosphatase Stp regulate cell wall synthesis in Staphylococcus aureus

The cell wall synthesis pathway producing peptidoglycan is a highly coordinated and tightly regulated process. Although the major components of bacterial cell walls have been known for decades, the complex regulatory network controlling peptidoglycan synthesis and many details of the cell division machinery are not well understood. The eukaryotic-like serine/threonine kinase Stk and the cognate phosphatase Stp play an important role in cell wall biosynthesis and drug resistance in S. aureus. We show that stp deletion has a pronounced impact on cell wall synthesis. Deletion of stp leads to a thicker cell wall and decreases susceptibility to lysostaphin. Stationary phase Δstp cells accumulate peptidoglycan precursors and incorporate higher amounts of incomplete muropeptides with non-glycine, monoglycine and monoalanine interpeptide bridges into the cell wall. In line with this cell wall phenotype, we demonstrate that the lipid II:glycine glycyltransferase FemX can be phosphorylated by the Ser/Thr kinase Stk in vitro. Mass spectrometric analyses identify Thr32, Thr36 and Ser415 as phosphoacceptors. The cognate phosphatase Stp dephosphorylates these phosphorylation sites. Moreover, Stk interacts with FemA and FemB, but is unable to phosphorylate them. Our data indicate that Stk and Stp modulate cell wall synthesis and cell division at several levels.

ESCRT-III mediates budding across the inner nuclear membrane and regulates its integrity

Vesicle-mediated nucleocytoplasmic transport is a nuclear pore-independent mechanism for the nuclear export of macromolecular complexes, but the molecular basis for this transport remains largely unknown. Here we show that endosomal sorting complex required for transport-III (ESCRT-III) is recruited to the inner nuclear membrane (INM) during the nuclear export of herpes simplex virus 1 (HSV-1). Scission during HSV-1 budding through the INM is prevented by depletion of ESCRT-III proteins. Interestingly, in uninfected human cells, the depletion of ESCRT-III proteins induces aberrant INM proliferation. Our results show that HSV-1 expropriates the ESCRT-III machinery in infected cells for scission of the INM to produce vesicles containing progeny virus nucleocapsids. In uninfected cells, ESCRT-III regulates INM integrity by downregulating excess INM.

The endosomal sorting complex required for transport-III (ESCRT-III) has been implicated in the packaging of HIV and HSV-1 viruses in the cytoplasm. Here the authors show that ESCRT-III proteins are required for the transport of HSV-1 nucleocapsids from nucleoplasm to cytosol through the nuclear envelope and confirm that the same mechanism is also used for the nucleocytoplasmic transport of RNP in Drosophila cells.

Overexpression of the lamina proteins Lamin and Kugelkern induces specific ultrastructural alterations in the morphology of the nuclear envelope of intestinal stem cells and enterocytes

The nuclear envelope has a stereotypic morphology consisting of a flat double layer of the inner and outer nuclear membrane, with interspersed nuclear pores. Underlying and tightly linked to the inner nuclear membrane is the nuclear lamina, a proteinous layer of intermediate filament proteins and associated proteins. Physiological, experimental or pathological alterations in the constitution of the lamina lead to changes in nuclear morphology, such as blebs and lobulations. It has so far remained unclear whether the morphological changes depend on the differentiation state and the specific lamina protein. Here we analysed the ultrastructural morphology of the nuclear envelope in intestinal stem cells and differentiated enterocytes in adult Drosophila flies, in which the proteins Lam, Kugelkern or a farnesylated variant of LamC were overexpressed. Surprisingly, we detected distinct morphological features specific for the respective protein. Lam induced envelopes with multiple layers of membrane and lamina, surrounding the whole nucleus whereas farnesylated LamC induced the formation of a thick fibrillary lamina. In contrast, Kugelkern induced single-layered and double-layered intranuclear membrane structures, which are likely be derived from infoldings of the inner nuclear membrane or of the double layer of the envelope.

An LMNB1 Duplication Caused Adult-Onset Autosomal Dominant Leukodystrophy in Chinese Family: Clinical Manifestations, Neuroradiology and Genetic Diagnosis

Autosomal dominant adult-onset demyelinating leukodystrophy (ADLD) is a very rare neurological disorder featured with late onset, slowly progressive central nervous system demyelination. Duplication or over expression of the lamin B1 (LMNB1) gene causes ADLD. In this study, we undertook a comprehensive clinical evaluation and genetic detection for a Chinese family with ADLD. The proband is a 52-year old man manifested with autonomic abnormalities, pyramidal tract dysfunction. MRI brain scan identified bilateral symmetric white matter (WM) hyper-intensities in periventricular and semi-oval WM, cerebral peduncles and middle cerebellar peduncles. The proband has a positive autosomal dominant family history with similar clinical manifestations with a trend of genetic anticipation. In order to understand the genetic cause of the disease in this family, target exome capture based next generation sequencing has been done, but no causative variants or possibly pathogenic variants has been identified. However, Multiplex ligand-dependent probe amplification (MLPA) showed whole duplication of LMNB1 gene which is co-segregated with the disease phenotype in this family. This is the first genetically confirmed LMNB1 associated ADLD pedigree from China.

Shared mechanisms in physiological and pathological nucleoplasmic reticulum formation

The mammalian nuclear envelope (NE) can develop complex dynamic membrane-bounded invaginations in response to both physiological and pathological stimuli. Since the formation of these nucleoplasmic reticulum (NR) structures can occur during interphase, without mitotic NE breakdown and reassembly, some other mechanism must drive their development. Here we consider models for deformation of the interphase NE, together with the evidence for their potential roles in NR formation.

New Insights into Mechanisms and Functions of Nuclear Size Regulation

Nuclear size is generally maintained within a defined range in a given cell type. Changes in cell size that occur during cell growth, development, and differentiation are accompanied by dynamic nuclear size adjustments in order to establish appropriate nuclear-to-cytoplasmic volume relationships. It has long been recognized that aberrations in nuclear size are associated with certain disease states, most notably cancer. Nuclear size and morphology must impact nuclear and cellular functions. Understanding these functional implications requires an understanding of the mechanisms that control nuclear size. In this review, we first provide a general overview of the diverse cellular structures and activities that contribute to nuclear size control, including structural components of the nucleus, effects of DNA amount and chromatin compaction, signaling, and transport pathways that impinge on the nucleus, extranuclear structures, and cell cycle state. We then detail some of the key mechanistic findings about nuclear size regulation that have been gleaned from a variety of model organisms. Lastly, we review studies that have implicated nuclear size in the regulation of cell and nuclear function and speculate on the potential functional significance of nuclear size in chromatin organization, gene expression, nuclear mechanics, and disease. With many fundamental cell biological questions remaining to be answered, the field of nuclear size regulation is still wide open.

Induction of intranuclear membranes by overproduction of Opi1p and Scs2p, regulators for yeast phospholipid biosynthesis, suggests a mechanism for Opi1p nuclear translocation

In the yeast Saccharomyces cerevisiae, the expression of phospholipid biosynthetic genes is suppressed by the Opi1p negative regulator. Opi1p enters into the nucleoplasm from the nuclear membrane to suppress the gene expression under repressing conditions. The binding of Opi1p to the nuclear membrane requires an integral membrane protein, Scs2p and phosphatidic acid (PA). Although it is demonstrated that the association of Opi1p with membranes is affected by PA levels, how Opi1p dissociates from Scs2p is unknown. Here, we found that fluorescently labelled Opi1p accumulated on a perinuclear region in an Scs2p-dependent manner. Electron microscopic analyses indicated that the perinuclear region consists of intranuclear membranes, which may be formed by the invagination of the nuclear membrane due to the accumulation of Opi1p and Scs2p in a restricted area. As expected, localization of Opi1p and Scs2p in the intranuclear membranes was detected by immunoelectron microscopy. Biochemical analysis showed that Opi1p recovered in the membrane fraction was detergent insoluble while Scs2p was soluble, implying that Opi1p behaves differently from Scs2p in the fraction. We hypothesize that Opi1p dissociates from Scs2p after targeting to the nuclear membrane, making it possible to be released from the membrane quickly when PA levels decrease.

3D Analysis of HCMV Induced-Nuclear Membrane Structures by FIB/SEM Tomography: Insight into an Unprecedented Membrane Morphology

We show that focused ion beam/scanning electron microscopy (FIB/SEM) tomography is an excellent method to analyze the three-dimensional structure of a fibroblast nucleus infected with human cytomegalovirus (HCMV). We found that the previously described infoldings of the inner nuclear membrane, which are unique among its kind, form an extremely complex network of membrane structures not predictable by previous two-dimensional studies. In all cases they contained further invaginations (2nd and 3rd order infoldings). Quantification revealed 5498HCMV capsids within two nuclear segments, allowing an estimate of 15,000 to 30,000 capsids in the entire nucleus five days post infection. Only 0.8% proved to be enveloped capsids which were exclusively detected in 1st order infoldings (perinuclear space). Distribution of the capsids between 1st, 2nd and 3rd order infoldings is in complete agreement with the envelopment/de-envelopment model for egress of HCMV capsids from the nucleus and we confirm that capsid budding does occur at the large infoldings. Based on our results we propose the pushing membrane model: HCMV infection induces local disruption of the nuclear lamina and synthesis of new membrane material which is pushed into the nucleoplasm, forming complex membrane infoldings in a highly abundant manner, which then may be also used by nucleocapsids for budding.

Concentration-dependent Effects of Nuclear Lamins on Nuclear Size in Xenopus and Mammalian Cells

A fundamental question in cell biology concerns the regulation of organelle size. While nuclear size is exquisitely controlled in different cell types, inappropriate nuclear enlargement is used to diagnose and stage cancer. Clarifying the functional significance of nuclear size necessitates an understanding of the mechanisms and proteins that control nuclear size. One structural component implicated in the regulation of nuclear morphology is the nuclear lamina, a meshwork of intermediate lamin filaments that lines the inner nuclear membrane. However, there has not been a systematic investigation of how the level and type of lamin expression influences nuclear size, in part due to difficulties in precisely controlling lamin expression levels in vivo. In this study, we circumvent this limitation by studying nuclei in Xenopus laevis egg and embryo extracts, open biochemical systems that allow for precise manipulation of lamin levels by the addition of recombinant proteins. We find that nuclear growth and size are sensitive to the levels of nuclear lamins, with low and high concentrations increasing and decreasing nuclear size, respectively. Interestingly, each type of lamin that we tested (lamins B1, B2, B3, and A) similarly affected nuclear size whether added alone or in combination, suggesting that total lamin concentration, and not lamin type, is more critical to determining nuclear size. Furthermore, we show that altering lamin levels in vivo, both in Xenopus embryos and mammalian tissue culture cells, also impacts nuclear size. These results have implications for normal development and carcinogenesis where both nuclear size and lamin expression levels change.

Cell shape dependent regulation of nuclear morphology

Recent studies suggest that actin filaments are essential in how a cell controls its nuclear shape. However, little is known about the relative importance of membrane tension in determining nuclear morphology. In this study, we used adhesive micropatterned substrates to alter the cellular geometry (aspect ratio, size, and shape) that allowed direct membrane tension or without membrane lateral contact with the nucleus and investigate nuclear shape remodeling and orientation on a series of rectangular shapes. Here we showed that at low cell aspect ratios the orientation of the nucleus was regulated by actin filaments while cells with high aspect ratios can maintain nuclear shape and orientation even when actin polymerization was blocked. A model adenocarcinoma cell showed similar behavior in the regulation of nuclear shape in response to changes in cell shape but actin filaments were essential in maintaining cell shape. Our results highlight the two distinct mechanisms to regulate nuclear shape through cell shape control and the difference between fibroblasts and a model cancerous cell in cell adhesion and cell shape control.

Do lamin A and lamin C have unique roles?

The A-type lamins, lamin A and lamin C, generated from a single gene, LMNA, are major structural components of the nuclear lamina. The two alternative splice products have mostly been studied together because they have been considered to be interchangeable. However, several lines of evidence indicate that in spite of being generated from the same gene and having high similarities in their primary sequences, the two isoforms are not equivalent in different biological aspects in both health and disease. The key question is whether they have both overlapping and unique functions and whether they are distinctly regulated. Based on the so far available experimental evidence, lamin A appears to be the most regulated A-type isoform during development, aging, and disease which indicates that lamin A is implicated in many different biological aspects and may have a greater repertoire of specialized functions than lamin C. The aim of this review is to point out differences between the two major LMNA splice variants and the consequences of these differences on their functions. This may guide further research and be of prime importance for the understanding of the pathogenesis of LMNA mutations.

Laminopathy-inducing mutations reduce nuclear import of expressed prelamin A

Lamins are structural components of the nuclear lamina and integral parts of the nucleoplasm. The tripartite domain structure partitions the molecule into an amino-terminal head, central rod and a carboxy-terminal tail domain. The tail domain contains a nuclear localization sequence and in most lamins an additional CaaX motif, which is necessary to post-translationally process prelamin to mature lamin. As players of nuclear and cellular integrity, lamins must possess unrestrained access to the nucleus. To study whether nuclear trafficking of lamins is compromised in laminopathies, we determined relative nuclear import activities between expressed prelamin A and selected laminopathy-inducing mutants thereof. Furthermore, the impact of inhibition of maturation on nuclear import of expressed prelamin A was examined. To perform quantitative transport measurements, import competent but lamina incorporation-deficient GFP- or DsRed-tagged prelamin A deletion mutants were used, which lacked the head and rod domain (ΔHR-prelamin A). Nuclear accumulation of ΔHR-prelamin A carrying the lipodystrophy and metabolic syndrome-inducing mutations R419C and L421P or progeria-causing deletions was significantly reduced, but that of the maturation-deficient mutant ΔHR-prelamin A SSIM was significantly increased. In the case of the full length prelamin A mutants R419C and L421P altered subcellular localization and reduced lamina incorporation were detected, with the prelamin A-binding protein Narf being redistributed into R419-containing aggregates. The results suggest that impaired nuclear transport of certain prelamin A mutants may represent a contributing factor in the pathogenesis of certain laminopathies.

The Novel Nuclear Envelope Protein KAKU4 Modulates Nuclear Morphology in Arabidopsis

In animals, the nuclear lamina is a fibrillar meshwork on the inner surface of the nuclear envelope, composed of coiled-coil lamin proteins and lamin binding membrane proteins. Plants also have a meshwork on the inner surface of the nuclear envelope, but little is known about its composition other than the presence of members of the CROWDED NUCLEI (CRWN) protein family, possible plant lamin analogs. Here, we describe a candidate lamina component, based on two Arabidopsis thaliana mutants (kaku2 and kaku4) with aberrant nuclear morphology. The responsible gene in kaku2 encodes CRWN1, and the responsible gene in kaku4 encodes a plant-specific protein of unknown function (KAKU4) that physically interacts with CRWN1 and its homolog CRWN4. Immunogold labeling revealed that KAKU4 localizes at the inner nuclear membrane. KAKU4 deforms the nuclear envelope in a dose-dependent manner, in association with nuclear membrane invagination and stack formation. The KAKU4-dependent nuclear envelope deformation was enhanced by overaccumulation of CRWN1, although KAKU4 can deform the nuclear envelope even in the absence of CRWN1 and/or CRWN4. Together, these results suggest that plants have evolved a unique lamina-like structure to modulate nuclear shape and size.

Expression of DNAJB12 or DNAJB14 causes coordinate invasion of the nucleus by membranes associated with a novel nuclear pore structure

DNAJB12 and DNAJB14 are transmembrane proteins in the endoplasmic reticulum (ER) that serve as co-chaperones for Hsc70/Hsp70 heat shock proteins. We demonstrate that over-expression of DNAJB12 or DNAJB14 causes the formation of elaborate membranous structures within cell nuclei, which we designate DJANGOS for DNAJ-associated nuclear globular structures. DJANGOS contain DNAJB12, DNAJB14, Hsc70 and markers of the ER lumen and ER and nuclear membranes. Strikingly, they are evenly distributed underneath the nuclear envelope and are of uniform size in any one nucleus. DJANGOS are composed primarily of single-walled membrane tubes and sheets that connect to the nuclear envelope via a unique configuration of membranes, in which the nuclear pore complex appears anchored exclusively to the outer nuclear membrane, allowing both the inner and outer nuclear membranes to flow past the circumference of the nuclear pore complex into the nucleus. DJANGOS break down rapidly during cell division and reform synchronously in the daughter cell nuclei, demonstrating that they are dynamic structures that undergo coordinate formation and dissolution. Genetic studies showed that the chaperone activity of DNAJ/Hsc70 is required for the formation of DJANGOS. Further analysis of these structures will provide insight into nuclear pore formation and function, activities of molecular chaperones, and mechanisms that maintain membrane identity.

WITHDRAWN: Nuclear matrix, nuclear envelope and premature aging syndromes in a translational research perspective

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/10.1016/j.semcdb.2014.03.022. The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

Nuclear matrix, nuclear envelope and premature aging syndromes in a translational research perspective

Lamin A-related progeroid syndromes are genetically determined, extremely rare and severe. In the past ten years, our knowledge and perspectives for these diseases has widely progressed, through the progressive dissection of their pathophysiological mechanisms leading to precocious and accelerated aging, from the genes mutations discovery until therapeutic trials in affected children. A-type lamins are major actors in several structural and functional activities at the nuclear periphery, as they are major components of the nuclear lamina. However, while this is usually poorly considered, they also play a key role within the rest of the nucleoplasm, whose defects are related to cell senescence. Although nuclear shape and nuclear envelope deformities are obvious and visible events, nuclear matrix disorganization and abnormal composition certainly represent the most important causes of cell defects with dramatic pathological consequences. Therefore, lamin-associated diseases should be better referred as laminopathies instead of envelopathies, this later being too restrictive, considering neither the key structural and functional roles of soluble lamins in the entire nucleoplasm, nor the nuclear matrix contribution to the pathophysiology of lamin-associated disorders and in particular in defective lamin A processing-associated aging diseases. Based on both our understanding of pathophysiological mechanisms and the biological and clinical consequences of progeria and related diseases, therapeutic trials have been conducted in patients and were terminated less than 10 years after the gene discovery, a quite fast issue for a genetic disease. Pharmacological drugs have been repurposed and used to decrease the toxicity of the accumulated, unprocessed and truncated prelaminA in progeria. To date, none of them may be considered as a cure for progeria and these clinical strategies were essentially designed toward reducing a subset of the most dramatic and morbid features associated to progeria. New therapeutic strategies under study, in particular targeting the protein expression pathway at the mRNA level, have shown a remarkable efficacy both in vitro in cells and in vivo in mice models. Strategies intending to clear the toxic accumulated proteins from the nucleus are also under evaluation. However, although exceedingly rare, improving our knowledge of genetic progeroid syndromes and searching for innovative and efficient therapies in these syndromes is of paramount importance as, even before they can be used to save lives, they may significantly (i) expand the affected childrens' lifespan and preserve their quality of life; (ii) improve our understanding of aging-related disorders and other more common diseases; and (iii) expand our fundamental knowledge of physiological aging and its links with major physiological processes such as those involved in oncogenesis.

Regulation of Myelination in the Central Nervous System by Nuclear Lamin B1 and Non-coding RNAs

Adult-onset autosomal dominant leukodystrophy (ADLD) is a progressive and fatal hereditary demyelination disorder characterized initially by autonomic dysfunction and loss of myelin in the central nervous system (CNS). Majority of ADLD is caused by a genomic duplication of the nuclear lamin B1 gene (LMNB1) encoding lamin B1 protein, resulting in increased gene dosage in brain tissue. In vitro, excessive lamin B1 at the cellular level reduces transcription of myelin genes, leading to premature arrest of oligodendrocyte differentiation. Murine models of ADLD overexpressing LMNB1 exhibited age-dependent motor deficits and myelin defects, which are associated with reduced occupancy of the Yin Yang 1 transcription factor at the promoter region of the proteolipid protein gene. Lamin B1 overexpression mediates oligodendrocyte cell-autonomous neuropathology in ADLD and suggests lamin B1 as an important regulator of myelin formation and maintenance during aging. Identification of microRNA-23 (miR-23) as a negative regulator of lamin B1 can ameliorate the consequences of excessive lamin B1 at the cellular level. miR-23a-overexpressing mice display enhanced oligodendrocyte differentiation and myelin synthesis. miR-23a targets include a protein coding transcript PTEN (phosphatase and tensin homolog on chromosome 10), and a long noncoding RNA (2700046G09Rik), indicating a unique role for miR-23a in the coordination of proteins and noncoding RNAs in generating and maintaining healthy myelin. Here, we provide a concise review of the current literature on clinical presentations of ADLD and how lamin B1 affects myelination and other developmental processes. Moreover, we address the emerging role of non-coding RNAs (ncRNAs) in modulating gene networks, specifically investigating miR-23 as a potential target for the treatment of ADLD and other demyelinating disorders.

Sizing and shaping the nucleus: mechanisms and significance

The size and shape of the nucleus are tightly regulated, indicating the physiological significance of proper nuclear morphology, yet the mechanisms and functions of nuclear size and shape regulation remain poorly understood. Correlations between altered nuclear morphology and certain disease states have long been observed, most notably many cancers are diagnosed and staged based on graded increases in nuclear size. Here we review recent studies investigating the mechanisms regulating nuclear size and shape, how mitotic events influence nuclear morphology, and the role of nuclear size and shape in subnuclear chromatin organization and cancer progression.

Mechanisms of nuclear size regulation in model systems and cancer

Changes in nuclear size have long been used by cytopathologists as an important parameter to diagnose, stage, and prognose many cancers. Mechanisms underlying these changes and functional links between nuclear size and malignancy are largely unknown. Understanding mechanisms of nuclear size regulation and the physiological significance of proper nuclear size control will inform the interplay between altered nuclear size and oncogenesis. In this chapter we review what is known about molecular mechanisms of nuclear size control based on research in model experimental systems including yeast, Xenopus, Tetrahymena, Drosophila, plants, mice, and mammalian cell culture. We discuss how nuclear size is influenced by DNA ploidy, nuclear structural components, cytoplasmic factors and nucleocytoplasmic transport, the cytoskeleton, and the extracellular matrix. Based on these mechanistic insights, we speculate about how nuclear size might impact cell physiology and whether altered nuclear size could contribute to cancer development and progression. We end with some outstanding questions about mechanisms and functions of nuclear size regulation.

Interactions of the Kaposi's Sarcoma-associated herpesvirus nuclear egress complex: ORF69 is a potent factor for remodeling cellular membranes

All herpesviruses encode a complex of two proteins, referred to as the nuclear egress complex (NEC), which together facilitate the exit of assembled capsids from the nucleus. Previously, we showed that the Kaposi's sarcoma-associated herpesvirus (KSHV) NEC specified by the ORF67 and ORF69 genes when expressed in insect cells using baculoviruses for protein expression forms a complex at the nuclear membrane and remodels these membranes to generate nuclear membrane-derived vesicles. In this study, we have analyzed the functional domains of the KSHV NEC proteins and their interactions. Site-directed mutagenesis of gammaherpesvirus conserved residues revealed functional domains of these two proteins, which in many cases abolish the formation of the NEC and remodeling of nuclear membranes. Small in-frame deletions within ORF67 in all cases result in loss of the ability of the mutant protein to induce cellular membrane proliferation as well as to interact with ORF69. Truncation of the C terminus of ORF67 that resides in the perinuclear space does not impair the functions of ORF67; however, deletion of the transmembrane domain of ORF67 produces a protein that cannot induce membrane proliferation but can still interact with ORF69 in the nucleus and can be tethered to the nuclear membrane by virtue of its interaction with the wild-type-membrane-anchored ORF67. In-frame deletions in ORF69 have varied effects on NEC formation, but all abolish remodeling of nuclear membranes into circular structures. One mutant interacts with ORF67 as well as the wild-type protein but cannot function in membrane curvature and fission events that generate circular vesicles. These studies genetically confirm that ORF67 is required for cellular membrane proliferation and that ORF69 is the factor required to remodel these duplicated membranes into circular-virion-size vesicles. Furthermore, we also investigated the NEC encoded by Epstein-Barr virus (EBV). The EBV complex comprised of BFRF1 and BFLF2 was visualized at the nuclear membrane using autofluorescent protein fusions. BFRF1 is a potent inducer of membrane proliferation; however, BFLF2 cannot remodel these membranes into circular structures. What was evident is the superior remodeling activity of ORF69, which could convert the host membrane proliferations induced by BFRF1 into circular structures.

Functional architecture of the nuclear pore complex

The nuclear pore complex (NPC) is the sole gateway between the nucleus and the cytoplasm. NPCs fuse the inner and outer nuclear membranes to form aqueous translocation channels that allow the free diffusion of small molecules and ions, as well as receptor-mediated transport of large macromolecules. The NPC regulates nucleocytoplasmic transport of macromolecules, utilizing soluble receptors that identify and present cargo to the NPC, in a highly selective manner to maintain cellular functions. The NPC is composed of multiple copies of approximately 30 different proteins, termed nucleoporins, which assemble to form one of the largest multiprotein assemblies in the cell. In this review, we address structural and functional aspects of this fundamental cellular machinery.

Visualization of Vascular Inflammation in the Atherosclerotic Mouse by Ultrasmall Superparamagnetic Iron Oxide Vascular Cell Adhesion Molecule-1–Specific Nanoparticles

Objective—

Noninvasive imaging of atherosclerosis remains challenging in clinical applications. Here, we applied noninvasive molecular imaging to detect vascular cell adhesion molecule-1 in early and advanced atherosclerotic lesions of apolipoprotein E–deficient mice.

Methods and Results—

Ultrasmall superparamagnetic iron oxide particles functionalized with (P03011) or without (P3007) vascular cell adhesion molecule-1−binding peptide were visualized by ultra high-field (17.6 T) magnetic resonance. Injection of P03011 resulted in a marked signal loss in the aortic root of apolipoprotein E–deficient mice fed a Western diet for 8 and 26 weeks in vivo and ex vivo, compared with preinjection measurements, P3007-injected mice, and P03011- or P3007-injected age-matched C57BL/6 controls. Histological analyses revealed iron accumulations in the intima, in colocalization with vascular cell adhesion molecule-1−expressing macrophages and endothelial cells. Coherent anti-Stokes Raman scattering microscopy demonstrated iron signals in the intima and media of the aortic root in the P03011-injected but not untreated apolipoprotein E–deficient mice, localized to macrophages, luminal endothelial-like cells, and medial regions containing smooth muscle cells. Electron microscopy confirmed iron particles enclosed in endothelial cells and in the vicinity of smooth muscle cells.

Conclusion—

Using a combination of innovative imaging modalities, in this study, we demonstrate the feasibility of applying P03011 as a contrast agent for imaging of atherosclerosis.

Dimerization and direct membrane interaction of Nup53 contribute to nuclear pore complex assembly

Nuclear pore formation depends on membrane curvature. The membrane deforming activity of Nup53 is required for nuclear pore complex (NPC) assembly during interphase.

Nuclear pore complexes (NPCs) fuse the two membranes of the nuclear envelope (NE) to a pore, connecting cytoplasm and nucleoplasm and allowing exchange of macromolecules between these compartments. Most NPC proteins do not contain integral membrane domains and thus it is largely unclear how NPCs are embedded and anchored in the NE. Here, we show that the evolutionary conserved nuclear pore protein Nup53 binds independently of other proteins to membranes, a property that is crucial for NPC assembly and conserved between yeast and vertebrates. The vertebrate protein comprises two membrane binding sites, of which the C-terminal domain has membrane deforming capabilities, and is specifically required for de novo NPC assembly and insertion into the intact NE during interphase. Dimerization of Nup53 contributes to its membrane interaction and is crucial for its function in NPC assembly.

Shaping the nucleus: factors and forces

Take a look at a textbook illustration of a cell and you will immediately be able to locate the nucleus, which is often drawn as a spherical or ovoid shaped structure. But not all cells have such nuclei. In fact, some disease states are diagnosed by the presence of nuclei that have an abnormal shape or size. What defines nuclear shape and nuclear size, and how does nuclear geometry affect nuclear function? While the answer to the latter question remains largely unknown, significant progress has been made towards understanding the former. In this review, we provide an overview of the factors and forces that affect nuclear shape and size, discuss the relationship between ER structure and nuclear morphology, and speculate on the possible connection between nuclear size and its shape. We also note the many interesting questions that remain to be explored.

Local translation of extranuclear lamin B promotes axon maintenance

Local protein synthesis plays a key role in regulating stimulus-induced responses in dendrites and axons. Recent genome-wide studies have revealed that thousands of different transcripts reside in these distal neuronal compartments, but identifying those with functionally significant roles presents a challenge. We performed an unbiased screen to look for stimulus-induced, protein synthesis-dependent changes in the proteome of Xenopus retinal ganglion cell (RGC) axons. The intermediate filament protein lamin B2 (LB2), normally associated with the nuclear membrane, was identified as an unexpected major target. Axonal ribosome immunoprecipitation confirmed translation of lb2 mRNA in vivo. Inhibition of lb2 mRNA translation in axons in vivo does not affect guidance but causes axonal degeneration. Axonal LB2 associates with mitochondria, and LB2-deficient axons exhibit mitochondrial dysfunction and defects in axonal transport. Our results thus suggest that axonally synthesized lamin B plays a crucial role in axon maintenance by promoting mitochondrial function.

Fission yeast Lem2 and Man1 perform fundamental functions of the animal cell nuclear lamina

In animal cells the nuclear lamina, which consists of lamins and lamin-associated proteins, serves several functions: it provides a structural scaffold for the nuclear envelope and tethers proteins and heterochromatin to the nuclear periphery. In yeast, proteins and large heterochromatic domains including telomeres are also peripherally localized, but there is no evidence that yeast have lamins or a fibrous nuclear envelope scaffold. Nonetheless, we found that the Lem2 and Man1 proteins of the fission yeast Schizosaccharomyces pombe, evolutionarily distant relatives of the Lap2/Emerin/Man1 (LEM) sub-family of animal cell lamin-associated proteins, perform fundamental functions of the animal cell lamina. These integral inner nuclear membrane localized proteins, with nuclear localized DNA binding Helix-Extension-Helix (HEH) domains, impact nuclear envelope structure and integrity, are essential for the enrichment of telomeres at the nuclear periphery and by means of their HEH domains anchor chromatin, most likely transcriptionally repressed heterochromatin, to the nuclear periphery. These data indicate that the core functions of the nuclear lamina are conserved between fungi and animal cells and can be performed in fission yeast, without lamins or other intermediate filament proteins.

The induction of a nucleoplasmic reticulum by prelamin A accumulation requires CTP:phosphocholine cytidylyltransferase-α

Farnesylated prelamin A accumulates when the final endoproteolytic maturation of the protein fails to occur and causes a dysmorphic nuclear phenotype; however, the morphology and mechanisms of biogenesis of these changes remain unclear. We show here that acute prelamin A accumulation after reduction in the activity of the ZMPSTE24 endoprotease by short interfering RNA knockdown, results in the generation of a complex nucleoplasmic reticulum that depends for its formation on the enzyme CTP:phosphocholine-cytidylyltransferase-α (CCT-α, also known as choline-phosphate cytidylyltransferase A). This structure can form during interphase, confirming that it is independent of mitosis and therefore not a consequence of disordered nuclear envelope assembly. Serial-section dual-axis electron tomography reveals that these invaginations can take two forms: one in which the inner nuclear membrane infolds alone with an inter membrane space interior, and the other in which an invagination of both nuclear membranes occurs, enclosing a cytoplasmic core. Both types of invagination can co-exist in one nucleus and both are frequently studded with nuclear pore complexes (NPC), which reduces NPC abundance on the nuclear surface.