Nesprins in health and disease

Unraveling the nexus of nesprin in dilated cardiomyopathy: From molecular insights to therapeutic prospects

Dilated cardiomyopathy is a complex and debilitating heart disorder characterized by the enlargement and weakening of the cardiac chambers, leading to impaired contractility and heart failure. Nesprins, a family of nuclear envelope spectrin repeat proteins that include isoforms Nesprin-1/-2, are integral components of the LInker of Nucleoskeleton and Cytoskeleton complex. They facilitate the connection between the nuclear envelope and the cytoskeleton, crucial for maintaining nuclear architecture, migration and positioning, and mechanical transduction and signaling. Nesprin-1/-2 are abundantly expressed in cardiac and skeletal muscles.They have emerged as key players in the pathogenesis of dilated cardiomyopathy. Mutations in synaptic nuclear envelope-1/-2 genes encoding Nesprin-1/-2 are associated with dilated cardiomyopathy, underscoring their significance in cardiac health. This review highlights the all known cases of Nesprin-1/-2 related dilated cardiomyopathy, focusing on their interactions with the nuclear envelope, their role in mechanical transduction, and their influence on gene expression. Moreover, it delves into the underlying mechanisms through which Nesprin dysfunction disrupts nuclear-cytoskeletal coupling, leading to abnormal nuclear morphology, impaired mechanotransduction, and altered gene regulation. The exploration of Nesprin's impact on dilated cardiomyopathy offers a promising avenue for therapeutic interventions aimed at ameliorating the disease. This review provides a comprehensive overview of recent advancements in understanding the pivotal role of Nesprins in dilated cardiomyopathy research.

Life outside the LINC complex - Do SUN proteins have LINC-independent functions?

Sad1 and UNC84 (SUN) and Klarsicht, ANC-1, and Syne homology (KASH) proteins interact at the nuclear periphery to form the linker of nucleoskeleton and cytoskeleton (LINC) complex, spanning the nuclear envelope (NE) and connecting the cytoskeleton with the nuclear interior. It is now well-documented that several cellular functions depend on LINC complex formation, including cell differentiation and migration. Intriguingly, recent studies suggest that SUN proteins participate in cellular processes where their association with KASH proteins may not be required. Building on this recent research, we elaborate on the hypothesis that SUN proteins may perform LINC-independent functions and discuss the modalities that may allow SUN proteins to function at the INM when they are not forming LINC complex.

Inhibition of PDIs Downregulates Core LINC Complex Proteins, Promoting the Invasiveness of MDA-MB-231 Breast Cancer Cells in Confined Spaces In Vitro

Eukaryotic cells tether the nucleoskeleton to the cytoskeleton via a conserved molecular bridge, called the LINC complex. The core of the LINC complex comprises SUN-domain and KASH-domain proteins that directly associate within the nuclear envelope lumen. Intra- and inter-chain disulphide bonds, along with KASH-domain protein interactions, both contribute to the tertiary and quaternary structure of vertebrate SUN-domain proteins. The significance of these bonds and the role of PDIs (protein disulphide isomerases) in LINC complex biology remains unclear. Reducing and non-reducing SDS-PAGE analyses revealed a prevalence of SUN2 homodimers in non-tumorigenic breast epithelia MCF10A cells, but not in the invasive triple-negative breast cancer MDA-MB-231 cell line. Furthermore, super-resolution microscopy revealed SUN2 staining alterations in MCF10A, but not in MDA-MB-231 nuclei, upon reducing agent exposure. While PDIA1 levels were similar in both cell lines, pharmacological inhibition of PDI activity in MDA-MB-231 cells led to SUN-domain protein down-regulation, as well as Nesprin-2 displacement from the nucleus. This inhibition also caused changes in perinuclear cytoskeletal architecture and lamin downregulation, and increased the invasiveness of PDI-inhibited MDA-MB-231 cells in space-restrictive in vitro environments, compared to untreated cells. These results emphasise the key roles of PDIs in regulating LINC complex biology, cellular architecture, biomechanics, and invasion.

Hyperphosphorylated Tau Inflicts Intracellular Stress Responses that Are Mitigated by Apomorphine

Abnormal phosphorylation of the microtubule-binding protein tau in the brain is a key pathological marker for Alzheimer's disease and additional neurodegenerative tauopathies. However, how hyperphosphorylated tau causes cellular dysfunction or death that underlies neurodegeneration remains an unsolved question critical for the understanding of disease mechanism and the design of efficacious drugs. Using a recombinant hyperphosphorylated tau protein (p-tau) synthesized by the PIMAX approach, we examined how cells responded to the cytotoxic tau and explored means to enhance cellular resistance to tau attack. Upon p-tau uptake, the intracellular calcium levels rose promptly. Gene expression analyses revealed that p-tau potently triggered endoplasmic reticulum (ER) stress, unfolded protein response (UPR), ER stress-associated apoptosis, and pro-inflammation in cells. Proteomics studies showed that p-tau diminished heme oxygenase-1 (HO-1), an ER stress-associated anti-inflammation and anti-oxidative stress regulator, while stimulated the accumulation of MIOS and other proteins. p-Tau-induced ER stress-associated apoptosis and pro-inflammation are ameliorated by apomorphine, a brain-permeable prescription drug widely used to treat Parkinson's disease symptoms, and by overexpression of HO-1. Our results reveal probable cellular functions targeted by hyperphosphorylated tau. Some of these dysfunctions and stress responses have been linked to neurodegeneration in Alzheimer's disease. The observations that the ill effects of p-tau can be mitigated by a small compound and by overexpressing HO-1 that is otherwise diminished in the treated cells inform new directions of Alzheimer's disease drug discovery.

Dissecting the shared genetic architecture between endometriosis and polycystic ovary syndrome

Background

Previous study suggested evidence for coexistence and similarities between endometriosis and polycystic ovary syndrome (PCOS), but it is unclear regarding the shared genetic architecture and causality underlying the phenotypic similarities observed for endometriosis and PCOS.

Methods

By leveraging summary statistics from public genome-wide association studies regarding endometriosis (European-based: N=470,866) and PCOS (European-based: N=210,870), we explored the genetic correlation that shared between endometriosis and PCOS using linkage disequilibrium score regression. Shared risk SNPs were derived using PLACO (Pleiotropic analysis under composite null hypothesis) and FUMA (Functional Mapping and Annotation of Genetic Associations). The potential causal association between endometriosis and PCOS was investigated using two-sample Mendelian randomization (MR). Linkage disequilibrium score for the specific expression of genes analysis (LDSC-SEG) were performed for tissue enrichment analysis. The expression profiles of the risk gene in tissues were further examined.

Results

A positive genetic association was observed between endometriosis and PCOS. 12 significant pleiotropic loci shared between endometriosis and PCOS were identified. Genetic associations between endometriosis and PCOS were particularly enriched in uterus, endometrium and fallopian tube. Two-sample MR analysis further indicated a potential causative effect of endometriosis on PCOS, and vice versa. Microarray and RNA-seq verified the expressions of SYNE1 and DNM3 were significantly altered in the endometrium of patients with endometriosis or PCOS compared to those of control subjects.

Conclusion

Our study indicates the genetic correlation and shared risk genes between PCOS and endometriosis. These findings provide insights into the potential mechanisms behind their comorbidity and the future development of therapeutics.

No-observed-adverse-effect-level (NOAEL) clothianidin, a neonicotinoid pesticide, impairs hippocampal memory and motor learning associated with alteration of gene expression in cerebellum

Neonicotinoid pesticides (NNs) have been associated with numerous neurobehavioral effects in rodents, raising concerns about their impact on cognitive function. Clothianidin (CLO), a type of NN, was orally administered to male mice (10 weeks old, C57BL/6N) at the no-observed-adverse-effect level (NOAEL) of 50 mg/kg/day as indicated in the pesticide risk assessment report. Behavioral tests (novel location recognition and rotarod tests) evaluated hippocampal memory and cerebellar motor learning. After each test, plasma monoamines (3-methoxytyramine, histamine, serotonin, tryptamine) were measured by LC-ESI/MS/MS (Liquid chromatography-electrospray ionization/tandem mass spectrometry), and cerebellar mRNA expression was quantified by microarray and qRT-PCR analyses. The NOAEL of CLO was found to impair hippocampal memory, leading to decreased spontaneous locomotor activity and motor function. We reported, for the first time, multiple alterations of gene expression in the cerebellum associated with motor dysfunction.

Mechanotransduction and epigenetic modulations of chromatin: Role of mechanical signals in gene regulation

Mechanical forces may be generated within a cell due to tissue stiffness, cytoskeletal reorganization, and the changes (even subtle) in the cell's physical surroundings. These changes of forces impose a mechanical tension within the intracellular protein network (both cytosolic and nuclear). Mechanical tension could be released by a series of protein-protein interactions often facilitated by membrane lipids, lectins and sugar molecules and thus generate a type of signal to drive cellular processes, including cell differentiation, polarity, growth, adhesion, movement, and survival. Recent experimental data have accentuated the molecular mechanism of this mechanical signal transduction pathway, dubbed mechanotransduction. Mechanosensitive proteins in the cell's plasma membrane discern the physical forces and channel the information to the cell interior. Cells respond to the message by altering their cytoskeletal arrangement and directly transmitting the signal to the nucleus through the connection of the cytoskeleton and nucleoskeleton before the information despatched to the nucleus by biochemical signaling pathways. Nuclear transmission of the force leads to the activation of chromatin modifiers and modulation of the epigenetic landscape, inducing chromatin reorganization and gene expression regulation; by the time chemical messengers (transcription factors) arrive into the nucleus. While significant research has been done on the role of mechanotransduction in tumor development and cancer progression/metastasis, the mechanistic basis of force-activated carcinogenesis is still enigmatic. Here, in this review, we have discussed the various cues and molecular connections to better comprehend the cellular mechanotransduction pathway, and we also explored the detailed role of some of the multiple players (proteins and macromolecular complexes) involved in mechanotransduction. Thus, we have described an avenue: how mechanical stress directs the epigenetic modifiers to modulate the epigenome of the cells and how aberrant stress leads to the cancer phenotype.

Autosomal Recessive Non-Syndromic Deafness: Is AAV Gene Therapy a Real Chance?

The etiology of sensorineural hearing loss is heavily influenced by genetic mutations, with approximately 80% of cases attributed to genetic causes and only 20% to environmental factors. Over 100 non-syndromic deafness genes have been identified in humans thus far. In non-syndromic sensorineural hearing impairment, around 75-85% of cases follow an autosomal recessive inheritance pattern. In recent years, groundbreaking advancements in molecular gene therapy for inner-ear disorders have shown promising results. Experimental studies have demonstrated improvements in hearing following a single local injection of adeno-associated virus-derived vectors carrying an additional normal gene or using ribozymes to modify the genome. These pioneering approaches have opened new possibilities for potential therapeutic interventions. Following the PRISMA criteria, we summarized the AAV gene therapy experiments showing hearing improvement in the preclinical phases of development in different animal models of DFNB deafness and the AAV gene therapy programs currently in clinical phases targeting autosomal recessive non syndromic hearing loss. A total of 17 preclinical studies and 3 clinical studies were found and listed. Despite the hurdles, there have been significant breakthroughs in the path of HL gene therapy, holding great potential for providing patients with novel and effective treatment.

SYNE1 Mutation Is Associated with Increased Tumor Mutation Burden and Immune Cell Infiltration in Ovarian Cancer

SYNE1, a nuclear envelope protein critical for cellular structure and signaling, is downregulated in numerous malignancies. SYNE1 alterations are found in 10% of gynecologic malignancies and 5% of epithelial ovarian cancers. Previous studies demonstrated an association between SYNE1 mutation, increased tumor mutation burden (TMB), and immunotherapy response. This study evaluates the SYNE1 mutation frequency, association with TMB, and downstream effects of SYNE1 mutation in ovarian cancer. Genetic information, including whole-exome sequencing, RNA analysis, and somatic tumor testing, was obtained for consenting ovarian cancer patients at an academic medical center. Mutation frequencies were compared between the institutional cohort and The Cancer Genome Atlas (TCGA). Bioinformatics analyses were performed. In our cohort of 50 patients, 16 had a SYNE1 mutation, and 15 had recurrent disease. Median TMB for SYNE1 mutated patients was 25 compared to 7 for SYNE1 wild-type patients (p < 0.0001). Compared to the TCGA cohort, our cohort had higher SYNE1 mutation rates (32% vs. 6%, p < 0.001). Gene expression related to immune cell trafficking, inflammatory response, and immune response (z > 2.0) was significantly increased in SYNE1 mutated patients. SYNE1 mutation is associated with increased TMB and immune cell infiltration in ovarian cancer and may serve as an additional biomarker for immunotherapy response.

Hyperphosphorylated tau Inflicts Intracellular Stress Responses That Are Mitigated by Apomorphine

Background

Abnormal phosphorylation of the microtubule-binding protein tau in the brain is a key pathological marker for Alzheimer's disease and additional neurodegenerative tauopathies. However, how hyperphosphorylated tau causes cellular dysfunction or death that underlie neurodegeneration remains an unsolved question critical for the understanding of disease mechanism and the design of efficacious drugs.

Methods

Using a recombinant hyperphosphorylated tau protein (p-tau) synthesized by the PIMAX approach, we examined how cells responded to the cytotoxic tau and explored means to enhance cellular resistance to tau attack.

Results

Upon p-tau uptake, the intracellular calcium levels rose promptly. Gene expression analyses revealed that p-tau potently triggered endoplasmic reticulum (ER) stress, Unfolded Protein Response (UPR), ER stress-associated apoptosis, and pro-inflammation in cells. Proteomics studies showed that p-tau diminished heme oxygenase-1 (HO-1), an ER stress associated anti-inflammation and anti-oxidative stress regulator, while stimulated the accumulation of MIOS and other proteins. P-tau-induced ER stress-associated apoptosis and pro-inflammation are ameliorated by apomorphine, a brain-permeable prescription drug widely used to treat Parkinson's disease symptoms, and by overexpression of HO-1.

Conclusion

Our results reveal probable cellular functions targeted by hyperphosphorylated tau. Some of these dysfunctions and stress responses have been linked to neurodegeneration in Alzheimer's disease. The observations that the ill effects of p-tau can be mitigated by a small compound and by overexpressing HO-1 that is otherwise diminished in the treated cells inform new directions of Alzheimer's disease drug discovery.

The LINC Complex Inhibits Excessive Chromatin Repression

The Linker of Nucleoskeleton and Cytoskeleton (LINC) complex transduces nuclear mechanical inputs suggested to control chromatin organization and gene expression; however, the underlying mechanism is currently unclear. We show here that the LINC complex is needed to minimize chromatin repression in muscle tissue, where the nuclei are exposed to significant mechanical inputs during muscle contraction. To this end, the genomic binding profiles of Polycomb, Heterochromatin Protein1 (HP1a) repressors, and of RNA-Pol II were studied in Drosophila larval muscles lacking functional LINC complex. A significant increase in the binding of Polycomb and parallel reduction of RNA-Pol-II binding to a set of muscle genes was observed. Consistently, enhanced tri-methylated H3K9 and H3K27 repressive modifications and reduced chromatin activation by H3K9 acetylation were found. Furthermore, larger tri-methylated H3K27me3 repressive clusters, and chromatin redistribution from the nuclear periphery towards nuclear center, were detected in live LINC mutant larval muscles. Computer simulation indicated that the observed dissociation of the chromatin from the nuclear envelope promotes growth of tri-methylated H3K27 repressive clusters. Thus, we suggest that by promoting chromatin-nuclear envelope binding, the LINC complex restricts the size of repressive H3K27 tri-methylated clusters, thereby limiting the binding of Polycomb transcription repressor, directing robust transcription in muscle fibers.

Mechanotherapy in oncology: Targeting nuclear mechanics and mechanotransduction

Mechanotherapy is proposed as a new option for cancer treatment. Increasing evidence suggests that characteristic differences are present in the nuclear mechanics and mechanotransduction of cancer cells compared with those of normal cells. Recent advances in understanding nuclear mechanics and mechanotransduction provide not only further insights into the process of malignant transformation but also useful references for developing new therapeutic approaches. Herein, we present an overview of the alterations of nuclear mechanics and mechanotransduction in cancer cells and highlight their implications in cancer mechanotherapy.

LINCing Senescence and Nuclear Envelope Changes

The nuclear envelope (NE) has emerged as a nexus for cellular organization, signaling, and survival. Beyond its role as a barrier to separate the nucleoplasm from the cytoplasm, the NE's role in supporting and maintaining a myriad of other functions has made it a target of study in many cellular processes, including senescence. The nucleus undergoes dramatic changes in senescence, many of which are driven by changes in the NE. Indeed, Lamin B1, a key NE protein that is consistently downregulated in senescence, has become a marker for senescence. Other NE proteins have also been shown to play a role in senescence, including LINC (linker of nucleoskeleton and cytoskeleton) complex proteins. LINC complexes span the NE, forming physical connections between the cytoplasm to the nucleoplasm. In this way, they integrate nuclear and cytoplasmic mechanical signals and are essential not only for a variety of cellular functions but are needed for cell survival. However, LINC complex proteins have been shown to have a myriad of functions in addition to forming a LINC complex, often existing as nucleoplasmic or cytoplasmic soluble proteins in a variety of isoforms. Some of these proteins have now been shown to play important roles in DNA repair, cell signaling, and nuclear shape regulation, all of which are important in senescence. This review will focus on some of these roles and highlight the importance of LINC complex proteins in senescence.

FBXO2 targets glycosylated SUN2 for ubiquitination and degradation to promote ovarian cancer development

SAD1/UNC84 domain protein-2 (SUN2) plays a tumor suppressor role in various types of cancer by inhibiting cancer cell proliferation, migration and promoting apoptosis. However, the post-translational regulation of SUN2 and the cellular mechanism responsible for its proteasomal degradation remains largely unknown. Here, we show that FBXO2, an E3 ubiquitin ligase of the F-box proteins (FBPs) family targets glycosylated SUN2 for ubiquitination and degradation via the ubiquitin-proteasome system (UPS). By integrating the Cancer Genome Atlas (TCGA), Gene Expression Omnibus (GEO), and the Encyclopedia of Cancer Cell Lines (CCLE) databases, we revealed that FBXO2 was selectively highly expressed in ovarian cancer (OV) tissues and cells. Patients with relatively high FBXO2 expression levels were associated with worse prognosis. Manipulation of the expression of FBXO2 affecting ovarian cancer cell proliferation, migration/invasion in vitro, and tumor growth in mice in vivo. The transcription factor SOX6 promoted FBXO2 expression by recognizing a putative response element localized on the promoter region of FBXO2. Abnormally highly expressed FBXO2 recognized and targeted glycosylated SUN2 protein for ubiquitination-depended degradation to prevent cell apoptosis, promote cell proliferation, and ultimately promote the progression of OV. Thus, we revealed a new SOX6-FBXO2-SUN2 axis that contributed to the development of OV, and targeting this axis may represent an effective OV treatment strategy.

Vincristine-Induced Peripheral Neuropathy in Childhood Acute Lymphoblastic Leukemia: Genetic Variation as a Potential Risk Factor

Vincristine (VCR) is the first-line chemotherapeutic medication often co-administered with other drugs to treat childhood acute lymphoblastic leukemia. Dose-dependent neurotoxicity is the main factor restricting VCR’s clinical application. VCR-induced peripheral neuropathy (VIPN) sometimes results in dose reduction or omission, leading to clinical complications or affecting the patient’s quality of life. With regard to the genetic basis of drug responses, preemptive pharmacogenomic testing and simultaneous blood level monitoring could be helpful for the transformation of various findings into individualized therapies. In this review, we discussed the potential associations between genetic variants in genes contributing to the pharmacokinetics/pharmacodynamics of VCR and VIPN incidence and severity in patients with acute lymphoblastic leukemia. Of note, genetic variants in the CEP72 gene have great potential to be translated into clinical practice. Such a genetic biomarker may help clinicians diagnose VIPN earlier. Besides, genetic variants in other genes, such as CYP3A5, ABCB1, ABCC1, ABCC2, TTPA, ACTG1, CAPG, SYNE2, SLC5A7, COCH, and MRPL47, have been reported to be associated with the VIPN, but more evidence is needed to validate the findings in the future. In fact, a variety of complex factors jointly determine the VIPN. In implementing precision medicine, the combination of genetic, environmental, and personal variables, along with therapeutic drug monitoring, will allow for a better understanding of the mechanisms of VIPN, improving the effectiveness of VCR treatment, reducing adverse reactions, and improving patients’ quality of life.

SYNE1 Exonic Variant rs9479297 Contributes to Concurrent Hepatocellular and Transitional Cell Carcinoma Double Primary Cancer

Unexpected high risk of synchronous/metachronous hepatocellular carcinoma (HCC) and transitional cell carcinoma (TCC) co-occurrence has been discovered previously. Here, we searched for genetic variation contributing to the co-occurrence of this double primary cancer (DPC). Using targeted exome sequencing, a panel of variants associated with concurrent DPC was identified. However, only a nonsynonymous variant within the Spectrin Repeat Containing Nuclear Envelope Protein 1 (SYNE1) gene was associated with DPC occurrence (p = 0.002), compared with that in the healthy population. Further independent cohort verification analysis revealed that the SYNE1-rs9479297-TT genotype (versus TC + CC genotypes) was enriched in patients with DPC, compared with that in those with TCC alone (p = 0.039), those with HCC alone (p = 0.006), those with non-HCC/non-TCC (p < 0.001), and healthy population (p < 0.001). SYNE1 mRNA expression reduced in both patients with HCC and TCC, and its lower expression in HCC was associated with shorter recurrence-free (p = 0.0314) and metastasis-free (p = 0.0479) survival. SYNE1-rs9479297 genotypes were correlated with tissue SYNE1 levels and clinical outcomes in HCC patients. Finally, SYNE1 silencing enhanced the cell proliferation and migration of HCC/TCC cells. In conclusion, SYNE1-rs9479297 genotypes were associated with HCC/TCC DPC co-occurrence and correlated with SYNE1 expression, which in turn contributed to HCC/TCC cell proliferation and migration, thereby affecting clinical outcomes.

Silencing of Nesprin-2 inhibits the differentiation of myofibroblasts from fibroblasts induced by mechanical stretch

Mechanical force plays a pivotal role in the pathogenesis of hypertrophic scar (HTS). Dermal fibroblasts and myofibroblasts are the key cells involved in HTS. Myofibroblasts in HTS possess different biochemical and biophysical characteristics by which myofibroblasts are often distinguished from fibroblasts. The role of mechanotransducers outside the nucleus in the pathogenesis of HTS has been reported in many studies. However, the role of Nesprin‐2 in HTS is not clear. Hence, we aim to construct a cell model of HTS and explore the role of Nesprin‐2 in this process. Myofibroblasts and fibroblasts were isolated from HTS and healthy skin tissues of the same patient. Fibroblasts were exposed to cyclic stretch with 10% magnitude and a frequency of 0.1 Hz for 3 days, 5 days, and 7 days, respectively. After the cell model was confirmed, fibroblasts transfected with siRNA targeting human Nesprin‐2 were exposed to cyclic stretch. The mechanical behaviour and biochemical reaction of the dermal fibroblasts were analysed. The stretched fibroblasts at day 5 showed the same mechanotransductive and biochemical features as unstretched myofibroblasts. Mechanical strain could induce the myofibroblasts differentiation and a cell model of HTS was established successfully at day 5. The expressions of lamin A/C, alpha‐smooth muscle actin, transforming growth factor beta 1, and collagen type I in fibroblasts were reduced by the silencing of Nesprin‐2. Mechanical strain could induce the myofibroblasts differentiation and silencing of Nesprin‐2 could block the mechanical stimulation of terminal myofibroblasts differentiation. Nesprin‐2 might be a potential target to treat the HTS.

Biallelic SYNE2 Missense Mutations Leading to Nesprin-2 Giant Hypo-Expression Are Associated with Intellectual Disability and Autism

Autism spectrum disorder (ASD) is a group of neurological and developmental disabilities characterised by clinical and genetic heterogeneity. The current study aimed to expand ASD genotyping by investigating potential associations with SYNE2 mutations. Specifically, the disease-causing variants of SYNE2 in 410 trios manifesting neurodevelopmental disorders using whole-exome sequencing were explored. The consequences of the identified variants were studied at the transcript level using quantitative polymerase chain reaction (qPCR). For validation, immunofluorescence and immunoblotting were performed to analyse mutational effects at the protein level. The compound heterozygous variants of SYNE2 (NM_182914.3:c.2483T>G; p.(Val828Gly) and NM_182914.3:c.2362G>A; p.(Glu788Lys)) were identified in a 4.5-year-old male, clinically diagnosed with autism spectrum disorder, developmental delay and intellectual disability. Both variants reside within the nesprin-2 giant spectrin repeat (SR5) domain and are predicted to be highly damaging using in silico tools. Specifically, a significant reduction of nesprin-2 giant protein levels is revealed in patient cells. SYNE2 transcription and the nuclear envelope localisation of the mutant proteins was however unaffected as compared to parental control cells. Collectively, these data provide novel insights into the cardinal role of the nesprin-2 giant in neurodevelopment and suggest that the biallelic hypomorphic SYNE2 mutations may be a new cause of intellectual disability and ASD.

SUN5 Interacting With Nesprin3 Plays an Essential Role in Sperm Head-to-Tail Linkage: Research on Sun5 Gene Knockout Mice

Acephalic spermatozoa syndrome is a rare genetic and reproductive disease. Recent studies have shown that approximately 33–47% of patients with acephalic spermatozoa syndrome have SUN5 mutations, but the molecular mechanism underlying this phenomenon has not been elucidated. In this study, we generated Sun5 knockout mice and found that the head-to-tail linkage was broken in Sun5^–/– mice, which was similar to human acephalic spermatozoa syndrome. Furthermore, ultrastructural imaging revealed that the head-tail coupling apparatus (HTCA) and the centrosome were distant from the nucleus at steps 9–10 during spermatid elongation. With the manchette disappearing at steps 13–14, the head and the tail segregated. To explore the molecular mechanism underlying this process, bioinformatic analysis was performed and showed that Sun5 may interact with Nesprin3. Further coimmunoprecipitation (Co-IP) and immunofluorescence assays confirmed that Sun5 and Nesprin3 were indeed bona fide interaction partners that formed the linker of the nucleoskeleton and cytoskeleton (LINC) complex participating in the connection of the head and tail of spermatozoa. Nesprin3 was located posterior and anterior to the nucleus during spermiogenesis in wild-type mice, whereas it lost its localization at the implantation fossa of the posterior region in Sun5^–/– mice. Without correct localization of Nesprin3 at the nuclear membrane, the centrosome, which is the originator of the flagellum, was distant from the nucleus, which led to the separation of the head and tail. In addition, isobaric tag for relative and absolute quantitation results showed that 47 proteins were upregulated, and 56 proteins were downregulated, in the testis in Sun5^–/– mice, and the downregulation of spermatogenesis-related proteins (Odf1 and Odf2) may also contribute to the damage to the spermatozoa head-to-tail linkage. Our findings suggested that Sun5 is essential for the localization of Nesprin3 at the posterior nuclear membrane, which plays an essential role in the sperm head-tail connection.

Syne2b/Nesprin-2 Is Required for Actin Organization and Epithelial Integrity During Epiboly Movement in Zebrafish

Syne2b/nesprin-2 is a giant protein implicated in tethering the nucleus to the cytoskeleton and plays an important role in maintaining cellular architecture. Epiboly is a conserved morphogenetic movement that involves extensive spreading and thinning of the epithelial blastoderm to shape the embryo and organize the three germ layers. Dynamic cytoskeletal organization is critical for this process, but how it is regulated remains elusive. Here we generated a zebrafish syne2b mutant line and analyzed the effects of impaired Syne2b function during early development. By CRISPR/Cas9-mediated genome editing, we obtained a large deletion in the syne2b locus, predicted to cause truncation of the nuclear localization KASH domain in the translated protein. Maternal and zygotic syne2b embryos showed delayed epiboly initiation and progression without defects in embryonic patterning. Remarkably, disruption of Syne2b function severely impaired cytoskeletal organization across the embryo, leading to aberrant clustering of F-actin at multiple cell contact regions and abnormal cell shape changes. These caused disintegration of the epithelial blastoderm before the end of gastrulation in most severely affected embryos. Moreover, the migration of yolk nuclear syncytium also became defective, likely due to disorganized cytoskeletal networks at the blastoderm margin and in the yolk cell. These findings demonstrate an essential function of Syne2b in maintaining cytoskeletal architecture and epithelial integrity during epiboly movement.

Culturing Keratinocytes on Biomimetic Substrates Facilitates Improved Epidermal Assembly In Vitro

Mechanotransduction is defined as the ability of cells to sense mechanical stimuli from their surroundings and translate them into biochemical signals. Epidermal keratinocytes respond to mechanical cues by altering their proliferation, migration, and differentiation. In vitro cell culture, however, utilises tissue culture plastic, which is significantly stiffer than the in vivo environment. Current epidermal models fail to consider the effects of culturing keratinocytes on plastic prior to setting up three-dimensional cultures, so the impact of this non-physiological exposure on epidermal assembly is largely overlooked. In this study, primary keratinocytes cultured on plastic were compared with those grown on 4, 8, and 50 kPa stiff biomimetic hydrogels that have similar mechanical properties to skin. Our data show that keratinocytes cultured on biomimetic hydrogels exhibited major changes in cellular architecture, cell density, nuclear biomechanics, and mechanoprotein expression, such as specific Linker of Nucleoskeleton and Cytoskeleton (LINC) complex constituents. Mechanical conditioning of keratinocytes on 50 kPa biomimetic hydrogels improved the thickness and organisation of 3D epidermal models. In summary, the current study demonstrates that the effects of extracellular mechanics on keratinocyte cell biology are significant and therefore should be harnessed in skin research to ensure the successful production of physiologically relevant skin models.

A genome-wide association study in human lymphoblastoid cells supports safety of mitochondrial complex I inhibitor

Novel therapeutic strategies for Alzheimer's disease (AD) are of the greatest priority given the consistent failure of recent clinical trials focused on Aβ or pTau. Earlier, we demonstrated that mild mitochondrial complex I inhibitor CP2 blocks neurodegeneration and cognitive decline in multiple mouse models of AD. To evaluate the safety of CP2 in humans, we performed a genome-wide association study (GWAS) using 196 lymphoblastoid cell lines and identified 11 SNP loci and 64 mRNA expression probe sets that potentially associate with CP2 susceptibility. Using primary mouse neurons and pharmacokinetic study, we show that CP2 is generally safe at a therapeutic dose.

Neonatal AAV gene therapy rescues hearing in a mouse model of SYNE4 deafness

Genetic variants account for approximately half the cases of congenital and early-onset deafness. Methods and technologies for viral delivery of genes into the inner ear have evolved over the past decade to render gene therapy a viable and attractive approach for treatment. Variants in SYNE4, encoding the protein nesprin-4, a member of the linker of nucleoskeleton and cytoskeleton (LINC), lead to DFNB76 human deafness. Syne4-/- mice have severe-to-profound progressive hearing loss and exhibit mislocalization of hair cell nuclei and hair cell degeneration. We used AAV9-PHP.B, a recently developed synthetic adeno-associated virus, to deliver the coding sequence of Syne4 into the inner ears of neonatal Syne4-/- mice. Here we report rescue of hair cell morphology and survival, nearly complete recovery of auditory function, and restoration of auditory-associated behaviors, without observed adverse effects. Uncertainties remain regarding the durability of the treatment and the time window for intervention in humans, but our results suggest that gene therapy has the potential to prevent hearing loss in humans with SYNE4 mutations.

Genome wide association studies for treatment-related adverse effects of pediatric acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the most common pediatric hematological malignancy; notwithstanding the success of ALL therapy, severe adverse drugs effects represent a serious issue in pediatric oncology, because they could be both an additional life threatening condition for ALL patients per se and a reason to therapy delay or discontinuation with important fallouts on final outcome. Cancer treatment-related toxicities have generated a significant need of finding predictive pharmacogenomic markers for the a priori identification of at risk patients. In the era of precision medicine, high throughput genomic screening such as genome wide association studies (GWAS) might provide useful markers to tailor therapy intensity on patients' genetic profile. Furthermore, these findings could be useful in basic research for better understanding the mechanistic and regulatory pathways of the biological functions associated with ALL treatment toxicities. The purpose of this review is to give an overview of high throughput genomic screening of the last 10 years that had investigated the landscape of ALL treatment-associated toxicities. This article is categorized under: Cancer > Genetics/Genomics/Epigenetics.

Increased Lamin B1 Levels Promote Cell Migration by Altering Perinuclear Actin Organization

Cell migration requires reposition and reshaping of the cell nucleus. The nuclear lamina is highly important for migration of both primary and cancer cells. B-type lamins are important for proper migration of epicardial cells and neurons and increased lamin B to lamin A ratio accelerates cancer cell migration through confined spaces. Moreover, a positive association between lamin B1 levels and tumor formation and progression is found in various cancer types. Still, the molecular mechanism by which B-type lamins promote cell migration is not fully understood. To better understand this mechanism, we tested the effects of lamin B1 on perinuclear actin organization. Here we show that induction of melanoma cell migration leads to the formation of a cytosolic Linker of Nucleoskeleton and Cytoskeleton (LINC) complex-independent perinuclear actin rim, which has not been detected in migrating cells, yet. Significantly, increasing the levels of lamin B1 but not the levels of lamin A prevented perinuclear actin rim formation while accelerated the cellular migration rate. To interfere with the perinuclear actin rim, we generated a chimeric protein that is localized to the outer nuclear membrane and cleaves perinuclear actin filaments in a specific manner without disrupting other cytosolic actin filaments. Using this tool, we found that disruption of the perinuclear actin rim accelerated the cellular migration rate in a similar manner to lamin B1 over-expression. Taken together, our results suggest that increased lamin B1 levels can accelerate cell migration by inhibiting the association of the nuclear envelope with actin filaments that may reduce nuclear movement and deformability.

Identification of candidate mediators of chemoresponse in breast cancer through therapy-driven selection of somatic variants

Purpose

More than a third of primary breast cancer patients are treated with cytotoxic chemotherapy, typically without guidance from predictive markers. Increased use of neoadjuvant chemotherapy provides opportunities for identification of molecules associated with treatment response, by comparing matched tumour samples before and after therapy. Our hypothesis was that somatic variants of increased prevalence after therapy promote resistance, while variants with reduced prevalence cause sensitivity.

Methods

We performed systematic analyses of matched pairs of cancer exomes from primary oestrogen receptor-positive/HER2-negative breast cancers (n = 6) treated with neoadjuvant epirubicin/cyclophosphamide. We identified candidate genes as mediators of chemotherapy response by consistent subclonal changes in somatic variant prevalence through therapy, predicted variant impact on gene function, and enrichment of specific functional pathways. Influence of candidate genes on breast cancer outcome was tested using publicly available breast cancer expression data (n = 1903).

Results

We identified 14 genes as the strongest candidate mediators of chemoresponse: TCHH, MUC17, ARAP2, FLG2, ABL1, CENPF, COL6A3, DMBT1, ITGA7, PLXNA1, S100PBP, SYNE1, ZFHX4, and CACNA1C. Genes contained somatic variants showing prevalence changes in up to 4 patients, with up to 3 being predicted as damaging. Genes coding for extra-cellular matrix components or related signalling pathways were significantly over-represented among variants showing prevalence changes. Expression of 5 genes (TCHH, ABL1, CENPF, S100PBP, and ZFHX4) was significantly associated with patient survival.

Conclusions

Genomic analysis of paired pre- and post-therapy samples resulting from neoadjuvant therapy provides a powerful method for identification of mediators of response. Genes we identified should be assessed as predictive markers or targets in chemo-sensitization.

Electronic supplementary material

The online version of this article (10.1007/s10549-020-05836-7) contains supplementary material, which is available to authorized users.

A minimal constraint device for imaging nuclei in live Drosophila contractile larval muscles reveals novel nuclear mechanical dynamics

Muscle contractions produce reiterated cytoplasmic mechanical variations, which potentially influence nuclear mechanotransduction, however information regarding the dynamics of muscle nuclei (myonuclei) in the course of muscle contraction is still missing. Towards that end, a minimal constraint device was designed in which intact live Drosophila larva is imaged, while its muscles still contract. The device is placed under spinning disc confocal microscope enabling imaging of fluorescently labeled sarcomeres and nuclei during muscle contraction, without any external stimulation. As a proof of principle we studied myonuclei dynamics in wild-type, as well as in Nesprin/klar mutant larvae lacking proper nuclear-cytoskeletal connections. Myonuclei in control larvae exhibited comparable dynamics in the course of multiple contractile events, independent of their position along the muscle fiber. In contrast, myonuclei of mutant larvae displayed differential dynamics at distinct positions along individual myofibers. Moreover, we identified a linear link between myonuclear volume and its acceleration values during muscle contraction which, in Nesprin/klar mutants exhibited an opposite tendency relative to control. Estimation of the drag force applied on individual myonuclei revealed that force fluctuations in time, but not the average force, differed significantly between control and Nesprin/klar mutant, and were considerably higher in the mutant myonuclei. Taken together these results imply significant alterations in the mechanical dynamics of individual myonuclei in the Nesprin/klar myonuclei relative to control. Such differences provide novel mechanical insight into Nesprin function in contractile muscles, and might reveal the mechanical basis underlying Nesprin-related human diseases.

Recapitulation of molecular regulators of nuclear motion during cell migration

Cell migration is a highly orchestrated cellular event that involves physical interactions of diverse subcellular components. The nucleus as the largest and stiffest organelle in the cell not only maintains genetic functionality, but also actively changes its morphology and translocates through dynamic formation of nucleus-bound contractile stress fibers. Nuclear motion is an active and essential process for successful cell migration and nucleus self-repairs in response to compression and extension forces in complex cell microenvironment. This review recapitulates molecular regulators that are crucial for nuclear motility during cell migration and highlights recent advances in nuclear deformation-mediated rupture and repair processes in a migrating cell.

Epigenetic gene regulation, chromatin structure, and force-induced chromatin remodelling in epidermal development and homeostasis

The skin epidermis is a constantly renewing stratified epithelium that provides essential protective barrier functions throughout life. Epidermal stratification is governed by a step-wise differentiation program that requires precise spatiotemporal control of gene expression. How epidermal self-renewal and differentiation are regulated remains a fundamental open question. Cell-intrinsic and cell-extrinsic mechanisms that modify chromatin structure and interactions have been identified as key regulators of epidermal differentiation and stratification. Here, we will review the recent advances in our understanding of how chromatin modifiers, tissue-specific transcription factors, and force-induced nuclear remodeling processes function to shape chromatin and to control epidermal tissue development and homeostasis.

Emery-Dreifuss muscular dystrophy type 4: A new SYNE1 mutation associated with hypertrophic cardiomyopathy masked by a perinatal distress-related spastic diplegia

Hypertrophic cardiomyopathy could be part of a more complex syndrome like Emery-Dreifuss muscular dystrophy type 4. Genetic analysis allowed to identify a de novo heterozygous missense mutation in SYNE1 gene (chr6:152665253:G > C), supporting physician to reach a correct diagnosis in patient affected by cardiomyopathy associated with a difficult clinical scenario.

Nesprin-2G knockout fibroblasts exhibit reduced migration, changes in focal adhesion composition, and reduced ability to generate traction forces

The nuclear envelope protein nesprin-2G is a component of the linker of nucleoskeleton and cytoskeleton (LINC) complex and is responsible for mechanical and signaling crosstalk between the nucleus and cytoskeleton. A prior study has demonstrated that nesprin-2G knockout mice show delayed wound healing. The goal was to elucidate the mechanism underlying the delayed wound closure in this mouse model. Primary fibroblasts from wild-type and knockout neonatal mice were isolated. Knockout cells exhibited decreased focal adhesion (FA) size, number, and intensity. Consistent with this result, FA protein expression levels were decreased in knockout cells. Additionally, knockout fibroblasts displayed an abnormal actin cytoskeleton, as evidenced by loss of TAN line formation and both cytoplasmic and peri-nuclear actin staining. Using collective and single cell motility assays, it was found that knockout cells exhibited a reduction in both speed and directed migration. Traction force microscopy revealed that knockout fibroblasts generated fewer traction forces compared with WT fibroblasts. In summary, the data indicated that changes in actin organization and defects in FAs result in a reduced ability of knockout fibroblasts to generate traction forces needed for efficient motility.

Identifying SYNE1 Ataxia With Novel Mutations in a Chinese Population

Objective: Variants in SYNE1 have been widely reported in ataxia patients in Europe, with highly variable clinical phenotype. Until now, no mutation of SYNE1 ataxia has been reported among the Chinese population. Our aim was to screen for SYNE1 ataxia patients in China and extend the clinicogenetic spectrum.

Methods: Variants in SYNE1 were detected by high-throughput sequencing on a cohort of 126 unrelated index patients with unexplained autosomal recessive or sporadic ataxia. Pathogenicity assessments of SYNE1 variants were interpreted according to the ACMG guidelines. Potential pathogenic variants were confirmed by Sanger sequencing. Clinical assessments were conducted by two experienced neurologists.

Results: Two Chinese families with variable ataxia syndrome were identified (accounting for 1.6%; 2/126), separately caused by the novel homozygous SYNE1 mutation (NM_033071.3: c.21568C>T, p.Arg7190Ter), and compound heterozygous SYNE1 mutation (NM_033071.3: c.18684G>A, p.Trp6228Ter; c.17944C>T, p.Arg5982Ter), characterized by motor neuron impairment, mental retardation and arthrogryposis.

Conclusions:SYNE1 ataxia exists in the Chinese population, as a rare form of autosomal recessive ataxia, with a complex phenotype. Our findings expanded the ethnic, phenotypic and genetic diversity of SYNE1 ataxia.

The Different Facades of Retinal and Choroidal Endothelial Cells in Response to Hypoxia

Ocular angiogenic diseases, such as proliferative diabetic retinopathy and neovascular age-related macular degeneration, are associated with severe loss of vision. These pathologies originate from different vascular beds, retinal and choroidal microvasculatures, respectively. The activation of endothelial cells (EC) plays pivotal roles in angiogenesis, often triggered by oxygen deficiency. Hypoxia-inducible factors in ECs mediate the transcription of multiple angiogenic genes, including the canonical vascular endothelial growth factors. ECs show notable heterogeneity in function, structure, and disease, therefore the understanding of retinal/choroidal ECs (REC; CEC) biochemical and molecular responses to hypoxia may offer key insights into tissue-specific vascular targeting treatments. The aim of this review is to discuss the differences spanning between REC and CEC, with focus on their response to hypoxia, which could provide innovative and sustainable strategies for site specific targeting of ocular neovascularization.

Conserved SUN-KASH Interfaces Mediate LINC Complex-Dependent Nuclear Movement and Positioning

Many nuclear positioning events involve linker of nucleoskeleton and cytoskeleton (LINC) complexes, which transmit forces generated by the cytoskeleton across the nuclear envelope. LINC complexes are formed by trans-luminal interactions between inner nuclear membrane SUN proteins and outer nuclear membrane KASH proteins, but how these interactions are regulated is poorly understood. We combine in vivo C. elegans genetics, in vitro wounded fibroblast polarization, and in silico molecular dynamics simulations to elucidate mechanisms of LINC complexes. The extension of the KASH domain by a single alanine residue or the mutation of the conserved tyrosine at -7 completely blocked the nuclear migration function of C. elegans UNC-83. Analogous mutations at -7 of mouse nesprin-2 disrupted rearward nuclear movements in NIH 3T3 cells, but did not disrupt ANC-1 in nuclear anchorage. Furthermore, conserved cysteines predicted to form a disulfide bond between SUN and KASH proteins are important for the function of certain LINC complexes, and might promote a developmental switch between nuclear migration and nuclear anchorage. Mutations of conserved cysteines in SUN or KASH disrupted ANC-1-dependent nuclear anchorage in C. elegans and Nesprin-2G-dependent nuclear movements in polarizing fibroblasts. However, the SUN cysteine mutation did not disrupt nuclear migration. Moreover, molecular dynamics simulations showed that a disulfide bond is necessary for the maximal transmission of cytoskeleton-generated forces by LINC complexes in silico. Thus, we have demonstrated functions for SUN-KASH binding interfaces, including a predicted intermolecular disulfide bond, as mechanistic determinants of nuclear positioning that may represent targets for regulation.

Genetic risk factors for VIPN in childhood acute lymphoblastic leukemia patients identified using whole-exome sequencing

AIM

To identify genetic markers associated with vincristine-induced peripheral neuropathy (VIPN) in childhood acute lymphoblastic leukemia.

PATIENTS & METHODS

Whole-exome sequencing data were combined with exome-wide association study to identify predicted-functional germline variants associated with high-grade VIPN. Genotyping was then performed for top-ranked signals (n = 237), followed by validation in independent replication group (n = 405).

RESULTS

Minor alleles of rs2781377/SYNE2 (p = 0.01) and rs10513762/MRPL47 (p = 0.01) showed increased risk, whereas that of rs3803357/BAHD1 had a protective effect (p = 0.007). Using a genetic model based on weighted genetic risk scores, an additive effect of combining these loci was observed (p = 0.003). The addition of rs1135989/ACTG1 further enhanced model performance (p = 0.0001).

CONCLUSION

Variants in SYNE2, MRPL47 and BAHD1 genes are putative new risk factors for VIPN in childhood acute lymphoblastic leukemia.

Nesprins and Lamins in Health and Diseases of Cardiac and Skeletal Muscles

Since the discovery of the inner nuclear transmembrane protein emerin in the early 1990s, nuclear envelope (NE) components and related involvement in nuclei integrity and functionality have been highly investigated. The NE is composed of two distinct lipid bilayers described as the inner (INM) and outer (ONM) nuclear membrane. NE proteins can be specifically “integrated” in the INM (such as emerin and SUN proteins) or in the ONM such as nesprins. Additionally, flanked to the INM, the nuclear lamina, a proteinaceous meshwork mainly composed of lamins A and C completes NE composition. This network of proteins physically interplays to guarantee NE integrity and most importantly, shape the bridge between cytoplasmic cytoskeletons networks (such as microtubules and actin) and the genome, through the anchorage to the heterochromatin. The essential network driving the connection of nucleoskeleton with cytoskeleton takes place in the perinuclear space (the space between ONM and INM) with the contribution of the LINC complex (for Linker of Nucleoskeleton to Cytoskeleton), hosting KASH and SUN proteins interactions. This close interplay between compartments has been related to diverse functions from nuclear integrity, activity and positioning through mechanotransduction pathways. At the same time, mutations in NE components genes coding for proteins such as lamins or nesprins, had been associated with a wide range of congenital diseases including cardiac and muscular diseases. Although most of these NE associated proteins are ubiquitously expressed, a large number of tissue-specific disorders have been associated with diverse pathogenic mutations. Thus, diagnosis and molecular explanation of this group of diseases, commonly called “nuclear envelopathies,” is currently challenging. This review aims, first, to give a better understanding of diverse functions of the LINC complex components, from the point of view of lamins and nesprins. Second, to summarize human congenital diseases with a special focus on muscle and heart abnormalities, caused by mutations in genes coding for these two types of NE associated proteins.

Angiogenic and Immunologic Proteins Identified by Deep Proteomic Profiling of Human Retinal and Choroidal Vascular Endothelial Cells: Potential Targets for New Biologic Drugs

PURPOSE

Diseases that involve retinal or choroidal vascular endothelial cells are leading causes of vision loss: age-related macular degeneration, retinal ischemic vasculopathies, and noninfectious posterior uveitis. Proteins differentially expressed by these endothelial cell populations are potential drug targets. We used deep proteomic profiling to define the molecular phenotype of human retinal and choroidal endothelial cells at the protein level.

METHODS

Retinal and choroidal vascular endothelial cells were separately isolated from 5 human eye pairs by selection on CD31. Total protein was extracted and digested, and peptide fractions were analyzed by reverse-phase liquid chromatography tandem mass spectrometry. Peptide sequences were assigned to fragment ion spectra, and proteins were inferred from openly accessible protein databases. Protein abundance was determined by spectral counting. Publicly available software packages were used to identify proteins that were differentially expressed between human retinal and choroidal endothelial cells, and to classify proteins that were highly abundant in each endothelial cell population.

RESULTS

Human retinal and/or choroidal vascular endothelial cells expressed 5042 nonredundant proteins. Setting the differential expression false discovery rate at 0.05, 498 proteins of 3454 quantifiable proteins (14.4%) with minimum mean spectral counts of 2.5 were differentially abundant in the 2 cell populations. Retinal and choroidal endothelial cells were enriched in angiogenic proteins, and retinal endothelial cells were also enriched in immunologic proteins.

CONCLUSIONS

This work describes the different protein expression profiles of human retinal and choroidal vascular endothelial cells, and provides multiple candidates for further study as novel treatments or drug targets for posterior eye diseases. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Actin-Based Cell Protrusion in a 3D Matrix

Cell migration controls developmental processes (gastrulation and tissue patterning), tissue homeostasis (wound repair and inflammatory responses), and the pathobiology of diseases (cancer metastasis and inflammation). Understanding how cells move in physiologically relevant environments is of major importance, and the molecular machinery behind cell movement has been well studied on 2D substrates, beginning over half a century ago. Studies over the past decade have begun to reveal the mechanisms that control cell motility within 3D microenvironments – some similar to, and some highly divergent from those found in 2D. In this review we focus on migration and invasion of cells powered by actin, including formation of actin-rich protrusions at the leading edge, and the mechanisms that control nuclear movement in cells moving in a 3D matrix.

Cell migration has been well studied in 2D, but how this relates to movement in physiological 3D tissues and matrix is not clear, particularly in vertebrate interstitial matrix.

In 3D matrix cells actin polymerisation directly contributes to the formation of lamellipodia to facilitate migration and invasion (mesenchymal movement), analogous to 2D migration; actomyosin contractility promotes bleb formation to indirectly promote protrusion (amoeboid movement).

Mesenchymal migration can be characterised by polymerisation of actin to form filopodial protrusions, in the absence of lamellipodia.

Translocation of the nucleus is emerging as a critical step due to the constrictive environment of 3D matrices, and the mechanisms that transmit force to the nucleus and allow movement are beginning to be uncovered.

Sperm‑associated antigen 4 (SPAG4) as a new cancer marker interacts with Nesprin3 to regulate cell migration in lung carcinoma

Lung cancer is the most common cause of cancer-related deaths, and early diagnosis and targeted therapy are extremely important in the treatment of this disease. Sperm-associated antigen 4 (SPAG4) was recently found to be a novel cancer biomarker. In the present study, the expression of SPAG4 was revealed to be high in lung adenocarcinoma tissues as determined by western blotting and immunohistochemistry. SPAG4 knockdown by RNAi efficiently reduced the migration of the lung cancer A549 cells in vitro. Mechanistically, SPAG4 exerted its tumor promoting functions by interacting with Nesprin3 as determined by co-immunoprecipitation (Co-IP) and bimolecular fluorescence complementation (BiFC) techniques. In addition, immunofluorescence revealed that the level of SPAG4 in lung cancer cells could affect the location and expression of Nesprin3. Furthermore, silencing of Nesprin3 reduced the migration of A549 cells and we provided evidence to demonstrate that SPAG4 acted as a positive regulator of Nesprin3. The results revealed that SPAG4, in cooperation with Nesprin3, has a fundamental pathological function in the migration of lung carcinoma cells, and the SPAG4 gene may be useful for the clinical diagnosis and new treatment strategies in patients with lung cancer.

Analysis of High Molecular Weight Isoforms of Nesprin-1 and Nesprin-2 with Vertical Agarose Gel Electrophoresis

The biochemical characterization of proteins most often require their identification by immunoblotting. Whereas SDS-PAGE provides satisfactory results for most proteins, the identification of larger proteins requires alternative methods to ensure their separation and complete transfer onto nitrocellulose membranes. Here, we describe the application of vertical agarose gel electrophoresis to identify large isoforms of nesprin-1 and nesprin-2.

Functions of nuclear actin-binding proteins in human cancer

Nuclear actin-binding proteins (ABPs) perform distinguishable functions compared with their cytoplasmic counterparts in extensive activities of living cells. In addition to the ability to regulate actin cytoskeleton dynamics, nuclear ABPs are associated with multiple nuclear biological processes, including chromatin remodeling, gene transcriptional regulation, DNA damage response, nucleocytoplasmic trafficking and nuclear structure maintenance. The nuclear translocation of ABPs is affected by numerous intracellular or extracellular stimuli, which may lead to developmental malformation, tumor initiation, tumor progression and metastasis. Abnormal expression of certain ABPs have been reported in different types of cancer. This review focuses on the newly identified roles of nuclear ABPs in the pathological processes associated with cancer.

Acute myeloid leukemia with t(14;21) involving RUNX1 and SYNE2: A novel favorable-risk translocation?

In acute myeloid leukemia (AML), a translocation between chromosomes 8q22 and 21q22 leads to the RUNX1-RUNXT1 fusion gene which, in the absence of a concomitant KIT mutation, generally portends a more favorable prognosis. Translocations at 21q22, other than those involving 8q22, are uncommon, and the specific prognostic and therapeutic implications are accordingly limited by the small number of reported cases. In this report, we describe the case of a 67-year-old gentleman who presented with AML harboring t(14;21)(q23;q22). Subsequent molecular analysis revealed mutations in RUNX1, ASXL1, and SF3B1, with translocation breakpoints identified within SYNE2 on chromosome 14 and RUNX1 on chromosome 21. The functional consequence of the DNA fusion between SYNE2 and RUNX1 is unclear. Nonetheless, despite several adverse risk factors associated with this patient's AML, he achieved a long-lasting remission with standard chemotherapy alone, potentially suggestive of a novel favorable-risk translocation in AML involving 21q22.

Lamin B Receptor: Interplay between Structure, Function and Localization

Lamin B receptor (LBR) is an integral protein of the inner nuclear membrane, containing a hydrophilic N-terminal end protruding into the nucleoplasm, eight hydrophobic segments that span the membrane and a short, nucleoplasmic C-terminal tail. Two seemingly unrelated functions have been attributed to LBR. Its N-terminal domain tethers heterochromatin to the nuclear periphery, thus contributing to the shape of interphase nuclear architecture, while its transmembrane domains exhibit sterol reductase activity. Mutations within the transmembrane segments result in defects in cholesterol synthesis and are associated with diseases such as the Pelger–Huët anomaly and Greenberg skeletal dysplasia, whereas no such harmful mutations related to the anchoring properties of LBR have been reported so far. Recent evidence suggests a dynamic regulation of LBR expression levels, structural organization, localization and function, in response to various signals. The molecular mechanisms underlying this dynamic behavior have not yet been fully unraveled. Here, we provide an overview of the current knowledge of the interplay between the structure, function and localization of LBR, and hint at the interconnection of the two distinct functions of LBR.

Nuclear envelopathies: a complex LINC between nuclear envelope and pathology

Since the identification of the first disease causing mutation in the gene coding for emerin, a transmembrane protein of the inner nuclear membrane, hundreds of mutations and variants have been found in genes encoding for nuclear envelope components. These proteins can be part of the inner nuclear membrane (INM), such as emerin or SUN proteins, outer nuclear membrane (ONM), such as Nesprins, or the nuclear lamina, such as lamins A and C. However, they physically interact with each other to insure the nuclear envelope integrity and mediate the interactions of the nuclear envelope with both the genome, on the inner side, and the cytoskeleton, on the outer side. The core of this complex, called LINC (LInker of Nucleoskeleton to Cytoskeleton) is composed of KASH and SUN homology domain proteins. SUN proteins are INM proteins which interact with lamins by their N-terminal domain and with the KASH domain of nesprins located in the ONM by their C-terminal domain.Although most of these proteins are ubiquitously expressed, their mutations have been associated with a large number of clinically unrelated pathologies affecting specific tissues. Moreover, variants in SUN proteins have been found to modulate the severity of diseases induced by mutations in other LINC components or interactors. For these reasons, the diagnosis and the identification of the molecular explanation of "nuclear envelopathies" is currently challenging.The aim of this review is to summarize the human diseases caused by mutations in genes coding for INM proteins, nuclear lamina, and ONM proteins, and to discuss their potential physiopathological mechanisms that could explain the large spectrum of observed symptoms.

Nuclear migration events throughout development

Moving the nucleus to a specific position within the cell is an important event during many cell and developmental processes. Several different molecular mechanisms exist to position nuclei in various cell types. In this Commentary, we review the recent progress made in elucidating mechanisms of nuclear migration in a variety of important developmental models. Genetic approaches to identify mutations that disrupt nuclear migration in yeast, filamentous fungi, Caenorhabditis elegans, Drosophila melanogaster and plants led to the identification of microtubule motors, as well as Sad1p, UNC-84 (SUN) domain and Klarsicht, ANC-1, Syne homology (KASH) domain proteins (LINC complex) that function to connect nuclei to the cytoskeleton. We focus on how these proteins and various mechanisms move nuclei during vertebrate development, including processes related to wound healing of fibroblasts, fertilization, developing myotubes and the developing central nervous system. We also describe how nuclear migration is involved in cells that migrate through constricted spaces. On the basis of these findings, it is becoming increasingly clear that defects in nuclear positioning are associated with human diseases, syndromes and disorders.

Nuclear pore complex tethers to the cytoskeleton

The nuclear envelope is tethered to the cytoskeleton. The best known attachments of all elements of the cytoskeleton are via the so-called LINC complex. However, the nuclear pore complexes, which mediate the transport of soluble and membrane bound molecules, are also linked to the microtubule network, primarily via motor proteins (dynein and kinesins) which are linked, most importantly, to the cytoplasmic filament protein of the nuclear pore complex, Nup358, by the adaptor BicD2. The evidence for such linkages and possible roles in nuclear migration, cell cycle control, nuclear transport and cell architecture are discussed.

Overview of the Muscle Cytoskeleton

Cardiac and skeletal striated muscles are intricately designed machines responsible for muscle contraction. Coordination of the basic contractile unit, the sarcomere, and the complex cytoskeletal networks are critical for contractile activity. The sarcomere is comprised of precisely organized individual filament systems that include thin (actin), thick (myosin), titin, and nebulin. Connecting the sarcomere to other organelles (e.g., mitochondria and nucleus) and serving as the scaffold to maintain cellular integrity are the intermediate filaments. The costamere, on the other hand, tethers the sarcomere to the cell membrane. Unique structures like the intercalated disc in cardiac muscle and the myotendinous junction in skeletal muscle help synchronize and transmit force. Intense investigation has been done on many of the proteins that make up these cytoskeletal assemblies. Yet the details of their function and how they interconnect have just started to be elucidated. A vast number of human myopathies are contributed to mutations in muscle proteins; thus understanding their basic function provides a mechanistic understanding of muscle disorders. In this review, we highlight the components of striated muscle with respect to their interactions, signaling pathways, functions, and connections to disease. © 2017 American Physiological Society. Compr Physiol 7:891-944, 2017.

Control of nuclear organization by F-actin binding proteins

The regulation of nuclear shape and deformability is a key factor in controlling diverse events from embryonic development to cancer cell metastasis, but the mechanisms governing this process are still unclear. Our recent study demonstrated an unexpected role for the F-actin bundling protein fascin in controlling nuclear plasticity through a direct interaction with Nesprin-2. Nesprin-2 is a component of the LINC complex that is known to couple the F-actin cytoskeleton to the nuclear envelope. We demonstrated that fascin, which is predominantly associated with peripheral F-actin rich filopodia, binds directly to Nesprin-2 at the nuclear envelope in a range of cell types. Depleting fascin or specifically blocking the fascin-Nesprin-2 complex leads to defects in nuclear polarization, movement and cell invasion. These studies reveal a novel role for an F-actin bundling protein in control of nuclear plasticity and underline the importance of defining nuclear-associated roles for F-actin binding proteins in future.

Homozygous SYNE1 mutation causes congenital onset of muscular weakness with distal arthrogryposis: a genotype-phenotype correlation

The exceptionally large SYNE1 (spectrin repeat-containing nuclear envelope protein 1) gene encodes different nesprin-1 isoforms, which are differentially expressed in striated muscle and in cerebellar and cerebral neurons. Nesprin-1 isoforms can function in cytoskeletal, nuclear, and vesicle anchoring. SYNE1 variants have been associated with a spectrum of neurological and neuromuscular disease. Homozygosity mapping combined with exome sequencing identified a disease-causing nonsense mutation in the ultimate exon of full-length SYNE1 transcript in an 8-year-old boy with distal arthrogryposis and muscular hypotonia. mRNA analysis showed that the mutant transcript is expressed at wild-type levels. The variant truncates nesprin-1 isoforms for the C-terminal KASH (Klarsicht-ANC-Syne homology) domain. This is the third family with recessive arthrogryposis caused by homozygous distal-truncating SYNE1 variants. There is a SYNE1 genotype-phenotype correlation emerging, with more proximal homozygous SYNE1 variants causing recessive cerebellar ataxia of variable onset (SCAR8; ARCA-1).