Man1, an inner nuclear membrane protein, regulates vascular remodeling by modulating transforming growth factor beta signaling

Suppression of TGF-β/SMAD signaling by an inner nuclear membrane phosphatase complex

Cytokines of the TGF-β superfamily control essential cell fate decisions via receptor regulated SMAD (R-SMAD) transcription factors. Ligand-induced R-SMAD phosphorylation in the cytosol triggers their activation and nuclear accumulation. We determine how R-SMADs are inactivated by dephosphorylation in the cell nucleus to counteract signaling by TGF-β superfamily ligands. We show that R-SMAD dephosphorylation is mediated by an inner nuclear membrane associated complex containing the scaffold protein MAN1 and the CTDNEP1-NEP1R1 phosphatase. Structural prediction, domain mapping and mutagenesis reveals that MAN1 binds independently to the CTDNEP1-NEP1R1 phosphatase and R-SMADs to promote their inactivation by dephosphorylation. Disruption of this complex causes nuclear accumulation of R-SMADs and aberrant signaling, even in the absence of TGF-β ligands. These findings establish CTDNEP1-NEP1R1 as the R-SMAD phosphatase, reveal the mechanistic basis for TGF-β signaling inactivation and highlight how this process is disrupted by disease-associated MAN1 mutations.

Nuclear Mechanosensation and Mechanotransduction in Vascular Cells

Vascular cells are constantly subjected to physical forces associated with the rhythmic activities of the heart, which combined with the individual geometry of vessels further imposes oscillatory, turbulent, or laminar shear stresses on vascular cells. These hemodynamic forces play an important role in regulating the transcriptional program and phenotype of endothelial and smooth muscle cells in different regions of the vascular tree. Within the aorta, the lesser curvature of the arch is characterized by disturbed, oscillatory flow. There, endothelial cells become activated, adopting pro-inflammatory and athero-prone phenotypes. This contrasts the descending aorta where flow is laminar and endothelial cells maintain a quiescent and atheroprotective phenotype. While still unclear, the specific mechanisms involved in mechanosensing flow patterns and their molecular mechanotransduction directly impact the nucleus with consequences to transcriptional and epigenetic states. The linker of nucleoskeleton and cytoskeleton (LINC) protein complex transmits both internal and external forces, including shear stress, through the cytoskeleton to the nucleus. These forces can ultimately lead to changes in nuclear integrity, chromatin organization, and gene expression that significantly impact emergence of pathology such as the high incidence of atherosclerosis in progeria. Therefore, there is strong motivation to understand how endothelial nuclei can sense and respond to physical signals and how abnormal responses to mechanical cues can lead to disease. Here, we review the evidence for a critical role of the nucleus as a mechanosensor and the importance of maintaining nuclear integrity in response to continuous biophysical forces, specifically shear stress, for proper vascular function and stability.

Molecular Pathology of Laminopathies

The nuclear envelope is composed of the nuclear membranes, nuclear lamina, and nuclear pore complexes. Laminopathies are diseases caused by mutations in genes encoding protein components of the lamina and these other nuclear envelope substructures. Mutations in the single gene encoding lamin A and C, which are expressed in most differentiated somatic cells, cause diseases affecting striated muscle, adipose tissue, peripheral nerve, and multiple systems with features of accelerated aging. Mutations in genes encoding other nuclear envelope proteins also cause an array of diseases that selectively affect different tissues or organs. In some instances, the molecular and cellular consequences of laminopathy-causing mutations are known. However, even when these are understood, mechanisms explaining specific tissue or organ pathology remain enigmatic. Current mechanistic hypotheses focus on how alterations in the nuclear envelope may affect gene expression, including via the regulation of signaling pathways, or cellular mechanics, including responses to mechanical stress.

PNET2 is a component of the plant nuclear lamina and is required for proper genome organization and activity

The interaction between chromatin and the nuclear lamina (NL) is intrinsically important to the establishment of three-dimensional chromatin architecture and spatiotemporal regulation of gene expression. However, critical regulators involved in this process are poorly understood in plants. Here, we report that Arabidopsis PNET2 and its two homologs are bona fide inner nuclear membrane proteins and integral components of the NL. PNET2s physically interact with the plant nucleoskeleton and engage nucleosome-enriched chromatin at the nuclear periphery. Loss of all three PNET2s leads to severely disrupted growth and development, concomitant activation of abiotic and biotic stress responses, and ultimate lethality in Arabidopsis. The pent2 triple mutant also displays drastic transcriptome changes accompanied by a globally altered chromatin architecture revealed by HiC analysis. Our study identified PNET2 as an inner nuclear membrane (INM) component of the NL, which associates with chromatin and play a critical role in orchestrating gene expression and chromatin organization in plants.

The Diverse Cellular Functions of Inner Nuclear Membrane Proteins

The nuclear compartment is delimited by a specialized expanded sheet of the endoplasmic reticulum (ER) known as the nuclear envelope (NE). Compared to the outer nuclear membrane and the contiguous peripheral ER, the inner nuclear membrane (INM) houses a unique set of transmembrane proteins that serve a staggering range of functions. Many of these functions reflect the exceptional position of INM proteins at the membrane-chromatin interface. Recent research revealed that numerous INM proteins perform crucial roles in chromatin organization, regulation of gene expression, genome stability, and mediation of signaling pathways into the nucleus. Other INM proteins establish mechanical links between chromatin and the cytoskeleton, help NE remodeling, or contribute to the surveillance of NE integrity and homeostasis. As INM proteins continue to gain prominence, we review these advancements and give an overview on the functional versatility of the INM proteome.

Lamin A/C Mechanotransduction in Laminopathies

Mechanotransduction translates forces into biological responses and regulates cell functionalities. It is implicated in several diseases, including laminopathies which are pathologies associated with mutations in lamins and lamin-associated proteins. These pathologies affect muscle, adipose, bone, nerve, and skin cells and range from muscular dystrophies to accelerated aging. Although the exact mechanisms governing laminopathies and gene expression are still not clear, a strong correlation has been found between cell functionality and nuclear behavior. New theories base on the direct effect of external force on the genome, which is indeed sensitive to the force transduced by the nuclear lamina. Nuclear lamina performs two essential functions in mechanotransduction pathway modulating the nuclear stiffness and governing the chromatin remodeling. Indeed, A-type lamin mutation and deregulation has been found to affect the nuclear response, altering several downstream cellular processes such as mitosis, chromatin organization, DNA replication-transcription, and nuclear structural integrity. In this review, we summarize the recent findings on the molecular composition and architecture of the nuclear lamina, its role in healthy cells and disease regulation. We focus on A-type lamins since this protein family is the most involved in mechanotransduction and laminopathies.

Penta-acetyl geniposide induces apoptosis of fibroblast-like synoviocytes from adjuvant-induced arthritis rats in vitro, associated with inhibition of NF-κB activation

BACKGROUND

Approaches promoting fibroblast-like synoviocytes (FLS) apoptosis are considered as a meaningful strategy for rheumatoid arthritis (RA) treatment. We have previously reported the anti-arthritic effect of penta-acetyl geniposide ((Ac)5GP, an active derivative of geniposide) on adjuvant-induced arthritis (AIA) rats in vivo. The present study aimed to investigate the pro-apoptotic effect of (Ac)5GP on AIA FLS in vitro and the underlying molecular mechanisms.

METHODS

Rat AIA was induced by complete Freund's adjuvant, and FLS were primary-cultured from synovial tissues. AIA FLS were treated with (Ac)5GP (50, 100 and 200 μM) for 48 h and cell proliferation and apoptosis were respectively examined. The involvement of apoptosis-related proteins (Bax, Bcl-2 and caspase 3) and nuclear factor kappa B (NF-κB) signaling pathway was checked.

RESULTS

(Ac)5GP inhibited the viability of AIA FLS and reduced the percentage of Ki67-positive cells in AIA FLS. Particularly, (Ac)5GP promoted AIA FLS apoptosis in vitro by inducing apoptotic nuclear morphology, facilitating DNA ladder formation and increasing percentages of both early and late apoptotic cells. (Ac)5GP treatment on AIA FLS decreased Bcl-2 protein level whereas increased the levels of Bax and caspase 3 proteins. Moreover, (Ac)5GP reduced the degradation and phosphorylation of IκBα, down-regulated NF-κB p65 protein level in nucleus and inhibited NF-κB p65 nuclear translocation.

CONCLUSIONS

(Ac)5GP had a potent pro-apoptotic effect on AIA FLS in vitro, which is associated with regulating apoptosis-related proteins and inhibiting NF-κB activation.

Ablation of SUN2-containing LINC complexes drives cardiac hypertrophy without interstitial fibrosis

The cardiomyocyte cytoskeleton, including the sarcomeric contractile apparatus, forms a cohesive network with cellular adhesions at the plasma membrane and nuclear--cytoskeletal linkages (LINC complexes) at the nuclear envelope. Human cardiomyopathies are genetically linked to the LINC complex and A-type lamins, but a full understanding of disease etiology in these patients is lacking. Here we show that SUN2-null mice display cardiac hypertrophy coincident with enhanced AKT/MAPK signaling, as has been described previously for mice lacking A-type lamins. Surprisingly, in contrast to lamin A/C-null mice, SUN2-null mice fail to show coincident fibrosis or upregulation of pathological hypertrophy markers. Thus, cardiac hypertrophy is uncoupled from profibrotic signaling in this mouse model, which we tie to a requirement for the LINC complex in productive TGFβ signaling. In the absence of SUN2, we detect elevated levels of the integral inner nuclear membrane protein MAN1, an established negative regulator of TGFβ signaling, at the nuclear envelope. We suggest that A-type lamins and SUN2 play antagonistic roles in the modulation of profibrotic signaling through opposite effects on MAN1 levels at the nuclear lamina, suggesting a new perspective on disease etiology.

Perturbations of BMP/TGF-β and VEGF/VEGFR signalling pathways in non-syndromic sporadic brain arteriovenous malformations (BAVM)

BACKGROUND

Brain arteriovenous malformations (BAVM) represent a congenital anomaly of the cerebral vessels with a prevalence of 10-18/100 000. BAVM is the leading aetiology of intracranial haemorrhage in children. Our objective was to identify gene variants potentially contributing to disease and to better define the molecular aetiology underlying non-syndromic sporadic BAVM.

METHODS

We performed whole-exome trio sequencing of 100 unrelated families with a clinically uniform BAVM phenotype. Pathogenic variants were then studied in vivo using a transgenic zebrafish model.

RESULTS

We identified four pathogenic heterozygous variants in four patients, including one in the established BAVM-related gene, ENG, and three damaging variants in novel candidate genes: PITPNM3, SARS and LEMD3, which we then functionally validated in zebrafish. In addition, eight likely pathogenic heterozygous variants (TIMP3, SCUBE2, MAP4K4, CDH2, IL17RD, PREX2, ZFYVE16 and EGFR) were identified in eight patients, and 16 patients carried one or more variants of uncertain significance. Potential oligogenic inheritance (MAP4K4 with ENG, RASA1 with TIMP3 and SCUBE2 with ENG) was identified in three patients. Regulation of sma- and mad-related proteins (SMADs) (involved in bone morphogenic protein (BMP)/transforming growth factor beta (TGF-β) signalling) and vascular endothelial growth factor (VEGF)/vascular endotheliual growth factor recepter 2 (VEGFR2) binding and activity (affecting the VEGF signalling pathway) were the most significantly affected biological process involved in the pathogenesis of BAVM.

CONCLUSIONS

Our study highlights the specific role of BMP/TGF-β and VEGF/VEGFR signalling in the aetiology of BAVM and the efficiency of intensive parallel sequencing in the challenging context of genetically heterogeneous paradigm.

Linker of nucleoskeleton and cytoskeleton complex proteins in cardiomyopathy

The linker of nucleoskeleton and cytoskeleton (LINC) complex couples the nuclear lamina to the cytoskeleton. The LINC complex and its associated proteins play diverse roles in cells, ranging from genome organization, nuclear morphology, gene expression, to mechanical stability. The importance of a functional LINC complex is highlighted by the large number of mutations in genes encoding LINC complex proteins that lead to skeletal and cardiac myopathies. In this review, the structure, function, and interactions between components of the LINC complex will be described. Mutations that are known to cause cardiomyopathy in patients will be discussed alongside their respective mouse models. Furthermore, future challenges for the field and emerging technologies to investigate LINC complex function will be discussed.

Messages from the voices within: regulation of signaling by proteins of the nuclear lamina

The nuclear lamina (NL) is a protein scaffold lining the nuclear envelope that consists of nuclear lamins and associated transmembrane proteins. It helps to organize the nuclear envelope, chromosomes, and the cytoplasmic cytoskeleton. The NL also has an important role in regulation of signaling, as highlighted by the wide range of human diseases caused by mutations in the genes for NL proteins with associated signaling defects. This review will consider diverse mechanisms for signaling regulation by the NL that have been uncovered recently, including interaction with signaling effectors, modulation of actin assembly and compositional alteration of the NL. Cells with discrete NL mutations often show disruption of multiple signaling pathways, however, and for the most part the mechanistic basis for these complex phenotypes remains to be elucidated.

Breaking the scale: how disrupting the karyoplasmic ratio gives cancer cells an advantage for metastatic invasion

Nuclear size normally scales with the size of the cell, but in cancer this 'karyoplasmic ratio' is disrupted. This is particularly so in more metastatic tumors where changes in the karyoplasmic ratio are used in both diagnosis and prognosis for several tumor types. However, the direction of nuclear size changes differs for particular tumor types: for example in breast cancer, larger nuclear size correlates with increased metastasis, while for lung cancer smaller nuclear size correlates with increased metastasis. Thus, there must be tissue-specific drivers of the nuclear size changes, but proteins thus far linked to nuclear size regulation are widely expressed. Notably, for these tumor types, ploidy changes have been excluded as the basis for nuclear size changes, and so, the increased metastasis is more likely to have a basis in the nuclear morphology change itself. We review what is known about nuclear size regulation and postulate how such nuclear size changes can increase metastasis and why the directionality can differ for particular tumor types.

The Role of the Nuclear Envelope Protein MAN1 in Mesenchymal Stem Cell Differentiation

Mutations in MAN1, a protein of the nuclear envelope, cause bone phenotypes characterized by hyperostosis. The mechanism of this pro-osteogenic phenotype remains unknown. We increased and decreased MAN1 expression in mesenchymal stem cells (MSC) upon which standard osteogenic and adipogenic differentiation were performed. MAN1 knockdown increased osteogenesis and mineralization. In contrast, osteogenesis remained stable upon MAN1 overexpression. Regarding a mechanism, we found that low levels of MAN1 facilitated the nuclear accumulation of regulatory smads and smads-related complexes, with a concurrently high expression of nuclear β-Catenin. In addition, we found adipogenesis to be decreased in both conditions, although predominantly affected by MAN1 overexpression. Finally, lamin A, a protein of the nuclear envelope that regulates MSC differentiation, was unaffected by changes in MAN1. In conclusion, our studies demonstrated that lower levels of MAN1 in differentiating MSC are associated with higher osteogenesis and lower adipogenesis. High levels of MAN1 only affected adipogenesis. These effects could have an important role in the understanding of the role of the proteins of the nuclear envelope in bone formation. J. Cell. Biochem. 118: 4425-4435, 2017. © 2017 Wiley Periodicals, Inc.

Role of Chromatin Modifications in Drosophila Germline Stem Cell Differentiation

During Drosophila oogenesis, germline stem cells (GSCs) self-renew and differentiate to give rise to a mature egg. Self-renewal and differentiation of GSCs are regulated by both intrinsic mechanisms such as regulation of gene expression in the germ line and extrinsic signaling pathways from the surrounding somatic niche. Epigenetic mechanisms, including histone-modifying proteins, nucleosome remodeling complexes, and histone variants, play a critical role in regulating intrinsic gene expression and extrinsic signaling cues from the somatic niche. In the GSCs, intrinsic epigenetic modifiers are required to maintain a stem cell fate by promoting expression of self-renewal factors and repressing the differentiation program. Subsequently, in the GSC daughters, epigenetic regulators activate the differentiation program to promote GSC differentiation. During differentiation, the GSC daughter undergoes meiosis to give rise to the developing egg, containing a compacted chromatin architecture called the karyosome. Epigenetic modifiers control the attachment of chromosomes to the nuclear lamina to aid in meiotic recombination and the release from the lamina for karyosome formation. The germ line is in close contact with the soma for the entirety of this developmental process. This proximity facilitates signaling from the somatic niche to the developing germ line. Epigenetic modifiers play a critical role in the somatic niche, modulating signaling pathways in order to coordinate the transition of GSC to an egg. Together, intrinsic and extrinsic epigenetic mechanisms modulate this exquisitely balanced program.

Mutation in LEMD3 (Man1) Associated with Osteopoikilosis and Late-Onset Generalized Morphea: A New Buschke-Ollendorf Syndrome Variant

Introduction. Buschke-Ollendorf syndrome (BOS) is an uncommon syndrome characterized by osteopoikilosis and other bone abnormalities, accompanied by skin lesions, most frequently connective tissue nevi. BOS is caused by mutations in the LEMD3 gene, which encodes the inner nuclear membrane protein Man1. We describe a unique case of osteopoikilosis associated with late-onset localized scleroderma and familial LEMD3 mutations. Case Report. A 72-year-old woman presented with adult-onset diffuse morphea and bullous skin lesions. Evaluation revealed multiple hyperostotic lesions (osteopoikilosis) suggestive of BOS. DNA sequencing identified a previously undescribed nonsense mutation (Trp621X) in the LEMD3 gene encoding Man1. Two additional family members were found to have osteopoikilosis and carry the same LEMD3 mutation. Conclusions and Relevance. We report a unique familial LEMD3 mutation in an individual with osteopoikilosis and late-onset morphea. We propose that this constellation represents a novel syndromic variant of BOS.

Aortic Remodelling Is Improved by 2,3,5,4'-Tetrahydroxystilbene-2-O-β-D-glucoside Involving the Smad3 Pathway in Spontaneously Hypertensive Rats

Hypertension is a common health problem that substantially increases the risk of cardiovascular disease. The condition increases blood pressure, which causes alterations in vascular structure and leads to the development of vascular pathologies. 2,3,5,4′-Tetrahydroxystilbene-2-O-β-D-glucoside (THSG), a resveratrol analogue extracted from a Chinese medicinal plant, has been proven to have numerous vascular protection functions. This study investigated whether THSG can improve vascular remodeling, which has thus far remained unclear. Orally administering THSG to spontaneously hypertensive rats (SHRs) aged 12 weeks for 14 weeks significantly inhibited intima-media thickness in the lower parts of the aortic arch, increased the vascular diastolic rate in response to acetylcholine, and reduced remodelling-related mRNA expression, such as that of ACTA2, CCL3, COL1A2, COL3A1, TIMP1 WISP2, IGFBP1, ECE1, KLF5, MYL1 BMP4, FN1, and PAI-1. Immunofluorescence staining also showed an inhibitory effect similar to that of THSG on PAI-1 protein expression in rat aortas. Results from immunoprecipitation and a Western blot assay showed that THSG inhibited the acetylation of Smad3. A chromatin immunoprecipitation assay showed that THSG prevented Smad3 binding to the PAI-1 proximal promoter in SHR aortas. In conclusion, our results demonstrated that the inhibitory effect of THSG on aortic remodelling involved the deacetylating role of Smad3 with increasing blood flow and with constant blood pressure.

Networking in the nucleus: a spotlight on LEM-domain proteins

Proteins resident in the inner nuclear membrane and underlying nuclear lamina form a network that regulates nuclear functions. This review highlights a prominent family of nuclear lamina proteins that carries the LAP2-emerin-MAN1-domain (LEM-D). LEM-D proteins share an ability to bind lamins and tether repressive chromatin at the nuclear periphery. The importance of this family is underscored by findings that loss of individual LEM-D proteins causes progressive, tissue-restricted diseases, known as laminopathies. Diverse functions of LEM-D proteins are linked to interactions with unique and overlapping partners including signal transduction effectors, transcription factors and architectural proteins. Recent investigations suggest that LEM-D proteins form hubs within the nuclear lamina that integrate external signals important for tissue homeostasis and maintenance of progenitor cell populations.

Nuclear envelope protein Lem2 is required for mouse development and regulates MAP and AKT kinases

The nuclear lamina, along with associated nuclear membrane proteins, is a nexus for regulating signaling in the nucleus. Numerous human diseases arise from mutations in lamina proteins, and experimental models for these disorders have revealed aberrant regulation of various signaling pathways. Previously, we reported that the inner nuclear membrane protein Lem2, which is expressed at high levels in muscle, promotes the differentiation of cultured myoblasts by attenuating ERK signaling. Here, we have analyzed mice harboring a disrupted allele for the Lem2 gene (Lemd2). No gross phenotypic defects were seen in heterozygotes, although muscle regeneration induced by cardiotoxin was delayed. By contrast, homozygous Lemd2 knockout mice died by E11.5. Although many normal morphogenetic hallmarks were observed in E10.5 knockout embryos, most tissues were substantially reduced in size. This was accompanied by activation of multiple MAP kinases (ERK1/2, JNK, p38) and AKT. Knockdown of Lem2 expression in C2C12 myoblasts also led to activation of MAP kinases and AKT. These findings indicate that Lemd2 plays an essential role in mouse embryonic development and that it is involved in regulating several signaling pathways. Since increased MAP kinase and AKT/mTORC signaling is found in other animal models for diseases linked to nuclear lamina proteins, LEMD2 should be considered to be another candidate gene for human disease.

Attenuation of Wnt/β-catenin activity reverses enhanced generation of cardiomyocytes and cardiac defects caused by the loss of emerin

Mutations in EMD, encoding emerin cause skeletal muscle and heart defects in patients with X-linked Emery-Dreifuss muscular dystrophy (X-EDMD) but the underlying mechanisms leading to cardiac defects are poorly understood. Here, we investigated the role of emerin in controlling cardiomyocyte proliferation and cardiac remodeling and explored its function in regulation of the Wnt/β-catenin pathway. We observed a remarkable increase of cardiomyocytes in emerin-null adult mice accompanied with decreased numbers of multinucleated cells. Depletion of emerin in mouse ES cell-derived cardiomyocytes by shRNA caused hyperactivation of Wnt/β-catenin signaling, increased proliferation and abrogated timely cardiac differentiation. Likewise, emerin-null mice exhibited increased Wnt/β-catenin signaling, cardiac dysfunction and perturbed hypertrophic remodeling following pressure overload. Pharmacological inhibition of β-catenin normalized proliferation and differentiation of ES cell-derived cardiomyocytes while inactivation of a single allele of β-catenin efficiently rescued cardiac dysfunction in emerin-null mice. We conclude that emerin constrains β-catenin signaling in the heart providing tight control of cardiomyocyte numbers. Enhanced Wnt/β-catenin signaling seems to contribute to cardiac defects observed in X-EDMD. Hence, therapeutic inhibition of Wnt/β-catenin signaling might be beneficial for X-EDMD patients.

Functional architecture of the cell's nucleus in development, aging, and disease

In eukaryotes, the function of the cell's nucleus has primarily been considered to be the repository for the organism's genome. However, this rather simplistic view is undergoing a major shift, as it is increasingly apparent that the nucleus has functions extending beyond being a mere genome container. Recent findings have revealed that the structural composition of the nucleus changes during development and that many of these components exhibit cell- and tissue-specific differences. Increasing evidence is pointing to the nucleus being integral to the function of the interphase cytoskeleton, with changes to nuclear structural proteins having ramifications affecting cytoskeletal organization and the cell's interactions with the extracellular environment. Many of these functions originate at the nuclear periphery, comprising the nuclear envelope (NE) and underlying lamina. Together, they may act as a "hub" in integrating cellular functions including chromatin organization, transcriptional regulation, mechanosignaling, cytoskeletal organization, and signaling pathways. Interest in such an integral role has been largely stimulated by the discovery that many diseases and anomalies are caused by defects in proteins of the NE/lamina, the nuclear envelopathies, many of which, though rare, are providing insights into their more common variants that are some of the major issues of the twenty-first century public health. Here, we review the contributions that mouse mutants have made to our current understanding of the NE/lamina, their respective roles in disease and the use of mice in developing potential therapies for treating the diseases.

Hutchinson-Gilford progeria syndrome through the lens of transcription

Lamins are nuclear intermediate filaments. In addition to their structural roles, they are implicated in basic nuclear functions such as chromatin organization, DNA replication, transcription, DNA repair, and cell-cycle progression. Mutations in human LMNA gene cause several diseases termed laminopathies. One of the laminopathic diseases is Hutchinson-Gilford progeria syndrome (HGPS), which is caused by a spontaneous mutation and characterized by premature aging. HGPS phenotypes share certain similarities with several apparently comparable medical conditions, such as aging and atherosclerosis, with the conspicuous absence of neuronal degeneration and cancer rarity during the short lifespan of the patients. Cell lines from HGPS patients are characterized by multiple nuclear defects, which include abnormal morphology, altered histone modification patterns, and increased DNA damage. These cell lines provide insight into the molecular pathways including senescence that require lamins A and B1. Here, we review recent data on HGPS phenotypes through the lens of transcriptional deregulation caused by lack of functional lamin A, progerin accumulation, and lamin B1 silencing.

The nuclear envelope LEM-domain protein emerin

Emerin, a conserved LEM-domain protein, is among the few nuclear membrane proteins for which extensive basic knowledge—biochemistry, partners, functions, localizations, posttranslational regulation, roles in development and links to human disease—is available. This review summarizes emerin and its emerging roles in nuclear “lamina” structure, chromatin tethering, gene regulation, mitosis, nuclear assembly, development, signaling and mechano-transduction. We also highlight many open questions, exploration of which will be critical to understand how this intriguing nuclear membrane protein and its “family” influence the genome.

Inhibition of TGF-β signaling at the nuclear envelope: characterization of interactions between MAN1, Smad2 and Smad3, and PPM1A

Signaling by transforming growth factor-β (TGF-β) is critical for various developmental processes and culminates in the activation of the transcription factors Smad2 and Smad3. MAN1, an integral protein of the inner nuclear membrane, inhibits TGF-β signaling by binding to Smad2 and Smad3. Depletion of the gene LEMD3 encoding MAN1 leads to developmental anomalies in mice, and heterozygous loss-of-function mutations in LEMD3 in humans cause sclerosing bone dysplasia. We modeled the three-dimensional structure of the MAN1-Smad2 complex from nuclear magnetic resonance and small-angle x-ray scattering data. As predicted by this model, we found that MAN1 competed in vitro and in cells with the transcription factor FAST1 (forkhead activin signal transducer 1) for binding to Smad2. The model further predicted that MAN1 bound to activated Smad2-Smad4 or Smad3-Smad4 complexes, which was confirmed by in vitro experiments; however, in cells, MAN1 bound only to Smad2 and Smad3 and not to the Smad4-containing complexes. Overexpression of MAN1 led to dephosphorylation of Smad2 and Smad3, thus hindering their recognition by Smad4, and MAN1 bound directly in vitro to the phosphatase PPM1A, which catalyzes the dephosphorylation of Smad2/3. These results demonstrate a nuclear envelope-localized mechanism of inactivating TGF-β signaling in which MAN1 competes with transcription factors for binding to Smad2 and Smad3 and facilitates their dephosphorylation by PPM1A.

Outfits for different occasions: tissue-specific roles of Nuclear Envelope proteins

The Nuclear Envelope (NE) contains over 100 different proteins that associate with nuclear components such as chromatin, the lamina and the transcription machinery. Mutations in genes encoding NE proteins have been shown to result in tissue-specific defects and disease, suggesting cell-type specific differences in NE composition and function. Consistent with these observations, recent studies have revealed unexpected functions for numerous NE associated proteins during cell differentiation and development. Here we review the latest insights into the roles played by the NE in cell differentiation, development, disease and aging, focusing primarily on inner nuclear membrane (INM) proteins and nuclear pore components.

LAP2 is widely overexpressed in diverse digestive tract cancers and regulates motility of cancer cells

Background

Lamina-associated polypeptides 2 (LAP2) is a nuclear protein that connects the nuclear lamina with chromatin. Although its critical roles in genetic disorders and hematopoietic malignancies have been described, its expression and roles in digestive tract cancers have been poorly characterized.

Methods

To examine the expression of LAP2 in patient tissues, we performed immunohistochemistry and real-time PCR. To examine motility of cancer cells, we employed Boyden chamber, wound healing and Matrigel invasion assays. To reveal its roles in metastasis in vivo, we used a liver metastasis xenograft model. To investigate the underlying mechanism, a cDNA microarray was conducted.

Results

Immunohistochemistry in patient tissues showed widespread expression of LAP2 in diverse digestive tract cancers including stomach, pancreas, liver, and bile duct cancers. Real-time PCR confirmed that LAP2β is over-expressed in gastric cancer tissues. Knockdown of LAP2β did not affect proliferation of most digestive tract cancer cells except pancreatic cancer cells. However, knockdown of LAP2β decreased motility of all tested cancer cells. Moreover, overexpression of LAP2β increased motility of gastric and pancreatic cancer cells. In the liver metastasis xenograft model, LAP2β increased metastatic efficacy of gastric cancer cells and mortality in tested mice. cDNA microarrays showed the possibility that myristoylated alanine-rich C kinase substrate (MARCKS) and interleukin6 (IL6) may mediate LAP2β-regulated motility of cancer cells.

Conclusions

From the above results, we conclude that LAP2 is widely overexpressed in diverse digestive tract cancers and LAP2β regulates motility of cancer cells and suggest that LAP2β may have utility for diagnostics and therapeutics in digestive tract cancers.

Few Smad proteins and many Smad-interacting proteins yield multiple functions and action modes in TGFβ/BMP signaling in vivo

Signaling by the many ligands of the TGFβ family strongly converges towards only five receptor-activated, intracellular Smad proteins, which fall into two classes i.e. Smad2/3 and Smad1/5/8, respectively. These Smads bind to a surprisingly high number of Smad-interacting proteins (SIPs), many of which are transcription factors (TFs) that co-operate in Smad-controlled target gene transcription in a cell type and context specific manner. A combination of functional analyses in vivo as well as in cell cultures and biochemical studies has revealed the enormous versatility of the Smad proteins. Smads and their SIPs regulate diverse molecular and cellular processes and are also directly relevant to development and disease. In this survey, we selected appropriate examples on the BMP-Smads, with emphasis on Smad1 and Smad5, and on a number of SIPs, i.e. the CPSF subunit Smicl, Ttrap (Tdp2) and Sip1 (Zeb2, Zfhx1b) from our own research carried out in three different vertebrate models.

TGFβ superfamily signaling regulators are differentially expressed in the developing and adult mouse testis

Transforming growth factor-beta (TGFβ) superfamily ligands are produced by and act upon testicular cells to control testis morphogenesis and adult fertility. Ligand production changes during testis development and dysregulated signaling affects the number of cells comprising each lineage and their development, with several components of this diverse signaling pathway linked to male infertility. To test the hypothesis that TGFβ superfamily signaling regulators are differentially expressed during mouse testis development, we surveyed expression of Hgs, Zfyve9, Smurf1 and Net25 by northern blot and in situ hybridization and SMURF2 and MAN1 by western blot and immunohistochemistry. Expression of these genes is highly regulated and differs between the first spermatogenic wave and adult spermatogenesis. Zfyve9 transcripts were first detected in Sertoli cells and spermatogonia at 5 days post partum (dpp) whereas Hgs mRNA was first detected in pachytene spermatocytes at 15 dpp. Smurf1 mRNA was broadly expressed at 0 and 5 dpp but restricted to spermatogonia and early spermatocytes at 15 dpp and spermatogonia, spermatocytes and round spermatids in adults. SMURF2 was limited to gonocyte nuclei at birth but was nuclear in all cells at 5 dpp. SMURF2 was absent from 15 dpp differentiating spermatogonia and early spermatocytes but readily detected in adult pachytene spermatocytes and round spermatids. MAN1 and Net25 also had different expression profiles, with MAN1 undetectable at 5 dpp. Differential synthesis of signaling modulators explains how Sertoli cells and spermatogenic cells, which all possess TGFβ superfamily signaling machinery and reside within the same microenvironment, respond differently to the same ligand.

Structural analysis of the Smad2-MAN1 interaction that regulates transforming growth factor-β signaling at the inner nuclear membrane

MAN1, an integral protein of the inner nuclear membrane, influences transforming growth factor-β (TGF-β) signaling by directly interacting with R-Smads. Heterozygous loss of function mutations in the gene encoding MAN1 cause sclerosing bone dysplasias and an increased level of TGF-β signaling in cells. As a first step in elucidating the mechanism of TGF-β pathway regulation by MAN1, we characterized the structure of the MAN1 C-terminal region that binds Smad2. Using nuclear magnetic resonance spectroscopy, we observed that this region is comprised of a winged helix domain, a structurally heterogeneous linker, a U2AF homology motif (UHM) domain, and a disordered C-terminus. From nuclear magnetic resonance and small-angle X-ray scattering data, we calculated a family of models for this MAN1 region. Our data indicate that the linker plays the role of an intramolecular UHM ligand motif (ULM) interacting with the UHM domain. We mapped the Smad2 binding site onto the MAN1 structure by combining GST pull-down, fluorescence, and yeast two-hybrid approaches. The linker region, the UHM domain, and the C-terminus are necessary for Smad2 binding with a micromolar affinity. Moreover, the intramolecular interaction between the linker and the UHM domain is critical for Smad2 binding. On the basis of the structural heterogeneity and binding properties of the linker, we suggest that it can interact with other UHM domains, thus regulating the MAN1-Smad2 interaction.

A molecular mechanism underlying the neural-specific defect in torsinA mutant mice

A striking but poorly understood feature of many diseases is the unique involvement of neural tissue. One example is the CNS-specific disorder DYT1 dystonia, caused by a 3-bp deletion ("DeltaE") in the widely expressed gene TOR1A. Disease mutant knockin mice (Tor1a(DeltaE/DeltaE)) exhibit disrupted nuclear membranes selectively in neurons, mimicking the tissue specificity of the human disease and providing a model system in which to dissect the mechanisms underlying neural selectivity. Our in vivo studies demonstrate that lamina-associated polypeptide 1 (LAP1) and torsinB function with torsinA to maintain normal nuclear membrane morphology. Moreover, we show that nonneuronal cells express dramatically higher levels of torsinB and that RNAi-mediated depletion of torsinB (but not other torsin family members) causes nuclear membrane abnormalities in Tor1a(DeltaE/DeltaE) nonneuronal cells. The Tor1a(DeltaE/DeltaE) neural selective phenotype therefore arises because high levels of torsinB protect nonneuronal cells from the consequences of torsinA dysfunction, demonstrating how tissue specificity may result from differential susceptibility of cell types to insults that disrupt ubiquitous biological pathways.

The Drosophila LEM-domain protein MAN1 antagonizes BMP signaling at the neuromuscular junction and the wing crossveins

BMP signaling responses are refined by distinct secreted and intracellular antagonists in different cellular and temporal contexts. Here, we show that the nuclear LEM-domain protein MAN1 is a tissue-specific antagonist of BMP signaling in Drosophila. MAN1 contains two potential Mad-binding sites. We generated MAN1DeltaC mutants, harbouring a MAN1 protein that lacks part of the C-terminus including the RNA recognition motif, a putative Mad-binding domain. MAN1DeltaC mutants show wing crossvein (CV) patterning defects but no detectable alterations in nuclear morphology. MAN1(DeltaC) pupal wings display expanded phospho-Mad (pMad) accumulation and ectopic expression of the BMP-responsive gene crossveinless-2 (cv-2) indicating that MAN1 restricts BMP signaling. Conversely, MAN1 overexpression in wing imaginal discs inhibited crossvein development and BMP signaling responses. MAN1 is expressed at high levels in pupal wing veins and can be activated in intervein regions by ectopic BMP signaling. The specific upregulation of MAN1 in pupal wing veins may thus represent a negative feedback circuit that limits BMP signaling during CV formation. MAN1DeltaC flies also show reduced locomotor activity, and electrophysiology recordings in MAN1DeltaC larvae uncover a new presynaptic role of MAN1 at the neuromuscular junction (NMJ). Genetic interaction experiments suggest that MAN1 is a BMP signaling antagonist both at the NMJ and during CV formation.

The nuclear envelope as a signaling node in development and disease

The development of a membrane-bound structure separating DNA from other cellular components was the epochal evolutionary event that gave rise to eukaryotes, possibly occurring up to 2 billion years ago. Yet, this view of the nuclear envelope as a physical barrier greatly underestimates its fundamental impact on cellular organization and complexity, much of which is only beginning to be understood. Indeed, alterations of nuclear envelope structure and protein composition are essential to many aspects of metazoan development and cellular differentiation. Mutations in genes encoding nuclear envelope proteins cause a fascinating array of diseases referred to as "nuclear envelopathies" or "laminopathies" that affect different tissues and organ systems. We review recent work on the nuclear envelope, including insights derived from the study of nuclear envelopathies. These studies are uncovering new functions for nuclear envelope proteins and underlie an emerging view of the nuclear envelope as a critical signaling node in development and disease.

The heterozygous Lemd3 +/GT mouse is not a murine model for osteopoikilosis in humans

Osteopoikilosis and the Buschke-Ollendorff syndrome are skeletal dysplasias with hyperostotic lesions in the long bones. These disorders are caused by heterozygous loss-of-function mutations in the LEMD3 gene. LEMD3 codes for a protein of the inner nuclear membrane that, through interaction with R-SMADs, antagonizes the BMP and TGF beta 1 pathway. It is suggested that the hyperostotic lesions in these disorders are caused by enhanced BMP and TGFbeta1 signaling. The exact mechanism by which mutations in the LEMD3 gene lead to these bone lesions has not yet been unraveled precisely. To further assess this, an Lemd3 gene-trapped mouse was created in a gene-trapping program by Baygenomics. To investigate whether the heterozygous gene-trapped mouse is a good model for osteopoikilosis in humans, we studied these mice radiologically with high-resolution micro-computed tomography (microCT) and histologically. X-ray images were evaluated by a trained radiologist, but no typical osteopoikilosis lesions could be recognized. On all microCT reconstructed images a 3D cortical and trabecular quantitative analysis was performed, investigating different histomorphometric parameters ranging from percent bone volume, bone surface/volume ratio over trabecular thickness, separation, number, and pattern factor to structure model index and fractal dimension. No significant differences were found after a t-test statistical analysis. Also, histological analysis did not reveal lesions typical for osteopoikilosis. We conclude that the heterozygous Lemd3 gene-trapped mouse is not a good model to study osteopoikilosis and the Buschke-Ollendorff syndrome.

The regulation of TGFbeta signal transduction

Transforming growth factor beta (TGFbeta) pathways are implicated in metazoan development, adult homeostasis and disease. TGFbeta ligands signal via receptor serine/threonine kinases that phosphorylate, and activate, intracellular Smad effectors as well as other signaling proteins. Oligomeric Smad complexes associate with chromatin and regulate transcription, defining the biological response of a cell to TGFbeta family members. Signaling is modulated by negative-feedback regulation via inhibitory Smads. We review here the mechanisms of TGFbeta signal transduction in metazoans and emphasize events crucial for embryonic development.

Overlapping functions of nuclear envelope proteins NET25 (Lem2) and emerin in regulation of extracellular signal-regulated kinase signaling in myoblast differentiation

Mutations in certain nuclear envelope (NE) proteins cause muscular dystrophies and other disorders, but the disease mechanisms remain unclear. The nuclear envelope transmembrane protein NET25 (Lem2) is a truncated paralog of MAN1, an NE component linked to bone disorders. NET25 and MAN1 share an approximately 40-residue LEM homology domain with emerin, the protein mutated in X-linked Emery-Dreifuss muscular dystrophy. However, roles for NET25 and MAN1 in myogenesis have not yet been described. Using RNA interference in C2C12 myoblasts, we show for the first time that both NET25 and MAN1 are required for myogenic differentiation. NET25 depletion causes hyperactivation of extracellular signal-regulated kinase 1/2 at the onset of differentiation, and pharmacological inhibition of this transient overactivation rescues myogenesis. In contrast, pharmacological inhibition of both mitogen-activated protein kinase and transforming growth factor beta signaling is required to rescue differentiation after MAN1 depletion. Ectopic expression of silencing-resistant NET25 rescues myogenesis after depletion of emerin but not after MAN1 silencing. Thus, NET25 and emerin have at least partially overlapping functions during myogenic differentiation, which are distinct from those of MAN1. Our work supports the hypothesis that deregulation of cell signaling contributes to NE-linked disorders and suggests that mutations in NET25 and MAN1 may cause muscle diseases.

Nuclear lamins: key regulators of nuclear structure and activities

The nuclear lamina is a proteinaceous structure located underneath the inner nuclear membrane (INM), where it associates with the peripheral chromatin. It contains lamins and lamin-associated proteins, including many integral proteins of the INM, chromatin modifying proteins, transcriptional repressors and structural proteins. A fraction of lamins is also present in the nucleoplasm, where it forms stable complexes and is associated with specific nucleoplasmic proteins. The lamins and their associated proteins are required for most nuclear activities, mitosis and for linking the nucleoplasm to all major cytoskeletal networks in the cytoplasm. Mutations in nuclear lamins and their associated proteins cause about 20 different diseases that are collectively called laminopathies'. This review concentrates mainly on lamins, their structure and their roles in DNA replication, chromatin organization, adult stem cell differentiation, aging, tumorogenesis and the lamin mutations leading to laminopathic diseases.

Involvement of an inner nuclear membrane protein, Nemp1, in Xenopus neural development through an interaction with the chromatin protein BAF

To clarify the molecular mechanisms of neural development in vertebrates, we analyzed a novel gene, termed nemp1 (nuclear envelope integral membrane protein 1), which is expressed in the Xenopus anterior neuroectoderm at the neurula stage. Nemp1 has a putative signal peptide and five transmembrane domains, but does not have any other known domains. We show that Nemp1 is localized to the inner nuclear membrane (INM) with its evolutionarily conserved C-terminal region facing the nucleoplasm. Both overexpression and knockdown of Nemp1 in Xenopus embryos reduced the expression of early eye marker genes, rax, tbx3, and pax6, and later resulted mainly in severe eye defects at the tailbud stage. In contrast, the expression of a forebrain/midbrain marker, otx2, and a pan-neural marker, sox2, was largely unaffected. Deletion analysis of Nemp1 showed that nuclear envelope-localization of the C-terminal region is necessary for its eye-reducing activity. Furthermore, nemp1 is coexpressed with baf (barrier-to-autointegration factor) in the eye anlagen, and that Nemp1 interacts with BAF through the BAF-binding site in the C-terminal region and this site is required for Nemp1 activity. These data suggest that Nemp1 is involved in the expression of eye marker genes by functioning at the INM at least partly through BAF.

Tissue-specific defects are caused by loss of the Drosophila MAN1 LEM domain protein

The nuclear lamina represents a protein network required for nuclear structure and function. One family of lamina proteins is defined by an approximately 40-aa LAP2, Emerin, and MAN1 (LEM) domain (LEM-D) that binds the nonspecific DNA-binding protein, barrier-to-autointegration factor (BAF). Through interactions with BAF, LEM-D proteins serve as a bridge between chromosomes and the nuclear envelope. Mutations in genes encoding LEM-D proteins cause human laminopathies that are associated with tissue-restricted pathologies. Drosophila has five genes that encode proteins with LEM homology. Using yeast two-hybrid analyses, we demonstrate that four encode proteins that bind Drosophila (d)BAF. In addition to dBAF, dMAN1 associates with lamins, the LEM-D protein Bocksbeutel, and the receptor-regulated Smads, demonstrating parallel protein interactions with vertebrate homologs. P-element mobilization was used to generate null dMAN1 alleles. These mutants showed decreased viability, with surviving adults displaying male sterility, decreased female fertility, wing patterning and positioning defects, flightlessness, and locomotion difficulties that became more severe with age. Increased phospho-Smad staining in dMAN1 mutant wing discs is consistent with a role in transforming growth factor (TGF)-beta/bone morphogenic protein (BMP) signaling. The tissue-specific, age-enhanced dMAN1 mutant phenotypes are reminiscent of human laminopathies, suggesting that studies in Drosophila will provide insights into lamina dysfunction associated with disease.

Otefin, a nuclear membrane protein, determines the fate of germline stem cells in Drosophila via interaction with Smad complexes

Nuclear envelope proteins play important roles in chromatin organization, gene regulation, and signal transduction; however, the physiological role of these proteins remains elusive. We found that otefin (ote), which encodes a nuclear lamin-binding protein [corrected], is essential for germline stem cell (GSC) maintenance. We show that Ote, as an intrinsic factor, is both necessary and sufficient to regulate GSC fate. Furthermore, we demonstrate that ote is required for the Dpp/BMP signaling pathway to silence bam transcription. By structure-function analysis, we demonstrate that the nuclear membrane localization of Ote is essential for its role in GSC maintenance. Finally, we show that Ote physically interacts with Medea/Smad4 at the bam silencer element to regulate GSC fate. Thus, we demonstrate that specific nuclear membrane components mediate signal-dependent transcriptional effects to control stem cell behavior.

Pushing the envelope: developmental regulation by the nuclear lamina

A surprising realization in recent years was that proteins of the nuclear lamina directly regulate gene expression and cell differentiation. Presented here are examples that highlight the diverse roles these proteins can inhabit. Accompanying the primer is a discussion of current topics in the field with nuclear lamina experts Colin Stewart, Ph.D., and Yosef Gruenbaum, Ph.D.

The inner nuclear envelope as a transcription factor resting place

Just as people head to the beaches for a well-deserved rest, accumulating evidence suggests that transcription factors take similar 'vacations' at the nuclear envelope. Recent studies indicate that the periphery of the nucleus provides a platform for sequestering transcription factors away from chromatin. Several transcriptional regulators, operating in different signal-transduction pathways, have been found to interact physically with components of the inner nuclear membrane. In general, this association seems to restrict access to their target genes and limit their transactivation or transrepression abilities. The mechanisms of inner nuclear membrane association are diverse, and include regulated associations with the nuclear lamina and integral membrane proteins. Together, these findings indicate that the inside of the nuclear envelope functions as a resting place for transcription factors and suggest a more direct role for the nuclear envelope in gene regulation than previously anticipated.

Fraying at the edge mouse models of diseases resulting from defects at the nuclear periphery

Eukaryotic cells compartmentalize their genetic material within the nucleus. The boundary separating the genetic material from the cytoplasm is the nuclear envelope (NE) and lamina. Historically, the NE was perceived as functioning primarily as a barrier regulating the entry and exit of macromolecules between the nucleus and cytoplasm via the nuclear pore complexes (NPCs) that traverse the nuclear membranes. However, recent findings have caused a fundamental reassessment with regard to NE and lamina functions. Evidence now points to the NE and lamina functioning as a "hub" in regulating and perhaps integrating critical cellular functions that include chromatin organization, transcriptional regulation, mechanical integrity of the cell, signaling pathways, as well as acting as a key component of the cytoskeleton. Such an integral role for the nuclear boundary has emerged from increased interest into the functions of the NE/lamina, which has been largely stimulated by the discovery that some 24 different diseases and anomalies are caused by defects in proteins of the NE and lamina.

"Laminopathies": a wide spectrum of human diseases

Mutations in genes encoding the intermediate filament nuclear lamins and associated proteins cause a wide spectrum of diseases sometimes called "laminopathies." Diseases caused by mutations in LMNA encoding A-type lamins include autosomal dominant Emery-Dreifuss muscular dystrophy and related myopathies, Dunnigan-type familial partial lipodystrophy, Charcot-Marie-Tooth disease type 2B1 and developmental and accelerated aging disorders. Duplication in LMNB1 encoding lamin B1 causes autosomal dominant leukodystrophy and mutations in LMNB2 encoding lamin B2 are associated with acquired partial lipodystrophy. Disorders caused by mutations in genes encoding lamin-associated integral inner nuclear membrane proteins include X-linked Emery-Dreifuss muscular dystrophy, sclerosing bone dysplasias, HEM/Greenberg skeletal dysplasia and Pelger-Huet anomaly. While mutations and clinical phenotypes of "laminopathies" have been carefully described, data explaining pathogenic mechanisms are only emerging. Future investigations will likely identify new "laminopathies" and a combination of basic and clinical research will lead to a better understanding of pathophysiology and the development of therapies.

Lamins and lamin-associated proteins in aging and disease

Lamins, together with the lamin-associated proteins of the inner nuclear membrane, are structural proteins in the nucleus that mediate mechanical stress resistance. Novel findings show that lamin complexes also have scaffolding functions in the formation and regulation of higher order chromatin and in epigenetic regulatory pathways. Furthermore, lamins serve as scavenging complexes and regulators of signaling molecules in diverse pathways. Lamin complexes in the nuclear interior contribute to retinoblastoma-mediated cell cycle regulation. Because of their multiple and diverse roles, lamins are linked to an increasing number of human diseases. The molecular mechanisms of these diseases, which are just beginning to emerge, may involve cell cycle and differentiation defects in adult stem cells and genomic instability.

Ethanol regulates angiogenic cytokines during neural development: evidence from an in vitro model of mitogen-withdrawal-induced cerebral cortical neuroepithelial differentiation

BACKGROUND

Heavy alcohol consumption during pregnancy can cause significant mental retardation and brain damage. We recently showed that ethanol depletes reserve cerebral cortical stem cell capacity. Moreover, proliferating neuroepithelial cells exposed to ethanol were resistant to subsequent retinoic acid-induced differentiation. Emerging evidence suggests that cytokines play a crucial growth-promoting role in the developing neural tube.

METHODS

We cultured murine cortical neurosphere cultures in control or ethanol-supplemented mitogenic medium, to mimic alcohol exposure during the period of neuroepithelial proliferation. Cultures were then treated with a step-wise mitogen-withdrawal, integrin-activation model to mimic subsequent phases of neuronal migration and early differentiation. We examined the impact of alcohol exposure during neurogenesis on the secretion of inflammatory and growth-promoting cytokines.

RESULTS

Cortical neurosphere cultures exhibit increasingly complex differentiation phenotypes in response to step-wise mitogen-withdrawal and laminin exposure. Some inflammation-modulating cytokines were secreted independent of differentiation state. However, chemotactic cytokines were specifically secreted at high levels, as a function of differentiation stage. monocyte chemotactic protein-1, vascular endothelial growth factor-A, and interleukin (IL)-10 were coordinately decreased during differentiation compared with neuroepithelial proliferation, while granulocyte macrophage-colony stimulating factor (GM-CSF) was induced during differentiation, compared with the neuroepithelial proliferation period. Ethanol exposure during the period of neuroepithelial proliferation prevented the early differentiation-induced increase in GM-CSF while inducing differentiation-associated increase in IL-12 secretion.

CONCLUSION

Embryonic cerebral cortical neuroepithelial-derived precursors secrete high levels of several angiogenic and neural-growth-promoting cytokines as they differentiate into neurons. Our data collectively suggest that ethanol exposure during the period of neuroepithelial proliferation significantly disrupts cytokine signals that are required for the support of emerging neurovascular networks, and the maintenance of neural stem cell beds.

LEM‐Domain Proteins: New Insights into Lamin‐Interacting Proteins

LEM-domain proteins present a growing family of nonrelated inner nuclear membrane and intranuclear proteins, including emerin, MAN1, LEM2, several alternatively spliced isoforms of LAP2, and various uncharacterized proteins in higher eukaryotes as well as the Drosophila-specific proteins otefin and Bocksbeutel. LEM-domain proteins are involved in diverse cellular processes including replication and cell cycle control, chromatin organization and nuclear assembly, the regulation of gene expression and signaling pathways, as well as retroviral infection. Genetic analyses in different model organisms reveal new insights into the various functions of LEM-domain proteins, lamins, and their involvement in laminopathic diseases. All these findings as well as previously proposed ideas and models have been summarized to broaden our view of this exciting protein family.