A protein-protein interaction of stress-responsive myosin VI endowed to inhibit neural progenitor self-replication with RNA binding protein, TLS, in murine hippocampus

Myosin superfamily members during myelin formation and regeneration

Myelin is an insulator that forms around axons that enhance the conduction velocity of nerve fibers. Oligodendrocytes dramatically change cell morphology to produce myelin throughout the central nervous system (CNS). Cytoskeletal alterations are critical for the morphogenesis of oligodendrocytes, and actin is involved in cell differentiation and myelin wrapping via polymerization and depolymerization, respectively. Various protein members of the myosin superfamily are known to be major binding partners of actin filaments and have been intensively researched because of their involvement in various cellular functions, including differentiation, cell movement, membrane trafficking, organelle transport, signal transduction, and morphogenesis. Some members of the myosin superfamily have been found to play important roles in the differentiation of oligodendrocytes and in CNS myelination. Interestingly, each member of the myosin superfamily expressed in oligodendrocyte lineage cells also shows specific spatial and temporal expression patterns and different distributions. In this review, we summarize previous findings related to the myosin superfamily and discuss how these molecules contribute to myelin formation and regeneration by oligodendrocytes.

FUS-mediated dysregulation of Sema5a, an autism-related gene, in FUS mice with hippocampus-dependent cognitive deficits

Pathological fused in sarcoma (FUS) inclusions are found in 10% of patients with frontotemporal dementia and those with amyotrophic lateral sclerosis (ALS) carrying FUS mutations. Current work indicates that FUS mutations may incur gain-of-toxic functions to drive ALS pathogenesis. However, how FUS dysfunction may affect cognition remains elusive. Using a mouse model expressing wild-type human FUS mimicking the endogenous expression pattern and level within the central nervous system, we found that they developed hippocampus-mediated cognitive deficits accompanied by an age-dependent reduction in spine density and long-term potentiation in their hippocampus. However, there were no apparent FUS aggregates, nuclear envelope defects and cytosolic FUS accumulation. These suggest that these proposed pathogenic mechanisms may not be the underlying causes for the observed cognitive deficits. Unbiased transcriptomic analysis identified expression changes in a small set of genes with preferential expression in the neurons and oligodendrocyte lineage cells. Of these, we focused on Sema5a, a gene involved in axon guidance, spine dynamics, Parkinson's disease and autism spectrum disorders. Critically, FUS binds directly to Sema5a mRNA and regulates Sema5a expression in a FUS-dose-dependent manner. Taken together, our data suggest that FUS-driven Sema5a deregulation may underlie the cognitive deficits in FUS transgenic mice.

Myosin VI in the nucleus of neurosecretory PC12 cells: Stimulation-dependent nuclear translocation and interaction with nuclear proteins

Myosin VI (MVI) is a unique actin-based motor protein moving towards the minus end of actin filaments, in the opposite direction than other known myosins. Besides well described functions of MVI in endocytosis and maintenance of Golgi apparatus, there are few reports showing its involvement in transcription. We previously demonstrated that in neurosecretory PC12 cells MVI was present in the cytoplasm and nucleus, and its depletion caused substantial inhibition of cell migration and proliferation. Here, we show an increase in nuclear localization of MVI upon cell stimulation, and identification of potential nuclear localization (NLS) and nuclear export (NES) signals within MVI heavy chain. These signals seem to be functional as the MVI nuclear presence was affected by the inhibitors of nuclear import (ivermectin) and export (leptomycin B). In nuclei of stimulated cells, MVI colocalized with active RNA polymerase II, BrUTP-containing transcription sites and transcription factor SP1 as well as SC35 and PML proteins, markers of nuclear speckles and PML bodies, respectively. Mass spectrometry analysis of samples of a GST-pull-down assay with the MVI tail domain as a "bait" identified several new potential MVI binding partners. Among them are proteins involved in transcription and post-transcriptional processes. We confirmed interaction of MVI with heterogeneous nuclear ribonucleoprotein U (hnRNPU) and nucleolin, proteins involved in pre-mRNA binding and transport, and nucleolar function, respectively. Our data provide an insight into mechanisms of involvement of MVI in nuclear processes via interaction with nuclear proteins and support a notion for important role(s) for MVI in gene expression.

Expression of Unconventional Myosin VI in Oligodendrocytes

Myelin is a specialized multilamellar structure involved in various functions of the nervous system. Oligodendrocytes are responsible for myelin formation in the central nervous system. Motor proteins play important roles in differentiation and myelin formation of the oligodendrocyte lineage. Recently, we revealed that one of the unconventional myosins, myosin ID (Myo1d), is expressed in mature oligodendrocytes and is required for myelin-like membrane formation in vitro. Previously, Cahoy et al. (J Neurosci 28:264-278, 2008) reported that another unconventional myosin VI (Myo6) is upregulated in transcriptome data of differentiated oligodendrocytes. However, it is uncertain whether Myo6 protein is present in oligodendrocytes. In this study, to analyze expression of Myo6 in oligodendrocytes, we performed immunofluorescence analysis on brains of adult normal and cuprizone-induced demyelination mice. Myo6 expression was detected in mature oligodendrocytes and oligodendrocyte progenitor cells in the cerebellum and corpus callosum. To compare temporal expression patterns of myosin superfamily members in vitro, double immunostainings using anti-Myo6, myosin Va (Myo5a), or Myo1d with each stage-specific oligodendrocyte marker antibody were performed. In cultured oligodendrocytes, although Myo1d was found only in mature oligodendrocytes, Myo6 and Myo5a signals were detected in all stages of differentiation, from oligodendrocyte progenitor cells to mature oligodendrocytes. Additionally, similar to Myo5a, Myo6-positive signals were confined to the cell body and processes. These results showed that Myo6 is one of the unconventional myosins in oligodendrocyte lineage cells, which could play a role in clathrin-related endocytosis.

Energy Homeostasis and Abnormal RNA Metabolism in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron disease that is clinically characterized by progressive muscle weakness and impaired voluntary movement due to the loss of motor neurons in the brain, brain stem and spinal cord. To date, no effective treatment is available. Ample evidence suggests that impaired RNA homeostasis and abnormal energy status are two major pathogenesis pathways in ALS. In the present review article, we focus on recent studies that report molecular insights of both pathways, and discuss the possibility that energy dysfunction might negatively regulate RNA homeostasis via the impairment of cytoplasmic-nuclear shuttling in motor neurons and subsequently contribute to the development of ALS.

FUS Mislocalization and Vulnerability to DNA Damage in ALS Patients Derived hiPSCs and Aging Motoneurons

Mutations within the FUS gene (Fused in Sarcoma) are known to cause Amyotrophic Lateral Sclerosis (ALS), a neurodegenerative disease affecting upper and lower motoneurons. The FUS gene codes for a multifunctional RNA/DNA-binding protein that is primarily localized in the nucleus and is involved in cellular processes such as splicing, translation, mRNA transport and DNA damage response. In this study, we analyzed pathophysiological alterations associated with ALS related FUS mutations (mFUS) in human induced pluripotent stem cells (hiPSCs) and hiPSC derived motoneurons. To that end, we compared cells carrying a mild or severe mFUS in physiological- and/or stress conditions as well as after induced DNA damage. Following hyperosmolar stress or irradiation, mFUS hiPS cells recruited significantly more cytoplasmatic FUS into stress granules accompanied by impaired DNA-damage repair. In motoneurons wild-type FUS was localized in the nucleus but also deposited as small punctae within neurites. In motoneurons expressing mFUS the protein was additionally detected in the cytoplasm and a significantly increased number of large, densely packed FUS positive stress granules were seen along neurites. The amount of FUS mislocalization correlated positively with both the onset of the human disease (the earlier the onset the higher the FUS mislocalization) and the maturation status of the motoneurons. Moreover, even in non-stressed post-mitotic mFUS motoneurons clear signs of DNA-damage could be detected. In summary, we found that the susceptibility to cell stress was higher in mFUS hiPSCs and hiPSC derived motoneurons than in controls and the degree of FUS mislocalization correlated well with the clinical severity of the underlying ALS related mFUS. The accumulation of DNA damage and the cellular response to DNA damage stressors was more pronounced in post-mitotic mFUS motoneurons than in dividing hiPSCs suggesting that mFUS motoneurons accumulate foci of DNA damage, which in turn might be directly linked to neurodegeneration.

FUS-mediated regulation of alternative RNA processing in neurons: insights from global transcriptome analysis

Fused in sarcoma (FUS) is an RNA-binding protein that is causally associated with oncogenesis and neurodegeneration. Recently, the role of FUS in neurodegeneration has been extensively studied, because mutations in FUS are associated with amyotrophic lateral sclerosis (ALS), and the FUS protein has been identified as a major component of intracellular inclusions in neurodegenerative disorders including ALS and frontotemporal lobar degeneration. FUS is a key molecule in transcriptional regulation and RNA processing including processes such as pre-messenger RNA (mRNA) splicing and polyadenylation. Interaction of FUS with various components of the transcription machinery, spliceosome, and the 3'-end processing machinery has been identified. Furthermore, recent advances in high-throughput transcriptomic profiling approaches have enabled us to determine the mechanisms of FUS-dependent RNA processing networks at a cellular level. These analyses have revealed that depletion of FUS in neuronal cells affects alternative splicing and alternative polyadenylation of thousands of mRNAs. Gene ontology analysis has suggested that FUS-modulated genes are implicated in neuronal functions and development. CLIP-seq of FUS has shown that FUS is frequently clustered around these alternative sites of nascent RNA. ChIP-seq of RNA polymerase II (RNAP II) has demonstrated that an interaction between FUS and nascent RNA downregulates local transcriptional activity of RNAP II, which is critically involved in RNA processing. Both alternative splicing and alternative polyadenylation are fundamental processes by which cells expand their transcriptomic diversity, and are particularly essential in the nervous system. Dependence of transcriptomic diversity on FUS makes the nervous system vulnerable to neurodegeneration, when FUS is functionally compromised. WIREs RNA 2016, 7:330-340. doi: 10.1002/wrna.1338 For further resources related to this article, please visit the WIREs website.

[Universality of amino acid signaling between diverse plasma cells]

Both glutamic (Glu) and gamma-aminobutyric (GABA) acids are believed to play roles as neurotransmitters released from particular neurons into synaptic clefts in the mammalian central nervous system. Although GABA has been shown to act as an extracellular signal outside the brain, little attention has been paid to the possible expression of machineries required for neuronal glutamatergic signaling in cells other than central neurons. We first demonstrated the presence of Glu receptors in peripheral tissues such as the adrenal and pituitary glands three decades ago. In this review, I will outline our experimental findings accumulated since then on the physiological and pathological significance of neuronal amino acids as an extracellular signal for the maintenance of homeostasis in a variety of plasma cells. For example, Glu is released upon stimulation in a Ca2+-dependent manner for signal output in osteoblasts, where Glu is essential for the expression of the master regulator of osteoblastogenesis through a particular inotropic receptor subtype. In contrast, GABA plays a role in mechanisms underlying the suppression of cellular differentiation and maturation through a particular metabotropic receptor subtype in osteoblasts. Taken together, osteoblastic maturation proceeds as a delicate balancing between excitatory glutamatergic and inhibitory GABAergic signals, as seen in the brain. Re-evaluation of drugs currently used could be beneficial for the efficient discovery and development of innovative drugs useful for the prophylaxis and/or therapy of a variety of diseases relevant to the disturbance of glutamatergic and GABAergic signaling in diverse plasma cells.

Functions of FUS/TLS from DNA repair to stress response: implications for ALS

Fused in sarcoma/translocated in liposarcoma (FUS/TLS or FUS) is a multifunctional DNA-/RNA-binding protein that is involved in a variety of cellular functions including transcription, protein translation, RNA splicing, and transport. FUS was initially identified as a fusion oncoprotein, and thus, the early literature focused on the role of FUS in cancer. With the recent discoveries revealing the role of FUS in neurodegenerative diseases, namely amyotrophic lateral sclerosis and frontotemporal lobar degeneration, there has been a renewed interest in elucidating the normal functions of FUS. It is not clear which, if any, endogenous functions of FUS are involved in disease pathogenesis. Here, we review what is currently known regarding the normal functions of FUS with an emphasis on DNA damage repair, RNA processing, and cellular stress response. Further, we discuss how ALS-causing mutations can potentially alter the role of FUS in these pathways, thereby contributing to disease pathogenesis.

Over-expression of hNGF in adult human olfactory bulb neural stem cells promotes cell growth and oligodendrocytic differentiation

The adult human olfactory bulb neural stem/progenitor cells (OBNC/PC) are promising candidate for cell-based therapy for traumatic and neurodegenerative insults. Exogenous application of NGF was suggested as a promising therapeutic strategy for traumatic and neurodegenerative diseases, however effective delivery of NGF into the CNS parenchyma is still challenging due mainly to its limited ability to cross the blood-brain barrier, and intolerable side effects if administered into the brain ventricular system. An effective method to ensure delivery of NGF into the parenchyma of CNS is the genetic modification of NSC to overexpress NGF gene. Overexpression of NGF in adult human OBNSC is expected to alter their proliferation and differentiation nature, and thus might enhance their therapeutic potential. In this study, we genetically modified adult human OBNS/PC to overexpress human NGF (hNGF) and green fluorescent protein (GFP) genes to provide insight about the effects of hNGF and GFP genes overexpression in adult human OBNS/PC on their in vitro multipotentiality using DNA microarray, immunophenotyping, and Western blot (WB) protocols. Our analysis revealed that OBNS/PC-GFP and OBNS/PC-GFP-hNGF differentiation is a multifaceted process involving changes in major biological processes as reflected in alteration of the gene expression levels of crucial markers such as cell cycle and survival markers, stemness markers, and differentiation markers. The differentiation of both cell classes was also associated with modulations of key signaling pathways such MAPK signaling pathway, ErbB signaling pathway, and neuroactive ligand-receptor interaction pathway for OBNS/PC-GFP, and axon guidance, calcium channel, voltage-dependent, gamma subunit 7 for OBNS/PC-GFP-hNGF as revealed by GO and KEGG. Differentiated OBNS/PC-GFP-hNGF displayed extensively branched cytoplasmic processes, a significant faster growth rate and up modulated the expression of oligodendroglia precursor cells markers (PDGFRα, NG2 and CNPase) respect to OBNS/PC-GFP counterparts. These findings suggest an enhanced proliferation and oligodendrocytic differentiation potential for OBNS/PC-GFP-hNGF as compared to OBNS/PC-GFP.

Myosin VI reduces proliferation, but not differentiation, in pluripotent P19 cells

Background

We have previously shown marked upregulation of the mRNA and corresponding protein for the cellular motor molecule myosin VI (Myo6) after an extremely traumatic stress experience, along with a delayed decrease in 5-bromo-2′-deoxyuridine incorporation in the murine hippocampus, a brain structure believed to undergo adult neurogenesis. In this study, we investigated the role of Myo6 in both proliferation and differentiation in pluripotent P19 cells by using stable transfection and RNA interference techniques.

Methodology/Principal Findings

Stable overexpression of Myo6 not only led to significant inhibition of the reducing activity of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) and the size of clustered aggregates in P19 cells, but also resulted in selectively decreased mRNA expression of the repressor type proneural gene Hes5 without affecting the expression of neuronal and astroglial marker proteins. In P19 cells transfected with Myo6 siRNA, by contrast, a significant increase was found in the size of aggregate and MTT reduction along with increased Sox2 protein levels, in addition to marked depletion of the endogenous Myo6 protein. In C6 glioma cells, however, introduction of Myo6 siRNA induced a drastic decrease in endogenous Myo6 protein levels without significantly affecting MTT reduction. The Ca²⁺ ionophore A23187 drastically increased the luciferase activity in P19 cells transfected with a Myo6 promoter reporter plasmid, but not in HEK293, Neuro2A and C6 glioma cells transfected with the same reporter.

Conclusions/Significance

These results suggest that Myo6 may play a predominant pivotal role in the mechanism underlying proliferation without affecting differentiation to progeny lineages in pluripotent P19 cells.

Myosin VI in skeletal muscle: its localization in the sarcoplasmic reticulum, neuromuscular junction and muscle nuclei

Myosin VI (MVI) is a unique unconventional motor moving backwards on actin filaments. In non-muscle cells, it is involved in cell migration, endocytosis and intracellular trafficking, actin cytoskeleton dynamics, and possibly in gene transcription. An important role for MVI in striated muscle functioning was suggested in a report showing that a point mutation (H236R) within the MVI gene was associated with cardiomyopathy (Mohiddin et al., J Med Genet 41:309–314, 2004). Here, we have addressed MVI function in striated muscle by examining its expression and distribution in rat hindlimb skeletal muscle. We found that MVI was present predominantly at the muscle fiber periphery, and it was also localized within muscle nuclei. Analysis of both the hindlimb and cardiac muscle longitudinal sections revealed ~3 μm striation pattern, corresponding to the sarcoplasmic reticulum. Moreover, MVI was detected in the sarcoplasmic reticulum fractions isolated from skeletal and cardiac muscle. The protein also localized to the postsynaptic region of the neuromuscular junction. In denervated muscle, the defined MVI distribution pattern was abolished and accompanied by significant increase in its amount in the muscle fibers. In addition, we have identified several novel potential MVI-binding partners, which seem to aid our observations that in striated muscle MVI could be involved in postsynaptic trafficking as well as in maintenance of and/or transport within the sarcoplasmic reticulum and non-sarcomeric cytoskeleton.

Promotion of both proliferation and neuronal differentiation in pluripotent P19 cells with stable overexpression of the glutamine transporter slc38a1

Background

We previously demonstrated the functional expression in newborn rat neocortical astrocytes of glutamine transporter (GlnT = slc38a1) believed to predominate in neurons over astroglia in the brain. In order to evaluate the possible role of this transporter in neurogenesis, we attempted to establish stable transfectants of GlnT in mouse embryonal carcinoma P19 cells endowed to proliferate for self-renewal and differentiate into progeny cells such as neurons and astroglia, in addition to in vitro pharmacological profiling of the green tea ingredient theanine, which is shown to be a potent inhibitor of glutamine transport mediated by GlnT in cultured neurons and astroglia.

Methodology/Principal Findings

The full-length coding region of rat GlnT was inserted into a vector for gene transfection along with selection by G418, followed by culture with all-trans retinoic acid under floating conditions and subsequent dispersion for spontaneous differentiation under adherent conditions. Stable overexpression of GlnT led to marked increases in the size of round spheres formed during the culture for 4 days and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide reduction, with concomitant promotion of subsequent differentiation into cells immunoreactive for a neuronal marker protein. In these stable GlnT transfectants before differentiation, drastic upregulation was seen for mRNA expression of several proneural genes with a basic helix-loop-helix domain such as NeuroD1. Although a drastic increase was seen in NeuroD1 promoter activity in stable GlnT transfectants, theanine doubled NeuroD1 promoter activity in stable transfectants of empty vector (EV), without affecting the promoter activity already elevated in GlnT transfectants. Similarly, theanine promoted cellular proliferation and neuronal differentiation in stable EV transfectants, but failed to further stimulate the acceleration of both proliferation and neuronal differentiation found in stable GlnT transfectants.

Conclusions/Significance

GlnT would promote both proliferation and neuronal differentiation through a mechanism relevant to the upregulation of particular proneural genes in undifferentiated P19 cells.

De novo microdeletions of chromosome 6q14.1-q14.3 and 6q12.1-q14.1 in two patients with intellectual disability - further delineation of the 6q14 microdeletion syndrome and review of the literature

Interstitial 6q deletions can cause a variable phenotype depending on the size and location of the deletion. 6q14 deletions have been associated with intellectual disability and a distinct pattern of minor anomalies, including upslanted palpebral fissures with epicanthal folds, a short nose with broad nasal tip, anteverted nares, long philtrum, and thin upper lip. In this study we describe two patients with overlapping 6q14 deletions presenting with developmental delay and characteristic dysmorphism. Molecular karyotyping using array CGH analysis revealed a de novo 8.9 Mb deletion at 6q14.1-q14.3 and a de novo 11.3 Mb deletion at 6q12.1-6q14.1, respectively. We provide a review of the clinical features of twelve other patients with 6q14 deletions detected by array CGH analysis. By assessing all reported data we could not identify a single common region of deletion. Possible candidate genes in 6q14 for intellectual disability might be FILIP1, MYO6, HTR1B, and SNX14.

Mutations of optineurin in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) has its onset in middle age and is a progressive disorder characterized by degeneration of motor neurons of the primary motor cortex, brainstem and spinal cord. Most cases of ALS are sporadic, but about 10% are familial. Genes known to cause classic familial ALS (FALS) are superoxide dismutase 1 (SOD1), ANG encoding angiogenin, TARDP encoding transactive response (TAR) DNA-binding protein TDP-43 (ref. 4) and fused in sarcoma/translated in liposarcoma (FUS, also known as TLS). However, these genetic defects occur in only about 20-30% of cases of FALS, and most genes causing FALS are unknown. Here we show that there are mutations in the gene encoding optineurin (OPTN), earlier reported to be a causative gene of primary open-angle glaucoma (POAG), in patients with ALS. We found three types of mutation of OPTN: a homozygous deletion of exon 5, a homozygous Q398X nonsense mutation and a heterozygous E478G missense mutation within its ubiquitin-binding domain. Analysis of cell transfection showed that the nonsense and missense mutations of OPTN abolished the inhibition of activation of nuclear factor kappa B (NF-kappaB), and the E478G mutation revealed a cytoplasmic distribution different from that of the wild type or a POAG mutation. A case with the E478G mutation showed OPTN-immunoreactive cytoplasmic inclusions. Furthermore, TDP-43- or SOD1-positive inclusions of sporadic and SOD1 cases of ALS were also noticeably immunolabelled by anti-OPTN antibodies. Our findings strongly suggest that OPTN is involved in the pathogenesis of ALS. They also indicate that NF-kappaB inhibitors could be used to treat ALS and that transgenic mice bearing various mutations of OPTN will be relevant in developing new drugs for this disorder.

TDP-43 and FUS/TLS: emerging roles in RNA processing and neurodegeneration

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are neurodegenerative diseases with clinical and pathological overlap. Landmark discoveries of mutations in the transactive response DNA-binding protein (TDP-43) and fused in sarcoma/translocated in liposarcoma (FUS/TLS) as causative of ALS and FTLD, combined with the abnormal aggregation of these proteins, have initiated a shifting paradigm for the underlying pathogenesis of multiple neurodegenerative diseases. TDP-43 and FUS/TLS are both RNA/DNA-binding proteins with striking structural and functional similarities. Their association with ALS and other neurodegenerative diseases is redirecting research efforts toward understanding the role of RNA processing regulation in neurodegeneration.