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Objective: Megalencephalic leukoencephalopathy with cysts (MLC) is a genetic disease characterized by infantile onset white matter edema and delayed onset neurological deterioration. Loss of MLC1 function causes MLC. MLC1 is involved in ion-water homeostasis, but its exact role is unknown. We generated Mlc1-null mice for further studies. Methods: We investigated which brain cell types express MLC1, compared developmental expression in mice and men, and studied the consequences of loss of MLC1 in Mlc1-null mice. Results: Like humans, mice expressed MLC1 only in astrocytes, especially those facing fluid-brain barriers. In mice, MLC1 expression increased until 3 weeks and then stabilized. In humans, MLC1 expression was highest in the first year, decreased, and stabilized from approximately 5 years. Mlc1-null mice had early onset megalencephaly and increased brain water content. From 3 weeks, abnormal astrocytes were present with swollen processes abutting fluid-brain barriers. From 3 months, widespread white matter vacuolization with intramyelinic edema developed. Mlc1-null astrocytes showed slowed regulatory volume decrease and reduced volume-regulated anion currents, which increased upon MLC1 re-expression. Mlc1-null astrocytes showed reduced expression of adhesion molecule GlialCAM and chloride channel ClC-2, but no substantial changes in other known MLC1-interacting proteins. Interpretation: Mlc1-null mice replicate early stages of the human disease with early onset intramyelinic edema. The cellular functional defects, described for human MLC, were confirmed. The earliest change was astrocytic swelling, substantiating that in MLC the primary defect is in volume regulation by astrocytes. MLC1 expression affects expression of GlialCAM and ClC-2. Abnormal interplay between these proteins is part of the pathomechanisms of MLC.

International audience; The autosomal recessive white matter disorder LBSL (leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation) is caused by mutations in DARS2, coding for mtAspRS (mitochondrial aspartyl-tRNA synthetase). Generally, patients are compound heterozygous for mutations in DARS2. Many different mutations have been identified in patients, including several missense mutations. In the present study, we have examined the effects of missense mutations found in LBSL patients on the expression, enzyme activity, localization and dimerization of mtAspRS, which is important for understanding the cellular defect underlying the pathogenesis of the disease. Nine different missense mutations were analysed and were shown to have various effects on mtAspRS properties. Several mutations have a direct effect on the catalytic activity of the enzyme; others have an effect on protein expression or dimerization. Most mutations have a clear impact on at least one of the properties of mtAspRS studied, probably resulting in a small contribution of the missense variants to the mitochondrial aspartylation activity in the cell.

LBSL (leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation) is an autosomal recessive white matter disorder with slowly progressive cerebellar ataxia, spasticity and dorsal column dysfunction. Magnetic resonance imaging shows characteristic abnormalities in the cerebral white matter and specific brain stem and spinal cord tracts. LBSL is caused by mutations in the gene DARS2, which encodes mtAspRS (mitochondrial aspartyl-tRNA synthetase). The selective involvement of specific white matter tracts in LBSL is striking since this protein is ubiquitously expressed. Almost all LBSL patients have one mutation in intron 2 of DARS2, affecting the splicing of the third exon. Using a splicing reporter construct, we find cell-type-specific differences in the sensitivity to these mutations: the mutations have a larger effect on exon 3 exclusion in neural cell lines, especially neuronal cell lines, than in nonneural cell lines. Furthermore, correct inclusion of exon 3 in the normal mtAspRS mRNA occurs less efficiently in neural cells than in other cell types, and this effect is again most pronounced in neuronal cells. The combined result of these two effects may explain the selective vulnerability of specific white matter tracts in LBSL patients. © The Authors Journal compilation © 2012 Biochemical Society.

Megalencephalic leucoencephalopathy with subcortical cysts is a genetic brain disorder with onset in early childhood. Affected infants develop macrocephaly within the first year of life, after several years followed by slowly progressive, incapacitating cerebellar ataxia and spasticity. From early on, magnetic resonance imaging shows diffuse signal abnormality and swelling of the cerebral white matter, with evidence of highly increased white matter water content. In most patients, the disease is caused by mutations in the gene MLC1, which encodes a plasma membrane protein almost exclusively expressed in brain and at lower levels in leucocytes. Within the brain, MLC1 is mainly located in astrocyte-astrocyte junctions adjacent to the blood-brain and cereborspinal fluid-brain barriers. Thus far, the function of MLC1 has remained unknown. We tested the hypothesis that MLC1 mutations cause a defect in ion currents involved in water and ion homeostasis, resulting in cerebral white matter oedema. Using whole-cell patch clamp studies we demonstrated an association between MLC1 expression and anion channel activity in different cell types, most importantly astrocytes. The currents were absent in chloride-free medium and in cells with disease-causing MLC1 mutations. MLC1-dependent currents were greatly enhanced by hypotonic pretreatment causing cell swelling, while ion channel blockers, including Tamoxifen, abolished the currents. Down regulation of endogenous MLC1 expression in astrocytes by small interfering RNA greatly reduced the activity of this channel, which was rescued by overexpression of normal MLC1. The current-voltage relationship and the pharmacological profiles of the currents indicated that the channel activated by MLC1 expression is a volume-regulated anion channel. Such channels are involved in regulatory volume decrease. We showed that regulatory volume decrease was hampered in lymphoblasts from patients with megalencephalic leucoencephalopathy. A similar trend was observed in astrocytes with decreased MLC1 expression; this effect was rescued by overexpression of normal MLC1. In the present study, we show that absence or mutations of the MLC1 protein negatively impact both volume-regulated anion channel activity and regulatory volume decrease, indicating that megalencephalic leucoencephalopathy is caused by a disturbance of cell volume regulation mediated by chloride transport. © 2011 The Author.

A 17-year-old Indian boy with gradually progressive ataxia with onset at 12 years of age is described. Magnetic resonance imaging (MRI) of the brain revealed extensive, inhomogeneous signal abnormalities in the cerebral white matter, with involvement of selected tracts in the brain stem and spinal cord. The imaging findings were characteristic of leukoencephalopathy with brain stem and spinal cord involvement and high lactate, a recently described leukodystrophy. Interestingly, magnetic resonance spectroscopy of the abnormal white matter did not reveal elevated lactate. The patient was compound heterozygous for 2 new mutations in DARS2, genetically confirming the diagnosis. © The Author(s) 2011.

Leukoencephalopathy with brainstem and spinal cord involvement and elevated brain lactate diagnosis is based on its highly characteristic pattern of abnormalities observed by magnetic resonance imaging and spectroscopy. Clinically, affected patients develop slowly progressive cerebellar ataxia, spasticity, and dorsal column dysfunction, sometimes with a mild cognitive deficit or decline. In 2007, the pathophysiology of this disorder was elucidated with the discovery of mutations in the DARS2 gene, which encodes mitochondrial aspartyl-tRNA synthetase, in affected individuals. Here, the authors present a case of leukoencephalopathy with brainstem and spinal cord involvement with normal brain lactate, in which genetic analysis revealed a new mutation in the DARS2 gene not previously described. © The Author(s) 2010.

Vanishing white matter (VWM) is one of the most prevalent inherited childhood leukoencephalopathies, but this may affect people ofall ages, including neonates and adults. It is a progressive disorder clinically dominated by cerebellar ataxia and in which minor stress conditions, such as fever or mild trauma, provoke major episodes of neurologic deterioration. Typical pathological findings include increasing white matter rarefaction and cystic degeneration, oligodendrocytosis with highly characteristic foamy oligodendrocytes, meager astrogliosis with dysmorphic astrocytes, and loss of oligodendrocytesby apoptosis. Vanishing white matter is caused by mutations in any of the genes encoding the 5 subunits of the eukaryotic translation initiation factor 2B (eIF2B), EIF2B1 through EIF2B5. eIF2B is a ubiquitously expressed protein complex that plays a crucial role in regulating the rate of protein synthesis. Vanishing white matter mutations reduce the activity of eIF2B and impair its function to couple protein synthesis to the cellular demands in basal conditions and during stress. Reduced eIF2B activity leads to sustained improper activation of the unfolded protein response, resulting in concomitant expression of proliferation, prosurvival, and proapoptotic downstream effectors. Consequently, VWM cells are constitutively predisposed and hyperreactive to stress. In view of the fact that VWM genes are housekeeping genes, it is surprising that the disease is primarily a leukoencephalopathy. The pathophysiology of selective glial vulnerability in VWM remains poorly understood. Copyright © 2010 by the American Association of Neuropathologists, Inc.

Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) is a recently described disorder with autosomal recessive mode of inheritance. Lately, mutations in the DARS2 gene, which encodes mitochondrial aspartyl-tRNA synthetase, have been found as the underlying defect. We report a 19-year-old male patient with cerebellar, pyramidal and dorsal column dysfunctions and specific magnetic resonance imaging (MRI) and characteristic magnetic resonance spectroscopy (MRS) abnormalities. The patient was compound-heterozygous for two mutations in DARS2. MRI showed selective involvement of cerebral and cerebellar white matter and superior and inferior cerebellar peduncles, without contrast enhancement. The U-fibers were spared. The sensory and the pyramidal tracts were affected over their entire length. Involvement of the intraparenchymal trajectories of the trigeminal nerves and mesencephalic trigeminal tracts was demonstrated. In the spinal cord, signal abnormalities were identified in the dorsal columns and the lateral corticospinal tracts. Proton-MRS of the frontal and cerebellar white matter showed elevated lactate, reduced N-acetylaspartate, increased myoinositol and mildly elevated choline. In LBSL, distinct MRI findings should lead to the diagnosis, which can be confirmed by the analysis of the disease gene DARS2. (c) 2008 Elsevier B.V. All rights reserved

Febrile infections are known to cause exacerbations in the white matter disorders 'vanishing white matter' (VWM) and multiple sclerosis (MS). We hypothesized that polymorphisms in EIF2B1-5, the genes involved in VWM, might be risk factors for the development of MS or temperature sensitivity in patients with MS. We found no difference in the frequencies of 15 EIF2B1-5 variants between patients with MS and healthy controls, and none of the variants showed significant deviation of the Hardy-Weinberg equilibrium. Furthermore, sequencing data of EIF2B1-5 in 20 patients with MS and measurement of the activity of eIF2B complex in patient-derived lymphoblasts did not support our hypothesis. © SAGE Publications 2008.

The list of genetic diseases caused by mutations that affect mRNA translation is rapidly growing. Although protein synthesis is a fundamental process in all cells, the disease phenotypes show a surprising degree of heterogeneity. Studies of some of these diseases have provided intriguing new insights into the functions of proteins involved in the process of translation; for example, evidence suggests that several have other functions in addition to their roles in translation. Given the numerous proteins involved in mRNA translation, it is likely that further inherited diseases will turn out to be caused by mutations in genes that are involved in this complex process.

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a progressive cerebral white matter disease with onset in childhood, caused by mutations in the MLC1 gene. MLC1 is a protein with unknown function that is mainly expressed in the brain in astrocytic endfeet at the blood-brain and cerebrospinal fluid-brain barriers. It shares its localization at astrocytic endfeet with the dystrophin-associated glycoprotein complex (DGC). The objective of the present study was to investigate the possible association of MLC1 with the DGC. To test this hypothesis, (co)-localization of DGC-proteins and MLC1 was analyzed by immunohistochemical stainings in gliotic brain tissue from a patient with multiple sclerosis, in glioblastoma tissue and in brain tissue from an MLC patient. In control tissue, a direct protein interaction was tested by immunoprecipitation. Results revealed that MLC1 is co-localized with DGC-proteins in gliotic brain tissue. We demonstrated that both MLC1 and aquaporin-4, a member of the DGC, were redistributed in glioblastoma cells. In MLC brain tissue, we showed absence of MLC1 and altered expression of several DGC-proteins. We demonstrated a direct protein interaction between MLC1 and Kir4.1. From these results we conclude that MLC1 is associated with the DGC at astrocytic endfeet.

Leukoencephalopathy with vanishing white matter (VWM) is an inherited childhood white matter disorder, caused by mutations in the genes encoding eukaryotic initiation factor 2B (eIF2B). The present study showed that, while the eIF2B activity was reduced in VWM lymphoblasts, the expression levels of the eIF2B subunits were similar to control lymphoblast lines. The mutations in eIF2B did not affect the interaction with eIF2. Strikingly, no apparent differences for the regulation of protein synthesis, measured by [ 35S]-methionine incorporation, were found between control and VWM lymphoblasts. Western blotting showed that, in some VWM cells, exposure to heat shock caused a decrease in the expression of specific eIF2B subunits. Most importantly, the increase in phosphorylation of eIF2α in response to heat shock was lower in VWM lymphoblasts than in control cells. These findings could form part of the explanation for the episodes of rapid and severe deterioration in VWM patients that are precipitated by febrile infections.

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is an autosomal recessive cerebral white matter disorder in children. This disease is histopathologically characterized by myelin splitting and intramyelinic vacuole formation. MLC is caused by mutations in the gene MLC1, which encodes a novel protein, MLC1. Since the first report, 50 mutations in this gene have been found. Mutations occur throughout the entire coding region and include all different types: 11 splice-site mutations; one nonsense mutation; 24 missense mutations; and 14 deletions and insertions. Until now, six polymorphisms within the coding sequence of MLC1 had been reported. In about 20% of the patients with a typical clinical and MRI picture, no mutations in the MLC1 gene are found. Several of the families, in which no mutations are found, also do not show linkage with the MLC1 locus, which suggests a second gene involved in MLC. The absence of mutations may also be the consequence of performing standard mutation analysis that can miss heterorygous deletions, mutations in the promoter, 3′ and 5′ untranslated regions (UTRs), and intron mutations, which may influence the amino acid composition of the end product. In this work we describe 13 novel mutations, including those found with extended mutation analysis on MLC patients. This study shows that extended mutation analysis is a valuable tool to identify at least some of the missing mutations. Therefore, we suggest extended mutation analysis for the MLC1 gene, if no mutations are found during standard analysis.

Leukoencephalopathy with vanishing white matter (VWM) is an autosomal-recessive disorder in which febrile infections may provoke major neurologic deterioration. Characteristic pathologic findings include cystic white matter degeneration, foamy oligodendrocytes, dysmorphic astrocytes and oligodendrocytes, oligodendrocytosis, and apoptotic losses of oligodendrocvtes. VWM is caused by mutations in eukaryotic initiation factor (eIF) 2B (eIF2B). eIF2B plays an important role in the regulation of protein synthesis. Mutant eIF2B may impair the ability of cells to regulate protein synthesis in response to stress and perhaps even under normal conditions. An overload of misfolded proteins in the endoplasmic reticulum activates the unfolded protein response (UPR), a compensatory mechanism that inhibits synthesis of new proteins and induces both prosurvival and proapoptotic signals. We have studied the activation of the UPR in VWM through the immunohistochemical expression of its upstream components PERK and phosphorylated eIF2α (eIF2αP) and combined immunohistochemical and Western blot analysis of the down-stream effector proteins activating transcription factor-4 (ATF4) and C/EBP homologous protein (CHOP) in 4 VWM brains and 3 age-matched controls. We demonstrate activation of the UPR in glia of patients with VWM. Our findings may point to a possible explanation for the dysmorphic glia, the increased numbers of oligodendrocytes, and the apoptotic loss of oligodendrocytes in VWM.

In Drosophila cells, phosphorylation of eIF4E (eukaryotic initiation factor 4E) is required for growth and development. In Drosophila melanogaster, LK6 is the closest homologue of mammalian Mnk1 and Mnk2 [MAPK (mitogen-activated protein kinase) signal-integrating kinases 1 and 2 respectively] that phosphorylate mammalian eIF4E. Mnk1 is activated by both mitogen- and stress-activated signalling pathways [ERK (extracellular-signal-regulated kinase) and p38 MAPK], whereas Mnk2 contains a MAPK-binding motif that is selective for ERKs. LK6 possesses a binding motif similar to that in Mnk2. In the present study, we show that LK6 can phosphorylate eIF4E at the physiological site. LK6 activity is increased by the ERK signalling pathway and not by the stress-activated p38 MAPK signalling pathway. Consistent with this, LK6 binds ERK in mammalian cells, and this requires an intact binding motif. LK6 can bind to eIF4G in mammalian cells, and expression of LK6 increases the phosphorylation of the endogenous eIF4E. In Drosophila S2 Schneider cells, LK6 binds the ERK homologue Rolled, but not the p38 MAPK homologue. LK6 phosphorylates Drosophila eIF4E in vitro. The phosphorylation of endogenous eIF4E in Drosophila cells is increased by activation of the ERK pathway but not by arsenite, an activator of p38 MAPK. RNA interference directed against LK6 significantly decreases eIF4E phosphorylation in Drosophila cells. These results show that LK6 binds to ERK and is activated by ERK signalling and it is responsible for phosphorylating eIF4E in Drosophila.

Megaloencephalic leukoencephalopathy with subcortical cysts (MLC) is a progressive cerebral white matter disease in children caused by mutations in the MLC1 gene. This disease is histopathologically characterized by myelin splitting and intramyelinic vacuole formation. MLC1 encodes a novel protein, MLC1, which is mainly expressed in the brain and leukocytes. The function is unknown, although a transport function has been suggested. In this article, we provide experimental data addressing the membrane topology and cellular localization of MLC1. We show that MLC1 contains an even number of transmembrane domains, supporting the possible transport function of MLC1. We demonstrate that MLC1 is specifically expressed in distal astroglial processes in perivascular, subependymal, and subpial regions. This localization suggests a role for MLC1 in a transport process across the blood-brain and brain-cerebrospinal fluid barriers. Astrocyte functions have long been debated. It is becoming increasingly clear that these cells are of fundamental importance in maintaining the structural and functional integrity of neural tissue. Elucidation of the function of MLC1 will contribute to a better understanding of not only the pathophysiology of the disease, but also the role of astrocytes in normal neural tissue.

The cap-binding protein eIF4E-binding protein 3 (4E-BP3) was identified some years ago, but its properties have not been investigated in detail. In this report, we investigated the regulation and localisation of 4E-BP3. We show that 4E-BP3 is present in the nucleus as well as in the cytoplasm in primary T cells, HEK293 cells and HeLa cells. 4E-BP3 was associated with eIF4E in both cell compartments. Furthermore, 4E-BP3/eIF4E association in the cytoplasm was regulated by serum or interleukin-2 starvation in the different cell types. Rapamycin did not affect the association of eIF4E with 4E-BP3 in the cytoplasm or in the nucleus.

Eukaryotic initiation factor 4E (eIF4E) plays an important role in mRNA translation by binding the 5?-cap structure of the mRNA and facilitating the recruitment to the mRNA of other translation factors and the 40S ribosomal subunit. eIF4E can interact either with the scaffold protein eIF4G or with repressor proteins termed eIF4E-binding proteins (4E-BPs). High levels of expression can disrupt cellular growth control and are associated with human cancers. A fraction of the cellular eIF4E is found in the nucleus where it may play a role in the transport of certain mRNAs to the cytoplasm. eIF4E undergoes regulated phosphorylation (at Ser209) by members of the Mnk group of kinases, which are activated by multiple MAP kinases (hence Mnk?=?MAP-kinase signal integrating kinase). The functional significance of its phosphorylation has been the subject of considerable interest. Recent genetic studies in Drosophila point to a key role for phosphorylation of eIF4E in growth and viability. Initial structural data suggested that phosphorylation of Ser209 might allow formation of a salt bridge with a basic residue (Lys159) that would clamp eIF4E onto the mRNA and increase its affinity for ligand. However, more recent structural data place Ser209 too far away from Lys159 to form such an interaction, and biophysical studies indicate that phosphorylation actually decreases the affinity of eIF4E for cap or capped RNA. The implications of these studies are discussed in the light of other, in vitro and in vivo, investigations designed to address the role of eIF4E phosphorylation in mRNA translation or its control.

Vanishing white matter disease is an inherited disorder, most frequently affecting children, caused by mutations in the genes encoding the subunits of the eIF2B complex. This disease is primarily diagnosed by magnetic resonance imaging (MRI). The diagnosis is confirmed when mutations are found in one of the eIF2B genes. Pathological hallmarks are foamy oligodendrocytes, dysmorphic astrocytes, and the presence of high numbers of glia progenitors that fail to mature. The selective involvement of the white matter is unexplained, and a causal role for reduced eIF2B activity is debatable.

Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation is a disorder caused by recessive mutations in the gene DARS2, which encodes mitochondrial aspartyl-tRNA synthetase. Recent observations indicate that the phenotypic range of the disease is much wider than initially thought. Currently, no treatment is available. The aims of our study were (i) to explore a possible genotype-phenotype correlation; and (ii) to identify potential therapeutic agents that modulate the splice site mutations in intron 2 of DARS2, present in almost all patients. A cross-sectional observational study was performed in 78 patients with two DARS2 mutations in the Amsterdam and Helsinki databases up to December 2012. Clinical information was collected via questionnaires. An inventory was made of the DARS2 mutations in these patients and those previously published. An assay was developed to assess mitochondrial aspartyl-tRNA synthetase enzyme activity in cells. Using a fluorescence reporter system we screened for drugs that modulate DARS2 splicing. Clinical information of 66 patients was obtained. The clinical severity varied from infantile onset, rapidly fatal disease to adult onset, slow and mild disease. The most common phenotype was characterized by childhood onset and slow neurological deterioration. Full wheelchair dependency was rare and usually began in adulthood. In total, 60 different DARS2 mutations were identified, 13 of which have not been reported before. Except for 4 of 42 cases published by others, all patients were compound heterozygous. Ninety-four per cent of the patients had a splice site mutation in intron 2. The groups of patients sharing the same two mutations were too small for formal assessment of genotype-phenotype correlation. However, some combinations of mutations were consistently associated with a mild phenotype. The mitochondrial aspartyl-tRNA synthetase activity was strongly reduced in patient cells. Among the compounds screened, cantharidin was identified as the most potent modulator of DARS2 splicing. In conclusion, the phenotypic spectrum of leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation is wide, but most often the disease has a relatively slow and mild course. The available evidence suggests that the genotype influences the phenotype, but because of the high number of private mutations, larger numbers of patients are necessary to confirm this. The activity of mitochondrial aspartyl-tRNA synthetase is significantly reduced in patient cells. A compound screen established a 'proof of principle' that the splice site mutation can be influenced. This finding is promising for future therapeutic strategies. © 2013 The Author.

Translation initiation is a key point of regulation in eukaryotic gene expression. 4E-binding proteins (4E-BPs) inhibit initiation by blocking the association of eIF4E with eIF4G, two integral components of the mRNA cap-binding complex. Phosphorylation of 4E-BP1 reduces its ability to bind to eIF4E and thereby to compete with eIF4G. A novel combination of biophysical and biochemical tools was used to measure the impact of phosphorylation and acidic side chain substitution at each potentially modulatory site in 4E-BP1. For each individual site, we have analyzed the effects of modification on eIF4E binding using affinity chromatography and surface plasmon resonance analysis, and on the regulatory function of the 4E-BP1 protein using a yeast in vivo model system and a mammalian in vitro translation assay. We find that modifications at the two sites immediately flanking the eIF4E-binding domain, Thr(46) and Ser(65), consistently have the most significant effects, and that phosphorylation of Ser(65) causes the greatest reduction in binding affinity. These results establish a quantitative framework that should contribute to understanding of the molecular interactions underlying 4E-BP1-mediated translational regulation.

Regulation of eukaryotic translation initiation is a process that requires collaboration between multiple proteins. The cap-binding factor eukaryotic initiation factor (eIF)4E, its binding protein 4E-BP1, and the guanine-nucleotide-exchange factor eIF2B play important roles in the regulation of the rate of protein synthesis. This review describes the regulation of the activity of these three proteins and the signal-transduction pathways involved therein.

Various factors are involved in the heat shock-induced inhibition of protein synthesis. Changes upon heat shock in phosphorylation, leading to inactivation, of eukaryotic initiation factors (eIFs) eIF2 and eIF4E have been shown for several cell types. However, in mammalian cells these changes occur at temperatures of 43 degrees C or higher while protein synthesis is already affected at milder heat shock temperatures. In searching for the cause for the inhibition of protein synthesis, the regulation of eIF2 and eIF4E by additional factors was analyzed. In this respect, the activity of eIF2B was measured during and after heat shock. A very clear correlation was found between the activity of this guanine exchange factor and the levels of protein synthesis, also at mild heat shock conditions. Changes in the phosphorylation of eIF4E and of the eIF4E-binding protein PHAS-I were also analyzed. Surprisingly, in H35 cells as well as in some other cell lines, PHAS-I phosphorylation was increased by heat shock, whereas in others it was decreased. Therefore, decreasing the eIF4E availability under stressful conditions does not seem to be a general mechanism to inhibit protein synthesis by heat shock. Regulation of eIF2B activity appears to be the main mechanism to control translation initiation after heat shock at mild temperatures.

Protein yields in the baculovirus expression system do not always correlate with the presence of abundant amounts of corresponding mRNAs. Therefore, a novel aspect of the baculovirus expression system was studied: initiation of translation of very late mRNAs of Autographa californica multicapsid nucleopolyhedrovirus. The untranslated regions (UTRs) of the p10 mRNA of this baculovirus were studied by in vitro translation and after transfection into Spodoptera frugiperda insect cells. Lysates from insect cells were optimized for translation of in vitro transcripts containing p10 sequences. The lysates were used to measure the effects of various deletions in either the 5' or 3'UTR on protein synthesis. Transcripts containing the p10 5'UTR were translated efficiently. Large deletions in the 5'UTR severely decreased this efficiency. Deletions in the 3'UTR negatively affected expression of the reporter gene in vivo; however, no effect on translational efficiency in the insect-cell lysates was measured. The translational properties of the p10 transcripts were very similar in lysates made from either uninfected or baculovirus-infected insect cells. Determination of optimal salt conditions for either uncapped or capped transcripts showed that the p10 5'UTR was used very efficiently for translation initiation in vitro, even in the absence of a cap-structure at its 5' end. Addition of cap-analogue to the in vitro translation assays did not inhibit p10 5'UTR-driven translation, while translation of a cap-dependent mRNA was severely inhibited. These data suggest that the very late mRNAs of baculovirus are translated in a cap-independent manner.

This article concerns the scientific value of the theory of autopoietic systems as developed by Maturana and Varela. In a first step, the explanatory power of the theory is investigated. It is argued that, due to the tautological nature of its core concept and the absence of the specification of the organization of the autopoietic system, the empirical counterparts of the theory's constructs cannot be determined. This renders the theory inadequate for descriptive and explanatory purposes. Proponents of autopoietic system theory do not agree with this kind of reasoning and its conclusion, since autopoietic systems, in their view, cannot be observed precisely because of its autopoietic nature. In a subsequent step, therefore, the epistemology advocated by Maturana and Varela on which this counter argument rests is discussed. It is shown that the interpretation of the ultrastable system, which underlies this epistemology, is not correct. Consequently, it is concluded that autopoietic system theory as developed by Maturana and Varela is unscientific.

AimLeukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) is known as a relatively mild leukoencephalopathy. We investigated the occurrence of severe variants of LBSL with extensive brain magnetic resonance imaging (MRI) abnormalities. MethodMRIs of approximately 3,000 patients with an unknown leukoencephalopathy were retrospectively reviewed for extensive signal abnormalities of the cerebral and cerebellar white matter, posterior limb of the internal capsule, cerebellar peduncles, pyramids, and medial lemniscus. Clinical data were retrospectively collected. ResultsEleven patients fulfilled the MRI criteria (six males); six had DARS2 mutations. Clinical and laboratory findings did not distinguish between patients with and without DARS2 mutations, but MRI did. Patients with DARS2 mutations more often had involvement of structures typically affected in LBSL, including decussatio of the medial lemniscus, anterior spinocerebellar tracts, and superior and inferior cerebellar peduncles. Also, involvement of the globus pallidus was associated with DARS2 mutations. Earliest disease onset was neonatal; earliest death at 20 months. InterpretationThis study confirms the occurrence of early infantile, severe LBSL, extending the known phenotypic range of LBSL. Abnormality of specific brainstem tracts and cerebellar peduncles are MRI findings that point to the correct diagnosis. Copyright © 2012 by Thieme Medical Publishers, Inc.

In concert with the translation initiation factors ‘ trans -acting’ factors function specifically during internal initiation on picornaviral mRNAs. Of these trans -acting factors, two have been identified as the La-protein and the polypyrimidine tract binding protein. Within the internal ribosomal entry site on the viral RNA, sequences are present that direct the ribosome to the initiation codon. We suggest that selection of the correct AUG initiation codon occurs through basepairing with a part of 18S ribosomal RNA.

The encephalomyocarditis virus 5′ untranslated region (EMC 5 UTR) has a binding site for eukaryotic initiation factor eIF-2. Mutations in the 3′ end or deletion of the 5′ end of the internal ribosomal entry site had a negative effect on the binding of eIF-2 to the EMC 5′ UTR. The binding of eIF-2 to the mutant 5′ UTRs was completely inhibited by the addition of competitor tRNA. Cross-linking of the EMC 5′UTR with proteins from rabbit reticulocyte lysates showed binding of trans -acting factors p52 and p57. Deletions in the 5′ end of the internal ribosomal entry site resulted in a loss of the ability to bind trans -acting factor p57, in accordance with literature data, while p52 binding to these deletion mutants was weak compared to the wildtype EMC 5′UTR. Mutations in the 3′ part of the 5′UTR of EMC still resulted in binding of both trans -acting factors, as with wild type RNA, but binding was more sensitive to competitor tRNA when compared to the binding of p52/p57 to the wild type 5′UTR.

International audience; Mutations in the nuclear gene coding for the mitochondrial aspartyl-tRNA synthetase, a key enzyme for mitochondrial translation, are correlated with leukoencephalopathy. A Ser45 to Gly45 mutation is located in the predicted targeting signal of the protein. We demonstrate in the present study, by in vivo and in vitro approaches, that this pathology-related mutation impairs the import process across mitochondrial membranes.

Autosomal recessive mutations in eukaryotic initiation factor 2B (eIF2B) cause leukoencephalopathy vanishing white matter with a wide clinical spectrum. eIF2B comprises five subunits (α-ε; genes EIF2B1, 2, 3, 4 and 5) and is the guanine nucleotide-exchange factor (GEF) for eIF2. It plays a key role in protein synthesis. Here, we have studied the functional effects of selected VWM mutations in EIF2B2-5 by coexpressing mutated and wild-type subunits in human cells. The observed functional effects are very diverse, including defects in eIF2B complex integrity; binding to the regulatory α-subunit; substrate binding; and GEF activity. Activity data for recombinant eIF2B complexes agree closely with those for patient-derived cells with the same mutations. Some mutations do not affect these parameters even though they cause severe disease. These findings are important for three reasons; they demonstrate that measuring eIF2B activity in patients' cells has limited value as a diagnostic test; they imply that severe disease can result from alterations in eIF2B function other than defects in complex integrity, substrate binding or GEF activity, and last, the diversity of functional effects of VWM mutations implies that seeking agents to manage or treat VWM should focus on downstream effectors of eIF2B, not restoring eIF2B activity. © 2011 Wiley-Liss, Inc.

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a rare type of leukodystrophy, in the majority of cases caused by mutations in the MLC1 gene. MRI from MLC patients shows diffuse cerebral white matter signal abnormality and swelling, with evidence of increased water content. Histopathology in a MLC patient shows vacuolation of myelin, which causes the cerebral white matter swelling. MLC1 protein is expressed in astrocytic processes that are part of blood- and cerebrospinal fluid-brain barriers. We aimed to create an astrocyte cell model of MLC disease. The characterization of rat astrocyte cultures revealed MLC1 localization in cell-cell contacts, which contains other proteins described typically in tight and adherent junctions. MLC1 localization in these contacts was demonstrated to depend on the actin cytoskeleton: it was not altered when disrupting the microtubule or the GFAP networks. In human tissues, MLC1 and the protein Zonula Occludens 1 (ZO-1), which is linked to the actin cytoskeleton, co-localized by EM immunostaining and were specifically co-immunoprecipitated. To create an MLC cell model, knockdown of MLC1 in primary astrocytes was performed. Reduction of MLC1 expression resulted in the appearance of intracellular vacuoles. This vacuolation was reversed by the co-expression of human MLC1. Re-examination of a human brain biopsy from an MLC patient revealed that vacuoles were also consistently present in astrocytic processes. Thus, vacuolation of astrocytes is also a hallmark of MLC disease. (C) 2011 Elsevier Inc. All rights reserved.

Vanishing white matter (VWM) disease is a genetic leukoencephalopathy linked to mutations in the eukaryotic translation initiation factor 2B. It is a disease of infants, children, and adults who experience a slowly progressive neurologic deterioration with episodes of rapid clinical worsening triggered by stress and eventually leading to death. Characteristic neuropathologic findings include cystic degeneration of the white matter with scarce reactive gliosis, dysmorphic astrocytes, and paucity of myelin despite an increase in oligodendrocytic density. To assess whether a defective maturation of macroglia may be responsible for the feeble gliosis and lack of myelin, weinvestigated the maturation status of astrocytes and oligodendrocytes in the brains of 8 VWM patients, 4 patients with other white matter disorders and 6 age-matched controls with a combination of immunocytochemistry, histochemistry, scratch-wound assays, Western blot, and quantitative polymerase chain reaction. We observed increased proliferation and a defect in the maturation of VWM astrocytes. They show an anomalous composition of their intermediate filament network with predominance of the δ-isoform of the glial fibrillary acidic protein and an increase in the heat shock protein αB-crystallin, supporting the possibility that a deficiency in astrocyte function may contribute to the loss of white matter in VWM. We also demonstrated a significant increase in numbers of premyelinating oligodendrocyte progenitors in VWM, which may explain the coexistence of oligodendrocytosis and myelin paucity in the patients' white matter. © 2010 by the American Association of Neuropathologists, Inc.

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a rare leukodystrophy caused by mutations in MLC1 or GLIALCAM. The GLIALCAM gene product functions as an MLC1 beta-subunit. We aim to further clarify the molecular mechanisms of MLC caused by mutations in MLC1 or GLIALCAM. For this purpose, we analyzed a human post-mortem brain obtained from an MLC patient, who was homozygous for a missense mutation (S69L) in MLC1. We showed that this mutation affects the stability of MLC1 in vitro and reduces MLC1 protein levels in the brain to almost undetectable. However, the amount of GlialCAM and its localization were nearly unaffected, indicating that MLC1 is not necessary for GlialCAM expression or tar- geting. These findings were supported by experiments in primary astrocytes and in heterologous cells. In addition, we demonstrated that MLC1 and GlialCAM form homo- and hetero-complexes and that MLC-causing mutations in GLIALCAM mainly reduce the formation of GlialCAM homo-complexes, leading to a defect in the trafficking of GlialCAM alone to cell junctions. GLIALCAM mutations also affect the trafficking of its associ- ated molecule MLC1, explaining why GLIALCAM and MLC1 mutations lead to the same disease: MLC. © The Author 2011. Published by Oxford University Press.

Megalencephalic leukoencephalopathy with subcortical cysts is a rare leukodystrophy that is characterized by macrocephaly and a slowly progressive clinical course. It is one of the most commonly reported leukoencephalopathies in Turkey. Mutations in the MLC1 gene are the main cause of the disease. We report two patients with megalencephalic leukoencephalopathy with subcortical cysts with confirmed mutations in the MLC1 gene. The mutation in the second patient was novel. We also review identified mutations in the Turkish population.

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is an autosomal recessive disease characterized by early infantile macrocephaly and delayed motor and cognitive deterioration. Magnetic resonance imaging (MRI) shows diffusely abnormal and swollen cerebral white matter and subcortical cysts. On follow-up, atrophy ensues. Approximately 80% of MLC patients have mutations in MLC1. We report 16 MLC patients without MLC1 mutations. Eight retained the classical clinical and MRI phenotype. The other 8 showed major MRI improvement. They lacked motor decline. Five had normal intelligence; 3 displayed cognitive deficiency. In conclusion, 2 phenotypes can be distinguished among the non-MLC1 mutated MLC patients: a classical and a benign phenotype.

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is an autosomal recessive disease characterized by early infantile macrocephaly and delayed motor and cognitive deterioration. Magnetic resonance imaging (MRI) shows diffusely abnormal and swollen cerebral white matter and subcortical cysts. On follow-up, atrophy ensues. Approximately 80% of MLC patients have mutations in MLC1. We report 16 MLC patients without MLC1 mutations. Eight retained the classical clinical and MRI phenotype. The other 8 showed major MRI improvement. They lacked motor decline. Five had normal intelligence; 3 displayed cognitive deficiency. In conclusion, 2 phenotypes can be distinguished among the non-MLC1 mutated MLC patients: a classical and a benign phenotype.

Mutations in the gene MLC1 are found in approximately 80% of the patients with the inherited childhood white matter disorder megalencephalic leukoencephalopathy with subcortical cysts (MLC). Genetic linkage studies have not led to the identification of another disease gene. We questioned whether mutations in CLCN2, coding for the chloride channel protein 2 (ClC-2), are involved in MLC. Mice lacking this protein develop white matter abnormalities, which are characterized by vacuole formation in the myelin sheaths, strikingly similar to the intramyelinic vacuoles in MLC. Sequence analysis of CLCN2 at genomic DNA and cDNA levels in 18 MLC patients without MLC1 mutations revealed some nucleotide changes, but they were predicted to be nonpathogenic. Further, in electrophysiological experiments, one of the observed amino acid changes was shown to have no effect on the ClC-2-mediated currents. In conclusion, we found no evidence suggesting that the CLCN2 gene is involved in MLC. © 2010, Mary Ann Liebert, Inc.

Objective: Vanishing white matter (VWM) is an autosomal recessive leukoencephalopathy characterized by slowly progressive ataxia and spasticity with additional stress-provoked episodes of rapid and major deterioration. The disease is caused by mutations in the genes encoding the subunits of eukaryotic initiation factor 2B, which is pivotal in translation of mRNAs into proteins. The disease onset, clinical severity, and disease course of VWM vary greatly. The influence of genotype and gender on the phenotype is unclear. Methods: From our database of 184 patients with VWM, we selected those with the following mutations in the gene EIF2B5: p.Arg113His in the homozygous state (n = 23), p.Arg113His in the compound-heterozygous state (n = 49), p.Thr91Ala in the homozygous state (n = 8), p.Arg113His/p.Arg339any (n = 9), and p.Thr91Ala/p.Arg339any (n = 7). We performed a cross-sectional observational study. Evaluated clinical characteristics were gender, age at onset, age at loss of walking without support, and age at death. Means, male/female ratios, and Kaplan-Meier curves were compared. Results: Patients homozygous for p.Arg113His had a milder disease than patients compound heterozygous for p.Arg113His and patients homozygous for p.Thr91Ala. Patients with p.Arg113His/p.Arg339any had a milder phenotype than patients with p.Thr91Ala/p.Arg339any. Overall, females tended to have a milder disease than males. Conclusions: The clinical phenotype in VWM is influenced by the combination of both mutations. Females tend to do better than males. Copyright © 2010 by AAN Enterprises, Inc.

The adenovirus tripartite leader (TPT) 5' untranslated region (5'UTR) allows translation in poliovirus-infected cells, in which the p220 subunit of eukaryotic initiation factor 4F is degraded. This p220-independent translation was investigated by measuring in vitro translation in a reticulocyte lysate of a reporter gene, chloramphenicol acetyltransferase, coupled to the TPT 5'UTR. The p220 subunit was degraded by translation of a foot-and-mouth-disease L-protease construct. Surprisingly, the TPT 5'UTR was dependent on intact p220, as are other naturally capped mRNA species. Translation of encephalomyocarditis virus RNA was p220 independent, as expected from its ability to support internal, cap-independent initiation. In vitro protein-synthesis experiments with purified initiation factors confirmed the dependence of TPT mRNA translation on eukaryotic initiation factor 4F. The relationship between adenovirus TPT-5'UTR-directed translation and poliovirus-induced host cell shut-off is discussed.

Two mechanisms of initiation of protein synthesis are known. The 5' cap-dependent model requires the activity of cap-binding eukaryotic initiation factors (eIF)1-4E and -4F, inducing unwinding of mRNA secondary structures. The internal initiation model is 5' cap-independent and requires a ribosomal entry site formed by higher order structures of the mRNA. It has been proposed that this mechanism does not need eIF-4E and eIF-4F. We prepared bicistronic transcripts on which both mechanisms of initiation occur, allowing the determination of the initiation factor dependence of these two mechanisms simultaneously. The unwinding factors eIF-4A, eIF-4B, and eIF-4F were found to be necessary for 5' cap-dependent initiation as well as for internal initiation. Surprisingly, efficient translation of both cistrons on the bicistronic mRNA required eIF-4E. A model is presented in which assembly of eIF-4E into a functional eIF-4F complex is a prerequisite for both types of initiation.

Vanishing white matter disease is a rare neurological disease. The majority of patients reported are Caucasian individuals. We describe the first Chinese patient with typical clinical and radiological features genetically confirmed to have vanishing white matter disease for a mutation in EIF2B4, followed by a brief review of the disease.

The "ovarioleukodystrophies" comprise a group of rare leukodystrophies associated with primary or premature ovarian failure. Some of the patients have a variant of "vanishing white matter disease" with mutations in subunits of eukaryotic initiation factor 2B (EIF2B). A 32-year-old woman who developed neurological signs related to an extensive leukoencephalopathy on magnetic resonance imaging (MRI) in the context of amenorrhea since the age of 18 years was found to be homozygous for a mutation in the EIF2B5 gene: c.338G>A/p.Arg113His. She had a progressive disease with development of tetraparesia in less than 6 years. Our observation confirms that ovarian failure in the context of a leukodystrophy warrants mutational analysis of the genes encoding the subunits of EIF2B. © 2008 Elsevier B.V. All rights reserved.

A 593 nucleotide fragment of the 5' leader of encephalomyocarditis virus RNA (EMCV-RNA) was linked to the SP6 promoter and inserted upstream of the reporter gene chloramphenicol acetyltransferase (CAT). The presence of the 5'-UTR of EMCV-RNA in the RNA transcripts, made in vitro with the SP6 polymerase, resulted in a strong translational enhancement when tested in the micrococcal nuclease-treated reticulocyte lysate. The transcripts were equally active with or without a 5' methylated capstructure as expected, since EMCV-RNA is one of the mRNAs capable of internal initiation. We searched for a signal in the 5' leader that allows the 43S preinitiation complex to bind internally and localized a hairpin containing a unique nucleotide sequence, CUUUA, present in a domain conserved among cardio- and aphtoviral RNAs. Replacing this sequence into AGCU resulted in a 50% loss of translational activity. A second mutation involving a U-G change in the stem of that hairpin resulted in an almost complete loss of initiation.

Contains fulltext : 52513.pdf (Publisher’s version ) (Closed access) Leukoencephalopathy with brain stem and spinal cord involvement and lactate elevation (LBSL) has recently been defined based on a highly characteristic constellation of abnormalities observed by magnetic resonance imaging and spectroscopy. LBSL is an autosomal recessive disease, most often manifesting in early childhood. Affected individuals develop slowly progressive cerebellar ataxia, spasticity and dorsal column dysfunction, sometimes with a mild cognitive deficit or decline. We performed linkage mapping with microsatellite markers in LBSL families and found a candidate region on chromosome 1, which we narrowed by means of shared haplotypes. Sequencing of genes in this candidate region uncovered mutations in DARS2, which encodes mitochondrial aspartyl-tRNA synthetase, in affected individuals from all 30 families. Enzyme activities of mutant proteins were decreased. We were surprised to find that activities of mitochondrial complexes from fibroblasts and lymphoblasts derived from affected individuals were normal, as determined by different assays.

Leukoencephalopathy with vanishing white matter (VWM) is a childhood white matter disorder with an autosomal-recessive mode of inheritance. The clinical course is chronic progressive with episodes of rapid neurologic deterioration after febrile infections. The disease is caused by mutations in the genes encoding the subunits of eukaryotic initiation factor 2B (eIF2B), a protein complex that is essential for protein synthesis. In VWM, mutations in the eIF2B genes are thought to impair the ability of cells to regulate protein synthesis under normal and stress conditions. It has been suggested that the pathophysiology of VWM involves inappropriate activation of the unfolded protein response (UPR). The UPR is a protective mechanism activated by an overload of unfolded or malfolded proteins in the endoplasmic reticulum. Activation of one pathway of the UPR, in which eIF2B is involved, has already been described in brain tissue of patients with VWM. In the present study, we demonstrate activation of all 3 UPR pathways in VWM brain tissue using real-time quantitative polymerase chain reaction and immunohistochemistry. We show that activation occurs exclusively in the white matter, predominantly in oligodendrocytes and astrocytes. The selective involvement of these cells suggests that inappropriate UPR activation may play a key role in the pathophysiology of VWM.