Mutant GlialCAM causes megalencephalic leukoencephalopathy with subcortical cysts, benign familial macrocephaly, and macrocephaly with retardation and autism

Spontaneously regressing leukoencephalopathy with bilateral temporal cysts in congenital rubella infection

Very little is known regarding neuroimaging findings in patients with congenital rubella syndrome. We report a 1.9-year-old boy with congenital rubella syndrome who presented in the neonatal period with severe multisystem involvement and diffuse leukoencephalopathy with subcortical anterior temporal cysts, which showed spontaneous improvement during a period of 3 years.

Disrupting MLC1 and GlialCAM and ClC-2 interactions in leukodystrophy entails glial chloride channel dysfunction

Defects in the astrocytic membrane protein MLC1, the adhesion molecule GlialCAM or the chloride channel ClC-2 underlie human leukoencephalopathies. Whereas GlialCAM binds ClC-2 and MLC1, and modifies ClC-2 currents in vitro, no functional connections between MLC1 and ClC-2 are known. Here we investigate this by generating loss-of-function Glialcam and Mlc1 mouse models manifesting myelin vacuolization. We find that ClC-2 is unnecessary for MLC1 and GlialCAM localization in brain, whereas GlialCAM is important for targeting MLC1 and ClC-2 to specialized glial domains in vivo and for modifying ClC-2's biophysical properties specifically in oligodendrocytes (OLs), the cells chiefly affected by vacuolization. Unexpectedly, MLC1 is crucial for proper localization of GlialCAM and ClC-2, and for changing ClC-2 currents. Our data unmask an unforeseen functional relationship between MLC1 and ClC-2 in vivo, which is probably mediated by GlialCAM, and suggest that ClC-2 participates in the pathogenesis of megalencephalic leukoencephalopathy with subcortical cysts.

Autism-epilepsy phenotype with macrocephaly suggests PTEN, but not GLIALCAM, genetic screening

BACKGROUND

With a complex and extremely high clinical and genetic heterogeneity, autism spectrum disorders (ASD) are better dissected if one takes into account specific endophenotypes. Comorbidity of ASD with epilepsy (or paroxysmal EEG) has long been described and seems to have strong genetic background. Macrocephaly also represents a well-known endophenotype in subgroups of ASD individuals, which suggests pathogenic mechanisms accelerating brain growth in early development and predisposing to the disorder. We attempted to estimate the association of gene variants with neurodevelopmental disorders in patients with autism-epilepsy phenotype (AEP) and cranial overgrowth, analyzing two genes previously reported to be associated with autism and macrocephaly.

METHODS

We analyzed the coding sequences and exon-intron boundaries of GLIALCAM, encoding an IgG-like cell adhesion protein, in 81 individuals with Autism Spectrum Disorders, either with or without comorbid epilepsy, paroxysmal EEG and/or macrocephaly, and the PTEN gene in the subsample with macrocephaly.

RESULTS

Among 81 individuals with ASD, 31 had concurrent macrocephaly. Head circumference, moreover, was over the 99.7th percentile ("extreme" macrocephaly) in 6/31 (19%) patients. Whilst we detected in GLIALCAM several single nucleotide variants without clear pathogenic effects, we found a novel PTEN heterozygous frameshift mutation in one case with "extreme" macrocephaly, autism, intellectual disability and seizures.

CONCLUSIONS

We did not find a clear association between GLIALCAM mutations and AEP-macrocephaly comorbidity. The identification of a novel frameshift variant of PTEN in a patient with "extreme" macrocephaly, autism, intellectual disability and seizures, confirms this gene as a major candidate in the ASD-macrocephaly endophenotype. The concurrence of epilepsy in the same patient also suggests that PTEN, and the downstream signaling pathway, might deserve to be investigated in autism-epilepsy comorbidity. Working on clinical endophenotypes might be of help to address genetic studies and establish actual causative correlations in autism-epilepsy.

Clinical, neuroimaging, and genetic characteristics of megalencephalic leukoencephalopathy with subcortical cysts in Egyptian patients

BACKGROUND

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a rare and genetically heterogeneous cerebral white matter disease. Clinically, it is characterized by macrocephaly, developmental delay, and seizures. We explore the clinical spectrum, neuroimaging characteristics, and gene involvement in the first patients with megalencephalic leukoencephalopathy with subcortical cysts described from Egypt.

PATIENTS

Six patients were enrolled from three unrelated families. Patient inclusion criteria were macrocephaly, developmental delay, normal urinary organic acids, and brain imaging of diffuse cerebral white matter involvement. Direct sequencing of the MLC1 gene in patients' families and GliaCAM in one questionable case was performed using BigDye Terminator cycle sequencing.

RESULTS

Clinical heterogeneity, both intra- and interfamilial, was clearly evident. Developmental delays ranged from globally severe or moderate to mild delay in achieving walking or speech. Head circumference above the ninety-seventh percentile was a constant feature. Neuroimaging featured variability in white matter involvement and subcortical cysts. However, findings of posterior fossa changes and brain stem atrophy were frequently (66.6%) identified in these Egyptian patients. Discrepancy between severe brain involvement and normal mental functions was evident, particularly in patients from the third family. MLC1 mutations were confirmed in all patients. Deletion/insertion mutation in exon 11 (c.908-918delinsGCA, p.Val303 Gly fsX96) was recurrent in two families, whereas a missense mutation in exon 10 (c.880 C > T, p.Pro294Ser) was identified in the third family.

CONCLUSIONS

This report extends our knowledge of the clinical and neuroimaging features of megalencephalic leukoencephalopathy with subcortical cysts. It confirms the apparent lack of selective disadvantage of MLC1 mutations on gamete conception and transmission as supported by the presence of multiple affected siblings in Egyptian families.

GlialCAM, a glial cell adhesion molecule implicated in neurological disease

GlialCAM (also named HepaCAM) is a cell adhesion molecule expressed mainly in glial cells from the central nervous system and the liver. GlialCAM plays different roles according to its cellular context. In epithelial cell lines, overexpression of GlialCAM increases cell adhesion and motility but also inhibits cell growth in tumor cell lines, leading to senescence. In glial cells, however, its function is quite different. GlialCAM acts a regulator of subcellular traffic of MLC1, a protein with unknown function involved in the pathogenesis of megalencephalic leukoencephalopathy with subcortical cysts (MLC), a rare neurological condition. Moreover, GlialCAM itself has been found to be responsible for some of the cases of this disease. Additionally, GlialCAM also works as an auxiliary subunit of the chloride channel ClC-2, regulating its targeting to cell-cell junctions and modifying its functional properties. In summary, GlialCAM has different functions not only related to its adhesive nature, and defects in these functions lead to neurological disease.

Brain white matter oedema due to ClC-2 chloride channel deficiency: an observational analytical study

BACKGROUND

Mutant mouse models suggest that the chloride channel ClC-2 has functions in ion and water homoeostasis, but this has not been confirmed in human beings. We aimed to define novel disorders characterised by distinct patterns of MRI abnormalities in patients with leukoencephalopathies of unknown origin, and to identify the genes mutated in these disorders. We were specifically interested in leukoencephalopathies characterised by white matter oedema, suggesting a defect in ion and water homoeostasis.

METHODS

In this observational analytical study, we recruited patients with leukoencephalopathies characterised by MRI signal abnormalities in the posterior limbs of the internal capsules, midbrain cerebral peduncles, and middle cerebellar peduncles from our databases of patients with leukoencephalopathies of unknown origin. We used exome sequencing to identify the gene involved. We screened the candidate gene in additional patients by Sanger sequencing and mRNA analysis, and investigated the functional effects of the mutations. We assessed the localisation of ClC-2 with immunohistochemistry and electron microscopy in post-mortem human brains of individuals without neurological disorders.

FINDINGS

Seven patients met our inclusion criteria, three with adult-onset disease and four with childhood-onset disease. We identified homozygous or compound-heterozygous mutations in CLCN2 in three adult and three paediatric patients. We found evidence that the CLCN2 mutations result in loss of function of ClC-2. The remaining paediatric patient had an X-linked family history and a mutation in GJB1, encoding connexin 32. Clinical features were variable and included cerebellar ataxia, spasticity, chorioretinopathy with visual field defects, optic neuropathy, cognitive defects, and headaches. MRI showed restricted diffusion suggesting myelin vacuolation that was confined to the specified white matter structures in adult patients, and more diffusely involved the brain white matter in paediatric patients. We detected ClC-2 in all components of the panglial syncytium, enriched in astrocytic endfeet at the perivascular basal lamina, in the glia limitans, and in ependymal cells.

INTERPRETATION

Our observations substantiate the concept that ClC-2 is involved in brain ion and water homoeostasis. Autosomal-recessive CLCN2 mutations cause a leukoencephalopathy that belongs to an emerging group of disorders affecting brain ion and water homoeostasis and characterised by intramyelinic oedema.

FUNDING

European Leukodystrophies Association, INSERM and Assistance Publique-Hôpitaux de Paris, Dutch Organisation for Scientific Research (ZonMw), E-Rare, Hersenstichting, Optimix Foundation for Scientific Research, Myelin Disorders Bioregistry Project, National Institute of Neurological Disorders and Stroke, and Genetic and Epigenetic Networks in Cognitive Dysfunction (GENCODYS) Project (funded by the European Union Framework Programme 7).

White matter integrity as an intermediate phenotype: exploratory genome-wide association analysis in individuals at high risk of bipolar disorder

White matter integrity, as measured using diffusion tensor imaging (DTI), is reduced in individuals with bipolar disorder (BD), their unaffected relatives and carriers of specific risk-alleles. Fractional anisotropy (FA), an index of white matter integrity, is highly heritable but the genetic architecture of this trait has received little investigation. In this study we performed a genome-wide association study with FA as quantitative phenotype, in unaffected relatives of patients with BD (N=70) and a matched control group (N=80). Amongst our top results were SNPs located in genes involved in cell adhesion, white matter development and neuronal plasticity. Pathway analysis of the top associated polymorphisms and genes confirmed the enrichment of processes relevant to BD and white matter development, including axon guidance, ErbB-signalling neurotrophin signalling, phosphatidylinositol signalling, and cell adhesion. The majority of genes implicated in these pathways were differentially associated with FA in individuals at high familial risk, suggesting interactions with genetic background or environmental factors secondary to familial risk for BD. Although the present findings require independent replication, the results encourage the use of global FA as a quantitative phenotype in future large-scale studies which may help to identify the biological processes underlying reduced FA in BD and other psychiatric disorders.

Advances in the diagnosis of leukoencephalopathies

Introduction : Leukoencephalopathies (LEs) are a diverse group of diseases involving cerebral white matter. Some of the disorders may be infectious or immunologically mediated and, therefore, tend to be more amenable to treatment. Most of these disorders have a genetic basis, for which genetic counseling becomes important as currently very few of them have effective therapies. Areas covered : This review calls attention to the diagnostic dilemmas, highlights the diagnostic tests of choice for separating conditions with similar clinical, laboratory or neuroimaging findings, and describes several LEs that have been newly discovered within the last 20 years. Imaging of LEs has progressed rapidly since the introduction of magnetic resonance imaging (MRI) and spectroscopy (MRS), allowing recognition of new diseases, with and without identifiable corresponding biochemical or genetic defects. The distinguishing MRI and MRS features of LEs are described, as well as the resources available for biochemical, CSF and blood sample testing for diagnosis and differentiation from previously known LEs. Expert opinion : Although there is no treatment at present for many of the LEs, their detection as a cause of intellectual and motor disabilities, and as inherited disorders, makes it necessary to accurately categorize them. This knowledge will then allow further elucidation of the etiology, understanding the biological underpinnings, and eventually progress toward rational therapies.

Macrocephaly as a clinical indicator of genetic subtypes in autism

An association between autism and macrocephaly has been previously described. A subset of cases with extreme macrocephaly (>3 standard deviation [SD], 99.7th percentile) have been correlated to mutations in the gene phosphatase and tensin homolog (PTEN). However, the phenotypic and genetic characterization of the remaining cases remains unclear. We report the phenotypic classification and genetic testing evaluation of a cohort of 33 patients with autism and macrocephaly. Within our cohort, we confirm the association of PTEN mutations and extreme macrocephaly (>3 SD, 99.7th percentile) and identify mutations in 22% of cases, including three novel PTEN mutations. In addition, we define three phenotypic subgroups: (a) those cases associated with somatic overgrowth, (b) those with disproportionate macrocephaly, and (c) those with relative macrocephaly. We have devised a novel way to segregate patients into these subgroups that will aide in the stratification of autism macrocephaly cases. Within these subgroups, we further expand the genetic etiologies for autism cases with macrocephaly by describing two novel suspected pathogenic copy number variants located at 6q23.2 and 10q24.32. These findings demonstrate the phenotypic heterogeneity of autism cases associated with macrocephaly and their genetic etiologies. The clinical yield from PTEN mutation analysis is 22% and 9% from chromosomal microarray (CMA) testing within this cohort. The identification of three distinct phenotypic subgroups within macrocephaly autism patients may allow for the identification of their respective distinct genetic etiologies that to date have remained elusive.

ASTROCYTES: EMERGING STARS IN LEUKODYSTROPHY PATHOGENESIS

Astrocytes are the predominant glial cell population in the central nervous system (CNS). Once considered only passive scaffolding elements, astrocytes are now recognised as cells playing essential roles in CNS development and function. They control extracellular water and ion homeostasis, provide substrates for energy metabolism, and regulate neurogenesis, myelination and synaptic transmission. Due to these multiple activities astrocytes have been implicated in almost all brain pathologies, contributing to various aspects of disease initiation, progression and resolution. Evidence is emerging that astrocyte dysfunction can be the direct cause of neurodegeneration, as shown in Alexander's disease where myelin degeneration is caused by mutations in the gene encoding the astrocyte-specific cytoskeleton protein glial fibrillary acidic protein. Recent studies point to a primary role for astrocytes in the pathogenesis of other genetic leukodystrophies such as megalencephalic leukoencephalopathy with subcortical cysts and vanishing white matter disease. The aim of this review is to summarize current knowledge of the pathophysiological role of astrocytes focusing on their contribution to the development of the above mentioned leukodystrophies and on new perspectives for the treatment of neurological disorders.

Megalencephalic leukoencephalopathy with subcortical cysts: chronic white matter oedema due to a defect in brain ion and water homoeostasis

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is characterised by chronic white matter oedema. The disease has an infantile onset and leads to slow neurological deterioration in most cases, but, surprisingly, some patients recover. The first disease gene, MLC1, identified in 2001, is mutated in 75% of patients. At that time, nothing was known about MLC1 protein function and the pathophysiology of MLC. More recently, HEPACAM (also called GLIALCAM) has been identified as a second disease gene. GlialCAM serves as an escort for MLC1 and the chloride channel CLC2. The defect in MLC1 has been shown to hamper the cell volume regulation of astrocytes. One of the most important consequences involves the potassium siphoning process, which is essential in brain ion and water homoeostasis. An understanding of the mechanisms of white matter oedema in MLC is emerging. Further insight into the specific function of MLC1 is necessary to find treatment targets.

Animal model of autism induced by prenatal exposure to valproate: altered glutamate metabolism in the hippocampus

Autism spectrum disorders (ASD) are characterized by deficits in social interaction, language and communication impairments and repetitive and stereotyped behaviors, with involvement of several areas of the central nervous system (CNS), including hippocampus. Although neurons have been the target of most studies reported in the literature, recently, considerable attention has been centered upon the functionality and plasticity of glial cells, particularly astrocytes. These cells participate in normal brain development and also in neuropathological processes. The present work investigated hippocampi from 15 (P15) and 120 (P120) days old male rats prenatally exposed to valproic acid (VPA) as an animal model of autism. Herein, we analyzed astrocytic parameters such as glutamate transporters and glutamate uptake, glutamine synthetase (GS) activity and glutathione (GSH) content. In the VPA group glutamate uptake was unchanged at P15 and increased 160% at P120; the protein expression of GLAST did not change neither in P15 nor in P120, while GLT1 decreased 40% at P15 and increased 92% at P120; GS activity increased 43% at P15 and decreased 28% at P120; GSH content was unaltered at P15 and had a 27% increase at P120. These data highlight that the astrocytic clearance and destination of glutamate in the synaptic cleft might be altered in autism, pointing out important aspects to be considered from both pathophysiologic and pharmacological approaches in ASD.

Systematic approaches to central nervous system myelin

Rapid signal propagation along vertebrate axons is facilitated by their insulation with myelin, a plasma membrane specialization of glial cells. The recent application of 'omics' approaches to the myelinating cells of the central nervous system, oligodendrocytes, revealed their mRNA signatures, enhanced our understanding of how myelination is regulated, and established that the protein composition of myelin is much more complex than previously thought. This review provides a meta-analysis of the > 1,200 proteins thus far identified by mass spectrometry in biochemically purified central nervous system myelin. Contaminating proteins are surprisingly infrequent according to bioinformatic prediction of subcellular localization and comparison with the transcriptional profile of oligodendrocytes. The integration of datasets also allowed the subcategorization of the myelin proteome into functional groups comprising genes that are coregulated during oligodendroglial differentiation. An unexpectedly large number of myelin-related genes cause-when mutated in humans-hereditary diseases affecting the physiology of the white matter. Systematic approaches to oligodendrocytes and myelin thus provide valuable resources for the molecular dissection of developmental myelination, glia-axonal interactions, leukodystrophies, and demyelinating diseases.

Advances in the diagnosis of leukodystrophies

Leukodystrophies are a heterogeneous group of inherited disorders that preferentially affect the CNS white matter. They are classified as demyelinating (or classic) or hypomyelinating according to brain MRI characteristics. As these disorders often have a similar clinical presentation according to their age of onset, the initial diagnostic approach is often challenging. This review aims to help clinicians approach these disorders using information from the history (e.g., age of onset), the examination (e.g., presence of macrocrania) and MRI scans in order to reduce the number of possible diagnoses for a given patient and to hopefully lead to a precise (molecular) diagnosis.

Brain connexins in demyelinating diseases: therapeutic potential of glial targets

Several demyelinating syndromes have been linked to mutations in glial gap junction proteins, the connexins. Although mutations in connexins of the myelinating cells, Schwann cells and oligodendrocytes, were initially described, recent data have shown that astrocytes also play a major role in the demyelination process. Alterations in astrocytic proteins directly affect the oligodendrocytes' ability to maintain myelin structure, and associated astrocytic proteins that regulate water and ionic fluxes, including aquaporins, can also regulate myelin integrity. Here, we will review the main evidence from human disorders and transgenic mouse models that implicate glial gap junction proteins in demyelinating diseases and the therapeutic potential of some of these targets. This article is part of a Special Issue entitled Electrical Synapses.

Megalencephalic leukoencephalopathy with subcortical cysts type 1 (MLC1) due to a homozygous deep intronic splicing mutation (c.895-226T>G) abrogated in vitro using an antisense morpholino oligonucleotide

Megalencephalic leukoencephalopathy with subcortical cysts is an autosomal recessive disease characterized by early onset macrocephaly; developmental delay; motor disability in the form of progressive spasticity and ataxia; seizures; cognitive decline; and characteristic magnetic resonance imaging findings. Mutations in two genes, MLC1 (22q13.33; 75 % of patients) or HEPACAM (11q24; 20 % of patients), are associated with the disease. We describe an adult MLC patient with moderate clinical symptoms. MLC1 cDNA analysis from lymphoblasts showed a strong transcript reduction and identified a 246-bp pseudoexon containing a premature stop codon between exons 10 and 11, due to a homozygous c.895-226 T>G deep-intronic mutation. This category of mutations is often overlooked, being outside of canonically sequenced genomic regions. The mutation c.895-226 T>G has a leaky effect on splicing leaving part of the full-length transcript. Its role on splicing was confirmed using a minigene assay and an antisense morpholinated oligonucleotide targeted to the aberrant splice site in vitro, which partially abrogated the mutation effect.

GlialCAM, a protein defective in a leukodystrophy, serves as a ClC-2 Cl(-) channel auxiliary subunit

Ion fluxes mediated by glial cells are required for several physiological processes such as fluid homeostasis or the maintenance of low extracellular potassium during high neuronal activity. In mice, the disruption of the Cl⁻ channel ClC-2 causes fluid accumulation leading to myelin vacuolation. A similar vacuolation phenotype is detected in humans affected with megalencephalic leukoencephalopathy with subcortical cysts (MLC), a leukodystrophy which is caused by mutations in MLC1 or GLIALCAM. We here identify GlialCAM as a ClC-2 binding partner. GlialCAM and ClC-2 colocalize in Bergmann glia, in astrocyte-astrocyte junctions at astrocytic endfeet around blood vessels, and in myelinated fiber tracts. GlialCAM targets ClC-2 to cell junctions, increases ClC-2 mediated currents, and changes its functional properties. Disease-causing GLIALCAM mutations abolish the targeting of the channel to cell junctions. This work describes the first auxiliary subunit of ClC-2 and suggests that ClC-2 may play a role in the pathology of MLC disease.

Video Abstract

A developmental and genetic classification for malformations of cortical development: update 2012

Malformations of cerebral cortical development include a wide range of developmental disorders that are common causes of neurodevelopmental delay and epilepsy. In addition, study of these disorders contributes greatly to the understanding of normal brain development and its perturbations. The rapid recent evolution of molecular biology, genetics and imaging has resulted in an explosive increase in our knowledge of cerebral cortex development and in the number and types of malformations of cortical development that have been reported. These advances continue to modify our perception of these malformations. This review addresses recent changes in our perception of these disorders and proposes a modified classification based upon updates in our knowledge of cerebral cortical development.

Functional studies of MLC1 mutations in Chinese patients with megalencephalic leukoencephalopathy with subcortical cysts

Megalencephalic leukoencephalopathy with subcortical cysts (MLC, MIM# 604004) is an autosomal recessive inherited disease mostly resulting from MLC1 mutations. In this study, we finished the functional analysis of MLC1 mutations identified recently in Chinese patients, including five newly described missense mutations (R22Q, A32V, G73E, A275T, Y278H), one known nonsense mutation (Y198X), and two known missense mutations (S69L, T118M). We found MLC1^wt was localized to the cell periphery, whereas mutant R22Q, A32V, G73E, S69L and T118M were trapped in the lumen of endoplasmic reticulum (ER) when we transfected the wild-type and mutant MLC1 in U373MG cells. Compared to wild type, the mutant G73E, T118M, Y198X and A275T transcript decreased and all mutants except R22Q had lower protein expression in transfected U373MG cells. Therefore, we propose that all these eight MLC1 mutations had functional effect either on their protein/mRNA expression, or on their intracellular protein localization, or both.

Megalencephalic leukoencephalopathy with subcortical cysts protein 1 functionally cooperates with the TRPV4 cation channel to activate the response of astrocytes to osmotic stress: dysregulation by pathological mutations

Megalencephalic leukoencephalopathy with subcortical cysts (MLC), a rare leukodystrophy characterized by macrocephaly, subcortical fluid cysts and myelin vacuolation, has been linked to mutations in the MLC1 gene. This gene encodes a membrane protein that is highly expressed in astrocytes. Based on MLC pathological features, it was proposed that astrocyte-mediated defects in ion and fluid homeostasis could account for the alterations observed in MLC-affected brains. However, the role of MLC1 and the effects of pathological mutations on astrocyte osmoregulatory functions have still to be demonstrated. Using human astrocytoma cells stably overexpressing wild-type MLC1 or three known MLC-associated pathological mutations, we investigated MLC1 involvement in astrocyte reaction to osmotic changes using biochemical, dynamic video imaging and immunofluorescence techniques. We have found that MLC1 overexpressed in astrocytoma cells is mainly localized in the plasma membrane, is part of the Na,K-ATPase-associated molecular complex that includes the potassium channel Kir4.1, syntrophin and aquaporin-4 and functionally interacts with the calcium permeable channel TRPV4 (transient receptor potential vanilloid-4 cation channel) which mediates swelling-induced cytosolic calcium increase and volume recovery in response to hyposmosis. Pathological MLC mutations cause changes in MLC1 expression and intracellular localization as well as in the astrocyte response to osmotic changes by altering MLC1 molecular interactions with the Na,K-ATPase molecular complex and abolishing the increase in calcium influx induced by hyposmosis and treatment with the TRPV4 agonist 4αPDD. These data demonstrate, for the first time, that MLC1 plays a role in astrocyte osmo-homeostasis and that defects in intracellular calcium dynamics may contribute to MLC pathogenesis.

A modification of the split-tobacco etch virus method for monitoring interactions between membrane proteins in mammalian cells

Despite progress in the development of methods to monitor protein interactions, studies of interactions between membrane proteins in mammalian cells remain challenging. Protein complementation assays (PCAs) are commonly used to study interactions between proteins due to their simplicity. They are based on interaction-mediated reconstitution of a reporter protein, which can be easily monitored. Recently, a protein complementation method named split-TEV (tobacco etch virus) has been developed and is based on the functional reconstitution of TEV protease and subsequent proteolytic-mediated activation of reporters. In this work, we have developed a modification of the split-TEV method to study the interactions between membrane proteins with increased specificity. This assay was validated by addressing the interactions between different membrane proteins, including G protein-coupled receptors (GPCRs) and ion channels. By comparing it with another PCA, we found that this new method showed a higher sensitivity.