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The endosymbiosis of mitochondrial ancestors resulted in the transfer of genetic material on an evolutionary scale for eukaryotic species. A new study in PLOS Biology expands this to the genome of somatic cells within individuals and highlights its correlation with aging and disease.
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Mitocondrias , Simbiosis , Simbiosis/genética , Mitocondrias/genética , Mitocondrias/metabolismo , Humanos , Animales , Envejecimiento/genética , Envejecimiento/fisiología , Genómica/métodos , Genoma/genética , Genoma MitocondrialRESUMEN
Debate remains around the anatomical origins of specific brain cell subtypes and lineage relationships within the human forebrain1-7. Thus, direct observation in the mature human brain is critical for a complete understanding of its structural organization and cellular origins. Here we utilize brain mosaic variation within specific cell types as distinct indicators for clonal dynamics, denoted as cell-type-specific mosaic variant barcode analysis. From four hemispheres and two different human neurotypical donors, we identified 287 and 780 mosaic variants, respectively, that were used to deconvolve clonal dynamics. Clonal spread and allele fractions within the brain reveal that local hippocampal excitatory neurons are more lineage-restricted than resident neocortical excitatory neurons or resident basal ganglia GABAergic inhibitory neurons. Furthermore, simultaneous genome transcriptome analysis at both a cell-type-specific and a single-cell level suggests a dorsal neocortical origin for a subgroup of DLX1+ inhibitory neurons that disperse radially from an origin shared with excitatory neurons. Finally, the distribution of mosaic variants across 17 locations within one parietal lobe reveals that restriction of clonal spread in the anterior-posterior axis precedes restriction in the dorsal-ventral axis for both excitatory and inhibitory neurons. Thus, cell-type-resolved somatic mosaicism can uncover lineage relationships governing the development of the human forebrain.
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Linaje de la Célula , Células Clonales , Mosaicismo , Neuronas , Prosencéfalo , Anciano , Femenino , Humanos , Alelos , Linaje de la Célula/genética , Células Clonales/citología , Células Clonales/metabolismo , Neuronas GABAérgicas/citología , Neuronas GABAérgicas/metabolismo , Hipocampo/citología , Proteínas de Homeodominio/metabolismo , Neocórtex/citología , Inhibición Neural , Neuronas/citología , Neuronas/metabolismo , Lóbulo Parietal/citología , Prosencéfalo/anatomía & histología , Prosencéfalo/citología , Prosencéfalo/metabolismo , Análisis de la Célula Individual , Transcriptoma/genéticaRESUMEN
Debate remains around anatomic origins of specific brain cell subtypes and lineage relationships within the human forebrain. Thus, direct observation in the mature human brain is critical for a complete understanding of the structural organization and cellular origins. Here, we utilize brain mosaic variation within specific cell types as distinct indicators for clonal dynamics, denoted as cell-type-specific Mosaic Variant Barcode Analysis. From four hemispheres from two different human neurotypical donors, we identified 287 and 780 mosaic variants (MVs), respectively that were used to deconvolve clonal dynamics. Clonal spread and allelic fractions within the brain reveal that local hippocampal excitatory neurons are more lineage-restricted compared with resident neocortical excitatory neurons or resident basal ganglia GABAergic inhibitory neurons. Furthermore, simultaneous genome-transcriptome analysis at both a cell-type-specific and single-cell level suggests a dorsal neocortical origin for a subgroup of DLX1+ inhibitory neurons that disperse radially from an origin shared with excitatory neurons. Finally, the distribution of MVs across 17 locations within one parietal lobe reveals restrictions of clonal spread in the anterior-posterior axis precedes that of the dorsal-ventral axis for both excitatory and inhibitory neurons. Thus cell-type resolved somatic mosaicism can uncover lineage relationships governing the development of the human forebrain.
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Genomic mosaicism describes the phenomenon where some but not all cells within a tissue harbor unique genetic mutations. Traditionally, research focused on the impact of genomic mosaicism on clinical phenotype-motivated by its involvement in cancers and overgrowth syndromes. More recently, we increasingly shifted towards the plethora of neutral mosaic variants that can act as recorders of cellular lineage and environmental exposures. Here, we summarize the current state of the field of genomic mosaicism research with a special emphasis on our current understanding of this phenomenon in brain development and homeostasis. Although the field of genomic mosaicism has a rich history, technological advances in the last decade have changed our approaches and greatly improved our knowledge. We will provide current definitions and an overview of contemporary detection approaches for genomic mosaicism. Finally, we will discuss the impact and utility of genomic mosaicism.
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Mosaic variants (MVs) reflect mutagenic processes during embryonic development and environmental exposure, accumulate with aging and underlie diseases such as cancer and autism. The detection of noncancer MVs has been computationally challenging due to the sparse representation of nonclonally expanded MVs. Here we present DeepMosaic, combining an image-based visualization module for single nucleotide MVs and a convolutional neural network-based classification module for control-independent MV detection. DeepMosaic was trained on 180,000 simulated or experimentally assessed MVs, and was benchmarked on 619,740 simulated MVs and 530 independent biologically tested MVs from 16 genomes and 181 exomes. DeepMosaic achieved higher accuracy compared with existing methods on biological data, with a sensitivity of 0.78, specificity of 0.83 and positive predictive value of 0.96 on noncancer whole-genome sequencing data, as well as doubling the validation rate over previous best-practice methods on noncancer whole-exome sequencing data (0.43 versus 0.18). DeepMosaic represents an accurate MV classifier for noncancer samples that can be implemented as an alternative or complement to existing methods.
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Exoma , Programas Informáticos , Secuenciación Completa del Genoma/métodos , Secuenciación del Exoma , Secuenciación de Nucleótidos de Alto Rendimiento/métodos , Polimorfismo de Nucleótido Simple/genética , NucleótidosRESUMEN
Malformations of cortical development (MCD) are neurological conditions involving focal disruptions of cortical architecture and cellular organization that arise during embryogenesis, largely from somatic mosaic mutations, and cause intractable epilepsy. Identifying the genetic causes of MCD has been a challenge, as mutations remain at low allelic fractions in brain tissue resected to treat condition-related epilepsy. Here we report a genetic landscape from 283 brain resections, identifying 69 mutated genes through intensive profiling of somatic mutations, combining whole-exome and targeted-amplicon sequencing with functional validation including in utero electroporation of mice and single-nucleus RNA sequencing. Genotype-phenotype correlation analysis elucidated specific MCD gene sets associated with distinct pathophysiological and clinical phenotypes. The unique single-cell level spatiotemporal expression patterns of mutated genes in control and patient brains indicate critical roles in excitatory neurogenic pools during brain development and in promoting neuronal hyperexcitability after birth.
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Epilepsia , Malformaciones del Desarrollo Cortical , Humanos , Multiómica , Encéfalo/metabolismo , Epilepsia/genética , Mutación , Malformaciones del Desarrollo Cortical/genética , Malformaciones del Desarrollo Cortical/metabolismoRESUMEN
Background: De novo mutations underlie individually rare but collectively common pediatric congenital disorders. Some of these mutations can also be detected in tissues and from cells in a parent, where their abundance and tissue distribution can be measured. We previously reported that a subset of these mutations is detectable in sperm from the father, predicted to impact the health of offspring. Methods: As a cohort study, in three independent couples undergoing in vitro fertilization, we first identified male gonadal mosaicism through deep whole genome sequencing. We then confirmed variants and assessed their transmission to preimplantation blastocysts (32 total) through targeted ultra-deep genotyping. Results: Across 55 gonadal mosaic variants, 15 were transmitted to blastocysts for a total of 19 transmission events. This represented an overall predictable but slight undertransmission based upon the measured mutational abundance in sperm. We replicated this conclusion in an independent, previously published family-based cohort. Conclusions: Unbiased preimplantation genetic testing for gonadal mosaicism may represent a feasible approach to reduce the transmission of potentially harmful de novo mutations. This-in turn-could help to reduce their impact on miscarriages and pediatric disease. Funding: No external funding was received for this work.
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Mosaicismo , Semen , Niño , Estudios de Cohortes , Humanos , Masculino , Programas Informáticos , EspermatozoidesRESUMEN
The structure of the human neocortex underlies species-specific traits and reflects intricate developmental programs. Here we sought to reconstruct processes that occur during early development by sampling adult human tissues. We analysed neocortical clones in a post-mortem human brain through a comprehensive assessment of brain somatic mosaicism, acting as neutral lineage recorders1,2. We combined the sampling of 25 distinct anatomic locations with deep whole-genome sequencing in a neurotypical deceased individual and confirmed results with 5 samples collected from each of three additional donors. We identified 259 bona fide mosaic variants from the index case, then deconvolved distinct geographical, cell-type and clade organizations across the brain and other organs. We found that clones derived after the accumulation of 90-200 progenitors in the cerebral cortex tended to respect the midline axis, well before the anterior-posterior or ventral-dorsal axes, representing a secondary hierarchy following the overall patterning of forebrain and hindbrain domains. Clones across neocortically derived cells were consistent with a dual origin from both dorsal and ventral cellular populations, similar to rodents, whereas the microglia lineage appeared distinct from other resident brain cells. Our data provide a comprehensive analysis of brain somatic mosaicism across the neocortex and demonstrate cellular origins and progenitor distribution patterns within the human brain.
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Células Clonales , Mosaicismo , Neocórtex , Linaje de la Célula , Células Cultivadas , Humanos , Microglía , Neocórtex/citología , Neocórtex/crecimiento & desarrolloRESUMEN
Throughout development and aging, human cells accumulate mutations resulting in genomic mosaicism and genetic diversity at the cellular level. Mosaic mutations present in the gonads can affect both the individual and the offspring and subsequent generations. Here, we explore patterns and temporal stability of clonal mosaic mutations in male gonads by sequencing ejaculated sperm. Through 300× whole-genome sequencing of blood and sperm from healthy men, we find each ejaculate carries on average 33.3 ± 12.1 (mean ± SD) clonal mosaic variants, nearly all of which are detected in serial sampling, with the majority absent from sampled somal tissues. Their temporal stability and mutational signature suggest origins during embryonic development from a largely immutable stem cell niche. Clonal mosaicism likely contributes a transmissible, predicted pathogenic exonic variant for 1 in 15 men, representing a life-long threat of transmission for these individuals and a significant burden on human population health.
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Crecimiento y Desarrollo , Mosaicismo , Espermatozoides/metabolismo , Adolescente , Envejecimiento/sangre , Alelos , Células Clonales , Estudios de Cohortes , Humanos , Masculino , Modelos Biológicos , Mutación/genética , Factores de Riesgo , Factores de Tiempo , Adulto JovenRESUMEN
While sperm mosaicism has few consequences for men, the offspring and future generations are unwitting recipients of gonadal cell mutations, often yielding severe disease. Recent studies, fueled by emergent technologies, show that sperm mosaicism is a common source of de novo mutations (DNMs) that underlie severe pediatric disease as well as human genetic diversity. Sperm mosaicism can be divided into three types: Type I arises during sperm meiosis and is non-age dependent; Type II arises in spermatogonia and increases as men age; and Type III arises during paternal embryogenesis, spreads throughout the body, and contributes stably to sperm throughout life. Where Types I and II confer little risk of recurrence, Type III may confer identifiable risk to future offspring. These mutations are likely to be the single largest contributor to human genetic diversity. New sequencing approaches may leverage this framework to evaluate and reduce disease risk for future generations.
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Enfermedad/genética , Genómica , Mosaicismo , Mutación , Espermatozoides/metabolismo , Humanos , Masculino , Espermatogonias/metabolismoRESUMEN
HEAT repeats are 37-47 amino acid flexible tandem repeat structural motifs occurring in a wide variety of eukaryotic proteins with diverse functions. Due to their ability to undergo elastic conformational changes, they often serve as scaffolds at sites of protein interactions. Here, we describe four affected children from two families presenting with pontocerebellar hypoplasia manifest clinically with neonatal seizures, severe intellectual disability, and motor delay. Whole exome sequencing identified biallelic variants at predicted splice sites in intron 31 of HEATR5B, encoding the HEAT repeat-containing protein 5B segregating in a recessive fashion. Aberrant splicing was found in patient fibroblasts, which correlated with reduced levels of HEATR5B protein. HEATR5B is expressed during brain development in human, and we failed to recover live-born homozygous Heatr5b knockout mice. Taken together, our results implicate loss of HEATR5B in pontocerebellar hypoplasia.
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Enfermedades Cerebelosas/genética , Discapacidades del Desarrollo/genética , Proteínas de Transporte Vesicular/genética , Animales , Encéfalo/metabolismo , Encéfalo/patología , Células Cultivadas , Enfermedades Cerebelosas/metabolismo , Enfermedades Cerebelosas/patología , Niño , Discapacidades del Desarrollo/metabolismo , Discapacidades del Desarrollo/patología , Femenino , Fibroblastos/metabolismo , Homocigoto , Humanos , Masculino , Ratones , Ratones Endogámicos C57BL , Mutación , SíndromeRESUMEN
Trafficking protein particle (TRAPP) complexes, which include the TRAPPC4 protein, regulate membrane trafficking between lipid organelles in a process termed vesicular tethering. TRAPPC4 was recently implicated in a recessive neurodevelopmental condition in four unrelated families due to a shared c.454+3A>G splice variant. Here, we report 23 patients from 17 independent families with an early-infantile-onset neurodegenerative presentation, where we also identified the homozygous variant hg38:11:119020256 A>G (NM_016146.5:c.454+3A>G) in TRAPPC4 through exome or genome sequencing. No other clinically relevant TRAPPC4 variants were identified among any of over 10,000 patients with neurodevelopmental conditions. We found the carrier frequency of TRAPPC4 c.454+3A>G was 2.4-5.4 per 10,000 healthy individuals. Affected individuals with the homozygous TRAPPC4 c.454+3A>G variant showed profound psychomotor delay, developmental regression, early-onset epilepsy, microcephaly and progressive spastic tetraplegia. Based upon RNA sequencing, the variant resulted in partial exon 3 skipping and generation of an aberrant transcript owing to use of a downstream cryptic splice donor site, predicting a premature stop codon and nonsense mediated decay. These data confirm the pathogenicity of the TRAPPC4 c.454+3A>G variant, and refine the clinical presentation of TRAPPC4-related encephalopathy.
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Homocigoto , Proteínas del Tejido Nervioso/genética , Trastornos del Neurodesarrollo/genética , Empalme del ARN , Proteínas de Transporte Vesicular/genética , Niño , Preescolar , Codón sin Sentido , Exoma , Exones , Femenino , Humanos , Masculino , Microcefalia/genética , Trastornos del Neurodesarrollo/diagnóstico por imagen , Linaje , Sitios de Empalme de ARN , SíndromeRESUMEN
Autosomal-recessive cerebellar hypoplasia and ataxia constitute a group of heterogeneous brain disorders caused by disruption of several fundamental cellular processes. Here, we identified 10 families showing a neurodegenerative condition involving pontocerebellar hypoplasia with microcephaly (PCHM). Patients harbored biallelic mutations in genes encoding the spliceosome components Peptidyl-Prolyl Isomerase Like-1 (PPIL1) or Pre-RNA Processing-17 (PRP17). Mouse knockouts of either gene were lethal in early embryogenesis, whereas PPIL1 patient mutation knockin mice showed neuron-specific apoptosis. Loss of either protein affected splicing integrity, predominantly affecting short and high GC-content introns and genes involved in brain disorders. PPIL1 and PRP17 form an active isomerase-substrate interaction, but we found that isomerase activity is not critical for function. Thus, we establish disrupted splicing integrity and "major spliceosome-opathies" as a new mechanism underlying PCHM and neurodegeneration and uncover a non-enzymatic function of a spliceosomal proline isomerase.
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Proteínas de Ciclo Celular/genética , Enfermedades Cerebelosas/genética , Microcefalia/genética , Mutación/genética , Isomerasa de Peptidilprolil/genética , Factores de Empalme de ARN/genética , Empalmosomas/genética , Secuencia de Aminoácidos , Animales , Proteínas de Ciclo Celular/química , Enfermedades Cerebelosas/complicaciones , Enfermedades Cerebelosas/diagnóstico por imagen , Estudios de Cohortes , Femenino , Técnicas de Inactivación de Genes/métodos , Células HEK293 , Trastornos Heredodegenerativos del Sistema Nervioso/complicaciones , Trastornos Heredodegenerativos del Sistema Nervioso/diagnóstico por imagen , Trastornos Heredodegenerativos del Sistema Nervioso/genética , Humanos , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Microcefalia/complicaciones , Microcefalia/diagnóstico por imagen , Linaje , Isomerasa de Peptidilprolil/química , Estructura Secundaria de Proteína , Estructura Terciaria de Proteína , Factores de Empalme de ARN/químicaRESUMEN
ABC membrane transporters are a large and complex superfamily of ATP-binding cassette transporters that are present in all domains of life. Both their essential function and complexity are reflected by their retention across large expanses of organismal diversity and by the extensive expansion of individual members and subfamilies during evolutionary history. This expansion has resulted in the diverse ABCA transporter family that has in turn evolved into multiple subfamilies. Here, we focus on the ABCA6-like subfamily of ABCA transporters with the goal of understanding their evolutionary history including potential functional changes in, or loss of, individual members. Our analysis finds that ABCA6-like genes, consisting of ABCA6, 8, 9, and 10, are absent from representatives of both monotremes and marsupials and thus the duplications that generated these families most likely occurred at the base of the Eutherian or placental mammals. We have found evidence of both positive and relaxed selection among the ABCA6-like genes, suggesting dynamic changes in function and the potential of gene redundancy. Analysis of the ABCA10 genes further suggests that this gene has undergone relaxed selection only within the human lineage. These findings are complemented by human population data, where we observe an excess of deactivating homozygous mutations. We describe the complex evolutionary history of this ABCA transporter subfamily and demonstrate through the combination of evolutionary and population genetic analysis that ABCA10 is undergoing pseudogenization within humans.
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Transportadoras de Casetes de Unión a ATP/genética , Evolución Molecular , Mamíferos/genética , Selección Genética , Animales , Duplicación de Gen , Expresión Génica , Variación Genética , Humanos , Familia de Multigenes , FilogeniaRESUMEN
OBJECTIVES: Recently, defects in the protein kinase mTOR (mammalian target of rapamycin) and its associated pathway have been correlated with hemimegalencephaly (HME). mTOR acts as a central regulator of important physiological cellular functions such as growth and proliferation, metabolism, autophagy, death, and survival. This study was aimed at identifying specific variants in mTOR signaling pathway genes in patients diagnosed with HME. METHODS: Using amplicon and whole exome sequencing (WES) of resected brain and paired blood samples from five HME patients, we were able to identify pathogenic mosaic variants in the mTOR pathway genes MTOR, PIK3CA, and DEPDC5. RESULTS: These results strengthen the hypothesis that somatic variants in PI3K-Akt-mTOR pathway genes contribute to HME. We also describe one patient presenting with a pathogenic variant on DEPDC5 gene, which reinforces the role of DEPDC5 on cortical structural changes due to mTORC1 hyperactivation. These findings also provide insights into when in brain development these variants occurred. An early developmental variant is expected to affect a larger number of cells and to result in a larger malformation, whereas the same variant occurring later in development would cause a minor malformation. SIGNIFICANCE: In the future, numerous somatic variants in known or new genes will undoubtedly be revealed in resected brain samples, making it possible to draw correlations between genotypes and phenotypes and allow for a genetic clinical diagnosis that may help to predict a given patient's outcome.
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De novo mutations arising on the paternal chromosome make the largest known contribution to autism risk, and correlate with paternal age at the time of conception. The recurrence risk for autism spectrum disorders is substantial, leading many families to decline future pregnancies, but the potential impact of assessing parental gonadal mosaicism has not been considered. We measured sperm mosaicism using deep-whole-genome sequencing, for variants both present in an offspring and evident only in father's sperm, and identified single-nucleotide, structural and short tandem-repeat variants. We found that mosaicism quantification can stratify autism spectrum disorders recurrence risk due to de novo mutations into a vast majority with near 0% recurrence and a small fraction with a substantially higher and quantifiable risk, and we identify novel mosaic variants at risk for transmission to a future offspring. This suggests, therefore, that genetic counseling would benefit from the addition of sperm mosaicism assessment.
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Trastorno Autístico/genética , Predisposición Genética a la Enfermedad , Mosaicismo , Espermatozoides/metabolismo , Trastorno Autístico/sangre , Femenino , Humanos , Masculino , Mutación/genética , Linaje , Polimorfismo de Nucleótido Simple/genética , Recurrencia , Factores de RiesgoRESUMEN
BACKGROUND: Protein disulfide isomerase (PDI) proteins are part of the thioredoxin protein superfamily. PDIs are involved in the formation and rearrangement of disulfide bonds between cysteine residues during protein folding in the endoplasmic reticulum and are implicated in stress response pathways. METHODS: Eight children from four consanguineous families residing in distinct geographies within the Middle East and Central Asia were recruited for study. All probands showed structurally similar microcephaly with lissencephaly (microlissencephaly) brain malformations. DNA samples from each family underwent whole exome sequencing, assessment for repeat expansions and confirmatory segregation analysis. RESULTS: An identical homozygous variant in TMX2 (c.500G>A), encoding thioredoxin-related transmembrane protein 2, segregated with disease in all four families. This variant changed the last coding base of exon 6, and impacted mRNA stability. All patients presented with microlissencephaly, global developmental delay, intellectual disability and epilepsy. While TMX2 is an activator of cellular C9ORF72 repeat expansion toxicity, patients showed no evidence of C9ORF72 repeat expansions. CONCLUSION: The TMX2 c.500G>A allele associates with recessive microlissencephaly, and patients show no evidence of C9ORF72 expansions. TMX2 is the first PDI implicated in a recessive disease, suggesting a protein isomerisation defect in microlissencephaly.
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Predisposición Genética a la Enfermedad , Proteínas de la Membrana/genética , Microcefalia/genética , Proteína Disulfuro Isomerasas/genética , Tiorredoxinas/genética , Secuencia de Aminoácidos/genética , Niño , Preescolar , Consanguinidad , Retículo Endoplásmico/genética , Exones/genética , Femenino , Homocigoto , Humanos , Masculino , Proteínas de la Membrana/ultraestructura , Microcefalia/patología , Mutación/genética , Pliegue de Proteína , Tiorredoxinas/ultraestructura , Secuenciación del ExomaRESUMEN
Corpus callosum malformations are associated with a broad range of neurodevelopmental diseases. We report that de novo mutations in MAST1 cause mega-corpus-callosum syndrome with cerebellar hypoplasia and cortical malformations (MCC-CH-CM) in the absence of megalencephaly. We show that MAST1 is a microtubule-associated protein that is predominantly expressed in post-mitotic neurons and is present in both dendritic and axonal compartments. We further show that Mast1 null animals are phenotypically normal, whereas the deletion of a single amino acid (L278del) recapitulates the distinct neurological phenotype observed in patients. In animals harboring Mast1 microdeletions, we find that the PI3K/AKT3/mTOR pathway is unperturbed, whereas Mast2 and Mast3 levels are diminished, indicative of a dominant-negative mode of action. Finally, we report that de novo MAST1 substitutions are present in patients with autism and microcephaly, raising the prospect that mutations in this gene give rise to a spectrum of neurodevelopmental diseases.
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Agenesia del Cuerpo Calloso/genética , Cerebelo/anomalías , Regulación del Desarrollo de la Expresión Génica/genética , Malformaciones del Desarrollo Cortical/genética , Proteínas Asociadas a Microtúbulos/genética , Mutación/genética , Malformaciones del Sistema Nervioso/genética , Agenesia del Cuerpo Calloso/complicaciones , Agenesia del Cuerpo Calloso/diagnóstico por imagen , Agenesia del Cuerpo Calloso/patología , Animales , Animales Recién Nacidos , Apoptosis/genética , Encéfalo/metabolismo , Encéfalo/patología , Células Cultivadas , Cerebelo/diagnóstico por imagen , Niño , Discapacidades del Desarrollo/complicaciones , Discapacidades del Desarrollo/diagnóstico por imagen , Discapacidades del Desarrollo/genética , Modelos Animales de Enfermedad , Embrión de Mamíferos , Femenino , Humanos , Masculino , Malformaciones del Desarrollo Cortical/complicaciones , Malformaciones del Desarrollo Cortical/diagnóstico por imagen , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Proteínas Asociadas a Microtúbulos/deficiencia , Proteínas del Tejido Nervioso/metabolismo , Malformaciones del Sistema Nervioso/complicaciones , Malformaciones del Sistema Nervioso/diagnóstico por imagen , Factor de Transcripción PAX6/metabolismoRESUMEN
The dynamic shape of the endoplasmic reticulum (ER) is a reflection of its wide variety of critical cell biological functions. Consequently, perturbation of ER-shaping proteins can cause a range of human phenotypes. Here, we describe three affected children (from two consanguineous families) who carry homozygous loss-of-function mutations in LNPK (previously known as KIAA1715); this gene encodes lunapark, which is proposed to serve as a curvature-stabilizing protein within tubular three-way junctions of the ER. All individuals presented with severe psychomotor delay, intellectual disability, hypotonia, epilepsy, and corpus callosum hypoplasia, and two of three showed mild cerebellar hypoplasia and atrophy. Consistent with a proposed role in neurodevelopmental disease, LNPK was expressed during brain development in humans and mice and was present in neurite-like processes in differentiating human neural progenitor cells. Affected cells showed the absence of full-length lunapark, aberrant ER structures, and increased luminal mass density. Together, our results implicate the ER junction stabilizer lunapark in establishing the corpus callosum.
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Retículo Endoplásmico/genética , Proteínas de Homeodominio/genética , Mutación/genética , Adolescente , Animales , Atrofia/genética , Diferenciación Celular/genética , Niño , Cuerpo Calloso/patología , Femenino , Humanos , Lactante , Discapacidad Intelectual/genética , Masculino , Proteínas de la Membrana , Ratones , Hipotonía Muscular/genética , Fenotipo , Trastornos Psicomotores/genética , Células Madre/patologíaRESUMEN
Neuronal migration defects, including pachygyria, are among the most severe developmental brain defects in humans. Here, we identify biallelic truncating mutations in CTNNA2, encoding αN-catenin, in patients with a distinct recessive form of pachygyria. CTNNA2 was expressed in human cerebral cortex, and its loss in neurons led to defects in neurite stability and migration. The αN-catenin paralog, αE-catenin, acts as a switch regulating the balance between ß-catenin and Arp2/3 actin filament activities1. Loss of αN-catenin did not affect ß-catenin signaling, but recombinant αN-catenin interacted with purified actin and repressed ARP2/3 actin-branching activity. The actin-binding domain of αN-catenin or ARP2/3 inhibitors rescued the neuronal phenotype associated with CTNNA2 loss, suggesting ARP2/3 de-repression as a potential disease mechanism. Our findings identify CTNNA2 as the first catenin family member with biallelic mutations in humans, causing a new pachygyria syndrome linked to actin regulation, and uncover a key factor involved in ARP2/3 repression in neurons.