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Rraku E, Kerstjens-Frederikse WS, Swertz MA, Dijkhuizen T, van Ravenswaaij-Arts CMA, Engwerda A. The phenotypic spectrum of terminal and subterminal 6p deletions based on a social media-derived cohort and literature review. Orphanet J Rare Dis 2023; 18:68. [PMID: 36964621 PMCID: PMC10039519 DOI: 10.1186/s13023-023-02670-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Accepted: 03/11/2023] [Indexed: 03/26/2023] Open
Abstract
BACKGROUND Terminal 6p deletions are rare, and information on their clinical consequences is scarce, which impedes optimal management and follow-up by clinicians. The parent-driven Chromosome 6 Project collaborates with families of affected children worldwide to better understand the clinical effects of chromosome 6 aberrations and to support clinical guidance. A microarray report is required for participation, and detailed phenotype information is collected directly from parents through a multilingual web-based questionnaire. Information collected from parents is then combined with case data from literature reports. Here, we present our findings on 13 newly identified patients and 46 literature cases with genotypically well-characterised terminal and subterminal 6p deletions. We provide phenotype descriptions for both the whole group and for subgroups based on deletion size and HI gene content. RESULTS The total group shared a common phenotype characterised by ocular anterior segment dysgenesis, vision problems, brain malformations, congenital defects of the cardiac septa and valves, mild to moderate hearing impairment, eye movement abnormalities, hypotonia, mild developmental delay and dysmorphic features. These characteristics were observed in all subgroups where FOXC1 was included in the deletion, confirming a dominant role for this gene. Additional characteristics were seen in individuals with terminal deletions exceeding 4.02 Mb, namely complex heart defects, corpus callosum abnormalities, kidney abnormalities and orofacial clefting. Some of these additional features may be related to the loss of other genes in the terminal 6p region, such as RREB1 for the cardiac phenotypes and TUBB2A and TUBB2B for the cerebral phenotypes. In the newly identified patients, we observed previously unreported features including gastrointestinal problems, neurological abnormalities, balance problems and sleep disturbances. CONCLUSIONS We present an overview of the phenotypic characteristics observed in terminal and subterminal 6p deletions. This reveals a common phenotype that can be highly attributable to haploinsufficiency of FOXC1, with a possible additional effect of other genes in the 6p25 region. We also delineate the developmental abilities of affected individuals and report on previously unrecognised features, showing the added benefit of collecting information directly from parents. Based on our overview, we provide recommendations for clinical surveillance to support clinicians, patients and families.
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Affiliation(s)
- Eleana Rraku
- Department of Genetics, University of Groningen, University Medical Centre Groningen, Groningen, The Netherlands
| | | | - Morris A Swertz
- Department of Genetics, University of Groningen, University Medical Centre Groningen, Groningen, The Netherlands
| | - Trijnie Dijkhuizen
- Department of Genetics, University of Groningen, University Medical Centre Groningen, Groningen, The Netherlands
| | - Conny M A van Ravenswaaij-Arts
- Department of Genetics, University of Groningen, University Medical Centre Groningen, Groningen, The Netherlands.
- ATN/Jonx, Groningen, The Netherlands.
| | - Aafke Engwerda
- Department of Genetics, University of Groningen, University Medical Centre Groningen, Groningen, The Netherlands
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Tantry MSA, Santhakumar K. Insights on the Role of α- and β-Tubulin Isotypes in Early Brain Development. Mol Neurobiol 2023; 60:3803-3823. [PMID: 36943622 DOI: 10.1007/s12035-023-03302-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2022] [Accepted: 03/05/2023] [Indexed: 03/23/2023]
Abstract
Tubulins are the highly conserved subunit of microtubules which involve in various fundamental functions including brain development. Microtubules help in neuronal proliferation, migration, differentiation, cargo transport along the axons, synapse formation, and many more. Tubulin gene family consisting of multiple isotypes, their differential expression and varied post translational modifications create a whole new level of complexity and diversity in accomplishing manifold neuronal functions. The studies on the relation between tubulin genes and brain development opened a new avenue to understand the role of each tubulin isotype in neurodevelopment. Mutations in tubulin genes are reported to cause brain development defects especially cortical malformations, referred as tubulinopathies. There is an increased need to understand the molecular correlation between various tubulin mutations and the associated brain pathology. Recently, mutations in tubulin isotypes (TUBA1A, TUBB, TUBB1, TUBB2A, TUBB2B, TUBB3, and TUBG1) have been linked to cause various neurodevelopmental defects like lissencephaly, microcephaly, cortical dysplasia, polymicrogyria, schizencephaly, subcortical band heterotopia, periventricular heterotopia, corpus callosum agenesis, and cerebellar hypoplasia. This review summarizes on the microtubule dynamics, their role in neurodevelopment, tubulin isotypes, post translational modifications, and the role of tubulin mutations in causing specific neurodevelopmental defects. A comprehensive list containing all the reported tubulin pathogenic variants associated with brain developmental defects has been prepared to give a bird's eye view on the broad range of tubulin functions.
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Affiliation(s)
- M S Ananthakrishna Tantry
- Department of Genetic Engineering, SRM Institute of Science and Technology, Kattankulathur, 603203, India
| | - Kirankumar Santhakumar
- Department of Genetic Engineering, SRM Institute of Science and Technology, Kattankulathur, 603203, India.
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3
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Park K, Hoff KJ, Wethekam L, Stence N, Saenz M, Moore JK. Kinetically Stabilizing Mutations in Beta Tubulins Create Isotype-Specific Brain Malformations. Front Cell Dev Biol 2021; 9:765992. [PMID: 34869359 PMCID: PMC8637541 DOI: 10.3389/fcell.2021.765992] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2021] [Accepted: 10/29/2021] [Indexed: 11/13/2022] Open
Abstract
Mutations in the family of genes encoding the tubulin subunits of microtubules are associated with a spectrum of human brain malformations known as tubulinopathies. How these mutations impact tubulin activity to give rise to distinct developmental consequences is poorly understood. Here we report two patients exhibiting brain malformations characteristic of tubulinopathies and heterozygous T178M missense mutations in different β-tubulin genes, TUBB2A or TUBB3. RNAseq analysis indicates that both TUBB2A and TUBB3 are expressed in the brain during development, but only TUBB2A maintains high expression in neurons into adulthood. The T178 residue is highly conserved in β-tubulins and located in the exchangeable GTP-binding pocket of β-tubulin. To determine the impact of T178M on β-tubulin function we created an analogous mutation in the β-tubulin of budding yeast and show that the substitution acts dominantly to produce kinetically stabilized microtubules that assemble and disassemble slowly, with fewer transitions between these states. In vitro experiments with purified mutant tubulin demonstrate that T178M decreases the intrinsic assembly activity of β-tubulin and forms microtubules that rarely transition to disassembly. We provide evidence that the T178M substitution disrupts GTPase-dependent conformational changes in tubulin, providing a mechanistic explanation for kinetic stabilization. Our findings demonstrate the importance of tubulin’s GTPase activity during brain development, and indicate that tubulin isotypes play different, important roles during brain development.
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Affiliation(s)
- Kristen Park
- Department of Pediatrics and Neurology, Children's Hospital Colorado, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Katelyn J Hoff
- Department of Cell and Developmental Biology, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Linnea Wethekam
- Department of Cell and Developmental Biology, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Nicholas Stence
- Section of Pediatric Radiology, Department of Radiology, Children's Hospital Colorado, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Margarita Saenz
- Section of Genetics, Department of Pediatrics, Children's Hospital Colorado, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Jeffrey K Moore
- Department of Cell and Developmental Biology, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
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4
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Brock S, Cools F, Jansen AC. Neuropathology of genetically defined malformations of cortical development-A systematic literature review. Neuropathol Appl Neurobiol 2021; 47:585-602. [PMID: 33480109 PMCID: PMC8359484 DOI: 10.1111/nan.12696] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Revised: 12/31/2020] [Accepted: 01/15/2021] [Indexed: 12/23/2022]
Abstract
AIMS Malformations of cortical development (MCD) include a heterogeneous spectrum of clinical, imaging, molecular and histopathological entities. While the understanding of genetic causes of MCD has improved with the availability of next-generation sequencing modalities, genotype-histopathological correlations remain limited. This is the first systematic review of molecular and neuropathological findings in patients with MCD to provide a comprehensive overview of the literature. METHODS A systematic review was performed between November 2019 and February 2020. A MEDLINE search was conducted for 132 genes previously linked to MCD in order to identify studies reporting macroscopic and/or microscopic findings in patients with a confirmed genetic cause. RESULTS Eighty-one studies were included in this review reporting neuropathological features associated with pathogenic variants in 46 genes (46/132 genes, 34.8%). Four groups emerged, consisting of (1) 13 genes with well-defined histological-genotype correlations, (2) 27 genes for which neuropathological reports were limited, (3) 5 genes with conflicting neuropathological features, and (4) 87 genes for which no histological data were available. Lissencephaly and polymicrogyria were reported most frequently. Associated brain malformations were variably present, with abnormalities of the corpus callosum as most common associated feature. CONCLUSIONS Neuropathological data in patients with MCD with a defined genetic cause are available only for a small number of genes. As each genetic cause might lead to unique histopathological features of MCD, standardised thorough neuropathological assessment and reporting should be encouraged. Histological features can help improve the understanding of the pathogenesis of MCD and generate hypotheses with impact on further research directions.
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Affiliation(s)
- Stefanie Brock
- Department of Pathology, Universitair Ziekenhuis Brussel (UZ Brussel), Brussels, Belgium.,Neurogenetics Research Group, Vrije Universiteit Brussel (VUB), Brussels, Belgium
| | - Filip Cools
- Department of Neonatology, Universitair Ziekenhuis Brussel (UZ Brussel), Brussels, Belgium
| | - Anna C Jansen
- Neurogenetics Research Group, Vrije Universiteit Brussel (VUB), Brussels, Belgium.,Pediatric Neurology Unit, Universitair Ziekenhuis Brussel (UZ Brussel), Brussels, Belgium
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5
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Schmidt L, Wain KE, Hajek C, Estrada-Veras JI, Guillen Sacoto MJ, Wentzensen IM, Malhotra A, Clause A, Perry D, Moreno-De-Luca A, Bell M. Expanding the Phenotype of TUBB2A-Related Tubulinopathy: Three Cases of a Novel, Heterozygous TUBB2A Pathogenic Variant p.Gly98Arg. Mol Syndromol 2020; 12:33-40. [PMID: 33776625 DOI: 10.1159/000512160] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2020] [Accepted: 10/08/2020] [Indexed: 01/22/2023] Open
Abstract
Tubulinopathies are a group of conditions caused by variants in 6 tubulin genes that present with a spectrum of brain malformations. One of these conditions is TUBB2A-related tubulinopathy. Currently, there are 9 reported individuals with pathogenic variants within the TUBB2A gene, with common manifestations including, but not limited to, global developmental delay, seizures, cortical dysplasia, and dysmorphic corpus callosum. We report 3 patients identified by exome and genome sequencing to have a novel, pathogenic, missense variant in TUBB2A (p.Gly98Arg). They presented similarly with intellectual disability, hypotonia, and global developmental delay and varied with respect to the type of cortical brain malformation, seizure history, diagnosis of autism spectrum disorder, and other features. This case series expands the natural history of TUBB2A-related tubulinopathy while describing the presentation of a novel, pathogenic, missense variant in 3 patients.
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Affiliation(s)
- Lindsey Schmidt
- Sanford Health, Augustana-Sanford Genetic Counseling Program, Sioux Falls, South Dakota, USA
| | - Karen E Wain
- Geisinger Autism & Developmental Medicine Institute, Lewisburg, Pennsylvania, USA
| | | | - Juvianee I Estrada-Veras
- Henry M Jackson Foundation for the Advancement of Military Medicine and Walter Reed National Military Medical Center, Bethesda, Maryland, USA
| | | | | | - Alka Malhotra
- Illumina Clinical Services Laboratory, San Diego, California, USA
| | - Amanda Clause
- Illumina Clinical Services Laboratory, San Diego, California, USA
| | - Denise Perry
- Illumina Clinical Services Laboratory, San Diego, California, USA
| | - Andres Moreno-De-Luca
- Department of Radiology, Geisinger Autism & Developmental Medicine Institute, Genomic Medicine Institute, Lewisburg, Pennsylvania, USA
| | - Megan Bell
- Sanford Health, Sioux Falls, South Dakota, USA
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6
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Microtubule Dysfunction: A Common Feature of Neurodegenerative Diseases. Int J Mol Sci 2020; 21:ijms21197354. [PMID: 33027950 PMCID: PMC7582320 DOI: 10.3390/ijms21197354] [Citation(s) in RCA: 58] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2020] [Revised: 09/24/2020] [Accepted: 10/01/2020] [Indexed: 12/13/2022] Open
Abstract
Neurons are particularly susceptible to microtubule (MT) defects and deregulation of the MT cytoskeleton is considered to be a common insult during the pathogenesis of neurodegenerative disorders. Evidence that dysfunctions in the MT system have a direct role in neurodegeneration comes from findings that several forms of neurodegenerative diseases are associated with changes in genes encoding tubulins, the structural units of MTs, MT-associated proteins (MAPs), or additional factors such as MT modifying enzymes which modulating tubulin post-translational modifications (PTMs) regulate MT functions and dynamics. Efforts to use MT-targeting therapeutic agents for the treatment of neurodegenerative diseases are underway. Many of these agents have provided several benefits when tested on both in vitro and in vivo neurodegenerative model systems. Currently, the most frequently addressed therapeutic interventions include drugs that modulate MT stability or that target tubulin PTMs, such as tubulin acetylation. The purpose of this review is to provide an update on the relevance of MT dysfunctions to the process of neurodegeneration and briefly discuss advances in the use of MT-targeting drugs for the treatment of neurodegenerative disorders.
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7
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Brock S, Vanderhasselt T, Vermaning S, Keymolen K, Régal L, Romaniello R, Wieczorek D, Storm TM, Schaeferhoff K, Hehr U, Kuechler A, Krägeloh-Mann I, Haack TB, Kasteleijn E, Schot R, Mancini GMS, Webster R, Mohammad S, Leventer RJ, Mirzaa G, Dobyns WB, Bahi-Buisson N, Meuwissen M, Jansen AC, Stouffs K. Defining the phenotypical spectrum associated with variants in TUBB2A. J Med Genet 2020; 58:33-40. [PMID: 32571897 PMCID: PMC7803914 DOI: 10.1136/jmedgenet-2019-106740] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Revised: 02/05/2020] [Accepted: 03/05/2020] [Indexed: 01/18/2023]
Abstract
BACKGROUND Variants in genes belonging to the tubulin superfamily account for a heterogeneous spectrum of brain malformations referred to as tubulinopathies. Variants in TUBB2A have been reported in 10 patients with a broad spectrum of brain imaging features, ranging from a normal cortex to polymicrogyria, while one patient has been reported with progressive atrophy of the cerebellar vermis. METHODS In order to further refine the phenotypical spectrum associated with TUBB2A, clinical and imaging features of 12 patients with pathogenic TUBB2A variants, recruited via the international network of the authors, were reviewed. RESULTS We report 12 patients with eight novel and one recurrent variants spread throughout the TUBB2A gene but encoding for amino acids clustering at the protein surface. Eleven patients (91.7%) developed seizures in early life. All patients suffered from intellectual disability, and 11 patients had severe motor developmental delay, with 4 patients (36.4 %) being non-ambulatory. The cerebral cortex was normal in five individuals and showed dysgyria of variable severity in seven patients. Associated brain malformations were less frequent in TUBB2A patients compared with other tubulinopathies. None of the patients had progressive cerebellar atrophy. CONCLUSION The imaging phenotype associated with pathogenic variants in TUBB2A is highly variable, ranging from a normal cortex to extensive dysgyria with associated brain malformations. For recurrent variants, no clear genotype-phenotype correlations could be established, suggesting the role of additional modifiers.
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Affiliation(s)
- Stefanie Brock
- Department of Pathology, Universitair Ziekenhuis Brussel, Brussels, Belgium .,Neurogenetics Research Group, Reproduction Genetics and Regenerative Medicine Research Cluster, Vrije Universiteit Brussel, Brussels, Belgium
| | - Tim Vanderhasselt
- Department of Radiology, Universitair Ziekenhuis Brussel, Brussels, Belgium
| | - Sietske Vermaning
- Belgium Center for Reproduction and Genetics, Universitair Ziekenhuis Brussel, Brussels, Belgium
| | - Kathelijn Keymolen
- Belgium Center for Reproduction and Genetics, Universitair Ziekenhuis Brussel, Brussels, Belgium
| | - Luc Régal
- Pediatric Neurology Unit, Department of Pediatrics, Universitair Ziekenhuis, Brussels, Belgium
| | - Romina Romaniello
- Neuropsychiatry and Neurorehabilitation Unit, Scientific Institute, IRCCS Eugenio Medea, Lecco, Italy
| | - Dagmar Wieczorek
- Institut fuer Humangenetik, Universitaetsklininikum Essen, Essen, Germany.,Institute of Human Genetics, Heinrich Heine University Düsseldorf, Dusseldorf, Nordrhein-Westfalen, Germany
| | - Tim Matthias Storm
- Institut für Humangenetik, Technische Universität München, Munchen, Bayern, Germany
| | - Karin Schaeferhoff
- Institute of Medical Genetics and Applied Genomics, University of Tübingen, Tübingen, Baden-Württemberg, Germany
| | - Ute Hehr
- Zentrum für Humangenetik Regensburg, Universitätsklinikum Regensburg, Regensburg, Bayern, Germany
| | - Alma Kuechler
- Institut fuer Humangenetik, Universitaetsklininikum Essen, Essen, Germany
| | - Ingeborg Krägeloh-Mann
- Department of Pediatric Neurology and Developmental Medicine, University Children's Hospital Tübingen, University of Tübingen, Tübingen, Germany
| | - Tobias B Haack
- Institute of Medical Genetics and Applied Genomics, Eberhard-Karls-Universitat Tubingen Medizinische Fakultat, Tübingen, Baden-Württemberg, Germany
| | - Esmee Kasteleijn
- Department of Clinical Genetics, Erasmus Medical Center, Rotterdam, Zuid-Holland, The Netherlands
| | - Rachel Schot
- Department of Clinical Genetics, Erasmus Medical Center, Rotterdam, Zuid-Holland, The Netherlands
| | - Grazia Maria Simonetta Mancini
- Department of Clinical Genetics, Erasmus Medical Center, Rotterdam, Zuid-Holland, The Netherlands.,ENCORE Expertise Center for Neurodevelopmental Disorders, Erasmus Medical Center, Rotterdam, Zuid-Holland, The Netherlands
| | - Richard Webster
- Department of Neurology, Children's Hospital at Westmead, Westmead, New South Wales, Australia
| | - Shekeeb Mohammad
- Department of Neurology, Children's Hospital at Westmead, Westmead, New South Wales, Australia
| | - Richard J Leventer
- Department of Neurology, Murdoch Childrens Research Institute, Melbourne, Victoria, Australia
| | - Ghayda Mirzaa
- Division of Genetic Medicine, Department of Pediatrics, Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, Washington, USA
| | - William B Dobyns
- Division of Genetic Medicine, Department of Pediatrics, Center for Integrative Brain Research, Seattle Children's Research Institute, Seattle, Washington, USA
| | - Nadia Bahi-Buisson
- Embryology and Genetics of Congenital Malformations, INSERM, Paris, Île-de-France, France
| | - Marije Meuwissen
- Center of Human Genetics, Universiteit Antwerpen, Antwerpen, Belgium
| | - Anna C Jansen
- Neurogenetics Research Group, Reproduction Genetics and Regenerative Medicine Research Cluster, Vrije Universiteit Brussel, Brussels, Belgium.,Pediatric Neurology Unit, Universitair Ziekenhuis Brussel, Brussels, Belgium
| | - Katrien Stouffs
- Neurogenetics Research Group, Reproduction Genetics and Regenerative Medicine Research Cluster, Vrije Universiteit Brussel, Brussels, Belgium.,Center for Medical Genetics, Universitair Ziekenhuis Brussel, Brussels, Belgium, Brussels, Belgium
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8
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De novo mutations of TUBB2A cause infantile-onset epilepsy and developmental delay. J Hum Genet 2020; 65:601-608. [PMID: 32203252 DOI: 10.1038/s10038-020-0739-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2019] [Revised: 02/06/2020] [Accepted: 02/27/2020] [Indexed: 01/20/2023]
Abstract
We analyzed our two new cases of infantile-onset epilepsy with developmental delay with de novo variant in TUBB2A and review the related literatures. Our two probands were both girls with infantile-onset epilepsy and global developmental delay. Case 1 had a novel de novo heterozygous missense variant: c.728C>T [p.Pro243Leu] (NM_001069.2). Her brain magnetic resonance imaging (MRI) showed nonspecific white matter myelination delay and slightly enlarged anterior horn of lateral ventricle. Her epilepsy had been controlled by TPM monotherapy. Case 2 had a reported de novo variant c.743C>T [p.Ala248Val] (NM_001069.2). Her brain MRI showed bilateral microgyria and corpus callosum dysplasia. A total of seven TUBB2A mutations cases had been published previously in five papers, therefore, until now, there were nine patients with TUBB2A mutations. All patients had developmental delay, among them seven cases also with infantile-onset epilepsy, one case with abnormal EEG but without clinical seizures. There are six cases that have different degree of cortical dysplasia, one case with cerebellar vermis atrophy and brainstem sacsinopathy, the rest two cases have no obvious brain structural abnormalities. There was one case with variant c.1249G>A (p.D417N) that had atypical clinical presentation, including prominent progressive spastic ataxia, sensory motor axonal neuropathy, and bilateral optic macular dystrophy, but relatively mild intellectual disability, his MRI showed cerebellar atrophy, thinning of the corpus callosum and pons sacsinopathy, but no cortical malformation. The p.A248V mutation was the most common mutation occurred in three patients (3/9). The clinical phenotypes of these three patients were similar, all of them had global developmental delay with no language and corpus callosum dysplasia, two cases with epilepsy and the other one only have EEG epileptic discharges without clinical seizure, two cases with cortical dysplasia and the other one without obvious brain malformation. In brief, global developmental delay was the most common phenotype of TUBB2A mutation-related disease, most cases also had infantile-onset epilepsy and cortical dysplasia and corpus callosum dysplasia. The region between seventh and eighth alpha-helix of TUBB2A may be a "hot spot" mutation domain.
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9
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Bittermann E, Abdelhamed Z, Liegel RP, Menke C, Timms A, Beier DR, Stottmann RW. Differential requirements of tubulin genes in mammalian forebrain development. PLoS Genet 2019; 15:e1008243. [PMID: 31386652 PMCID: PMC6697361 DOI: 10.1371/journal.pgen.1008243] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2018] [Revised: 08/16/2019] [Accepted: 06/12/2019] [Indexed: 11/24/2022] Open
Abstract
Tubulin genes encode a series of homologous proteins used to construct microtubules which are essential for multiple cellular processes. Neural development is particularly reliant on functional microtubule structures. Tubulin genes comprise a large family of genes with very high sequence similarity between multiple family members. Human genetics has demonstrated that a large spectrum of cortical malformations are associated with de novo heterozygous mutations in tubulin genes. However, the absolute requirement for many of these genes in development and disease has not been previously tested in genetic loss of function models. Here we directly test the requirement for Tuba1a, Tubb2a and Tubb2b in the mouse by deleting each gene individually using CRISPR-Cas9 genome editing. We show that loss of Tubb2a or Tubb2b does not impair survival but does lead to relatively mild cortical malformation phenotypes. In contrast, loss of Tuba1a is perinatal lethal and leads to significant forebrain dysmorphology. We also present a novel mouse ENU allele of Tuba1a with phenotypes similar to the null allele. This demonstrates the requirements for each of the tubulin genes and levels of functional redundancy are quite different throughout the gene family. The ability of the mouse to survive in the absence of some tubulin genes known to cause disease in humans suggests future intervention strategies for these devastating tubulinopathy diseases.
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Affiliation(s)
- Elizabeth Bittermann
- Division of Human Genetics, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, United States of America
| | - Zakia Abdelhamed
- Division of Human Genetics, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, United States of America
- Department of Anatomy and Embryology, Faculty of Medicine (Girl’s Section), Al-Azhar University, Cairo, Egypt
| | - Ryan P. Liegel
- Division of Human Genetics, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, United States of America
| | - Chelsea Menke
- Division of Human Genetics, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, United States of America
| | - Andrew Timms
- Center for Developmental Biology and Regenerative Medicine, Seattle Children’s Research Institute, Seattle, Washington, United States of America
| | - David R. Beier
- Center for Developmental Biology and Regenerative Medicine, Seattle Children’s Research Institute, Seattle, Washington, United States of America
- Department of Pediatrics, University of Washington Medical School, Seattle, Washington, United States of America
| | - Rolf W. Stottmann
- Division of Human Genetics, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, United States of America
- Division of Developmental Biology, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, United States of America
- Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America
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10
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Tubulin genes and malformations of cortical development. Eur J Med Genet 2018; 61:744-754. [PMID: 30016746 DOI: 10.1016/j.ejmg.2018.07.012] [Citation(s) in RCA: 80] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Revised: 06/03/2018] [Accepted: 07/12/2018] [Indexed: 01/18/2023]
Abstract
A large number of genes encoding for tubulin proteins are expressed in the developing brain. Each is subject to specific spatial and temporal expression patterns. However, most are highly expressed in post-mitotic neurons during stages of neuronal migration and differentiation. The major tubulin subclasses (alpha- and beta-tubulin) share high sequence and structural homology. These globular proteins form heterodimers and subsequently co-assemble into microtubules. Microtubules are dynamic, cytoskeletal polymers which play key roles in cellular processes crucial for cortical development, including neuronal proliferation, migration and cortical laminar organisation. Mutations in seven genes encoding alpha-tubulin (TUBA1A), beta-tubulin (TUBB2A, TUBB2B, TUBB3, TUBB4A, TUBB) and gamma-tubulin (TUBG1) isoforms have been associated with a wide and overlapping range of brain malformations or "Tubulinopathies". The majority of cortical phenotypes include lissencephaly, polymicrogyria, microlissencephaly and simplified gyration. Well-known hallmarks of the tubulinopathies include dysmorphism of the basal ganglia (fusion of the caudate nucleus and putamen with absence of the anterior limb of the internal capsule), midline commissural structures hypoplasia and/or agenesis (anterior commissure, corpus callosum and fornix), hypoplasia of the oculomotor and optic nerves, cerebellar hypoplasia or dysplasia and dysmorphism of the hind-brain structures. The cortical and extra-cortical brain phenotypes observed are largely dependent on the specific tubulin gene affected. In the present review, all the published data on tubulin family gene mutations and the associated cortical phenotypes are summarized. In addition, the most typical neuroimaging patterns of malformations of cortical development associated with tubulin gene mutations detected on the basis of our own experience are described.
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