De novo mutations in the beta-tubulin gene TUBB2A cause simplified gyral patterning and infantile-onset epilepsy.

Tubulins, and microtubule polymers into which they incorporate, play critical mechanical roles in neuronal function during cell proliferation, neuronal migration, and postmigrational development: the three major overlapping events of mammalian cerebral cortex development. A number of neuronally expressed tubulin genes are associated with a spectrum of disorders affecting cerebral cortex formation. Such "tubulinopathies" include lissencephaly/pachygyria, polymicrogyria-like malformations, and simplified gyral patterns, in addition to characteristic extracortical features, such as corpus callosal, basal ganglia, and cerebellar abnormalities. Epilepsy is a common finding in these related disorders. Here we describe two unrelated individuals with infantile-onset epilepsy and abnormalities of brain morphology, harboring de novo variants that affect adjacent amino acids in a beta-tubulin gene TUBB2A. Located in a highly conserved loop, we demonstrate impaired tubulin and microtubule function resulting from each variant in vitro and by using in silico predictive modeling. We propose that the affected functional loop directly associates with the alpha-tubulin-bound guanosine triphosphate (GTP) molecule, impairing the intradimer interface and correct formation of the alpha/beta-tubulin heterodimer. This study associates mutations in TUBB2A with the spectrum of "tubulinopathy" phenotypes. As a consequence, genetic variations affecting all beta-tubulin genes expressed at high levels in the brain (TUBB2B, TUBB3, TUBB, TUBB4A, and TUBB2A) have been linked with malformations of cortical development.

[1]  Amy Bernard,et al.  A mutation in Tubb2b, a human polymicrogyria gene, leads to lethality and abnormal cortical development in the mouse. , 2013, Human molecular genetics.

[2]  M. Kirschner,et al.  Dynamic instability of microtubule growth , 1984, Nature.

[3]  T. Mitchison,et al.  Microtubule polymerization dynamics. , 1997, Annual review of cell and developmental biology.

[4]  Steve D. M. Brown,et al.  Mutations in α-Tubulin Cause Abnormal Neuronal Migration in Mice and Lissencephaly in Humans , 2007, Cell.

[5]  D. Keays,et al.  Large spectrum of lissencephaly and pachygyria phenotypes resulting from de novo missense mutations in tubulin alpha 1A (TUBA1A) , 2007, Human mutation.

[6]  T. Araki,et al.  ZNRF1 promotes Wallerian degeneration by degrading AKT to induce GSK3B-dependent CRMP2 phosphorylation , 2011, Nature Cell Biology.

[7]  M. Rees,et al.  Fine architecture and mutation mapping of human brain inhibitory system ligand gated ion channels by high-throughput homology modeling. , 2010, Advances in protein chemistry and structural biology.

[8]  R. Kuzniecky,et al.  A developmental and genetic classification for malformations of cortical development , 2005, Neurology.

[9]  L. Lagae,et al.  A de novo mutation in the β-tubulin gene TUBB4A results in the leukoencephalopathy hypomyelination with atrophy of the basal ganglia and cerebellum. , 2013, American journal of human genetics.

[10]  E. Engle,et al.  Distinct alpha- and beta-tubulin isotypes are required for the positioning, differentiation and survival of neurons: new support for the 'multi-tubulin' hypothesis. , 2010, Bioscience reports.

[11]  R. Kuzniecky,et al.  A developmental and genetic classification for malformations of cortical development: update 2012 , 2012, Brain : a journal of neurology.

[12]  D. Bonthron,et al.  Mutation of the variant alpha-tubulin TUBA8 results in polymicrogyria with optic nerve hypoplasia. , 2009, American journal of human genetics.

[13]  M. Steinmetz,et al.  Molecular Mechanism of Action of Microtubule-Stabilizing Anticancer Agents , 2013, Science.

[14]  L. Goldstein,et al.  Microtubule-dependent transport in neurons: steps towards an understanding of regulation, function and dysfunction. , 2004, Current opinion in cell biology.

[15]  T. Meitinger,et al.  Human TUBB3 Mutations Perturb Microtubule Dynamics, Kinesin Interactions, and Axon Guidance , 2010, Cell.

[16]  Martin W. Breuss,et al.  Mutations in the β-Tubulin Gene TUBB5 Cause Microcephaly with Structural Brain Abnormalities , 2012, Cell reports.

[17]  M. Dolan,et al.  Regulatory Polymorphisms in β-Tubulin IIa Are Associated with Paclitaxel-Induced Peripheral Neuropathy , 2012, Clinical Cancer Research.

[18]  Ravinesh A. Kumar,et al.  TUBA1A mutations cause wide spectrum lissencephaly (smooth brain) and suggest that multiple neuronal migration pathways converge on alpha tubulins , 2010, Human molecular genetics.

[19]  C. Fallet-Bianco,et al.  Mutations in the neuronal ß-tubulin subunit TUBB3 result in malformation of cortical development and neuronal migration defects. , 2010, Human molecular genetics.

[20]  Nicholas J. Cowan,et al.  The α- and β-tubulin folding pathways , 1997 .

[21]  Leif Dehmelt,et al.  Actin and microtubules in neurite initiation: are MAPs the missing link? , 2004, Journal of neurobiology.

[22]  S. Hatakeyama,et al.  ZNRF1 interacts with tubulin and regulates cell morphogenesis. , 2009, Biochemical and biophysical research communications.

[23]  A. Fry,et al.  Overlapping cortical malformations and mutations in TUBB2B and TUBA1A. , 2013, Brain : a journal of neurology.

[24]  E. Nogales,et al.  Refined structure of alpha beta-tubulin at 3.5 A resolution. , 2001, Journal of molecular biology.

[25]  A. Represa,et al.  Mutations in the β-tubulin gene TUBB2B result in asymmetrical polymicrogyria , 2009, Nature Genetics.

[26]  R. Letón,et al.  Tumoral and tissue‐specific expression of the major human β‐tubulin isotypes , 2010, Cytoskeleton.

[27]  F. Hamdan,et al.  Polymicrogyria with dysmorphic basal ganglia? Think tubulin! , 2014, Clinical genetics.

[28]  E. Nogales,et al.  High-Resolution Model of the Microtubule , 1999, Cell.

[29]  Renzo Guerrini,et al.  Mutations in TUBG1, DYNC1H1, KIF5C and KIF2A cause malformations of cortical development and microcephaly , 2013, Nature Genetics.