Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance

The Coming of Age for Big Data in Systems Radiobiology, an Engineering Perspective

As high-throughput approaches in biological and biomedical research are transforming the life sciences into information-driven disciplines, modern analytics platforms for big data have started to address the needs for efficient and systematic data analysis and interpretation. We observe that radiobiology is following this general trend, with -omics information providing unparalleled depth into the biomolecular mechanisms of radiation response-defined as systems radiobiology. We outline the design of computational frameworks and discuss the analysis of big data in low-dose ionizing radiation (LDIR) responses of the mammalian brain. Following successful examples and best practices of approaches for the analysis of big data in life sciences and health care, we present the needs and requirements for radiation research. Our goal is to raise awareness for the radiobiology community about the new technological possibilities that can capture complex information and execute data analytics on a large scale. The production of large data sets from genome-wide experiments (quantity) and the complexity of radiation research with multidimensional experimental designs (quality) will necessitate the adoption of latest information technologies. The main objective was to translate research results into applied clinical and epidemiological practice and understand the responses of biological tissues to LDIR to define new radiation protection policies. We envisage a future where multidisciplinary teams include data scientists, artificial intelligence experts, DevOps engineers, and of course radiation experts to fulfill the augmented needs of the radiobiology community, accelerate research, and devise new strategies.

Lysosomal Function and Axon Guidance: Is There a Meaningful Liaison?

Axonal trajectories and neural circuit activities strongly rely on a complex system of molecular cues that finely orchestrate the patterning of neural commissures. Several of these axon guidance molecules undergo continuous recycling during brain development, according to incompletely understood intracellular mechanisms, that in part rely on endocytic and autophagic cascades. Based on their pivotal role in both pathways, lysosomes are emerging as a key hub in the sophisticated regulation of axonal guidance cue delivery, localization, and function. In this review, we will attempt to collect some of the most relevant research on the tight connection between lysosomal function and axon guidance regulation, providing some proof of concepts that may be helpful to understanding the relation between lysosomal storage disorders and neurodegenerative diseases.

Differentiating Moebius syndrome and other congenital facial weakness disorders with electrodiagnostic studies

INTRODUCTION

Congenital facial weakness (CFW) can result from facial nerve paresis with or without other cranial nerve and systemic involvement, or generalized neuropathic and myopathic disorders. Moebius syndrome is one type of CFW. In this study we explored the utility of electrodiagnostic studies (EDx) in the evaluation of individuals with CFW.

METHODS

Forty-three subjects enrolled prospectively into a dedicated clinical protocol and had EDx evaluations, including blink reflex and facial and peripheral nerve conduction studies, with optional needle electromyography.

RESULTS

MBS and hereditary congenital facial paresis (HCFP) subjects had low-amplitude cranial nerve 7 responses without other neuropathic or myopathic findings. Carriers of specific pathogenic variants in TUBB3 had, in addition, a generalized sensorimotor axonal polyneuropathy with demyelinating features. Myopathic findings were detected in individuals with Carey-Fineman-Ziter syndrome, myotonic dystrophy, other undefined myopathies, or CFW with arthrogryposis, ophthalmoplegia, and other system involvement.

DISCUSSION

EDx in CFW subjects can assist in characterizing the underlying pathogenesis, as well as guide diagnosis and genetic counseling.

New insights into the molecular mechanisms of axon guidance receptor regulation and signaling

As the nervous system develops, newly differentiated neurons need to extend their axons toward their synaptic targets to form functional neural circuits. During this highly dynamic process of axon pathfinding, guidance receptors expressed at the tips of motile axons interact with soluble guidance cues or membrane tethered molecules present in the environment to be either attracted toward or repelled away from the source of these cues. As competing cues are often present at the same location and during the same developmental period, guidance receptors need to be both spatially and temporally regulated in order for the navigating axons to make appropriate guidance decisions. This regulation is exerted by a diverse array of molecular mechanisms that have come into focus over the past several decades and these mechanisms ensure that the correct complement of surface receptors is present on the growth cone, a fan-shaped expansion at the tip of the axon. This dynamic, highly motile structure is defined by a lamellipodial network lining the periphery of the growth cone interspersed with finger-like filopodial projections that serve to explore the surrounding environment. Once axon guidance receptors are deployed at the right place and time at the growth cone surface, they respond to their respective ligands by initiating a complex set of signaling events that serve to rearrange the growth cone membrane and the actin and microtubule cytoskeleton to affect axon growth and guidance. In this review, we highlight recent advances that shed light on the rich complexity of mechanisms that regulate axon guidance receptor distribution, activation and downstream signaling.

Second trimester fetal MRI features in a fetus with TUBB3 gene mutation

Tubulinopathies are a heterogeneous group of complex cortical malformations that are associated with mutations in tubulin genes. TUBB3 gene mutation is associated with a broader spectrum of central nervous system malformations and constitutes about 10% of all tubulinopathies. The diagnosis may not be immediately apparent on imaging, though the differential diagnosis may be narrowed based on imaging findings and allow for more directed genetic testing. We report a 22-year-old gravida-1 nulliparous female whose routine second trimester fetal ultrasound revealed ventriculomegaly and possible agenesis of the corpus callosum. Fetal magnetic resonance imaging showed severe lateral and third ventriculomegaly and a dysplastic, z-shaped brainstem without any evidence of ocular abnormalities. Genetic testing revealed a pathogenic mutation in TUBB3.

KIF21A pathogenic variants cause congenital fibrosis of extraocular muscles type 3

Background: Congenital fibrosis of the extraocular muscles (CFEOM) is characterized by ptosis and non-progressive restrictive ophthalmoplegia. CFEOM1 is a stereotypical phenotype with isolated bilateral ptosis, bilateral ophthalmoplegia, absent upgaze, and globe infraduction. CFEOM3 is a more variable phenotype that can include unilateral disease, absent ptosis, residual upgaze, and/or orthotropia. Most cases of CFEOM1 result from recurrent heterozygous KIF21A missense mutations and less commonly from recurrent heterozygous TUBB3 missense mutations. While most cases of CFEOM3 result from recurrent heterozygous TUBB3 missense mutations, several pedigrees harbored pathogenic variants in KIF21A. Here, we asked if Lebanese pedigrees with CFEOM3 harbor pathogenic variants in TUBB3 or KIF21A.Materials and Methods: Families affected with congenital cranial dysinnervation disorders were prospectively recruited from the American University of Beirut pediatric ophthalmology clinic and included two probands with CFEOM. KIF21A hotspot exons and TUBB3 coding sequence were sequenced. Available family members were sequenced for co-segregation analysis.Results: Both families were found to have CFEOM3 and to harbor pathogenic variants in KIF21A(OMIM 608283). A simplex proband with CFEOM3 from a consanguineous Iraqi family harbored a de novo heterozygous KIF21A c.2860 C > T variant (p.R954W); this variant accounts for the majority of reported KIF21A mutations but is typically implicated in CFEOM1. A Lebanese father with CFEOM3 and his son with CFEOM1 segregated a heterozygous KIF21A c.2830 G > C variant (p.E944Q), previously reported in an individual with CFEOM1.Conclusions: These results support prior reports of KIF21A mutations as a rare cause of CFEOM3. These families are Middle Eastern or Chinese, supporting a genetic modifier in these populations.

The Dis1/Stu2/XMAP215 Family Gene FgStu2 Is Involved in Vegetative Growth, Morphology, Sexual and Asexual Reproduction, Pathogenicity and DON Production of Fusarium graminearum

The conserved Dis1/Stu2/XMAP215 microtubule association proteins (MAPs) family plays an important role in microtubule dynamics, nucleation, and kinetochore-microtubule attachments. However, function of Dis1/Stu2/XMAP215 homolog in plant pathogenic fungi has not been determined. Here, we identified and investigated the Dis1/Stu2/XMAP215 homolog (FGSG_10528) in Fusarium graminearum (FgStu2p). Co-localization experiment and co-immunoprecipitation (Co-IP) assay demonstrated that FgStu2p is a microtubule associated protein. Besides, FgStu2 could also interact with Fgγ-tubulin and presumed FgNdc80, which suggested that the FgStu2 gene might associate with microtubule nucleation and kinetochore-microtubule attachments like Dis1/Stu2/XMAP215 homologs in other species. Moreover, the FgStu2 promoter replacement mutants (FgStu2-Si mutants) produced twisted hyphae and decreased growth rate. Microscope examination further showed that the microtubule polymerization was reduced in FgStu2-Si mutants, which could account for the aberrant morphology. Although the microtubule polymerization was affected in FgStu2-Si mutants, the FgStu2-Si mutants didn't show highly increased sensitivity to anti-microtubule fungicide carbendazim (methyl benzimidazol-2-ylcarbamate [MBC]). In addition, the FgStu2-Si mutants exhibited curved conidia, decreased number of conidial production, blocked ability of perithecia production, decreased pathogenicity and deoxynivalenol (DON) production. Taken together, these results indicate that the FgStu2 gene plays a crucial role in vegetative growth, morphology, sexual reproduction, asexual reproduction, virulence and deoxynivalenol (DON) production of F. graminearum, which brings new insights into the functions of Dis1/Stu2/XMAP215 homolog in plant pathogenic fungi.

Tubulin mutations in neurodevelopmental disorders as a tool to decipher microtubule function

Malformations of cortical development (MCDs) are a group of severe brain malformations associated with intellectual disability and refractory childhood epilepsy. Human missense heterozygous mutations in the 9 α-tubulin and 10 β-tubulin isoforms forming the heterodimers that assemble into microtubules (MTs) were found to cause MCDs. However, how a single mutated residue in a given tubulin isoform can perturb the entire microtubule population in a neuronal cell remains a crucial question. Here, we examined 85 MCD-associated tubulin mutations occurring in TUBA1A, TUBB2, and TUBB3 and their location in a three-dimensional (3D) microtubule cylinder. Mutations hitting residues exposed on the outer microtubule surface are likely to alter microtubule association with partners, while alteration of intradimer contacts may impair dimer stability and straightness. Other types of mutations are predicted to alter interdimer and lateral contacts, which are responsible for microtubule cohesion, rigidity, and dynamics. MCD-associated tubulin mutations surprisingly fall into all categories, thus providing unexpected insights into how a single mutation may impair microtubule function and elicit dominant effects in neurons.

A proteomic survey of microtubule-associated proteins in a R402H TUBA1A mutant mouse

Microtubules play a critical role in multiple aspects of neurodevelopment, including the generation, migration and differentiation of neurons. A recurrent mutation (R402H) in the α-tubulin gene TUBA1A is known to cause lissencephaly with cerebellar and striatal phenotypes. Previous work has shown that this mutation does not perturb the chaperone-mediated folding of tubulin heterodimers, which are able to assemble and incorporate into the microtubule lattice. To explore the molecular mechanisms that cause the disease state we generated a new conditional mouse line that recapitulates the R402H variant. We show that heterozygous mutants present with laminar phenotypes in the cortex and hippocampus, as well as a reduction in striatal size and cerebellar abnormalities. We demonstrate that homozygous expression of the R402H allele causes neuronal death and exacerbates a cell intrinsic defect in cortical neuronal migration. Microtubule sedimentation assays coupled with quantitative mass spectrometry demonstrated that the binding and/or levels of multiple microtubule associated proteins (MAPs) are perturbed by the R402H mutation including VAPB, REEP1, EZRIN, PRNP and DYNC1l1/2. Consistent with these data we show that the R402H mutation impairs dynein-mediated transport which is associated with a decoupling of the nucleus to the microtubule organising center. Our data support a model whereby the R402H variant is able to fold and incorporate into microtubules, but acts as a gain of function by perturbing the binding of MAPs.

Microtubules are polymers composed of tubulin proteins, which play an important role in the development of the human brain. Genetic mutations in tubulin genes are known to cause neurodevelopmental diseases, including lissencephaly which is characterised by an impairment in the migration of neurons. In this study we investigate how a common mutation (R402H) in TUBA1A causes lissencephaly by generating and characterising a mouse with the same variant. We show that affected animals recapitulate multiple aspects of the human disease; including laminar perturbations in the cortex and hippocampus, attributable to defects in neuronal migration at key developmental time points. To characterize the molecular implications of the R402H mutation we purified microtubules from the developing brain, and analysed the proteins present by mass spectrometry. This revealed that the binding of DYNC1I1/2 to microtubules is altered in mice with the R402H mutation. Our results provide insight into the molecular pathology underlying tubulin related disease states, and provide a foundation for the rational design of therapeutic interventions.

Cross-sectional quantitative analysis of the natural history of TUBA1A and TUBB2B tubulinopathies

Purpose

TUBA1A and TUBB2B tubulinopathies are rare neurodevelopmental disorders characterized by cortical and extracortical malformations and heterogenic phenotypes. There is a need for quantitative clinical endpoints that will be beneficial for future diagnostic and therapeutic trials.

Methods

Quantitative natural history modeling of individuals with TUBA1A and TUBB2B tubulinopathies from clinical reports and database entries of DECIPHER and ClinVar. Main outcome measures were age at disease onset, survival, and diagnostic delay. Phenotypical, neuroradiological, and histopathological features were descriptively illustrated.

Results

Mean age at disease onset was 4 (TUBA1A) and 6 months (TUBB2B), respectively. Mortality was equally estimated with 7% at 3.2 (TUBA1A) and 8.0 years (TUBB2B). Diagnostic delay was significantly higher in TUBB2B (12.3 years) compared with TUBA1A tubulinopathy (4.2 years). We delineated the isotype-dependent clinical, neuroradiological, and histopathological phenotype of affected individuals and present brain malformations associated with epilepsy and an unfavorable course of disease.

Conclusion

The natural history of tubulinopathies is defined by the genotype and associated brain malformations. Defined data on estimated survival, diagnostic delay, and disease characteristics of TUBA1A and TUBB2B tubulinopathy will help to raise disease awareness and encourage future clinical trials to optimize genetic testing, family counseling, and supportive care.

Transcranial Magnetic Stimulation-Induced Plasticity Mechanisms: TMS-Related Gene Expression and Morphology Changes in a Human Neuron-Like Cell Model

Transcranial Magnetic Stimulation (TMS) is a form of non-invasive brain stimulation, used to alter cortical excitability both in research and clinical applications. The intermittent and continuous Theta Burst Stimulation (iTBS and cTBS) protocols have been shown to induce opposite after-effects on human cortex excitability. Animal studies have implicated synaptic plasticity mechanisms long-term potentiation (LTP, for iTBS) and depression (LTD, for cTBS). However, the neural basis of TMS effects has not yet been studied in human neuronal cells, in particular at the level of gene expression and synaptogenesis. To investigate responses to TBS in living human neurons, we differentiated human SH-SY5Y cells toward a mature neural phenotype, and stimulated them with iTBS, cTBS, or sham (placebo) TBS. Changes in (a) mRNA expression of a set of target genes (previously associated with synaptic plasticity), and (b) morphological parameters of neurite outgrowth following TBS were quantified. We found no general effects of stimulation condition or time on gene expression, though we did observe a significantly enhanced expression of plasticity genes NTRK2 and MAPK9 24 h after iTBS as compared to sham TBS. This specific effect provides unique support for the widely assumed plasticity mechanisms underlying iTBS effects on human cortex excitability. In addition to this protocol-specific increase in plasticity gene expression 24 h after iTBS stimulation, we establish the feasibility of stimulating living human neuron with TBS, and the importance of moving to more complex human in vitro models to understand the underlying plasticity mechanisms of TBS stimulation.

Microtubule Dysfunction: A Common Feature of Neurodegenerative Diseases

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.

The Mechanism of Tubulin Assembly into Microtubules: Insights from Structural Studies

Microtubules are cytoskeletal components involved in pivotal eukaryotic functions such as cell division, ciliogenesis, and intracellular trafficking. They assemble from αβ-tubulin heterodimers and disassemble in a process called dynamic instability, which is driven by GTP hydrolysis. Structures of the microtubule and of soluble tubulin have been determined by cryo-EM and by X-ray crystallography, respectively. Altogether, these data define the mechanism of tubulin assembly-disassembly at atomic or near-atomic level. We review here the structural changes that occur during assembly, tubulin switching from a curved conformation in solution to a straight one in the microtubule core. We also present more subtle changes associated with GTP binding, leading to tubulin activation for assembly. Finally, we show how cryo-EM and X-ray crystallography are complementary methods to characterize the interaction of tubulin with proteins involved either in intracellular transport or in microtubule dynamics regulation.

Rat Model of Cockayne Syndrome Neurological Disease

Cockayne syndrome (CS) is a rare genetic neurodevelopmental disorder, characterized by a deficiency in transcription-coupled subpathway of nucleotide excision DNA repair (TC-NER). Mutation of the Cockayne syndrome B (CSB) gene affects basal transcription, which is considered a major cause of CS neurologic dysfunction. Here, we generate a rat model by mimicking a nonsense mutation in the CSB gene. In contrast to that of the Csb^-/- mouse models, the brains of the CSB-deficient rats are more profoundly affected. The cerebellar cortex shows significant atrophy and dysmyelination. Aberrant foliation of the cerebellum and deformed hippocampus are visible. The white matter displays high glial fibrillary acidic protein (GFAP) staining indicative of reactive astrogliosis. RNA sequencing (RNA-seq) analysis reveals that CSB deficiency affects the expression of hundreds of genes, many of which are neuronal genes, suggesting that transcription dysregulation could contribute to the neurologic disease seen in the CSB rat models.

Microtubule Dynamics and Neuronal Excitability: Advances on Cytoskeletal Components Implicated in Epileptic Phenomena

Extensive researches have deepened knowledge on the role of synaptic components in epileptogenesis, but limited attention has been devoted to the potential implication of the cytoskeleton. The study of the development of epilepsy and hyperexcitability states involves molecular, synaptic, and structural alterations of neuronal bioelectric activity. In this paper we aim to explore the neurobiological targets involved in microtubule functioning and cytoskeletal transport, i.e. how dynamic scaffolding of microtubules can influence neuronal morphology and excitability, in order to suggest a potential role for microtubule dynamics in the processes turning a normal neuronal network in a hyperexcited one. Pathophysiological alterations of microtubule dynamics inducing neurodegeneration, network remodeling and relative impairment on synaptic transmission were overviewed. Recent researches were reported on the phosphorylation state of microtubule-associated proteins such as tau in neurodegenerative diseases and epileptic states, but also on the effect of microtubule-active agents influencing cytoskeleton destabilization in epilepsy models. The manipulation of microtubule polymerization was found effective in the modulation of hyperexcitability. In addition, it was considered the importance of microtubules and related neurotrophic factors during neural development since they are essential for the formation of a properly functional neuronal network. Otherwise, this can lead to cognitive deficits, hyperexcitability phenomena and neurodevelopmental disorders. Lastly, we evaluated the role of microtubule dynamics on neuronal efficiency considering their importance in the transport of mitochondria, cellular elements fulfilling energy requirements for neuronal activity, and a putative influence on cannabinoid-mediated neuroprotection. This review provides novel perspectives for the implication of microtubule dynamics in the development of epileptic phenomena.

Detrimental Effects of Multiple Mutations in Position 240 of Fusarium graminearum β2-Tubulin

Fusarium graminearum causes Fusarium head blight (FHB), a destructive disease of cereal crops worldwide. Carbendazim (methylbenzimidazol-2-ylcarbamate [MBC]) is widely used for controlling FHB. A previous study showed that the F240L mutation in the β₂-tubulin of F. graminearum (Fgβ₂-tubulin) confers hypersensitivity to MBC. Whether the substitution of phenylalanine by other amino acids in position 240 of the Fgβ₂-tubulin gene also confers hypersensitivity to MBC is unknown. Moreover, the biological fitness of these mutants is poorly understood. In this study, we substituted position 240 of Fgβ₂-tubulin with other amino acids. We found that the F240A, F240E, F240I, and F240Y mutations in Fgβ₂-tubulin could also confer F. graminearum hypersensitivity to MBC, although the effective concentration resulting in 50% inhibition (EC₅₀) differed among the mutations. The F240G mutation, in contrast, decreased the sensitivity to MBC. In addition, a molecular docking assay indicated that the binding affinity between Fgβ₂-tubulin and MBC were increased by the F240A, F240E, F240I, and F240Y mutations but decreased by the F240G mutation. All mutants had normal conidial morphology, but the growth rates and pathogenicity of the F240A, F240E, F240G, F240I, and F240Y mutants were significantly decreased. Moreover, the F240A and F240G mutants produced twisted hyphae. In addition, microtubules were sparse and rarely observed in β₂F240A-EGFP, β₂F240E-EGFP, and β₂F240G-EGFP. These results indicate that position 240 (phenylalanine) is not only vital to the function of Fgβ₂-tubulin but also plays an important role in regulating the sensitivity of F. graminearum to MBC. Any mutation in this site would be detrimental to survival.

Systematic Humanization of the Yeast Cytoskeleton Discerns Functionally Replaceable from Divergent Human Genes

Many gene families have been expanded by gene duplications along the human lineage, relative to ancestral opisthokonts, but the extent to which the duplicated genes function similarly is understudied. Here, we focused on structural cytoskeletal genes involved in critical cellular processes, including chromosome segregation, macromolecular transport, and cell shape maintenance. To determine functional redundancy and divergence of duplicated human genes, we systematically humanized the yeast actin, myosin, tubulin, and septin genes, testing ∼81% of human cytoskeletal genes across seven gene families for their ability to complement a growth defect induced by inactivation or deletion of the corresponding yeast ortholog. In five of seven families-all but α-tubulin and light myosin, we found at least one human gene capable of complementing loss of the yeast gene. Despite rescuing growth defects, we observed differential abilities of human genes to rescue cell morphology, meiosis, and mating defects. By comparing phenotypes of humanized strains with deletion phenotypes of their interaction partners, we identify instances of human genes in the actin and septin families capable of carrying out essential functions, but failing to fully complement the cytoskeletal roles of their yeast orthologs, thus leading to abnormal cell morphologies. Overall, we show that duplicated human cytoskeletal genes appear to have diverged such that only a few human genes within each family are capable of replacing the essential roles of their yeast orthologs. The resulting yeast strains with humanized cytoskeletal components now provide surrogate platforms to characterize human genes in simplified eukaryotic contexts.

The recurrent TUBB3 Gly98Ser substitution is the first described to inconsistently result in CFEOM3

Missense variants in TUBB3 have historically been associated with either congenital fibrosis of the extraocular muscles type 3 (CFEOM3) or malformations of cortical development (MCD). Until a recent report identified two amino acid substitutions in four patients that had clinical features of both disorders, pathogenic variants of TUBB3 were thought distinct to either respective disorder. Three recurrent de novo Gly71Arg TUBB3 substitutions and a single patient with a de novo Gly98Ser substitution blurred the MCD and CFEOM3 phenotypic distinctions. Here we report a second patient with a missense c.292G>A (p.Gly98Ser) substitution, but without CFEOM3, the first reported evidence that even the same TUBB3 substitution can produce a spectrum of TUBB3 syndrome phenotypes. Our patient presented with amblyopia, exotropia, optic disc pallor, and developmental delay. Neuroimaging identified hypoplasia of the corpus callosum, interdigitation of the frontal lobe gyri, and dysplasia or hypoplasia of the optic nerves, basal ganglia, brainstem, and cerebellum. This report identifies the TUBB3 Gly98Ser substitution to be recurrent but inconsistently including CFEOM3, and identifies the absence of joint contractures and the presence of optic disc abnormalities that may be genotype-specific to the TUBB3 Gly98Ser substitution.

Altered White Matter Organization in the TUBB3 E410K Syndrome

Seven unrelated individuals (four pediatric, three adults) with the TUBB3 E410K syndrome, harboring identical de novo heterozygous TUBB3 c.1228 G>A mutations, underwent neuropsychological testing and neuroimaging. Despite the absence of cortical malformations, they have intellectual and social disabilities. To search for potential etiologies for these deficits, we compared their brain's structural and white matter organization to 22 controls using structural and diffusion magnetic resonance imaging. Diffusion images were processed to calculate fractional anisotropy (FA) and perform tract reconstructions. Cortical parcellation-based network analysis and gyral topology-based FA analyses were performed. Major interhemispheric, projection and intrahemispheric tracts were manually segmented. Subjects had decreased corpus callosum volume and decreased network efficiency. While only pediatric subjects had diffuse decreases in FA predominantly affecting mid- and long-range tracts, only adult subjects had white matter volume loss associated with decreased cortical surface area. All subjects showed aberrant corticospinal tract trajectory and bilateral absence of the dorsal language network long segment. Furthermore, pediatric subjects had more tracts with decreased FA compared with controls than did adult subjects. These findings define a TUBB3 E410K neuroimaging endophenotype and lead to the hypothesis that the age-related changes are due to microscopic intrahemispheric misguided axons that are pruned during maturation.

Targeting the Inositol-Requiring Enzyme-1 Pathway Efficiently Reverts Zika Virus-Induced Neurogenesis and Spermatogenesis Marker Perturbations

Zika virus (ZIKV) is an emerging flavivirus that may be associated with congenital anomalies in infected fetuses and severe neurological and genital tract complications in infected adults. Currently, antiviral treatments to revert these ZIKV-induced complications are lacking. ZIKV infection has recently been suggested to upregulate the host unfolded protein response, which may contribute to the congenital neurological anomalies. As an extension from these findings, we thoroughly investigated the ZIKV-induced unfolded protein response using a combination of the neuronal cell line, induced pluripotent stem cell-derived human neuronal stem and progenitor cells, and an interferon receptor-deficient A129 mouse model. Our results revealed a critical contribution of the inositol-requiring enzyme-1 (IRE1) arm of the unfolded protein response to ZIKV-induced neurological and testicular complications. Importantly, the inhibition of the IRE1 signaling pathway activation with KIRA6 (kinase-inhibiting RNAse attenuator 6), a selective small molecule IRE1 inhibitor that promotes cell survival, potently reverted the ZIKV-induced perturbations of the key gene expressions associated with neurogenesis and spermatogenesis in vitro and in vivo, highlighting the potential of IRE1 inhibition as a novel host-targeting antiviral strategy in combating against ZIKV-induced neurological and testicular pathologies.

Recovery of motor function after traumatic spinal cord injury by using plasma-synthesized polypyrrole/iodine application in combination with a mixed rehabilitation scheme

Traumatic spinal cord injury (TSCI) can cause paralysis and permanent disability. Rehabilitation (RB) is currently the only accepted treatment, although its beneficial effect is limited. The development of biomaterials has provided therapeutic possibilities for TSCI, where our research group previously showed that the plasma-synthesized polypyrrole/iodine (PPy/I), a biopolymer with different physicochemical characteristics than those of the PPy synthesized by conventional methods, promotes recovery of motor function after TSCI. The present study evaluated if the plasma-synthesized PPy/I applied in combination with RB could increase its beneficial effects and the mechanisms involved. Adult rats with TSCI were divided into no treatment (control); biopolymer (PPy/I); mixed RB by swimming and enriched environment (SW/EE); and combined treatment (PPy/I + SW/EE) groups. Eight weeks after TSCI, the general health of the animals that received any of the treatments was better than the control animals. Functional recovery evaluated by two scales was better and was achieved in less time with the PPy/I + SW/EE combination. All treatments significantly increased βIII-tubulin (nerve plasticity) expression, but only PPy/I increased GAP-43 (nerve regeneration) and MBP (myelination) expression when were analyzed by immunohistochemistry. The expression of GFAP (glial scar) decreased in treated groups when determined by histochemistry, while morphometric analysis showed that tissue was better preserved when PPy/I and PPy/I + SW/EE were administered. The application of PPy/I + SW/EE, promotes the preservation of nervous tissue, and the expression of molecules related to plasticity as βIII-tubulin, reduces the glial scar, improves general health and allows the recovery of motor function after TSCI. The implant of the biomaterial polypyrrole/iodine (PPy/I) synthesized by plasma (an unconventional synthesis method), in combination with a mixed rehabilitation scheme with swimming and enriched environment applied after a traumatic spinal cord injury, promotes expression of GAP-43 and βIII-tubulin (molecules related to plasticity and nerve regeneration) and reduces the expression of GFAP (molecule related to the formation of the glial scar). Both effects together allow the formation of nerve fibers, the reconnection of the spinal cord in the area of injury and the recovery of lost motor function. The figure shows the colocalization (yellow) of βIII-tubilin (red) and GAP-43 (green) in fibers crossing the epicenter of the injury (arrowheads) that reconnect the rostral and caudal ends of the injured spinal cord and allowed recovery of motor function.

TUBB3 Is Associated with High-Grade Histology, Poor Prognosis, p53 Expression, and Cancer Stem Cell Markers in Clear Cell Renal Cell Carcinoma

BACKGROUND

βIII-Tubulin, encoded by the TUBB3 gene, is a microtubule protein. Several studies have shown that overexpression of TUBB3 is linked to poor prognosis and is involved in taxane resistance in some cancers.

OBJECTIVE

The aim of this study was to analyze the expression and function of TUBB3 in clear cell renal cell carcinoma (ccRCC).

METHODS

The expression of TUBB3 was determined using immuno-histochemistry in ccRCC specimens. The effects of TUBB3 knockdown on cell growth and invasion were evaluated in RCC cell lines. We analyzed the interaction between TUBB3, p53, cancer stem cell markers, and PD-L1.

RESULTS

In 137 cases of ccRCC, immunohistochemistry showed that 28 (20%) of the ccRCC cases were positive for TUBB3. High TUBB3 expression was significantly correlated with high nuclear grade, high T stage, and N stage. A Kaplan-Meier analysis showed that high expression of TUBB3 was associated with poor overall survival after nephrectomy. In silico analysis also showed that high TUBB3 expression was correlated with overall survival. Knockdown of TUBB3 suppressed cell growth and invasion in 786-O and Caki-1 cells. High TUBB3 expression was associated with CD44, CD133, PD-L1, and p53 in ccRCC. We generated p53 knockout cells using the CRISPR-Cas9 system. Western blotting revealed that p53 knockout upregulated the expression of TUBB3.

CONCLUSION

These results suggest that TUBB3 may play an oncogenic role and could be a potential therapeutic target in ccRCC.

TUBB3 E410K syndrome: Case report and review of the clinical spectrum of TUBB3 mutations

The tubulinopathies refer to a wide range of brain malformations caused by mutations in one of the seven genes encoding different tubulin's isotypes. The β-tubulin isotype III (TUBB3) gene has a primary function in nervous system development and axon generation and maintenance, due to its neuron-specific expression pattern. A recurrent heterozygous mutation, c.1228G > A; p.E410K, in TUBB3 gene is responsible of a rare disorder clinically characterized by congenital fibrosis of the extraocular muscle type 3 (CFEOM3), intellectual disability and a wide range of neurological and endocrine abnormalities. Other mutations have been described spanning the entire gene and genotype-phenotype correlations have been proposed. We report on a 3-year-old boy in whom clinical exome sequencing allowed to identify a de novo TUBB3 E410K mutation as the molecular cause underlying a complex phenotype characterized by a severe bilateral palpebral ptosis refractory to eye surgery, psychomotor delay, absent speech, hypogonadism, celiac disease, and cyclic vomiting. Brain MRI revealed thinning of the corpus callosum with no evidence of malformation cortical dysplasia. We reviewed available records of patients with TUBB3 E410K mutation and compared their phenotype with the clinical outcome of patients with other mutations in TUBB3 gene. The present study confirms that TUBB3 E410K results in a clinically recognizable phenotype, unassociated to the distinct cortical dysplasia caused by other mutations in the same gene. Early molecular characterization of TUBB3 E410K syndrome is critical for targeted genetic counseling and prompt prospective care in term of neurological, ophthalmological, endocrine, and gastrointestinal follow-up.

Defining the phenotypical spectrum associated with variants in TUBB2A

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.

Autoantibodies and Malaria: Where We Stand? Insights Into Pathogenesis and Protection

Autoantibodies are frequently reported in patients with malaria, but whether they contribute to protection or to pathology is an issue of debate. A large body of evidence indicates that antibodies against host-self components are associated to malaria clinical outcomes such as cerebral malaria, renal dysfunction and anemia. Nonetheless, self-reactive immunoglobulins induced during an infection can also mediate protection. In light of these controversies, we summarize here the latest findings in our understanding of autoimmune responses in malaria, focusing on Plasmodium falciparum and Plasmodium vivax. We review the main targets of self-antibody responses in malaria as well as the current, but still limited, knowledge of their role in disease pathogenesis or protection.

MRI Features in a Rat Model of H-ABC Tubulinopathy

Tubulinopathies are a group of recently described diseases characterized by mutations in the tubulin genes. Mutations in TUBB4A produce diseases such as dystonia type 4 (DYT4) and hypomyelination with atrophy of the basal ganglia and cerebellum (H-ABC), which are clinically diagnosed by magnetic resonance imaging (MRI). We propose the taiep rat as the first animal model for tubulinopathies. The spontaneous mutant suffers from a syndrome related to a central leukodystrophy and characterized by tremor, ataxia, immobility, epilepsy, and paralysis. The pathological signs presented by these rats and the morphological changes we found by our longitudinal MRI study are similar to those of patients with mutations in TUBB4A. The diffuse atrophy we found in brain, cerebellum and spinal cord is related to the changes detectable in many human tubulinopathies and in particular in H-ABC patients, where myelin degeneration at the level of putamen and cerebellum is a clinical trademark of the disease. We performed Tubb4a exon analysis to corroborate the genetic defect and formulated hypotheses about the effect of amino acid 302 change on protein physiology. Optical microscopy of taiep rat cerebella and spinal cord confirmed the optical density loss in white matter associated with myelin loss, despite the persistence of neural fibers.

Autosomal dominant TUBB3-related syndrome: Fetal, radiologic, clinical and morphological features

OBJECTIVE

To describe fetal, clinical, radiological, morphological features of TUBB3 related syndrome.

METHODS

We report two families each of two generations harboring a novel and a previously described heterozygous TUBB3 pathogenic variants. We compared these patients with other published TUBB3-related cases. We describe the pathological features of dysgyria in the two aborted fetuses.

RESULTS

The mother and son from family 1 had a history of mild developmental delay in motor and language skills and demonstrated mild cerebellar signs and mirror movements. Neuroimaging findings included: hypoplastic corpus callosum (CC), asymmetric ventriculomegaly and cerebellar vermis hypoplasia in all patients and frontal dysgyria in three. Autopsy of the fetal brain showed an unusual shape and orientation of the frontal sulci and gyri with normal cortical layering and no abnormal cell types. The mother of family 2 had congenital strabismus, mild muscle weakness on the right and a past history of developmental delay. Fetal brain MRI showed abnormal cerebral sulcation, hemispheric asymmetry, asymmetric ventriculomegaly, dysmorphic short CC and frontal cortical interdigitation. Autopsy demonstrated fronto-parietal predominant dysgyria, bilateral ventriculomegaly, hippocampal and CC hypoplasia, abnormal Sylvian fissure. Lamination and neuron morphology in the areas of dysgyria were normal.

CONCLUSIONS

TUBB3 related cortical malformations can be mild, consistent with dysgyria rather than typical pachygyria or polymicrogyria. The autopsy findings in fetal TUBB3 related dysgyria are abnormal orientation of sulci and gyri, but normal neuron morphology and layering. We suggest that TUBB3 - associated brain malformations can be suspected in-utero which in turn can aid in prognostic counselling and interpretation of genetic testing.

Alpha- and beta-tubulin isotypes are differentially expressed during brain development

Alpha- and beta-tubulin dimers polymerize into protofilaments that associate laterally to constitute a hollow tube, the microtubule. A dynamic network of interlinking filaments forms the microtubule cytoskeleton, which maintains the structure of cells and is key to various cellular processes including cell division, cell migration, and intracellular transport. Individual microtubules have an identity that depends on the differential integration of specific alpha- and beta-tubulin isotypes and is further specified by a variety of posttranslational modifications (PTMs). It is barely understood to which extent neighboring microtubules differ in their tubulin composition or whether specific tubulin isotypes cluster along the polymer. Furthermore, our knowledge about the spatio-temporal expression patterns of tubulin isotypes is limited, not at least due to the lack of antibodies or antibody cross-reactivities. Here, we asked which alpha- and beta-tubulin mRNAs and proteins are expressed in developing hippocampal neuron cultures and ex vivo brain tissue lysates. Using heterologous expression of GFP-tubulin fusion proteins, we systematically tested antibody-specificities against various tubulin isotypes. Our data provide quantitative information about tubulin expression levels in the mouse brain and classify tubulin isotypes during pre- and postnatal development.

Conformational change and GTPase activity of human tubulin: A comparative study on Alzheimer's disease and healthy brain

In Alzheimer's disease (AD), the most common form of dementia, microtubules (MTs) play a pivotal role through their highly dynamic structure and instability. They mediate axonal transport that is crucial to synaptic viability. MT assembly, dynamic instability and stabilization are modulated by tau proteins, whose detachment initiates MT disintegration. Albeit extensive research, the role of GTPase activity in molecular mechanism of stability remains controversial. We hypothesized that GTPase activity is altered in AD leading to microtubule dynamic dysfunction and ultimately to neuronal death. In this paper, fresh tubulin was purified by chromatography from normal young adult, normal aged, and Alzheimer's brain tissues. Polymerization pattern, assembly kinetics and dynamics, critical concentration, GTPase activity, interaction with tau, intermolecular geometry, and conformational changes were explored via Förster Resonance Energy Transfer (FRET) and various spectroscopy methods. Results showed slower MT assembly process in samples from the brains of people with AD compared with normal young and aged brains. This observation was characterized by prolonged lag phase and increased critical and inactive concentration of tubulin. In addition, the GTPase activity in samples from AD brains was significantly higher than in both normal young and normal aged samples, concurrent with profound conformational changes and contracted intermolecular MT-tau distances as revealed by FRET. These alterations were partially restored in the presence of a microtubule stabilizer, paclitaxel. We proposed that alterations of both tubulin function and GTPase activity may be involved in the molecular neuropathogenesis of AD, thus providing new avenues for therapeutic approaches.

Suckling, Feeding, and Swallowing: Behaviors, Circuits, and Targets for Neurodevelopmental Pathology

All mammals must suckle and swallow at birth, and subsequently chew and swallow solid foods, for optimal growth and health. These initially innate behaviors depend critically upon coordinated development of the mouth, tongue, pharynx, and larynx as well as the cranial nerves that control these structures. Disrupted suckling, feeding, and swallowing from birth onward-perinatal dysphagia-is often associated with several neurodevelopmental disorders that subsequently alter complex behaviors. Apparently, a broad range of neurodevelopmental pathologic mechanisms also target oropharyngeal and cranial nerve differentiation. These aberrant mechanisms, including altered patterning, progenitor specification, and neurite growth, prefigure dysphagia and may then compromise circuits for additional behavioral capacities. Thus, perinatal dysphagia may be an early indicator of disrupted genetic and developmental programs that compromise neural circuits and yield a broad range of behavioral deficits in neurodevelopmental disorders.

Axonal precursor miRNAs hitchhike on endosomes and locally regulate the development of neural circuits

Various species of non‐coding RNAs (ncRNAs) are enriched in specific subcellular compartments, but the mechanisms orchestrating their localization and their local functions remain largely unknown. We investigated both aspects using the elongating retinal ganglion cell axon and its tip, the growth cone, as models. We reveal that specific endogenous precursor microRNAs (pre‐miRNAs) are actively trafficked to distal axons by hitchhiking primarily on late endosomes/lysosomes. Upon exposure to the axon guidance cue semaphorin 3A (Sema3A), pre‐miRNAs are processed specifically within axons into newly generated miRNAs, one of which, in turn, silences the basal translation of tubulin beta 3 class III (TUBB3), but not amyloid beta precursor protein (APP). At the organismal level, these mature miRNAs are required for growth cone steering and a fully functional visual system. Overall, our results uncover a novel mode of ncRNA transport from one cytosolic compartment to another within polarized cells. They also reveal that newly generated miRNAs are critical components of a ncRNA‐based signaling pathway that transduces environmental signals into the structural remodeling of subcellular compartments.

The microtubule skeleton and the evolution of neuronal complexity in vertebrates

The evolution of a highly developed nervous system is mirrored by the ability of individual neurons to develop increased morphological complexity. As microtubules (MTs) are crucially involved in neuronal development, we tested the hypothesis that the evolution of complexity is driven by an increasing capacity of the MT system for regulated molecular interactions as it may be implemented by a higher number of molecular players and a greater ability of the individual molecules to interact. We performed bioinformatics analysis on different classes of components of the vertebrate neuronal MT cytoskeleton. We show that the number of orthologs of tubulin structure proteins, MT-binding proteins and tubulin-sequestering proteins expanded during vertebrate evolution. We observed that protein diversity of MT-binding and tubulin-sequestering proteins increased by alternative splicing. In addition, we found that regions of the MT-binding protein tau and MAP6 displayed a clear increase in disorder extent during evolution. The data provide evidence that vertebrate evolution is paralleled by gene expansions, changes in alternative splicing and evolution of coding sequences of components of the MT system. The results suggest that in particular evolutionary changes in tubulin-structure proteins, MT-binding proteins and tubulin-sequestering proteins were prominent drivers for the development of increased neuronal complexity.

Nerve guidance conduit design based on self-rolling tubes

The current gold standard in peripheral nerve repair is nerve autografts for bridging gaps larger than a centimeter. However, autografts are associated with a low availability and the loss of function at the donor site. Nerve guidance conduits (NGCs) made of biocompatible and biodegradable materials reflect suitable alternatives. Clinically approved NGCs comprise either wraps that are rolled around the loose ends of the nerve or steady-state tubes; however, both lack internal guidance structures. Here, we established self-rolling NGCs to allow for gentle encapsulation of nerve cells together with supportive microenvironments, such as (1) an inner tube wall coating with a bioactive spider silk film, (2) an inner tube wall lining using an anisotropic spider silk non-woven mat, or (3) a luminal filler using an anisotropic collagen cryogel. Neuronal cells adhered and differentiated inside the modified tubes and formed neurites, which were oriented along the guidance structures provided by the spider silk non-woven mat or by the fibrillary structure of the collagen cryogel. Thus, our size-adaptable NGCs provide several features useful for peripheral nerve repair, and distinct combinations of the used elements might support and enhance the clinical outcome.

RAG-2 deficiency results in fewer phosphorylated histone H2AX foci, but increased retinal ganglion cell death and altered axonal growth

DNA double-strand breaks (DSBs), selectively visualized as γ-H2AX⁺ foci, occur during the development of the central nervous system, including the retina, although their origin and biological significance are poorly understood. Mutant mice with DSB repair mechanism defects exhibit increased numbers of γ-H2AX⁺ foci, increased cell death during neural development, and alterations in axonogenesis in the embryonic retina. The aim of this study was to identify putative sources of DSBs. One of the identified DSBs sources is LINE-1 retrotransposition. While we did not detect changes in LINE-1 DNA content during the early period of cell death associated with retinal neurogenesis, retinal development was altered in mice lacking RAG-2, a component of the RAG-1,2-complex responsible for initiating somatic recombination in lymphocytes. Although γ-H2AX⁺ foci were less abundant in the rag2^−/− mouse retina, retinal ganglion cell death was increased and axonal growth and navigation were impaired in the RAG-2 deficient mice, a phenotype shared with mutant mice with defective DNA repair mechanisms. These findings demonstrate that RAG-2 is necessary for proper retinal development, and suggest that both DSB generation and repair are genuine processes intrinsic to neural development.

Congenital fibrosis of the extra-ocular muscles (CFEOM) and the cranial dysinnervation disorders

Congenital fibrosis of the extraocular muscles (CFEOM) is one of the congenital cranial dysinnervation disorders (CCDDs). This review discusses the characteristics of the CFEOM phenotypes and the CCDDs, the fibrosis associated with these disorders and the processes, and genes involved in the embryological development of cranial neuromuscular units. In particular, it focuses on the genetics of neural crest identity, axon guidance, and axon construction in relation to the CFEOMs and some consideration of treatment strategies.

Carbendazim-resistance associated β2 -tubulin substitutions increase deoxynivalenol biosynthesis by reducing the interaction between β2 -tubulin and IDH3 in Fusarium graminearum

Microtubule is a well-known structural protein participating in cell division, motility and vesicle traffic. In this study, we found that β₂ -tubulin, one of the microtubule components, plays an important role in regulating secondary metabolite deoxynivalenol (DON) biosynthesis in Fusarium graminearum by interacting with isocitrate dehydrogenase subunit 3 (IDH3). We found IDH3 negatively regulate DON biosynthesis by reducing acetyl-CoA accumulation in F. graminearum and DON biosynthesis was stimulated by exogenous acetyl-CoA. In addition, the expression of IDH3 significantly decreased in the carbendazim-resistant mutant nt167 (Fgβ₂ ^F167Y ). Furthermore, we found that carbendazim-resistance associated β₂ -tubulin substitutions reducing the interaction intensity between β₂ -tubulin and IDH3. Interestingly, we demonstrated that β₂ -tubulin inhibitor carbendazim can disrupt the interaction between β₂ -tubulin and IDH3. The decreased interaction intensity between β₂ -tubulin and IDH3 resulted in the decreased expression of IDH3, which can cause the accumulation of acetyl-CoA, precursor of DON biosynthesis in F. graminearum. Thus, we revealed that carbendazim-resistance associated β₂ -tubulin substitutions or carbendazim treatment increases DON biosynthesis by reducing the interaction between β₂ -tubulin and IDH3 in F. graminearum. Taken together, the novel findings give the new perspectives of β₂ -tubulin in regulating secondary metabolism in phytopathogenic fungi.

Anomalous superior oblique muscles and tendons in congenital fibrosis of the extraocular muscles

PURPOSE

To evaluate the finding of anomalous superior oblique muscles in congenital fibrosis of the extraocular muscles (CFEOM), a feature not previously emphasized in this condition.

METHODS

The medical records of all patients clinically or genetically diagnosed with CFEOM at Boston Children's Hospital between 2010 and 2018 were reviewed retrospectively. Those who underwent strabismus surgery during the study period were included in the analysis. Baseline patient characteristics, type of CFEOM, results of genetic testing, and intraoperative features of the superior oblique muscle or tendon were recorded.

RESULTS

Of 24 patients identified (age range, 1 month to 62 years), 10 (42%) had genetically confirmed CFEOM, and 22 underwent strabismus surgery, 14 (64%) involving the superior oblique muscle. Of these, 7 (50%) had anomalously inserted tendons (most commonly attached nasal to the superior rectus muscle), whereas 7 (50%) had increased superior oblique muscle tension.

CONCLUSIONS

Half of CFEOM patients who underwent superior oblique surgery had abnormally inserted superior oblique tendons, and 50% had tight muscles or abnormally thin tendons, findings that have not been well-characterized in this condition. The findings suggest that abnormal insertion of the superior oblique muscles and tendons are additional features of the disease process in CFEOM that have not been described previously. These features may contribute to the severe upgaze limitation in CFEOM and highlight the importance of superior oblique tenotomy in surgical management.

Bi-allelic Pathogenic Variants in TUBGCP2 Cause Microcephaly and Lissencephaly Spectrum Disorders

Lissencephaly comprises a spectrum of malformations of cortical development. This spectrum includes agyria, pachygyria, and subcortical band heterotopia; each represents anatomical malformations of brain cortical development caused by neuronal migration defects. The molecular etiologies of neuronal migration anomalies are highly enriched for genes encoding microtubules and microtubule-associated proteins, and this enrichment highlights the critical role for these genes in cortical growth and gyrification. Using exome sequencing and family based rare variant analyses, we identified a homozygous variant (c.997C>T [p.Arg333Cys]) in TUBGCP2, encoding gamma-tubulin complex protein 2 (GCP2), in two individuals from a consanguineous family; both individuals presented with microcephaly and developmental delay. GCP2 forms the multiprotein γ-tubulin ring complex (γ-TuRC) together with γ-tubulin and other GCPs to regulate the assembly of microtubules. By querying clinical exome sequencing cases and through GeneMatcher-facilitated collaborations, we found three additional families with bi-allelic variation and similarly affected phenotypes including a homozygous variant (c.1843G>C [p.Ala615Pro]) in two families and compound heterozygous variants consisting of one missense variant (c.889C>T [p.Arg297Cys]) and one splice variant (c.2025-2A>G) in another family. Brain imaging from all five affected individuals revealed varying degrees of cortical malformations including pachygyria and subcortical band heterotopia, presumably caused by disruption of neuronal migration. Our data demonstrate that pathogenic variants in TUBGCP2 cause an autosomal recessive neurodevelopmental trait consisting of a neuronal migration disorder, and our data implicate GCP2 as a core component of γ-TuRC in neuronal migrating cells.

Tubulin mutations in brain development disorders: Why haploinsufficiency does not explain TUBA1A tubulinopathies

The neuronal cytoskeleton performs incredible feats during nervous system development. Extension of neuronal processes, migration, and synapse formation rely on the proper regulation of microtubules. Mutations that disrupt the primary α-tubulin expressed during brain development, TUBA1A, are associated with a spectrum of human brain malformations. One model posits that TUBA1A mutations lead to a reduction in tubulin subunits available for microtubule polymerization, which represents a haploinsufficiency mechanism. We propose an alternative model for the majority of tubulinopathy mutations, in which the mutant tubulin polymerizes into the microtubule lattice to dominantly "poison" microtubule function. Nine distinct α-tubulin and ten β-tubulin genes have been identified in the human genome. These genes encode similar tubulin proteins, called isotypes. Multiple tubulin isotypes may partially compensate for heterozygous deletion of a tubulin gene, but may not overcome the disruption caused by missense mutations that dominantly alter microtubule function. Here, we describe disorders attributed to haploinsufficiency versus dominant negative mechanisms to demonstrate the hallmark features of each disorder. We summarize literature on mouse models that represent both knockout and point mutants in tubulin genes, with an emphasis on how these mutations might provide insight into the nature of tubulinopathy patient mutations. Finally, we present data from a panel of TUBA1A tubulinopathy mutations generated in yeast α-tubulin that demonstrate that α-tubulin mutants can incorporate into the microtubule network and support viability of yeast growth. This perspective on tubulinopathy mutations draws on previous studies and additional data to provide a fresh perspective on how TUBA1A mutations disrupt neurodevelopment.

Outcomes of strabismus surgery in genetically confirmed congenital fibrosis of the extraocular muscles

PURPOSE

To detail surgical strategy and strabismus outcomes in a genetically defined cohort of patients with congenital fibrosis of the extraocular muscles (CFEOM).

METHODS

A total of 13 patients with genetically confirmed CFEOM (via genetic testing for mutations in KIF21A, PHOX2A, and TUBB3) were retrospectively identified after undergoing strabismus surgery at Boston Children's Hospital and surgical outcomes were compared.

RESULTS

Age at first surgery ranged from 11 months to 63 years, with an average of 3 strabismus procedures per patient. Ten patients had CFEOM1, of whom 9 had the KIF21A R954W amino acid substitution and 1 had the M947T amino acid substitution. Of the 3 with CFEOM3, 2 had the TUBB3 E410K amino acid substitution, and 1 had a previously unreported E410V amino acid substitution. CFEOM1 patients all underwent at least 1 procedure to address chin-up posture. Chin-up posture improved from 24° ± 8° before surgery to 10.0° ± 8° postoperatively (P < 0.001). Three CFEOM1 patients developed exotropia after vertical muscle surgery alone; all had the R954W amino acid substitution. Postoperatively, 1 CFEOM1 patient developed a corneal ulcer. All CFEOM3 patients appeared to have underlying exposure keratopathy, successfully treated with prosthetic replacement of the ocular surface ecosystem (PROSE) lens in 2 patients.

CONCLUSIONS

CFEOM is a complex strabismus disorder for which surgical management is difficult. Despite an aggressive surgical approach, multiple procedures may be necessary to achieve a desirable surgical effect. Knowledge of the underlying genetic diagnosis may help to inform surgical management.

[JNK/c-Jun signaling pathway mediates arginine vasopressin neuron regeneration by promoting cytoskeleton reconstruction in rats with electrical lesions of the pituitary stalk]

OBJECTIVE

To investigate the mechanism by which doublecortin promotes the recovery of cytoskeleton in arginine vasopressin (AVP) neurons in rats with electrical lesions of the pituitary stalk (PEL).

METHODS

Thirty-two SD rats were randomized into PEL group with electrical lesions of the pituitary stalk through the floor of the skull base (n=25) and sham operation group (n=7), and the daily water consumption (DWC), daily urine volume (DUV) and urine specific gravity (USG) of the rats were recorded. Four rats on day 1 and 7 rats on each of days 3, 7 and 14 after PEL as well as the sham-operated rats were sacrificed for detection of the expressions of β-Tubulin (Tuj1), doublecortin and caspase- 3 in the AVP neurons of the supraoptic nucleus using immunofluorescence assay and Western blotting.

RESULTS

After PEL, the rats exhibited a typical triphasic pattern of diabetes insipidus, with the postoperative days 1-2 as the phase one, days 3-5 as the phase two, and days 6-14 as the phase three. Immunofluorescent results indicated the repair of the AVP neurons evidenced by significantly increased doublecortin expressions in the AVP neurons following PEL; similarly, the expression of Tuj1 also increased progressively after PEL, reaching the peak level on day 7 after PEL. The apoptotic rates of the AVP neurons exhibited a reverse pattern of variation, peaking on postoperative day 3 followed by progressive reduction till day 14. Western blotting showed that the expressions of c-Jun and p-c-Jun were up-regulated significantly on day 3 (P < 0.05) and 7 (P < 0.01) after PEL, while an upregulated p-JNK expression was detected only on day 3 (P < 0.05), as was consistent with the time-courses of neuronal recovery and apoptosis after PEL.

CONCLUSIONS

JNK/c-Jun pathway is activated after PEL to induce apoptosis of AVP neurons in the acute phase and to promote the repair of neuronal cytoskeleton by up-regulation of doublecortin and Tuj1 expressions.

FIGNL1 associates with KIF1Bβ and BICD1 to restrict dynein transport velocity during axon navigation

Atkins et al. identify a new role for Fidgetin-like 1 in motor axon navigation via its regulation of bidirectional axonal transport. They show that Fidgetin-like 1 binds Kif1bβ and the opposed polarity-directed motor dynein/dynactin in a molecular complex and controls circuit wiring by reducing dynein velocity in developing motor axons.

Neuronal connectivity relies on molecular motor-based axonal transport of diverse cargoes. Yet the precise players and regulatory mechanisms orchestrating such trafficking events remain largely unknown. We here report the ATPase Fignl1 as a novel regulator of bidirectional transport during axon navigation. Using a yeast two-hybrid screen and coimmunoprecipitation assays, we showed that Fignl1 binds the kinesin Kif1bβ and the dynein/dynactin adaptor Bicaudal D-1 (Bicd1) in a molecular complex including the dynactin subunit dynactin 1. Fignl1 colocalized with Kif1bβ and showed bidirectional mobility in zebrafish axons. Notably, Kif1bβ and Fignl1 loss of function similarly altered zebrafish motor axon pathfinding and increased dynein-based transport velocity of Rab3 vesicles in these navigating axons, pinpointing Fignl1/Kif1bβ as a dynein speed limiter complex. Accordingly, disrupting dynein/dynactin activity or Bicd1/Fignl1 interaction induced motor axon pathfinding defects characteristic of Fignl1 gain or loss of function, respectively. Finally, pharmacological inhibition of dynein activity partially rescued the axon pathfinding defects of Fignl1-depleted larvae. Together, our results identify Fignl1 as a key dynein regulator required for motor circuit wiring.

Differential requirements of tubulin genes in mammalian forebrain development

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.

Ex Vivo Oculomotor Slice Culture from Embryonic GFP-Expressing Mice for Time-Lapse Imaging of Oculomotor Nerve Outgrowth

Accurate eye movements are crucial for vision, but the development of the ocular motor system, especially the molecular pathways controlling axon guidance, has not been fully elucidated. This is partly due to technical limitations of traditional axon guidance assays. To identify additional axon guidance cues influencing the oculomotor nerve, an ex vivo slice assay to image the oculomotor nerve in real-time as it grows towards the eye was developed. E10.5 Isl^MN-GFP embryos are used to generate ex vivo slices by embedding them in agarose, slicing on a vibratome, then growing them in a microscope stage-top incubator with time-lapse photomicroscopy for 24-72 h. Control slices recapitulate the in vivo timing of outgrowth of axons from the nucleus to the orbit. Small molecule inhibitors or recombinant proteins can be added to the culture media to assess the role of different axon guidance pathways. This method has the advantages of maintaining more of the local microenvironment through which axons traverse, not axotomizing the growing axons, and assessing the axons at multiple points along their trajectory. It can also identify effects on specific subsets of axons. For example, inhibition of CXCR4 causes axons still within the midbrain to grow dorsally rather than ventrally, but axons that have already exited ventrally are not affected.

Congenital monocular elevation deficiency associated with a novel TUBB3 gene variant

Background

The genetic basis of monocular elevation deficiency (MED) is unclear. It has previously been considered to arise due to a supranuclear abnormality.

Methods

Two brothers with MED were referred to Leicester Royal Infirmary, UK from the local opticians. Their father had bilateral ptosis and was unable to elevate both eyes, consistent with the diagnosis of congenital fibrosis of extraocular muscles (CFEOM). Candidate sequencing was performed in all family members.

Results

Both affected siblings (aged 7 and 12 years) were unable to elevate the right eye. Their father had bilateral ptosis, left esotropia and bilateral limitation of elevation. Chin up head posture was present in the older sibling and the father. Bell’s phenomenon and vertical rotational vestibulo-ocular reflex were absent in the right eye for both children. Mild bilateral facial nerve palsy was present in the older sibling and the father. Both siblings had slight difficulty with tandem gait. MRI revealed hypoplastic oculomotor nerve. Left anterior insular focal cortical dysplasia was seen in the older sibling. Sequencing of TUBB3 revealed a novel heterozygous variant (c.1263G>C, p.E421D) segregating with the phenotype. This residue is in the C-terminal H12 α-helix of β-tubulin and is one of three putative kinesin binding sites.

Conclusion

We show that familial MED can arise from a TUBB3 variant and could be considered a limited form of CFEOM. Neurological features such as mild facial palsy and cortical malformations can be present in patients with MED. Thus, in individuals with congenital MED, consideration may be made for TUBB3 mutation screening.

Nasal Placode Development, GnRH Neuronal Migration and Kallmann Syndrome

The development of Gonadotropin releasing hormone-1 (GnRH) neurons is important for a functional reproduction system in vertebrates. Disruption of GnRH results in hypogonadism and if accompanied by anosmia is termed Kallmann Syndrome (KS). From their origin in the nasal placode, GnRH neurons migrate along the olfactory-derived vomeronasal axons to the nasal forebrain junction and then turn caudally into the developing forebrain. Although research on the origin of GnRH neurons, their migration and genes associated with KS has identified multiple factors that influence development of this system, several aspects still remain unclear. This review discusses development of the olfactory system, factors that regulate GnRH neuron formation and development of the olfactory system, migration of the GnRH neurons from the nose into the brain, and mutations in humans with KS that result from disruption of normal GnRH/olfactory systems development.