TUBA1A mutations identified in lissencephaly patients dominantly disrupt neuronal migration and impair dynein activity

Abstract

Tubulinopathies' are severe human brain malformations associated with mutations in tubulin genes. Despite the identification of many tubulin mutations in patients, we do not understand how these mutations impact the microtubule cytoskeleton, how the changes to microtubule function lead to brain malformations, or how different tubulin isotypes regulate microtubules to support normal neurodevelopment. TUBA1A α-tubulin is the most commonly affected tubulin isotype in tubulinopathy patients. Heterozygous mutations in TUBA1A have been identified in patients with diverse cortical malformations including microlissencephaly, lissencephaly, pachygyria, and polymicrogyria. Here we focus on mutations affecting the conserved arginine at position 402 (R402), which account for 30% of all reported TUBA1A mutations in patients. We demonstrate that exogenous expression of TUBA1A-R402C and TUBA1A-R402H patient alleles is sufficient to dominantly disrupt cortical neuron migration in the developing mouse brain, recapitulating the human lissencephaly phenotype. Intriguingly, ectopic expression of TUBA1A-R402C/H alleles does not alter morphology, axonal trafficking, or microtubule polymerization rates in cultured neurons, but does lead to subtle changes in axonal microtubule orientation. Further, we find that budding yeast α-tubulin with analogous R402C and R402H mutations assembles into microtubules but disrupts the activity of the microtubule motor dynein. The level of dynein impairment scales with abundance of R402 mutant α-tubulin in the cell. Together, our results support a model in which tubulinopathy mutations at R402 poison the microtubule network in young neurons by creating defective binding sites for dynein at the microtubule surface.

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

“…The haploinsufficiency hypothesis suggests that heterozygous TUBA1A mutations deplete the functional TUBA1A protein and therefore neurons do not have sufficient functional tubulin to support an array of demanding developmental processes. Alternatively, the dominant gain‐of‐function hypothesis posits that mutant TUBA1A is present in abundance, forms heterodimers that polymerize into microtubules, and then dominantly disrupts microtubule network properties, for example by poisoning interactions between microtubules and critical developmental MAPs (Aiken et al, ). The latter hypothesis is consistent with examples from other multi‐gene families, such as ion channels, which are resistant to disease caused by haploinsufficiency due to the availability of related genes that can compensate for loss‐of‐function.…”

“…Based on current literature, we developed specific predictions for how each selected patient mutation may alter α‐tubulin function to lead to the observed cortical malformation phenotype (Figure ). We purposefully included mutations that are hypothesized to act similarly to the TUBA1A mouse model mutants, with predicted haploinsufficiency consequences (N101S, R264C), as well as mutants which we predict act in a dominant manner to poison interactions with microtubule associated proteins (R402C/H, V409A/I, R422H, S158L) (Aiken et al, ; Al‐Bassam et al, ; Das et al, ; Fourniol et al, ; Löwe et al, ; Nogales, ; Tian et al, ; Uchimura et al, ; Zhang et al, ).…”

“…R264 residue mediates binding to tubulin chaperone cofactor TBCB (Tian et al, ) and structural data hints that it may mediate DCX binding (Fourniol et al, ). R402 residue facilitates dynein activity (Aiken, Moore, & Bates, ; Uchimura et al, ). Structural data suggests that V409 residue interacts with TOG domains (Das, Dickinson, Wood, Goldstein, & Slep, ).…”

Multiomics global landscape of stemness-related gene clusters in adipose-derived mesenchymal stem cells

“…CDC45 is an important component of the replication fork, participating in DNA unwinding [59]. TUBA1B is involved in mitosis, cell movement, intracellular movement, and other biological processes [60]. When activated in response to DNA damage, E2F1 can promote proliferation or apoptosis [61].…”

Microtubule Dysfunction: A Common Feature of Neurodegenerative Diseases

“…By contrast, TUBA1A is the most prevalent α-tubulin gene expressed in neurons [ 75 , 104 , 105 ]. Expression studies on its mRNA have shown that that this isotype is the most prevalent α-tubulin expressed in embryonic nervous system, representing more than 95% of total α-tubulin mRNA [ 106 , 107 ], consistent with its pathogenic role in migration disorders such as pachygyria, lissencephaly, and polymicrogyria [ 104 , 108 , 109 , 110 , 111 , 112 , 113 , 114 ]. The loss of Tuba1a in mouse is perinatal lethal and leads to significant forebrain dysmorphology [ 10 ].…”