Alternative titles; symbols
HGNC Approved Gene Symbol: TUBA4A
Cytogenetic location: 2q35 Genomic coordinates (GRCh38): 2:219,249,710-219,254,740 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 2q35 | Amyotrophic lateral sclerosis 22 with or without frontotemporal dementia | 616208 | Autosomal dominant | 3 |
See 602529 for general information about the alpha-tubulin gene family. Villasante et al. (1986) noted that testis-specific alpha-tubulin isotype (see also TUBA, 602528) constitutes a separate subfamily in both humans and mice. They stated that members of this subfamily have a fourth intron which is located at an identical position.
See Khodiyar et al. (2007) for a revised nomenclature of the alpha-tubulin gene family.
Using a chicken alpha-tubulin cDNA to screen a human genomic library, Wilde et al. (1982) cloned the H2-alpha gene.
Villasante et al. (1986) reported that the amino acid sequence of H2-alpha is identical to those of the mouse testis-specific alpha-tubulins, M-alpha-3 and M-alpha-7. In addition, the 3-prime untranslated region of the H2-alpha gene is 58% identical to those of the mouse genes. By Northern blot analysis, the authors determined that the M-alpha-3 and M-alpha-7 genes are expressed exclusively in testis.
Strassel et al. (2019) found that TUBA4A is upregulated during the late stages of human megakaryocyte differentiation and is highly expressed in platelets, where it may play a role in formation of the marginal band, which maintains the lenticular shape of platelets.
By heteroduplex analysis, Wilde et al. (1982) showed that the human H2-alpha gene has 4 exons spanning 5 kb. Todd and Naylor (1991) found that the testis-specific alpha-tubulin gene contains a polymorphic GT repeat sequence.
Crystal Structure
Ravelli et al. (2004) determined the crystal structure, at 3.5-angstrom resolution, of tubulin in complex with colchicine and with the stathmin-like domain of RB3 (RB3-SLD). It shows the interaction of RB3-SLD with 2 tubulin heterodimers in a curved complex capped by the SLD amino-terminal domain, which prevents the incorporation of the complexed tubulin into microtubules. A comparison with the structure of tubulin in protofilaments showed changes in the subunits of tubulin as it switches from its straight conformation to a curved one. These changes correlated with the loss of lateral contacts and provided a rationale for the rapid microtubule depolymerization characteristic of dynamic instability. Moreover, Ravelli et al. (2004) concluded that the structure of the tubulin-colchicine complex sheds light on the mechanism of colchicine's activity; they demonstrated that colchicine binds at a location where it prevents curved tubulin from adopting a straight structure, which inhibits assembly.
By somatic cell hybrid analysis, Gerhard et al. (1985) found complete coordinate segregation of the testis-specific alpha-tubulin gene with IDH1 (147700), a chromosome 2 marker. Since 4 of 22 cases showed discordance with the 2p marker MDH1 (154200), they concluded that the gene is probably on 2q.
Khodiyar et al. (2007) stated that the TUBA4A gene maps to chromosome 2q35 and the mouse homolog to chromosome 1C3.
Smith et al. (2014) detected heterozygous mutations in exon 4 of the TUBA4A gene (191110.0001-191110.0006) in patients with amyotrophic lateral sclerosis (ALS22; 616208). In functional studies, Smith et al. (2014) found that W407X mutant protein (191110.0003) did not incorporate into the microtubule network and formed small ubiquitinated cytoplasmic inclusions in about 40% of transfected primary motor neurons (PMNs) and about 85% of transfected HEK293 cells. Smith et al. (2014) also investigated the ability of mutant TUBA4A to efficiently form microtubules using a cell-free system to quantify its incorporation into alpha/beta-tubulin dimers. They found that TUBA4A-W407X yielded no discernible dimers, while the A383T (191110.0005) and both R320 mutants (191110.0001 and 191110.0002) displayed significantly lower levels of assembly relative to the wildtype protein. The other variants did not differ from controls, save for a small but reproducible migration difference for TUBA4A-R215C (191110.0004). Overall, Smith et al. (2014) found that FALS-associated variants inefficiently form alpha/beta-tubulin dimers in vitro, display decreased incorporation into microtubules in cultured cells, and inhibit microtubule network assembly and reduce structural stability. Based on these data, Smith et al. (2014) concluded that TUBA4A missense mutations appear to disrupt microtubule dynamics and stability through a dominant-negative mechanism. A different mechanism was proposed for the W407X mutation.
Associations Pending Confirmation
For discussion of a possible association between isolated macrothrombocytopenia (see MACTHC1, 613112) and variation in the TUBA4A gene, see 191110.0007.
Strassel et al. (2019) identified a mutant mouse strain (Plt68) that exhibited macrothrombocytopenia associated with a homozygous V260E missense variant in the Tuba4a gene. Electron microscopic analysis of platelets showed loss of the typical flat discoid shape and a reduction in the number of microtubule coils in the marginal band compared to controls. Western blot analysis of platelets from mutant mice showed a significant decrease in Tuba4a expression. Megakaryocytes in mutant mice were unable to form and extend well-developed proplatelets compared to wildtype. These findings were consistent with defects in the later stages of megakaryocyte maturation.
In a patient with amyotrophic lateral sclerosis-22 (ALS22; 616208), Smith et al. (2014) identified a G-to-A transition in exon 4 of the TUBA4A gene that resulted in an arg320-to-cys (R320C) mutation. Age of onset was 64 years. There was no history of dementia in the patient or in the family. No relatives of the patient were available to test segregation; however, this mutation was not observed in 13,023 control samples. The R320C mutation occurs at an arginine completely conserved through zebrafish, and functional studies showed that R320C mutant protein displayed significantly lower levels of dimer assembly relative to the wildtype protein.
In 1 patient with ALS22 (616208) identified from a total of 363 index cases with familial ALS, Smith et al. (2014) detected a C-to-T transition in exon 4 of the TUBA4A gene that resulted in an arg320-to-his (R320H) mutation. Age at onset was 41 years. There was no history of dementia in the patient or in the family. No relatives of the patient were available to test segregation; however, this mutation was not observed in 13,023 control samples. The R320H mutation occurs at an arginine completely conserved through zebrafish, and functional studies showed that R320H mutant protein displayed significantly lower levels of dimer assembly relative to the wildtype protein.
In a single patient with ALS22 (616208) identified from a total of 363 index cases with familial ALS, Smith et al. (2014) detected a C-to-T transition in exon 4 of the TUBA4A gene that resulted in a trp407-to-ter (W407X) substitution and subsequent deletion of the last 41 amino acids of the protein. Age of disease onset was 66 years. There was no history of dementia in the patient or in the family. No relatives of the patient were available to test segregation; however, this mutation was not observed in 13,023 control samples. The C-terminal region truncated in the W407X mutant contacts the beta-tubulin subunit (191130) as well as the motor domains of kinesins and other microtubule-associated proteins. Functional studies showed that the W407X mutant protein was deficient in forming dimers or incorporating into the microtubule network. There was also an increase in multiple aggregate-like inclusions. While the missense mutations studied appeared to act through a dominant-negative mechanism, Smith et al. (2014) proposed that, since W407X showed aggregation propensities analogous to other ALS-associated mutant proteins, its deleterious effect may be via a different mechanism, such as trapping tubulin-binding proteins into aggregates or by overburdening the ubiquitin proteasome system.
In a single patient with ALS22 (616208) and frontotemporal dementia (FTD; 600274) identified from a total of 363 index cases with familial ALS, Smith et al. (2014) detected a G-to-A transition in exon 4 of the TUBA4A gene that resulted in an arg215-to-cys (R215C) mutation. Age of onset was 78 years. The patient's mother had had FTD as well. This mutation displayed significantly different distribution relative to the wildtype protein in terms of incorporation into microtubules. No relatives of the patient were available to test segregation; however, this mutation was not observed in 13,023 control samples.
In an individual with ALS22 (616208) identified from a total of 363 index cases with familial ALS, Smith et al. (2014) detected a C-to-T transition in exon 4 of the TUBA4A gene resulting in an ala383-to-thr (A383T) mutation. Age of onset was 71 years. There was no history of dementia in the patient or the patient's family. This mutation was identified in 1 of 2,200 individuals of African descent out of 13,023 total samples in the Exome Variant Server database. Protein carrying this mutation showed significantly lower levels of dimer assembly relative to the wildtype protein, as well as a different distribution throughout the cell. The mutation was also shown to destabilize the microtubule network.
In a proband with ALS22 (616208), Smith et al. (2014) identified a C-to-T transition in exon 4 of the TUBA4A gene that resulted in a thr145-to-pro (T145P) substitution. The variant segregated with disease in the proband's family. Age of onset in the proband was 48 years. A family history of frontotemporal dementia (FTD; 600274) was reported.
This variant is classified as a variant of unknown significance because its contribution to isolated macrothrombocytopenia (see MACTHC1, 613112) has not been confirmed.
In an individual with isolated macrothrombocytopenia identified through blood donation, Strassel et al. (2019) found a heterozygous double substitution in cis in the TUBA4A gene: a c.541G-A transition, resulting in a val181-to-met (V181M) substitution, and a c.547G-C transversion, resulting in a glu183-to-gln (E183Q) substitution. The variants, which were found by targeted sequencing and confirmed by Sanger sequencing, were both found at low frequencies in public databases (less than 8.0 x 10(-5)). Electron microscopy of the individual's platelets showed loss of the discoid shape and a profound disorganization of the marginal band with loosely assembled microtubules. Strassel et al. (2019) noted that TUBA4A lacks the C-terminal tyrosine residue found in all other alpha-tubulins. Tubulin tyrosination defects were observed in patient platelets, suggesting alterations of posttranslationally controlled tubulin modification that may impact platelet shape.
Gerhard, D. S., Dobner, P. R., Bruns, G. Testis specific alpha-tubulin is on chromosome 2q. (Abstract) Cytogenet. Cell Genet. 40: 639-640, 1985.
Khodiyar, V. K., Maltais, L. J., Ruef, B. J., Sneddon, K. M. B., Smith, J. R., Shimoyama, M., Cabral, F., Dumontet, C., Dutcher, S. K., Harvey, R. J., Lafanechere, L., Murray, J. M., Nogales, E., Piquemal, D., Stanchi, F., Povey, S., Lovering, R. C. A revised nomenclature for the human and rodent alpha-tubulin gene family. Genomics 90: 285-289, 2007. Note: Erratum: Genomics 93: 397 only, 2009. [PubMed: 17543498] [Full Text: https://doi.org/10.1016/j.ygeno.2007.04.008]
Ravelli, R. B. G., Gigant, B., Curmi, P. A., Jourdain, I., Lachkar, S., Sobel, A., Knossow, M. Insight into tubulin regulation from a complex with colchicine and a stathmin-like domain. Nature 428: 198-202, 2004. [PubMed: 15014504] [Full Text: https://doi.org/10.1038/nature02393]
Smith, B. N., Ticozzi, N., Fallini, C., Gkazi, A. S., Topp, S., Kenna, K. P., Scotter, E. L., Kost, J., Keagle, P., Miller, J. W., Calini, D., Vance, C., and 54 others. Exome-wide rare variant analysis identifies TUBA4A mutations associated with familial ALS. Neuron 84: 324-331, 2014. [PubMed: 25374358] [Full Text: https://doi.org/10.1016/j.neuron.2014.09.027]
Strassel, C., Magiera, M. M., Dupuis, A., Batzenschlager, M., Hovasse, A., Pleines, I., Gueguen, P., Eckly, A., Moog, S., Mallo, L., Kimmerlin, Q., Chappaz, S., and 11 others. An essential role for alpha4A-tubulin in platelet biogenesis. Life Sci. Alliance 2: e201900309, 2019. Note: Erratum: Life Sci. Alliance 4: e202101132, 2021. [PubMed: 30760556] [Full Text: https://doi.org/10.26508/lsa.201900309]
Todd, S., Naylor, S. L. Dinucleotide repeat polymorphism in the human tubulin alpha 1 (testis specific) gene (TUBA1). Nucleic Acids Res. 19: 3755 only, 1991. [PubMed: 1852622] [Full Text: https://doi.org/10.1093/nar/19.13.3755]
Villasante, A., Wang, D., Dobner, P., Dolph, P., Lewis, S. A., Cowan, N. J. Six mouse alpha-tubulin mRNAs encode five distinct isotypes: testis-specific expression of two sister genes. Molec. Cell. Biol. 6: 2409-2419, 1986. [PubMed: 3785200] [Full Text: https://doi.org/10.1128/mcb.6.7.2409-2419.1986]
Wilde, C. D., Chow, L. T., Wefald, F. C., Cowan, N. J. Structure of two human alpha-tubulin genes. Proc. Nat. Acad. Sci. 79: 96-100, 1982. [PubMed: 6275393] [Full Text: https://doi.org/10.1073/pnas.79.1.96]