Tubulin isotype specificity in neuronal migration: Tuba8 can't fill in for Tuba1a

Deciphering the Tubulin Language: Molecular Determinants and Readout Mechanisms of the Tubulin Code in Neurons

Microtubules (MTs) are dynamic components of the cell cytoskeleton involved in several cellular functions, such as structural support, migration and intracellular trafficking. Despite their high similarity, MTs have functional heterogeneity that is generated by the incorporation into the MT lattice of different tubulin gene products and by their post-translational modifications (PTMs). Such regulations, besides modulating the tubulin composition of MTs, create on their surface a "biochemical code" that is translated, through the action of protein effectors, into specific MT-based functions. This code, known as "tubulin code", plays an important role in neuronal cells, whose highly specialized morphologies and activities depend on the correct functioning of the MT cytoskeleton and on its interplay with a myriad of MT-interacting proteins. In recent years, a growing number of mutations in genes encoding for tubulins, MT-interacting proteins and enzymes that post-translationally modify MTs, which are the main players of the tubulin code, have been linked to neurodegenerative processes or abnormalities in neural migration, differentiation and connectivity. Nevertheless, the exact molecular mechanisms through which the cell writes and, downstream, MT-interacting proteins decipher the tubulin code are still largely uncharted. The purpose of this review is to describe the molecular determinants and the readout mechanisms of the tubulin code, and briefly elucidate how they coordinate MT behavior during critical neuronal events, such as neuron migration, maturation and axonal transport.

Diaphragmatic paralysis in a neonate with circumferential skin creases Kunze type

Background

A range of clinical features have been confirmed with heterozygous mutations in Beta Tubulin (TUBB), including skin creases, facial deformities, abnormal cerebral structures, and intellectual disability, and were defined as Circumferential Skin Creases Kunze type (CSC‐KT).

Methods

Clinical information was obtained retrospectively on a neonate hospitalized in the Neonatal Intensive Care Unit, Wuhan Children’s Hospital. Genomic DNA was extracted from circulating leukocytes of the proband according to standard procedures.

Results

The neonate presented dyspnea resulting from diaphragmatic paralysis, accompanied by other typical features of CSC‐KT. Additionally, exome sequencing confirmed a new variant (NM_178,014. 4: c. 1114 A > G) in TUBB. We also summarized features described in previous cases, thus representing phenotype extension of CSC‐KT.

Conclusion

Our report is the youngest confirmed case, which could extend the current phenotype of CSC‐KT as well as the clinical diagnostic approach.

Tubulin isotypes - functional insights from model organisms

The microtubule cytoskeleton is assembled from the α- and β-tubulin subunits of the canonical tubulin heterodimer, which polymerizes into microtubules, and a small number of other family members, such as γ-tubulin, with specialized functions. Overall, microtubule function involves the collective action of multiple α- and β-tubulin isotypes. However, despite 40 years of awareness that most eukaryotes harbor multiple tubulin isotypes, their role in the microtubule cytoskeleton has remained relatively unclear. Various model organisms offer specific advantages for gaining insight into the role of tubulin isotypes. Whereas simple unicellular organisms such as yeast provide experimental tractability that can facilitate deeper access to mechanistic details, more complex organisms, such as the fruit fly, nematode and mouse, can be used to discern potential specialized functions of tissue- and structure-specific isotypes. Here, we review the role of α- and β-tubulin isotypes in microtubule function and in associated tubulinopathies with an emphasis on the advances gained using model organisms. Overall, we argue that studying tubulin isotypes in a range of organisms can reveal the fundamental mechanisms by which they mediate microtubule function. It will also provide valuable perspectives on how these mechanisms underlie the functional and biological diversity of the cytoskeleton.

Dysregulation of SAA1, TUBA8 and Monocytes Are Key Factors in Ankylosing Spondylitis With Femoral Head Necrosis

Introduction

The mechanism of ankylosing spondylitis with femoral head necrosis is unknown, and our study aimed investigate the effects of genetic and immune cell dysregulation on ankylosing spondylitis.

Materials and Methods

The protein expression of all ligaments in ankylosing spondylitis with femoral head necrosis was obtained using label-free quantification protein park analysis of six pairs of specimens. The possible pathogenesis was explored using differential protein analysis, weighted gene co-expression network analysis, recording intersections with hypoxia-related genes, immune cell correlation analysis, and drug sensitivity analysis. Finally, routine blood test data from 502 AS and 162 healthy controls were collected to examine immune cell differential analysis.

Results

SAA1 and TUBA8 were significantly expressed differentially in these two groups and correlated quite strongly with macrophage M0 and resting mast cells (P < 0.05). Routine blood data showed that monocytes were significantly more expressed in AS than in healthy controls (P < 0.05). SAA1 and TUBA8 were closely related to the sensitivity of various drugs, which might lead to altered drug sensitivity.

Conclusion

Dysregulation of SAA1, TUBA8 and monocytes are key factors in ankylosing spondylitis with femoral head necrosis.

TUBB Variants Underlying Different Phenotypes Result in Altered Vesicle Trafficking and Microtubule Dynamics

Tubulinopathies are rare neurological disorders caused by alterations in tubulin structure and function, giving rise to a wide range of brain abnormalities involving neuronal proliferation, migration, differentiation and axon guidance. TUBB is one of the ten β-tubulin encoding genes present in the human genome and is broadly expressed in the developing central nervous system and the skin. Mutations in TUBB are responsible for two distinct pathological conditions: the first is characterized by microcephaly and complex structural brain malformations and the second, also known as “circumferential skin creases Kunze type” (CSC-KT), is associated to neurological features, excess skin folding and growth retardation. We used a combination of immunocytochemical and cellular approaches to explore, on patients’ derived fibroblasts, the functional consequences of two TUBB variants: the novel mutation (p.N52S), associated with basal ganglia and cerebellar dysgenesis, and the previously reported variant (p.M73T), linked to microcephaly, corpus callosum agenesis and CSC-KT skin phenotype. Our results demonstrate that these variants impair microtubule (MT) function and dynamics. Most importantly, our studies show an altered epidermal growth factor (EGF) and transferrin (Tf) intracellular vesicle trafficking in both patients’ fibroblasts, suggesting a specific role of TUBB in MT-dependent vesicular transport.