TUBB4Bvariants specifically impact ciliary function, causing a ciliopathic spectrum

Abstract

Cilia are small microtubule-based structures found on the surface of most mammalian cells, which have key sensory and sometimes motile functions. Primary ciliary dyskinesia (PCD) is a type of ciliopathy caused by defects in motile cilia. The genetic basis of PCD is only partially understood. Studying a cohort of 11 human patients with PCD, we find thatde novomutations inTUBB4B, a beta tubulin isotype, cause three distinct classes of ciliopathic disease.In vivostudies in mice show thatTubb4bplays a specific role in cilia, building centrioles and axonemes in multiciliated cells. Examining the effects of specific TUBB4B variants in cells and in mice, we further demonstrate that distinctTUBB4Bmutations differentially affect microtubule dynamics and cilia formation in a dominant negative manner. Finally, structure-function studies reveal that different TUBB4B mutations disrupt distinct tubulin interfaces. Importantly, these molecular differences correlate with disease features. We show that tubulin heterodimer-impairing TUBB4B variants underlie nonsyndromic PCD, whilst additional renal and sensorineural ciliopathic features in a syndromic PCD subtype arise from microtubule lumenal interface-impaired TUBB4B variants. These findings suggest that specific tubulin isotypes have distinct and non-redundant subcellular functions, and demonstrate that human tubulinopathies can be drivers of ciliopathic syndromes.

High diagnostic rate of whole genome sequencing in primary ciliary dyskinesia

“…This included a de novo missense mutation p.P259L (chr9:g.137242994:C>T (hg38)) in the gene TUBB4B only in the patient, and not present in either parent or found on gnomAD 4.0 or other publicly available databases. Whilst interpretation of pathogenicity from a single patient is limiting, as part of a large international collaboration, we were able to identify a further eleven patients with PCD carrying TUBB4B variants identified by next-generation sequencing (NGS) (26). This included five patients with PCD-only carrying the identical p.P259L (chr9:g.137242994:C>T) variant, one carrying a different missense p.P259S (chr9:g.137242993:C>T (hg38)) variant and one patient carried an in-frame ten amino acid duplication p.F242_R251dup (chr9: g.137242941_137242970dup (hg38)) (26).…”

“…Whilst interpretation of pathogenicity from a single patient is limiting, as part of a large international collaboration, we were able to identify a further eleven patients with PCD carrying TUBB4B variants identified by next-generation sequencing (NGS) (26). This included five patients with PCD-only carrying the identical p.P259L (chr9:g.137242994:C>T) variant, one carrying a different missense p.P259S (chr9:g.137242993:C>T (hg38)) variant and one patient carried an in-frame ten amino acid duplication p.F242_R251dup (chr9: g.137242941_137242970dup (hg38)) (26). Moreover, we also identified a recurrent de novo TUBB4B variant four patients with a p.P358S (chr9:g.137243290:C>T (hg38)) variant, who presented with features of both PCD with Leber congenital amaurosis and sensorineural hearing loss.…”

Intrinsic microtubule destabilization of multiciliated choroid plexus epithelial cells during postnatal lifetime

“…While the aberration of tubulin PTMs, as polyglutamylation and acetylation, is sufficient to induce neurodegeneration 32,67,68,69 , no unifying molecular mechanism underlying microtubule stability has so far been found. Future experiments will be essential to uncover the specific role of tubulin in the ChP 13 and how the fate of ChP ciliated cells is regulated, in particular the mechanisms involved in cilia function and maintenance.…”

“…These organelles are essential for both embryonic and postnatal organ development and function. Mutations in over 200 cilia genes, including tubulin genes, like TUBB4B 12,13 and TUBB8 14 , result in a group of disorders called ciliopathies 15 . Tubulin assembly and disassembly depend on tubulin posttranslational modification (PTM) events 11 , such as acetylation, glutamylation and glycylation.…”

Artificial Intelligence-Enabled AlphaFold II Pipeline Guides Functional Fluorescence Labeling of Tubulin Across Species

“…The symptomatic spectrum of tubulinopathies extends from severe intellectual deficits to nuanced cognitive impairments, accentuating the indispensable role of tubulins in cerebral ontogeny (Tischfield et al, 2011). Also, tubulinopathies encompass ocular and renal anomalies (Mechaussier et al, 2022).…”