Hypomorphic mutations of TRIP11 cause odontochondrodysplasia
Anika Wehrle, Tomasz M. Witkos, Sheila Unger, Judith Schneider, John A. Follit, Johannes Hermann, Tim Welting, Virginia Fano, Marja Hietala, Nithiwat Vatanavicharn, Katharina Schoner, Jürgen Spranger, Miriam Schmidts, Bernhard Zabel, Gregory J. Pazour, Agnes Bloch-Zupan, Gen Nishimura, Andrea Superti-Furga, Martin Lowe, Ekkehart Lausch
Anika Wehrle, Tomasz M. Witkos, Sheila Unger, Judith Schneider, John A. Follit, Johannes Hermann, Tim Welting, Virginia Fano, Marja Hietala, Nithiwat Vatanavicharn, Katharina Schoner, Jürgen Spranger, Miriam Schmidts, Bernhard Zabel, Gregory J. Pazour, Agnes Bloch-Zupan, Gen Nishimura, Andrea Superti-Furga, Martin Lowe, Ekkehart Lausch
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Research Article Bone biology Genetics

Hypomorphic mutations of TRIP11 cause odontochondrodysplasia

Abstract

Odontochondrodysplasia (ODCD) is an unresolved genetic disorder of skeletal and dental development. Here, we show that ODCD is caused by hypomorphic TRIP11 mutations, and we identify ODCD as the nonlethal counterpart to achondrogenesis 1A (ACG1A), the known null phenotype in humans. TRIP11 encodes Golgi-associated microtubule-binding protein 210 (GMAP-210), an essential tether protein of the Golgi apparatus that physically interacts with intraflagellar transport 20 (IFT20), a component of the ciliary intraflagellar transport complex B. This association and extraskeletal disease manifestations in ODCD point to a cilium-dependent pathogenesis. However, our functional studies in patient-derived primary cells clearly support a Golgi-based disease mechanism. In spite of reduced abundance, residual GMAP variants maintain partial Golgi integrity, normal global protein secretion, and subcellular distribution of IFT20 in ODCD. These functions are lost when GMAP-210 is completely abrogated in ACG1A. However, a similar defect in chondrocyte maturation is observed in both disorders, which produces a cellular achondrogenesis phenotype of different severity, ensuing from aberrant glycan processing and impaired extracellular matrix proteoglycan secretion by the Golgi apparatus.

Authors

Anika Wehrle, Tomasz M. Witkos, Sheila Unger, Judith Schneider, John A. Follit, Johannes Hermann, Tim Welting, Virginia Fano, Marja Hietala, Nithiwat Vatanavicharn, Katharina Schoner, Jürgen Spranger, Miriam Schmidts, Bernhard Zabel, Gregory J. Pazour, Agnes Bloch-Zupan, Gen Nishimura, Andrea Superti-Furga, Martin Lowe, Ekkehart Lausch

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Figure 4

GMAP-210 protein analysis in achondrogenesis 1A (ACG1A) and odontochondrodysplasia (ODCD) patient–derived primary cells.

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GMAP-210 protein analysis in achondrogenesis 1A (ACG1A) and odontochondr...
(A) Schematic of the 1,979 amino acid GMAP-210 protein. The backbone of coiled-coil domains is shown in gray; the amphipathic lipid sensor (ALPS) in red, which participates in vesicle tethering with an overlapping second motif (not shown); Rab-binding domains 1 and 2 (RBD1 and RBD2) in light gray, which mediate RAB2 binding; and the GRIP-related Arf-binding (GRAB) domain in blue, which mediates membrane anchoring of GMAP. The IFT20 binding site (IFT20 BS, in black) is necessary for Golgi targeting of IFT20. Mutations identified in 5 ACG1A and 10 ODCD cases are indicated below; those amenable to functional analysis are indicated above. Amino acids deleted by in-frame exon skipping are hatched; nonsense and frameshift mutations are depicted in black, splice mutations in blue, and mutations shared by ACG1A and ODCD in red; recurrent mutations are underlined. (B) GMAP proteins in whole-cell protein lysates of patients and controls; GAPDH staining demonstrates total protein loading. The mean of triplicate quantitative blot signal analyses is represented in C; error bars indicate ± SEM. (D–E) GMAP-210 in whole-cell protein lysates of patients and controls using more sensitive enhanced chemiluminescence (ECL) substrate to analyze low-abundant GMAP protein variants with polyclonal antibodies directed against the N-terminus and the C-terminus. (D) Note the ~3 kDa lower protein variant in case 3 (consistent with the loss of exon 9) and the ~10 kDa lower protein variant in case 10 (consistent with the loss of exon 4). Red asterisks mark specific signals in the ACG1A cases (consistent with biallelic stop mutations and a predicted protein size of about 142 kDa in case A2 and 134 kDa in case A1). Additional bands for GMAP-210 marked with blue asterisks in CTL cells may represent shorter variants or proteolytic cleavage products. (E) Green asterisks mark the putative GMAP-190 protein corresponding to TRIP11-ΔEx9short.