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 3

Aberrant splicing of TRIP11 in odontochondrodysplasia.

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Aberrant splicing of TRIP11 in odontochondrodysplasia. (A–C) Exon-spanni...
(A–C) Exon-spanning reverse transcription PCR (RT-PCR) analysis of TRIP11 using cDNA derived from patient and control (CTL) fibroblasts; amplicons resulting from aberrantly spliced mRNA are marked by red arrowheads. (A) The c.586C>T TRIP11 mutation causes in-frame skipping of exon 4, as indicated by the reduced PCR product size of 229 bp in case 10. (B) The recurrent c.1228G>T mutation causes in-frame deletion of exon 9, as indicated by the 87-bp shorter PCR product in case 3. (C) The c.5416A>G mutation generates an ectopic splice donor site within exon 18, as indicated by a 46-bp shorter PCR product in case 6. In addition, a PCR product of similar intensity indicating regular splicing is visible at 475 bp. (D) Schematic representation of TRIP11 transcript variants including their 5′ and 3′ untranslated region detected in control (CTL) and patient fibroblasts (cases 10, 3, and 6). Exons 1–21 are shown as boxes, the size of the box correlates to the size of each exon; introns represented as lines are not to scale. Triangular-shaped lines above indicate splicing. Gray horizontal arrows indicate the relative position of primers (E1, E5, E7, E10, E11, E14, and E19) used in this study. Red vertical arrows indicate mutations. FL, full-length transcript. 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.