Loss of DDRGK1 modulates SOX9 ubiquitination in spondyloepimetaphyseal dysplasia
Adetutu T. Egunsola, … , Mordechai Shohat, Brendan H. Lee
Adetutu T. Egunsola, … , Mordechai Shohat, Brendan H. Lee
Published March 6, 2017
Citation Information: J Clin Invest. 2017;127(4):1475-1484. https://doi.org/10.1172/JCI90193.
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Research Article Bone biology Genetics

Loss of DDRGK1 modulates SOX9 ubiquitination in spondyloepimetaphyseal dysplasia

Abstract

Shohat-type spondyloepimetaphyseal dysplasia (SEMD) is a skeletal dysplasia that affects cartilage development. Similar skeletal disorders, such as spondyloepiphyseal dysplasias, are linked to mutations in type II collagen (COL2A1), but the causative gene in SEMD is not known. Here, we have performed whole-exome sequencing to identify a recurrent homozygous c.408+1G>A donor splice site loss-of-function mutation in DDRGK domain containing 1 (DDRGK1) in 4 families affected by SEMD. In zebrafish, ddrgk1 deficiency disrupted craniofacial cartilage development and led to decreased levels of the chondrogenic master transcription factor sox9 and its downstream target, col2a1. Overexpression of sox9 rescued the zebrafish chondrogenic and craniofacial phenotype generated by ddrgk1 knockdown, thus identifying DDRGK1 as a regulator of SOX9. Consistent with these results, Ddrgk1–/– mice displayed delayed limb bud chondrogenic condensation, decreased SOX9 protein expression and Col2a1 transcript levels, and increased apoptosis. Furthermore, we determined that DDRGK1 can directly bind to SOX9 to inhibit its ubiquitination and proteasomal degradation. Taken together, these data indicate that loss of DDRGK1 decreases SOX9 expression and causes a human skeletal dysplasia, identifying a mechanism that regulates chondrogenesis via modulation of SOX9 ubiquitination.

Authors

Adetutu T. Egunsola, Yangjin Bae, Ming-Ming Jiang, David S. Liu, Yuqing Chen-Evenson, Terry Bertin, Shan Chen, James T. Lu, Lisette Nevarez, Nurit Magal, Annick Raas-Rothschild, Eric C. Swindell, Daniel H. Cohn, Richard A. Gibbs, Philippe M. Campeau, Mordechai Shohat, Brendan H. Lee

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Figure 3

Deletion of Ddrgk1 delays chondrogenic mesenchymal condensation and increases apoptosis in mouse limb buds.

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Deletion of Ddrgk1 delays chondrogenic mesenchymal condensation and incr...
(A and B) Mesenchymal condensation is detected in WT, but not in Ddrgk1–/–, limb buds stained with H&E at (A) E11.5 and (B) E12.5. Red asterisks indicate regions undergoing mesenchymal condensation. Images on the right are higher magnification depictions of the boxed regions of the images to the left. (C) After 7 days, micromass cultures of dissociated Ddrgk1–/– (n = 2) mesenchymal cells produced fewer Alcian blue–positive cartilaginous nodules than WT (n = 2) mesenchymal cells. Images are of 2 independent experiments. (D) TUNEL staining reveals Ddrgk1–/– limb buds (n = 3) have increased apoptosis compared with WT limb buds (n = 4) at E11.5, trending toward significance. Values are represented as mean ± SEM. Two-tailed t test. Scale bars: 100 μM.