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 2

Overexpression of ddrgk1 mRNA rescues the ddrgk1 knockdown cartilage phenotype in zebrafish.

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Overexpression of ddrgk1 mRNA rescues the ddrgk1 knockdown cartilage phe...
(A) Ventral view at 120 h.p.f. of Alcian blue–stained WT embryos and embryos injected with either control MO or ddrgk1 MO with or without exogenous ddrgk1 mRNA. M, Meckel’s cartilage; CH, ceratohyal cartilage; N, neurocranial cartilage; CB, ceratobranchial cartilage. Scale bars: 100 μM. (B) Quantification of the craniofacial phenotype in the embryos. Embryos with normal craniofacial features had properly formed Meckel’s cartilage, ceratohyal cartilage, neurocranial cartilage, and ceratobranchial cartilage. Embryos lacking ceratobranchial cartilage showed mild craniofacial defects, while embryos with several craniofacial defects had no neurocranial or ceratobranchial cartilage and poorly developed Meckel’s cartilage and ceratohyal cartilage. WT, n = 44; 5 pg control MO, n = 36; 3 pg ddrgk1 MO, n = 50; 4 pg ddrgk1 MO, n = 47; 5 pg ddrgk1 MO, n = 43; 5 pg ddrgk1 MO + 25 pg ddrgk1 mRNA, n = 45; 5 pg ddrgk1 MO + 50 pg ddrgk1 mRNA, n = 38. *P < 0.05; ***P < 0.001; Kruskal-Wallis rank-sum test followed by Wilcoxon’s rank-sum test with continuity correction.