Egunsola Adetutu T, Bae Yangjin, Jiang Ming-Ming, Liu David S, Chen-Evenson Yuqing, Bertin Terry, Chen Shan, Lu James T, Nevarez Lisette, Magal Nurit, Raas-Rothschild Annick, Swindell Eric C, Cohn Daniel H, Gibbs Richard A, Campeau Philippe M, Shohat Mordechai, Lee Brendan H
J Clin Invest. 2017 Apr 3;127(4):1475-1484. doi: 10.1172/JCI90193. Epub 2017 Mar 6.
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.
肖哈特型脊椎骨骺发育不良（SEMD）是一种影响软骨发育的骨骼发育不良疾病。类似的骨骼疾病，如脊椎骨骺发育不良，与II型胶原蛋白（COL2A1）的突变有关，但SEMD的致病基因尚不清楚。在这里，我们进行了全外显子组测序，在4个受SEMD影响的家庭中，发现了一个在含DDRGK结构域1（DDRGK1）中反复出现的纯合子c.408+1G>A供体剪接位点功能丧失突变。在斑马鱼中，ddrgk1缺乏会破坏颅面软骨发育，并导致软骨生成主转录因子sox9及其下游靶点col2a1的水平降低。sox9的过表达挽救了由ddrgk1敲低产生的斑马鱼软骨生成和颅面表型，从而确定DDRGK1为SOX9的调节因子。与这些结果一致，Ddrgk1-/-小鼠表现出肢体芽软骨生成凝聚延迟、SOX9蛋白表达和Col2a1转录水平降低以及细胞凋亡增加。此外，我们确定DDRGK1可以直接与SOX9结合，以抑制其泛素化和蛋白酶体降解。综上所述，这些数据表明DDRGK1的缺失会降低SOX9的表达，并导致人类骨骼发育不良，确定了一种通过调节SOX9泛素化来调节软骨生成的机制。
