Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA.
Hum Mol Genet. 2022 Aug 23;31(16):2820-2830. doi: 10.1093/hmg/ddac078.
Loss-of-function mutations in DDRGK1 have been shown to cause Shohat type spondyloepimetaphyseal dysplasia (SEMD). In zebrafish, loss of function of ddrgk1 leads to defects in early cartilage development. Ddrgk1-/- mice show delayed mesenchymal condensation in the limb buds and early embryonic lethality. Mechanistically, Ddrgk1 interacts with Sox9 and reduces ubiquitin-mediated proteasomal degradation of Sox9 protein. To investigate the cartilage-specific role of DDRGK1, conditional knockout mice were generated by intercrossing Prx1-Cre transgenic mice with Ddrgkfl/fl mice to delete its expression in limb mesenchymal cells. Mutant mice showed progressive severe shortening of the limbs and joint abnormalities. The growth plate showed disorganization with shortened proliferative zone and enlarged hypertrophic zone. In correlation with these findings, Sox9 and Col2a1 protein levels were decreased, while Col10a1 expression was expanded. These data demonstrate the importance of Ddrgk1 during growth plate development. In contrast, deletion of Ddrgk1 with the osteoblast-specific Osteocalcin-Cre and Leptin receptor-Cre lines did not show bone phenotypes, suggesting that the effect on limb development is cartilage-specific. To evaluate the role of DDRGK1 in cartilage postnatal homeostasis, inducible Agc1-CreERT2; Ddrgklfl/fl mice were generated. Mice in which Ddrgk1 was deleted at 3 months of age showed disorganized growth plate, with significant reduction in proteoglycan deposition. These data demonstrate a postnatal requirement for Ddrgk1 in maintaining normal growth plate morphology. Together, these findings highlight the physiological role of Ddrgk1 in the development and maintenance of the growth plate cartilage. Furthermore, these genetic mouse models recapitulate the clinical phenotype of short stature and joint abnormalities observed in patients with Shohat type SEMD.
DDRGK1 的功能丧失突变已被证明会导致 Shohat 型脊椎干骺端发育不良 (SEMD)。在斑马鱼中，ddrgk1 的功能丧失导致早期软骨发育缺陷。Ddrgk1-/- 小鼠表现出肢体芽间充质凝聚延迟和早期胚胎致死性。在机制上，Ddrgk1 与 Sox9 相互作用，减少 Sox9 蛋白的泛素介导的蛋白酶体降解。为了研究 DDRGK1 在软骨中的特异性作用，通过将 Prx1-Cre 转基因小鼠与 Ddrgkfl/fl 小鼠杂交，生成条件性敲除小鼠以在肢体间充质细胞中删除其表达。突变小鼠表现出肢体进行性严重缩短和关节异常。生长板显示出紊乱，有丝分裂区缩短，肥大区扩大。与此相关的发现是 Sox9 和 Col2a1 蛋白水平降低，而 Col10a1 表达扩大。这些数据表明 DDRGK1 在生长板发育过程中的重要性。相反，用成骨细胞特异性骨钙素-Cre 和瘦素受体-Cre 线删除 Ddrgk1 并未显示出骨骼表型，表明对肢体发育的影响是特异性软骨的。为了评估 DDRGK1 在软骨出生后稳态中的作用，生成了诱导型 AGC1-CreERT2; Ddrgklfl/fl 小鼠。在 3 个月大时删除 Ddrgk1 的小鼠表现出生长板紊乱，糖胺聚糖沉积显著减少。这些数据表明 Ddrgk1 在维持正常生长板形态方面存在出生后需求。总的来说，这些发现强调了 DDRGK1 在生长板软骨发育和维持中的生理作用。此外，这些遗传小鼠模型重现了 Shohat 型 SEMD 患者中观察到的身材矮小和关节异常的临床表型。
