Knockout of the golgin giantin leads to skeletal and craniofacial defects driven by poorly studied changes in glycosylation and extracellular matrix deposition. Here, we sought to determine how giantin impacts the production of healthy bone tissue by focussing on the main protein component of the osteoid, type I collagen. Giantin mutant zebrafish accumulate multiple spontaneous fractures in their caudal fin, suggesting their bones may be more brittle. Inducing new experimental fractures revealed defects in the mineralisation of newly deposited collagen as well as diminished procollagen reporter expression in mutant fish. Analysis of giantin knockout cells expressing a GFP-tagged procollagen showed that procollagen trafficking is independent of giantin. However, our data show that intracellular N-propeptide processing of pro-α1(I) is defective in the absence of giantin. These data demonstrate a conserved role for giantin in collagen biosynthesis and extracellular matrix assembly. Our work also provides evidence of a giantin-dependent pathway for intracellular procollagen processing.

中文翻译：

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I型原胶原的细胞内N末端加工需要巨蛋白

敲除高尔金巨蛋白会导致骨骼和颅面缺陷，这是由于对糖基化和细胞外基质沉积的研究不足而导致的。在这里，我们试图通过关注类骨质的主要蛋白质成分（I型胶原蛋白）来确定巨人蛋白如何影响健康的骨组织的生产。Giantin突变斑马鱼在其尾鳍中积聚了多个自发性骨折，表明它们的骨骼可能更脆。诱导新的实验性骨折揭示了新沉积的胶原蛋白矿化的缺陷以及突变鱼类中前胶原报告基因的表达减少。分析表达GFP标签的胶原蛋白的巨蛋白敲除细胞表明，胶原蛋白的运输与巨蛋白无关。然而，我们的数据显示，在缺少巨蛋白的情况下，pro-α1（I）的细胞内N肽加工存在缺陷。这些数据证明巨人蛋白在胶原生物合成和细胞外基质组装中的保守作用。我们的工作还提供了细胞内胶原蛋白加工过程中依赖大青霉素的途径的证据。