Collagen secretion screening in Drosophila supports a common secretory machinery and multiple Rab requirements

Collagens are large secreted trimeric proteins making up most of the animal extracellular matrix. Secretion of collagen has been a focus of interest for cell biologists in recent years because collagen trimers are too large and rigid to fit into the COPII vesicles mediating transport from the endoplasmic reticulum (ER) to the Golgi. Collagen-specific mechanisms to create enlarged ER-to-Golgi transport carriers have been postulated, including cargo loading by conserved ER exit site (ERES) protein Tango1. Here, we report an RNAi screening for genes involved in collagen secretion in Drosophila. In this screening, we examined distribution of GFP-tagged Collagen IV in live animals and found 88 gene hits for which the knockdown produced intracellular accumulation of Collagen IV in the fat body, the main source of matrix proteins in the larva. Among these hits, only two affected collagen secretion specifically: PH4αEFB and Plod, encoding enzymes known to mediate posttranslational modification ...胶原蛋白（Collagens）是一类大型分泌型三聚体蛋白，构成了绝大多数动物细胞外基质（extracellular matrix）的核心组分。近年来，胶原蛋白的分泌一直是细胞生物学家的重点研究方向，原因在于胶原蛋白三聚体体积过大且刚性过强，无法适配介导内质网（endoplasmic reticulum, ER）至高尔基体（Golgi）运输的COPII囊泡（COPII vesicles）。学界已提出多种适配胶原蛋白的特殊机制，以构建增大的内质网-高尔基体运输载体，其中包括由保守的内质网退出位点（ER exit site, ERES）蛋白Tango1介导的货物装载过程。本研究针对果蝇（Drosophila）中参与胶原蛋白分泌的基因开展了RNA干扰（RNA interference, RNAi）筛选实验。本次筛选中，我们观测了活体动物体内绿色荧光蛋白（green fluorescent protein, GFP）标记的IV型胶原蛋白（Collagen IV）的分布情况，最终得到88个候选基因——敲低这些基因会导致幼虫体内基质蛋白的主要来源——脂肪体中出现IV型胶原蛋白的胞内积累。在上述候选基因中，仅有两个基因可特异性影响胶原蛋白的分泌：PH4αEFB与Plod，二者编码的酶类已知可介导胶原蛋白的翻译后修饰……