早胞内体是细胞内吞途径上的分选枢纽，由空泡分选和管状循环微区构成。细胞分选蛋白SNXs对早胞内体上不同分选功能的膜微区的形成有着举足轻重的作用。与clathrin内吞途径相比，非clathrin途径（CIE）内吞的物质在胞内的运输与调控的研究在近年才有较快发展。早胞内体上不同的内涵体管具有怎样不同的蛋白分子与脂质特征，导致其在货物分选及剪切囊泡化的命运等方面不同？SNXs家族成员在CIE途径的运输中又扮演怎样的角色？我们近期在线虫肠细胞上研究证实，Arf6调控的CIE循环途径主要通过内涵体间的管网运输实现；SNX-3功能缺失导致膜管运输载体破坏，货物蛋白有被降解的趋势。基于此，本项目将综合运用活体高分辨的动态荧光显微成像技术，结合生化、分子等手段，阐释线虫SNX-3在早胞内体上特定膜运输载体形成中的新功能与分子机理，研究将有助于揭示CIE途径货物蛋白在早胞内体上的分选和运输如何被精密调控。

Early endosome is the sorting hub on the endocytic pathway and consists of vacuolar sorting and tubular recycling domains that segregate components fated for degradation in lysosomes or reuse by recycling to the plasma membrane or Golgi. Mechanisms underlying tubule generation from vacuolar sorting endosomes remain less known. Sorting Nexins (SNXs) are vital for formation of the distinct membranous microdomains with different sorting functions. Studies on the intracelluar transport and regulation of nonclathrin-endocytic pathway haven’t been developed as well as those on the clathrin-endocytic pathway. The open questions include: What’s the distinction of the protein molecules and lipids decorated on the different endosomal tubules emanated from the early endosomes? How does this distinction underlie the sorting of cargoes and fate of the transport intermediates, for example, to be vesiculated or not? Particularly, how do the SNX members play their roles for the endosomal transport along the nonclathrin-endocytic pathways? Our recent published work of C. elegans intestine confirmed that, the transport intermediates of Arf6-associated clathrin-indpendent recycling cargoes were membranous tubules interconnected between early endosomes and recycling endosomes, disctinct from the classical vesicular carriers. We further found that depletion of SNX-3 resulted in disruption of the tubular intermediates and the cargoes were possibly switched from recycling into degradation in lysosomes. Based on these previous work, we propose this project, by using in vivo real-time high-resolution fluorescent microscopy technology with conventional biochemistry and molecular coloning methods, to investigate the novel functional roles and molecular mechanisms of SNX-3 underlying the formation of specific membranous transport intermediates emanating from the early endosomes. Results will help to clarify the detailed regulation of sorting and transportation of nonclathrin-endocytic cargo proteins.