Endocytic trafficking controls the density of molecules at the plasma membrane and by doing so, the cell surface profile, which in turn determines how cells interact with their environment. A full apprehension of any cellular process necessitates to understand how proteins associated with the plasma membrane are endocytosed, how they are sorted after internalisation and if and how they are recycled to the plasma membrane. To date, it is still difficult to experimentally gain access to this information, even more to do it in a quantitative way. Here we present a toolset based on photoactivation of fluorescent proteins that enabled us to generate quantitative information on endocytosis, incorporation into sorting and recycling endosomes, delivery from endosomes to the plasma membrane and on the type of vesicles performing intracellular transport. We illustrate these approaches by revealing striking differences in the endocytic trafficking of T cell receptor (TCR) and CD4, which bind to the same molecule at the surface of antigen presenting cells during T cell activation.

内吞运输控制质膜上的分子密度，从而控制细胞表面轮廓，进而决定细胞如何与其环境相互作用。对任何细胞过程的全面理解都需要了解与质膜相关的蛋白质是如何被内吞的，它们在内化后如何分类，以及它们是否以及如何被回收到质膜。迄今为止，通过实验获取这些信息仍然很困难，更难的是以定量的方式来获取。在这里，我们提出了一个基于荧光蛋白光活化的工具集，它使我们能够生成关于内吞作用、并入分选和回收内体、从内体到质膜的传递以及执行细胞内转运的囊泡类型的定量信息。