| Popis: |
Endosomal maturation is a critical and fundamental process for robust transport of cargo (such as activated receptors) to specific cellular compartments in a timely manner. The most prominent model of endosomal maturation involves a phosphoinositide-driven gain or loss of specific proteins at the level of individual endosomes, emphasising an autonomous and stochastic model of maturation. However, to date, direct whole cell-level measurements of absolute number of maturation events have not been performed, owing to limitations in fast, volumetric imaging. Here, we use lattice light-sheet imaging to track individual very early and early endosomes over the entire population. We demonstrate that direct inter-endosomal contact drives the maturation from very early (APPL1-positive) to early (EEA1-positive) endosomes. Using fluorescence lifetime, we show that this endosomal interaction is underpinned by the asymmetric binding of EEA1 to very early and early endosomes through the N- and C-termini, respectively. Thus, stochastic microtubule-mediated inter-endosomal interactions through EEA1 provide a mechanism to bring temporal and population-level control to the process of endosome maturation. Our findings indicate that APPL1- to EEA1-positive endosomal maturation is not a result of autonomous endosomal events but is driven by heterotypic EEA1-mediated endosomal interactions. |
