Secretory Vesicle Polar Sorting， Endosome Recycling and Cytoskeleton Organization Require the AP-1 Complex in .

The AP-1 complex is essential for membrane protein traffic via its role in the pinching-off and sorting of secretory vesicles (SVs) from the -Golgi and/or endosomes. While its essentiality is undisputed in metazoa， its role in simpler eukaryotes seems less clear. Here， we dissect the role of AP-1 in the filamentous fungus and show that it is absolutely essential for growth due to its role in clathrin-dependent maintenance of polar traffic of specific membrane cargoes toward the apex of growing hyphae. We provide evidence that AP-1 is involved in both anterograde sorting of RabE-labeled SVs and RabA/B-dependent endosome recycling. Additionally， AP-1 is shown to be critical for microtubule and septin organization， further rationalizing its essentiality in cells that face the challenge of cytoskeleton-dependent polarized cargo traffic. This work also opens a novel issue on how nonpolar cargoes， such as transporters， are sorted to the eukaryotic plasma membrane.