Non-classical membrane trafficking processes galore.

Dogmatic views of how proteins and other cellular components may traffic within and between eukaryotic cells have been challenged in the past few years. Beyond the classical secretory/exocytic pathway and its established players, other pathways of cell surface membrane transport, generally termed "unconventional secretion," are now better understood. More insights have also been gleaned on the roles of secreted or shedding microvesicles, either exosomal or ectosomal in origin, in unconventional secretion. Recent works have also revealed key molecular components, particularly the Golgi reassembly stacking protein (GRASP), and the importance of stress-induced autophagy, in unconventional exocytic transport. This GRASP and autophagy-dependent (GAD) mode appears to underlie the unconventional exocytosis of many soluble and membrane cargoes. Likewise, recent findings have revealed transport processes that contrast the classically known mitochondria import, namely vesicular transport from the mitochondria to peroxisomes and lysosomes. Mitochondria-peroxisomal targeting of mitochondria-derived vesicles appears to involve the retromer complex, which was classically associated with endosome-Golgi membrane traffic. The routes of intracellular membrane transport and communications between eukaryotic organelles now appear far more complex that one would have imagined 10 years ago.