Abstract
Saccharomyces cerevisiae is one of the best model organisms for the study of endocytic membrane trafficking. While studies in mammalian cells have characterized the temporal and morphological features of the endocytic pathway, studies in budding yeast have led the way in the analysis of the endosomal trafficking machinery components and their functions. Eukaryotic endomembrane systems were thought to be highly conserved from yeast to mammals, with the fusion of plasma membrane-derived vesicles to the early or recycling endosome being a common feature. Upon endosome maturation, cargos are then sorted for reuse or degraded via the endo-lysosomal (endo-vacuolar in yeast) pathway. However, recent studies have shown that budding yeast has a minimal endomembrane system that is fundamentally different from that of mammalian cells, with plasma membrane-derived vesicles fusing directly to a trans-Golgi compartment which acts as an early endosome. Thus, the Golgi, rather than the endosome, acts as the primary acceptor of endocytic vesicles, sorting cargo to pre-vacuolar endosomes for degradation. The field must now integrate these new findings into a broader understanding of the endomembrane system across eukaryotes. This article synthesizes what we know about the machinery mediating endocytic membrane fusion with this new model for yeast endomembrane function.
Highlights
The budding yeast Saccharomyces cerevisiae has long been regarded as an excellent model organism for studying a wide variety of cellular processes, including endocytosis and the secretory pathway.It was the first eukaryote to have its genome fully sequenced, and many of the proteins found in yeast are conserved in mammalian cells
Cargo is permitted to gradually dissociate from its receptor as the early endosome acidifies and matures—allowing receptor molecules to be recycled back to the plasma membrane via the trans-Golgi network (TGN), which acts as a recycling endosome in yeast [10]
The recently proposed yeast minimal endomembrane system has provided a new outlook on eukaryotic endocytic processes
Summary
The budding yeast Saccharomyces cerevisiae has long been regarded as an excellent model organism for studying a wide variety of cellular processes, including endocytosis and the secretory pathway. One possible explanation comes from a recent study demonstrating that plasma membrane derived endocytic vesicles dock and fuse to the late Golgi, and not to recycling or early endosomes, as previously thought [23]. In this new model, yeast is proposed to have a minimal endomembrane system, in which the late Golgi functions both as an early endosome and a recycling endosome, serving as a central hub for the endo- and exocytic pathways [23]. This review article aims to reexamine studies that defined SNARE functions in yeast, and to discuss their implications for the emerging model of the yeast minimal endomembrane system and the endocytic pathway
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