Early stages of the secretory pathway, but not endosomes, are required for Cvt vesicle and autophagosome assembly in Saccharomyces cerevisiae.
The Cvt pathway is a biosynthetic transport route for a distinct subset of resident yeast vacuolar hydrolases, whereas macroautophagy is a nonspecific degradative mechanism that allows cell survival during starvation. Yet, these two vacuolar trafficking pathways share a number of identical molecular components and are morphologically very similar. For example, one of the hallmarks of both pathways is the formation of double-membrane cytosolic vesicles that sequester cargo before vacuolar delivery. The origin of the vesicle membrane has been controversial and various lines of evidence have implicated essentially all compartments of the endomembrane system. Despite the analogies between the Cvt pathway and autophagy, earlier work has suggested that the origin of the engulfing vesicle membranes is different; the endoplasmic reticulum is proposed to be required only for autophagy. In contrast, in this study we demonstrate that the endoplasmic reticulum and/or Golgi complex, but not endosomal compartments, play an important role for both yeast transport routes. Along these lines, we demonstrate that Berkeley bodies, a structure generated from the Golgi complex in sec7 cells, are immunolabeled with Atg8, a structural component of autophagosomes. Finally, we also show that none of the yeast t-SNAREs are located at the preautophagosomal structure, the presumed site of double-membrane vesicle formation. Based on our results, we propose two models for Cvt vesicle biogenesis.
Life Sciences Institute and Departments of Biological Chemistry, University of Michigan, Ann Arbor, MI 48109, USA.
Fulvio
F
Reggiori
Chao-Wen
CW
Wang
Usha
U
Nair
Takahiro
T
Shintani
Hagai
H
Abeliovich
Daniel J
DJ
Klionsky
D000626:Aminopeptidases / Q000502:physiology; D000071190:Autophagy-Related Protein 8 Family; D000071183:Autophagy-Related Proteins; D002352:Carrier Proteins / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000502:physiology*; D011992:Endosomes / Q000378:metabolism / Q000502:physiology*; D006056:Golgi Apparatus / Q000502:physiology*; D049452:Green Fluorescent Proteins / Q000032:analysis; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D008561:Membrane Fusion / Q000502:physiology; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008954:Models, Biological; D010588:Phagosomes / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism; D050600:SNARE Proteins; D012441:Saccharomyces cerevisiae / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism* / Q000502:physiology; D022161:Transport Vesicles / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000032:analysis / Q000378:metabolism / Q000502:physiology
C113757:ATG8 protein, S cerevisiae; D000071190:Autophagy-Related Protein 8 Family; D000071183:Autophagy-Related Proteins; D002352:Carrier Proteins; D020662:Guanine Nucleotide Exchange Factors; D008869:Microtubule-Associated Proteins; D050600:SNARE Proteins; D029701:Saccharomyces cerevisiae Proteins; C066755:Sec7 guanine nucleotide exchange factors; D033921:Vesicular Transport Proteins; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D011494:Protein Kinases; C477823:ATG1 protein, S cerevisiae; D000626:Aminopeptidases; C019689:APE1 protein, S cerevisiae