The structure and function of presynaptic endosomes.
The function of endosomes and of endosome-like structures in the presynaptic compartment is still controversial. This is in part due to the absence of a consensus on definitions and markers for these compartments. Synaptic endosomes are sometimes seen as stable organelles, permanently present in the synapse. Alternatively, they are seen as short-lived intermediates in synaptic vesicle recycling, arising from the endocytosis of large vesicles from the plasma membrane, or from homotypic fusion of small vesicles. In addition, the potential function of the endosome is largely unknown in the synapse. Some groups have proposed that the endosome is involved in the sorting of synaptic vesicle proteins, albeit others have produced data that deny this possibility. In this review, we present the existing evidence for synaptic endosomes, we discuss their potential functions, and we highlight frequent technical pitfalls in the analysis of this elusive compartment. We also sketch a roadmap to definitely determine the role of synaptic endosomes for the synaptic vesicle cycle. Finally, we propose a common definition of synaptic endosome-like structures.
Department of Neuro- and Sensory Physiology, University of Göttingen Medical Center, Cluster of Excellence Nanoscale Microscopy and Molecular Physiology of the Brain, Humboldtallee 23, 37073 Göttingen, Germany; International Max Planck Research School for Neurosciences, 37077 Göttingen, Germany. Electronic address: sebastian.jaehne1@stud.uni-goettingen.de.
Sebastian
S
Jähne
Department of Neuro- and Sensory Physiology, University of Göttingen Medical Center, Cluster of Excellence Nanoscale Microscopy and Molecular Physiology of the Brain, Humboldtallee 23, 37073 Göttingen, Germany.
Silvio O
SO
Rizzoli
Department of Neuro- and Sensory Physiology, University of Göttingen Medical Center, Cluster of Excellence Nanoscale Microscopy and Molecular Physiology of the Brain, Humboldtallee 23, 37073 Göttingen, Germany; International Max Planck Research School for Molecular Biology, 37077 Göttingen, Germany. Electronic address: martin.helm@med.uni-goettingen.de.
Martin S
MS
Helm
D000818:Animals; D004705:Endocytosis; D011992:Endosomes / Q000502:physiology* / Q000648:ultrastructure; D006801:Humans; D017729:Presynaptic Terminals / Q000502:physiology* / Q000648:ultrastructure; D009435:Synaptic Transmission; D013572:Synaptic Vesicles / Q000378:metabolism
Endocytosis; Endosome; Presynapse; Protein degradation; Protein sorting; Synaptic vesicle recycling