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The GTPase Rab26 links synaptic vesicles to the autophagy pathway.

Binotti B, Pavlos NJ, Riedel D, Wenzel D, Vorbrüggen G, Schalk AM, Kühnel K, Boyken J, Erck C, Martens H, Chua JJ, Jahn R - Elife (2015)

Bottom Line: Small GTPases of the Rab family not only regulate target recognition in membrane traffic but also control other cellular functions such as cytoskeletal transport and autophagy.Both endogenous and induced clusters co-localize with autophagy-related proteins such as Atg16L1, LC3B and Rab33B but not with other organelles.Furthermore, Atg16L1 appears to be a direct effector of Rab26 and binds Rab26 in its GTP-bound form, albeit only with low affinity.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.

ABSTRACT
Small GTPases of the Rab family not only regulate target recognition in membrane traffic but also control other cellular functions such as cytoskeletal transport and autophagy. Here we show that Rab26 is specifically associated with clusters of synaptic vesicles in neurites. Overexpression of active but not of GDP-preferring Rab26 enhances vesicle clustering, which is particularly conspicuous for the EGFP-tagged variant, resulting in a massive accumulation of synaptic vesicles in neuronal somata without altering the distribution of other organelles. Both endogenous and induced clusters co-localize with autophagy-related proteins such as Atg16L1, LC3B and Rab33B but not with other organelles. Furthermore, Atg16L1 appears to be a direct effector of Rab26 and binds Rab26 in its GTP-bound form, albeit only with low affinity. We propose that Rab26 selectively directs synaptic and secretory vesicles into preautophagosomal structures, suggesting the presence of a novel pathway for degradation of synaptic vesicles.

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EGFP-Rab26WT induces massive vesicle clustering in neuronal cell bodies.Ultrathin cryosections obtained from hippocampal neurons expressing EGFP-Rab26WT were immunogold labeled for EGFP and analyzed by electron microscopy. Transient expression of EGFP-Rab26WT results in the clustering of enormous numbers of vesicles positive for EGFP-Rab26.DOI:http://dx.doi.org/10.7554/eLife.05597.012
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fig5s1: EGFP-Rab26WT induces massive vesicle clustering in neuronal cell bodies.Ultrathin cryosections obtained from hippocampal neurons expressing EGFP-Rab26WT were immunogold labeled for EGFP and analyzed by electron microscopy. Transient expression of EGFP-Rab26WT results in the clustering of enormous numbers of vesicles positive for EGFP-Rab26.DOI:http://dx.doi.org/10.7554/eLife.05597.012

Mentions: To better understand the nature of these structures we carried out immunogold-TEM on ultrathin cryosections of transfected neurons. As shown in Figure 5A, the soma contained large clusters of numerous small vesicles that were positive for both EGFP-Rab26WT and synaptobrevin (Sybv). In many cases, these clusters were rather homogenous, but occasionally also contained larger vesicles and mitochondria (Figure 5B). Although no systematic quantification was performed, some of these clusters reached enormous dimensions containing possibly 1000s of small vesicles (Figure 5—figure supplement 1). In some cases, these clusters were surrounded by a single and/or double membrane (Figure 5C, inset), although this was somewhat variable. We also assessed neuromuscular junctions of Drosophila strains overexpressing YFP-Rab26WT by TEM. Here, dense clusters of vesicles (devoid of surrounding membranes) were regularly observable that were clearly set apart from surrounding synaptic vesicles (Figure 5D, indicated by an arrow) but were clearly absent in controls.10.7554/eLife.05597.011Figure 5.Ultrastructure of EGFP-Rab26 induced vesicle clusters in cultured hippocampal neurons and in neuromuscular junctions of Drosophila third instar larvae.


The GTPase Rab26 links synaptic vesicles to the autophagy pathway.

Binotti B, Pavlos NJ, Riedel D, Wenzel D, Vorbrüggen G, Schalk AM, Kühnel K, Boyken J, Erck C, Martens H, Chua JJ, Jahn R - Elife (2015)

EGFP-Rab26WT induces massive vesicle clustering in neuronal cell bodies.Ultrathin cryosections obtained from hippocampal neurons expressing EGFP-Rab26WT were immunogold labeled for EGFP and analyzed by electron microscopy. Transient expression of EGFP-Rab26WT results in the clustering of enormous numbers of vesicles positive for EGFP-Rab26.DOI:http://dx.doi.org/10.7554/eLife.05597.012
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4337689&req=5

fig5s1: EGFP-Rab26WT induces massive vesicle clustering in neuronal cell bodies.Ultrathin cryosections obtained from hippocampal neurons expressing EGFP-Rab26WT were immunogold labeled for EGFP and analyzed by electron microscopy. Transient expression of EGFP-Rab26WT results in the clustering of enormous numbers of vesicles positive for EGFP-Rab26.DOI:http://dx.doi.org/10.7554/eLife.05597.012
Mentions: To better understand the nature of these structures we carried out immunogold-TEM on ultrathin cryosections of transfected neurons. As shown in Figure 5A, the soma contained large clusters of numerous small vesicles that were positive for both EGFP-Rab26WT and synaptobrevin (Sybv). In many cases, these clusters were rather homogenous, but occasionally also contained larger vesicles and mitochondria (Figure 5B). Although no systematic quantification was performed, some of these clusters reached enormous dimensions containing possibly 1000s of small vesicles (Figure 5—figure supplement 1). In some cases, these clusters were surrounded by a single and/or double membrane (Figure 5C, inset), although this was somewhat variable. We also assessed neuromuscular junctions of Drosophila strains overexpressing YFP-Rab26WT by TEM. Here, dense clusters of vesicles (devoid of surrounding membranes) were regularly observable that were clearly set apart from surrounding synaptic vesicles (Figure 5D, indicated by an arrow) but were clearly absent in controls.10.7554/eLife.05597.011Figure 5.Ultrastructure of EGFP-Rab26 induced vesicle clusters in cultured hippocampal neurons and in neuromuscular junctions of Drosophila third instar larvae.

Bottom Line: Small GTPases of the Rab family not only regulate target recognition in membrane traffic but also control other cellular functions such as cytoskeletal transport and autophagy.Both endogenous and induced clusters co-localize with autophagy-related proteins such as Atg16L1, LC3B and Rab33B but not with other organelles.Furthermore, Atg16L1 appears to be a direct effector of Rab26 and binds Rab26 in its GTP-bound form, albeit only with low affinity.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.

ABSTRACT
Small GTPases of the Rab family not only regulate target recognition in membrane traffic but also control other cellular functions such as cytoskeletal transport and autophagy. Here we show that Rab26 is specifically associated with clusters of synaptic vesicles in neurites. Overexpression of active but not of GDP-preferring Rab26 enhances vesicle clustering, which is particularly conspicuous for the EGFP-tagged variant, resulting in a massive accumulation of synaptic vesicles in neuronal somata without altering the distribution of other organelles. Both endogenous and induced clusters co-localize with autophagy-related proteins such as Atg16L1, LC3B and Rab33B but not with other organelles. Furthermore, Atg16L1 appears to be a direct effector of Rab26 and binds Rab26 in its GTP-bound form, albeit only with low affinity. We propose that Rab26 selectively directs synaptic and secretory vesicles into preautophagosomal structures, suggesting the presence of a novel pathway for degradation of synaptic vesicles.

Show MeSH
Related in: MedlinePlus