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Synaptotagmin 1 directs repetitive release by coupling vesicle exocytosis to the Rab3 cycle.

Cheng Y, Wang J, Wang Y, Ding M - Elife (2015)

Bottom Line: How this harmonization is achieved is not known.In the absence of Ca(2+), synaptotagmin 1 binds to Rab3 GTPase activating protein (GAP) and inhibits the GTP hydrolysis of Rab3 protein.In the presence of Ca(2+), synaptotagmin 1 releases Rab3 GAP and promotes membrane disassociation of Rab3.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China.

ABSTRACT
In response to Ca(2+) influx, a synapse needs to release neurotransmitters quickly while immediately preparing for repeat firing. How this harmonization is achieved is not known. In this study, we found that the Ca(2+) sensor synaptotagmin 1 orchestrates the membrane association/disassociation cycle of Rab3, which functions in activity-dependent recruitment of synaptic vesicles. In the absence of Ca(2+), synaptotagmin 1 binds to Rab3 GTPase activating protein (GAP) and inhibits the GTP hydrolysis of Rab3 protein. Rab3 GAP resides on synaptic vesicles, and synaptotagmin 1 is essential for the synaptic localization of Rab3 GAP. In the presence of Ca(2+), synaptotagmin 1 releases Rab3 GAP and promotes membrane disassociation of Rab3. Without synaptotagmin 1, the tight coupling between vesicle exocytosis and Rab3 membrane disassociation is disrupted. We uncovered the long-sought molecular apparatus linking vesicle exocytosis to Rab3 cycling and we also revealed the important function of synaptotagmin 1 in repetitive synaptic vesicle release.

No MeSH data available.


Related in: MedlinePlus

Synaptic vesicle clustering is unaffected by loss of snt-1 function.(A) SNB-1::GFP puncta distribution in wild type and snt-1 mutants. (B) The synaptic enrichment of SNB-1::GFP puncta is indistinguishable in wild type and snt-1. Data are presented as mean ± SD; NS, not significant. In both wild type (C, C′ and C″) and snt-1 (D, D′ and D″), the SNB-1::GFP puncta are present in the synaptic area on the ventral cord, which is outside of the cell body (C″ and D″). In unc-104 (E, E′ and E″) or snt-1 unc-104 double mutants (F, F′ and F″), SNB-1::GFP accumulates in the cell bodies on the ventral cord (E″ and F″). (G) In wild type, GFP::RAB-3 is distributed in a punctate pattern in the pre-synaptic regions on the ventral cord (G“). (H) GFP::RAB-3 is diffuse throughout the whole axon including both dorsal (H') and ventral (H″) processes. (I) GFP::RAB-3 accumulates in ventral cell bodies (I″). (J) In snt-1 unc-104 double mutants, GFP::RAB-3 is diffuse throughout the whole axon in both dorsal (J') and ventral (J″) regions. Yellow boxes indicate part of the dorsal cord, which is enlarged in the lower left panels. Red boxes indicate part of the ventral cord, which is enlarged in the lower right panels (white arrows indicate DD cell bodies in the ventral cord). A schematic drawing of a DD neuron during the L1 stage is presented underneath the fluorescence images of each genotype, with the SNB-1::GFP or GFP::RAB-3 signal shown in green. Small green dots represent the pre-synaptic areas. Individual DD cell bodies are indicated as large ovals at the bottom right of each diagram. Scale bars, 5 µm.DOI:http://dx.doi.org/10.7554/eLife.05118.005
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fig2: Synaptic vesicle clustering is unaffected by loss of snt-1 function.(A) SNB-1::GFP puncta distribution in wild type and snt-1 mutants. (B) The synaptic enrichment of SNB-1::GFP puncta is indistinguishable in wild type and snt-1. Data are presented as mean ± SD; NS, not significant. In both wild type (C, C′ and C″) and snt-1 (D, D′ and D″), the SNB-1::GFP puncta are present in the synaptic area on the ventral cord, which is outside of the cell body (C″ and D″). In unc-104 (E, E′ and E″) or snt-1 unc-104 double mutants (F, F′ and F″), SNB-1::GFP accumulates in the cell bodies on the ventral cord (E″ and F″). (G) In wild type, GFP::RAB-3 is distributed in a punctate pattern in the pre-synaptic regions on the ventral cord (G“). (H) GFP::RAB-3 is diffuse throughout the whole axon including both dorsal (H') and ventral (H″) processes. (I) GFP::RAB-3 accumulates in ventral cell bodies (I″). (J) In snt-1 unc-104 double mutants, GFP::RAB-3 is diffuse throughout the whole axon in both dorsal (J') and ventral (J″) regions. Yellow boxes indicate part of the dorsal cord, which is enlarged in the lower left panels. Red boxes indicate part of the ventral cord, which is enlarged in the lower right panels (white arrows indicate DD cell bodies in the ventral cord). A schematic drawing of a DD neuron during the L1 stage is presented underneath the fluorescence images of each genotype, with the SNB-1::GFP or GFP::RAB-3 signal shown in green. Small green dots represent the pre-synaptic areas. Individual DD cell bodies are indicated as large ovals at the bottom right of each diagram. Scale bars, 5 µm.DOI:http://dx.doi.org/10.7554/eLife.05118.005

Mentions: The diffuse RAB-3 phenotype in snt-1 may be caused by failure of SV clustering at the synaptic terminal. Therefore, we examined the localization of another synaptic vesicle protein SNB-1. SNB-1 is the C. elegans synaptobrevin homologue (Nonet, 1999). In worm DD and VD motor neurons, SNB-1 is distributed evenly in punctate structures along neuronal processes, similar to RAB-3 (Figure 2A) (Zhen and Jin, 1999). In snt-1 animals, some of the SNB-1 puncta are enlarged, but the punctate distribution of SNB-1 is not altered (Figure 2A,B). This observation is consistent with recent findings (Yu et al., 2013), suggesting that SV clustering is probably not affected by snt-1.10.7554/eLife.05118.005Figure 2.Synaptic vesicle clustering is unaffected by loss of snt-1 function.


Synaptotagmin 1 directs repetitive release by coupling vesicle exocytosis to the Rab3 cycle.

Cheng Y, Wang J, Wang Y, Ding M - Elife (2015)

Synaptic vesicle clustering is unaffected by loss of snt-1 function.(A) SNB-1::GFP puncta distribution in wild type and snt-1 mutants. (B) The synaptic enrichment of SNB-1::GFP puncta is indistinguishable in wild type and snt-1. Data are presented as mean ± SD; NS, not significant. In both wild type (C, C′ and C″) and snt-1 (D, D′ and D″), the SNB-1::GFP puncta are present in the synaptic area on the ventral cord, which is outside of the cell body (C″ and D″). In unc-104 (E, E′ and E″) or snt-1 unc-104 double mutants (F, F′ and F″), SNB-1::GFP accumulates in the cell bodies on the ventral cord (E″ and F″). (G) In wild type, GFP::RAB-3 is distributed in a punctate pattern in the pre-synaptic regions on the ventral cord (G“). (H) GFP::RAB-3 is diffuse throughout the whole axon including both dorsal (H') and ventral (H″) processes. (I) GFP::RAB-3 accumulates in ventral cell bodies (I″). (J) In snt-1 unc-104 double mutants, GFP::RAB-3 is diffuse throughout the whole axon in both dorsal (J') and ventral (J″) regions. Yellow boxes indicate part of the dorsal cord, which is enlarged in the lower left panels. Red boxes indicate part of the ventral cord, which is enlarged in the lower right panels (white arrows indicate DD cell bodies in the ventral cord). A schematic drawing of a DD neuron during the L1 stage is presented underneath the fluorescence images of each genotype, with the SNB-1::GFP or GFP::RAB-3 signal shown in green. Small green dots represent the pre-synaptic areas. Individual DD cell bodies are indicated as large ovals at the bottom right of each diagram. Scale bars, 5 µm.DOI:http://dx.doi.org/10.7554/eLife.05118.005
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fig2: Synaptic vesicle clustering is unaffected by loss of snt-1 function.(A) SNB-1::GFP puncta distribution in wild type and snt-1 mutants. (B) The synaptic enrichment of SNB-1::GFP puncta is indistinguishable in wild type and snt-1. Data are presented as mean ± SD; NS, not significant. In both wild type (C, C′ and C″) and snt-1 (D, D′ and D″), the SNB-1::GFP puncta are present in the synaptic area on the ventral cord, which is outside of the cell body (C″ and D″). In unc-104 (E, E′ and E″) or snt-1 unc-104 double mutants (F, F′ and F″), SNB-1::GFP accumulates in the cell bodies on the ventral cord (E″ and F″). (G) In wild type, GFP::RAB-3 is distributed in a punctate pattern in the pre-synaptic regions on the ventral cord (G“). (H) GFP::RAB-3 is diffuse throughout the whole axon including both dorsal (H') and ventral (H″) processes. (I) GFP::RAB-3 accumulates in ventral cell bodies (I″). (J) In snt-1 unc-104 double mutants, GFP::RAB-3 is diffuse throughout the whole axon in both dorsal (J') and ventral (J″) regions. Yellow boxes indicate part of the dorsal cord, which is enlarged in the lower left panels. Red boxes indicate part of the ventral cord, which is enlarged in the lower right panels (white arrows indicate DD cell bodies in the ventral cord). A schematic drawing of a DD neuron during the L1 stage is presented underneath the fluorescence images of each genotype, with the SNB-1::GFP or GFP::RAB-3 signal shown in green. Small green dots represent the pre-synaptic areas. Individual DD cell bodies are indicated as large ovals at the bottom right of each diagram. Scale bars, 5 µm.DOI:http://dx.doi.org/10.7554/eLife.05118.005
Mentions: The diffuse RAB-3 phenotype in snt-1 may be caused by failure of SV clustering at the synaptic terminal. Therefore, we examined the localization of another synaptic vesicle protein SNB-1. SNB-1 is the C. elegans synaptobrevin homologue (Nonet, 1999). In worm DD and VD motor neurons, SNB-1 is distributed evenly in punctate structures along neuronal processes, similar to RAB-3 (Figure 2A) (Zhen and Jin, 1999). In snt-1 animals, some of the SNB-1 puncta are enlarged, but the punctate distribution of SNB-1 is not altered (Figure 2A,B). This observation is consistent with recent findings (Yu et al., 2013), suggesting that SV clustering is probably not affected by snt-1.10.7554/eLife.05118.005Figure 2.Synaptic vesicle clustering is unaffected by loss of snt-1 function.

Bottom Line: How this harmonization is achieved is not known.In the absence of Ca(2+), synaptotagmin 1 binds to Rab3 GTPase activating protein (GAP) and inhibits the GTP hydrolysis of Rab3 protein.In the presence of Ca(2+), synaptotagmin 1 releases Rab3 GAP and promotes membrane disassociation of Rab3.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China.

ABSTRACT
In response to Ca(2+) influx, a synapse needs to release neurotransmitters quickly while immediately preparing for repeat firing. How this harmonization is achieved is not known. In this study, we found that the Ca(2+) sensor synaptotagmin 1 orchestrates the membrane association/disassociation cycle of Rab3, which functions in activity-dependent recruitment of synaptic vesicles. In the absence of Ca(2+), synaptotagmin 1 binds to Rab3 GTPase activating protein (GAP) and inhibits the GTP hydrolysis of Rab3 protein. Rab3 GAP resides on synaptic vesicles, and synaptotagmin 1 is essential for the synaptic localization of Rab3 GAP. In the presence of Ca(2+), synaptotagmin 1 releases Rab3 GAP and promotes membrane disassociation of Rab3. Without synaptotagmin 1, the tight coupling between vesicle exocytosis and Rab3 membrane disassociation is disrupted. We uncovered the long-sought molecular apparatus linking vesicle exocytosis to Rab3 cycling and we also revealed the important function of synaptotagmin 1 in repetitive synaptic vesicle release.

No MeSH data available.


Related in: MedlinePlus