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The vesicle protein SAM-4 regulates the processivity of synaptic vesicle transport.

Zheng Q, Ahlawat S, Schaefer A, Mahoney T, Koushika SP, Nonet ML - PLoS Genet. (2014)

Bottom Line: Processivity, but not velocity, of SV transport was reduced in sam-4 mutants. sam-4 displayed strong genetic interactions with mutations in the cargo binding but not the motor domain of unc-104.Gain-of-function mutations in the unc-104 motor domain, identified in this study, suppress the sam-4 defects by increasing processivity of the SV transport.Our data support a model in which the SV protein SAM-4 regulates the processivity of SV transport.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy and Neurobiology, Washington University Medical School, St. Louis, Missouri, United States of America.

ABSTRACT
Axonal transport of synaptic vesicles (SVs) is a KIF1A/UNC-104 mediated process critical for synapse development and maintenance yet little is known of how SV transport is regulated. Using C. elegans as an in vivo model, we identified SAM-4 as a novel conserved vesicular component regulating SV transport. Processivity, but not velocity, of SV transport was reduced in sam-4 mutants. sam-4 displayed strong genetic interactions with mutations in the cargo binding but not the motor domain of unc-104. Gain-of-function mutations in the unc-104 motor domain, identified in this study, suppress the sam-4 defects by increasing processivity of the SV transport. Genetic analyses suggest that SAM-4, SYD-2/liprin-α and the KIF1A/UNC-104 motor function in the same pathway to regulate SV transport. Our data support a model in which the SV protein SAM-4 regulates the processivity of SV transport.

No MeSH data available.


Related in: MedlinePlus

sam-4 and syd-2 interact with unc-104 in transporting SVs.GFP-RAB-3 (jsIs821) distribution in PLM neurons of wild type and mutant animals as indicated. A–G panels are focused on the PLM synaptic varicosities and A′–G′ panels are focused on the PLM soma and the proximal portion of the neurite. Alleles tested: sam-4(js415), unc-104(js901) and syd-2(ok217). Arrowheads: synaptic varicosities; solid arrows: PLM soma; open arrows: PLM neurites; asterisk: vulva. Scale bar: 20 µm.
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pgen-1004644-g003: sam-4 and syd-2 interact with unc-104 in transporting SVs.GFP-RAB-3 (jsIs821) distribution in PLM neurons of wild type and mutant animals as indicated. A–G panels are focused on the PLM synaptic varicosities and A′–G′ panels are focused on the PLM soma and the proximal portion of the neurite. Alleles tested: sam-4(js415), unc-104(js901) and syd-2(ok217). Arrowheads: synaptic varicosities; solid arrows: PLM soma; open arrows: PLM neurites; asterisk: vulva. Scale bar: 20 µm.

Mentions: Axonal transport of SVs in synapses is mediated by anterograde transport (largely the KIF1A motor system) and retrograde transport (the dynein motor system). To understand mechanisms by which SAM-4 regulates SV trafficking, we examined genetic interactions of sam-4 with mutations in both unc-104 and the dynein heavy chain gene dhc-1. Hypomorphic mutations were used because mutations in both genes are lethal and because point mutations in different domains of UNC-104 are available for analysis. We first tested if SAM-4 is involved in regulating the UNC-104 transport machinery by examining sam-4 unc-104 interactions. We previously isolated a hypomorphic unc-104 loss-of-function (lf) mutant, js901, with a G1466V lesion in the cargo binding PH domain of UNC-104 that displays very similar phenotypes to sam-4 (materials and methods for details). These mutants show decreased GFP-RAB-3 levels in PLM synaptic varicosities and increased accumulations in the proximal portion of PLM neurites (Figure 3A–3C′). Furthermore, they displayed mild locomotion defects (Figure 4A, 4C and 4I) while remaining grossly normal in PLM neurite morphology, growth rate and egg-laying behavior. js901 males remained competent to mate. Overall, the phenotypic defects of unc-104(js901) are mild compared to other unc-104 alleles such as the e1265 PH domain and the rh43 motor domain lesions which have severe locomotory defects and slow growth rates. If SAM-4 interacts with UNC-104 to regulate SV transport, we reasoned that sam-4 mutations would exaggerate the mild js901 defects. Indeed, we observed that SV soma accumulations are further increased in the sam-4 unc-104(js901) double mutant relative to either single mutant (Figure 3A–3D′). Additionally, we found that sam-4 unc-104(js901) double mutants exhibit very severe locomotion defects relative to either single mutant, exhibiting defects comparable to severe unc-104 mutants (Figure 4A–4D, 4I). These results suggest that SAM-4 functions in concert with the UNC-104 protein to regulate the SV trafficking.


The vesicle protein SAM-4 regulates the processivity of synaptic vesicle transport.

Zheng Q, Ahlawat S, Schaefer A, Mahoney T, Koushika SP, Nonet ML - PLoS Genet. (2014)

sam-4 and syd-2 interact with unc-104 in transporting SVs.GFP-RAB-3 (jsIs821) distribution in PLM neurons of wild type and mutant animals as indicated. A–G panels are focused on the PLM synaptic varicosities and A′–G′ panels are focused on the PLM soma and the proximal portion of the neurite. Alleles tested: sam-4(js415), unc-104(js901) and syd-2(ok217). Arrowheads: synaptic varicosities; solid arrows: PLM soma; open arrows: PLM neurites; asterisk: vulva. Scale bar: 20 µm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4199485&req=5

pgen-1004644-g003: sam-4 and syd-2 interact with unc-104 in transporting SVs.GFP-RAB-3 (jsIs821) distribution in PLM neurons of wild type and mutant animals as indicated. A–G panels are focused on the PLM synaptic varicosities and A′–G′ panels are focused on the PLM soma and the proximal portion of the neurite. Alleles tested: sam-4(js415), unc-104(js901) and syd-2(ok217). Arrowheads: synaptic varicosities; solid arrows: PLM soma; open arrows: PLM neurites; asterisk: vulva. Scale bar: 20 µm.
Mentions: Axonal transport of SVs in synapses is mediated by anterograde transport (largely the KIF1A motor system) and retrograde transport (the dynein motor system). To understand mechanisms by which SAM-4 regulates SV trafficking, we examined genetic interactions of sam-4 with mutations in both unc-104 and the dynein heavy chain gene dhc-1. Hypomorphic mutations were used because mutations in both genes are lethal and because point mutations in different domains of UNC-104 are available for analysis. We first tested if SAM-4 is involved in regulating the UNC-104 transport machinery by examining sam-4 unc-104 interactions. We previously isolated a hypomorphic unc-104 loss-of-function (lf) mutant, js901, with a G1466V lesion in the cargo binding PH domain of UNC-104 that displays very similar phenotypes to sam-4 (materials and methods for details). These mutants show decreased GFP-RAB-3 levels in PLM synaptic varicosities and increased accumulations in the proximal portion of PLM neurites (Figure 3A–3C′). Furthermore, they displayed mild locomotion defects (Figure 4A, 4C and 4I) while remaining grossly normal in PLM neurite morphology, growth rate and egg-laying behavior. js901 males remained competent to mate. Overall, the phenotypic defects of unc-104(js901) are mild compared to other unc-104 alleles such as the e1265 PH domain and the rh43 motor domain lesions which have severe locomotory defects and slow growth rates. If SAM-4 interacts with UNC-104 to regulate SV transport, we reasoned that sam-4 mutations would exaggerate the mild js901 defects. Indeed, we observed that SV soma accumulations are further increased in the sam-4 unc-104(js901) double mutant relative to either single mutant (Figure 3A–3D′). Additionally, we found that sam-4 unc-104(js901) double mutants exhibit very severe locomotion defects relative to either single mutant, exhibiting defects comparable to severe unc-104 mutants (Figure 4A–4D, 4I). These results suggest that SAM-4 functions in concert with the UNC-104 protein to regulate the SV trafficking.

Bottom Line: Processivity, but not velocity, of SV transport was reduced in sam-4 mutants. sam-4 displayed strong genetic interactions with mutations in the cargo binding but not the motor domain of unc-104.Gain-of-function mutations in the unc-104 motor domain, identified in this study, suppress the sam-4 defects by increasing processivity of the SV transport.Our data support a model in which the SV protein SAM-4 regulates the processivity of SV transport.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy and Neurobiology, Washington University Medical School, St. Louis, Missouri, United States of America.

ABSTRACT
Axonal transport of synaptic vesicles (SVs) is a KIF1A/UNC-104 mediated process critical for synapse development and maintenance yet little is known of how SV transport is regulated. Using C. elegans as an in vivo model, we identified SAM-4 as a novel conserved vesicular component regulating SV transport. Processivity, but not velocity, of SV transport was reduced in sam-4 mutants. sam-4 displayed strong genetic interactions with mutations in the cargo binding but not the motor domain of unc-104. Gain-of-function mutations in the unc-104 motor domain, identified in this study, suppress the sam-4 defects by increasing processivity of the SV transport. Genetic analyses suggest that SAM-4, SYD-2/liprin-α and the KIF1A/UNC-104 motor function in the same pathway to regulate SV transport. Our data support a model in which the SV protein SAM-4 regulates the processivity of SV transport.

No MeSH data available.


Related in: MedlinePlus