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Loss of the Synaptic Vesicle Protein SV2B results in reduced neurotransmission and altered synaptic vesicle protein expression in the retina.

Morgans CW, Kensel-Hammes P, Hurley JB, Burton K, Idzerda R, McKnight GS, Bajjalieh SM - PLoS ONE (2009)

Bottom Line: Of the three isoforms expressed in mammals, SV2B is the most divergent.Immunolabeling studies revealed that SV2B is detected in rod photoreceptor synaptic terminals where it is the primary isoform.

View Article: PubMed Central - PubMed

Affiliation: Casey Eye Institute, Oregon Health & Sciences University, Portland, OR, USA.

ABSTRACT
The Synaptic Vesicle Protein 2 (SV2) family of transporter-like proteins is expressed exclusively in vesicles that undergo calcium-regulated exocytosis. Of the three isoforms expressed in mammals, SV2B is the most divergent. Here we report studies of SV2B location and function in the retina. Immunolabeling studies revealed that SV2B is detected in rod photoreceptor synaptic terminals where it is the primary isoform. In mice lacking SV2B, synaptic transmission at the synapse between photoreceptors and bipolar neurons was decreased, as evidenced by a significant reduction in the amplitude of the b-wave in electroretinogram recordings. Quantitative immunoblot analyses of whole eyes revealed that loss of SV2B was associated with reduced levels of synaptic vesicle proteins including synaptotagmin, VAMP, synaptophysin and the vesicular glutamate transporter V-GLUT1. Immunolabeling studies revealed that SV2B is detected in rod photoreceptor synaptic terminals where it is the primary isoform. Thus, SV2B contributes to the modulation of synaptic vesicle exocytosis and plays a significant role in regulating synaptic protein content.

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SV2A and SV2B are differentially distributed in photoreceptor terminals.A) SV2A is expressed in both inner and outer plexiform layers whereas SV2B is expressed primarily in the outer plexiform layer. Retina sections from SV2B knockout (−/−) and wild-type (+/+) mice were labeled by fluorescence with antibodies recognizing all SV2 subtypes (total SV2), or antibodies specific for either SV2A or SV2B. B) SV2A is the predominant SV2 isoform in cone terminals and SV2B predominates in rod terminals. The outer plexiform layer is shown for wild-type retina sections double labeled for peanut agglutinin (PNA) conjugated to Alexa-488 (green) and either SV2A or SV2B (red). Areas of overlap between the two fluorophores appear yellow. Both anti-SV2A and anti-SV2B labeled PNA-negative synapses, consistent with both isoforms being present in rod photoreceptor terminals. Abbreviations: opl, outer plexiform layer; ipl, inner plexiform layer. The scale bars represent 30 µm.
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pone-0005230-g002: SV2A and SV2B are differentially distributed in photoreceptor terminals.A) SV2A is expressed in both inner and outer plexiform layers whereas SV2B is expressed primarily in the outer plexiform layer. Retina sections from SV2B knockout (−/−) and wild-type (+/+) mice were labeled by fluorescence with antibodies recognizing all SV2 subtypes (total SV2), or antibodies specific for either SV2A or SV2B. B) SV2A is the predominant SV2 isoform in cone terminals and SV2B predominates in rod terminals. The outer plexiform layer is shown for wild-type retina sections double labeled for peanut agglutinin (PNA) conjugated to Alexa-488 (green) and either SV2A or SV2B (red). Areas of overlap between the two fluorophores appear yellow. Both anti-SV2A and anti-SV2B labeled PNA-negative synapses, consistent with both isoforms being present in rod photoreceptor terminals. Abbreviations: opl, outer plexiform layer; ipl, inner plexiform layer. The scale bars represent 30 µm.

Mentions: We examined SV2A, SV2B and total SV2 in retina from wild-type and SV2B knockout mice using isoform-specific antibodies and an antibody that recognizes all three isoforms. SV2B was previously reported to be the sole SV2 isoform in rod photoreceptor synapses [9] and we therefore anticipated that these synapses would lack all SV2 in SV2B knockouts. We compared the presence of SV2A and SV2B to the cone marker peanut agglutinin (PNA) in retina from wild-type and SV2B knockout mice. As previously reported, we observed strong SV2A immunoreactivity in PNA-positive cone terminals, and SV2B immunoreactivity primarily in rod (PNA-negative) terminals in the outer plexiform synaptic layer (OPL) of wild-type mice, (Figure 2). In contrast to the findings of Wang et al. (2003), however, we observed faint labeling of PNA-negative synapses with anti-SV2A, indicating that SV2A is expressed in rod synapses. This labeling of rod terminals is unlikely to be a fixation artifact, since the sections were lightly fixed and labeling was specific to synaptic terminals. Also in contrast to the findings of Wang et al. (2003), we saw little SV2B labeling in the inner plexiform layer, consistent with SV2B being expressed primarily in rod photoreceptor terminals.


Loss of the Synaptic Vesicle Protein SV2B results in reduced neurotransmission and altered synaptic vesicle protein expression in the retina.

Morgans CW, Kensel-Hammes P, Hurley JB, Burton K, Idzerda R, McKnight GS, Bajjalieh SM - PLoS ONE (2009)

SV2A and SV2B are differentially distributed in photoreceptor terminals.A) SV2A is expressed in both inner and outer plexiform layers whereas SV2B is expressed primarily in the outer plexiform layer. Retina sections from SV2B knockout (−/−) and wild-type (+/+) mice were labeled by fluorescence with antibodies recognizing all SV2 subtypes (total SV2), or antibodies specific for either SV2A or SV2B. B) SV2A is the predominant SV2 isoform in cone terminals and SV2B predominates in rod terminals. The outer plexiform layer is shown for wild-type retina sections double labeled for peanut agglutinin (PNA) conjugated to Alexa-488 (green) and either SV2A or SV2B (red). Areas of overlap between the two fluorophores appear yellow. Both anti-SV2A and anti-SV2B labeled PNA-negative synapses, consistent with both isoforms being present in rod photoreceptor terminals. Abbreviations: opl, outer plexiform layer; ipl, inner plexiform layer. The scale bars represent 30 µm.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2667261&req=5

pone-0005230-g002: SV2A and SV2B are differentially distributed in photoreceptor terminals.A) SV2A is expressed in both inner and outer plexiform layers whereas SV2B is expressed primarily in the outer plexiform layer. Retina sections from SV2B knockout (−/−) and wild-type (+/+) mice were labeled by fluorescence with antibodies recognizing all SV2 subtypes (total SV2), or antibodies specific for either SV2A or SV2B. B) SV2A is the predominant SV2 isoform in cone terminals and SV2B predominates in rod terminals. The outer plexiform layer is shown for wild-type retina sections double labeled for peanut agglutinin (PNA) conjugated to Alexa-488 (green) and either SV2A or SV2B (red). Areas of overlap between the two fluorophores appear yellow. Both anti-SV2A and anti-SV2B labeled PNA-negative synapses, consistent with both isoforms being present in rod photoreceptor terminals. Abbreviations: opl, outer plexiform layer; ipl, inner plexiform layer. The scale bars represent 30 µm.
Mentions: We examined SV2A, SV2B and total SV2 in retina from wild-type and SV2B knockout mice using isoform-specific antibodies and an antibody that recognizes all three isoforms. SV2B was previously reported to be the sole SV2 isoform in rod photoreceptor synapses [9] and we therefore anticipated that these synapses would lack all SV2 in SV2B knockouts. We compared the presence of SV2A and SV2B to the cone marker peanut agglutinin (PNA) in retina from wild-type and SV2B knockout mice. As previously reported, we observed strong SV2A immunoreactivity in PNA-positive cone terminals, and SV2B immunoreactivity primarily in rod (PNA-negative) terminals in the outer plexiform synaptic layer (OPL) of wild-type mice, (Figure 2). In contrast to the findings of Wang et al. (2003), however, we observed faint labeling of PNA-negative synapses with anti-SV2A, indicating that SV2A is expressed in rod synapses. This labeling of rod terminals is unlikely to be a fixation artifact, since the sections were lightly fixed and labeling was specific to synaptic terminals. Also in contrast to the findings of Wang et al. (2003), we saw little SV2B labeling in the inner plexiform layer, consistent with SV2B being expressed primarily in rod photoreceptor terminals.

Bottom Line: Of the three isoforms expressed in mammals, SV2B is the most divergent.Immunolabeling studies revealed that SV2B is detected in rod photoreceptor synaptic terminals where it is the primary isoform.

View Article: PubMed Central - PubMed

Affiliation: Casey Eye Institute, Oregon Health & Sciences University, Portland, OR, USA.

ABSTRACT
The Synaptic Vesicle Protein 2 (SV2) family of transporter-like proteins is expressed exclusively in vesicles that undergo calcium-regulated exocytosis. Of the three isoforms expressed in mammals, SV2B is the most divergent. Here we report studies of SV2B location and function in the retina. Immunolabeling studies revealed that SV2B is detected in rod photoreceptor synaptic terminals where it is the primary isoform. In mice lacking SV2B, synaptic transmission at the synapse between photoreceptors and bipolar neurons was decreased, as evidenced by a significant reduction in the amplitude of the b-wave in electroretinogram recordings. Quantitative immunoblot analyses of whole eyes revealed that loss of SV2B was associated with reduced levels of synaptic vesicle proteins including synaptotagmin, VAMP, synaptophysin and the vesicular glutamate transporter V-GLUT1. Immunolabeling studies revealed that SV2B is detected in rod photoreceptor synaptic terminals where it is the primary isoform. Thus, SV2B contributes to the modulation of synaptic vesicle exocytosis and plays a significant role in regulating synaptic protein content.

Show MeSH
Related in: MedlinePlus