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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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Loss of SV2B results in reduced neurotransmission between photoreceptors and bipolar neurons of the retina.A) Average ERG traces from wild-type and SV2B−/− retina in response to stimuli of (top to bottom) 90,000, 9,000, 900, 90 and 9 photo-isomerizations per rod per flash. (n = 5 wt, 8 SV2B−/− mice). B) Average b-wave amplitudes at different light intensities showing average intensity decrease in mice from SV2B knockouts (n = 5 wt, 8 SV2B−/− mice). Error bars represent S.E.M. C) Average a-wave amplitudes showing no difference in amplitude in wt and SV2B knockouts. D) The ratio of b- to a-wave amplitude at the two strongest stimulus intensities was ∼50% lower in SV2B−/− mice (p = 0.015 for 90,000, p = 0.026 for 9000, students t-test).
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pone-0005230-g003: Loss of SV2B results in reduced neurotransmission between photoreceptors and bipolar neurons of the retina.A) Average ERG traces from wild-type and SV2B−/− retina in response to stimuli of (top to bottom) 90,000, 9,000, 900, 90 and 9 photo-isomerizations per rod per flash. (n = 5 wt, 8 SV2B−/− mice). B) Average b-wave amplitudes at different light intensities showing average intensity decrease in mice from SV2B knockouts (n = 5 wt, 8 SV2B−/− mice). Error bars represent S.E.M. C) Average a-wave amplitudes showing no difference in amplitude in wt and SV2B knockouts. D) The ratio of b- to a-wave amplitude at the two strongest stimulus intensities was ∼50% lower in SV2B−/− mice (p = 0.015 for 90,000, p = 0.026 for 9000, students t-test).

Mentions: To explore the function of SV2B, we compared neurotransmission in the retinas of wild-type and SV2B knockout mice by measuring the electroretinographic response to light flashes of varying intensity [22]. This procedure measures electric potential flux in the retina. The amplitudes of the a-wave component of the measure, which reflects closure of cGMP-gated ion channels in the outer segment membrane, were not significantly different in SV2B−/− retinas (Figure 3C), indicating that the channels regulating membrane conductance in photoreceptors function normally in the absence of SV2B. In contrast, b-wave amplitudes, which reflect synaptic transmission between photoreceptors and bipolar neurons, were reduced ∼30% in retinas of SV2B−/− mice compared to SV2B+/+ mice (Figure 3A–B). Decreased b-wave amplitudes were observed at stimulus intensities in which only rod photoreceptors were activated (9 and 900 photoisomerisations/sec) and those in which both rods and cones were activated (9000 and 90,000 photoisomerisations/sec) (Table 1). When b-wave amplitudes were normalized by calculating the b/a wave ratio, we observed that values from SV2B knockouts were ∼50% lower at the two highest stimulus intensities (Figure 3D). Examination of ribbon synapses in retinas from wild-type and SV2B −/− mice did not reveal obvious differences in photoreceptor synapse ultrastructure (Supplemental Figure S1). This contrasts with the striking change in ribbon morphology observed in Bassoon knockout mice, which demonstrate a similar neurotransmission phenotype [24]. Thus diminished transmission between photoreceptors and bipolar neurons does not appear to be due to gross changes in ribbon synapse development. Taken together, these observations indicate that SV2B, like SV2A [18], [25], is a positive modulator of synaptic transmission.


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)

Loss of SV2B results in reduced neurotransmission between photoreceptors and bipolar neurons of the retina.A) Average ERG traces from wild-type and SV2B−/− retina in response to stimuli of (top to bottom) 90,000, 9,000, 900, 90 and 9 photo-isomerizations per rod per flash. (n = 5 wt, 8 SV2B−/− mice). B) Average b-wave amplitudes at different light intensities showing average intensity decrease in mice from SV2B knockouts (n = 5 wt, 8 SV2B−/− mice). Error bars represent S.E.M. C) Average a-wave amplitudes showing no difference in amplitude in wt and SV2B knockouts. D) The ratio of b- to a-wave amplitude at the two strongest stimulus intensities was ∼50% lower in SV2B−/− mice (p = 0.015 for 90,000, p = 0.026 for 9000, students t-test).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2667261&req=5

pone-0005230-g003: Loss of SV2B results in reduced neurotransmission between photoreceptors and bipolar neurons of the retina.A) Average ERG traces from wild-type and SV2B−/− retina in response to stimuli of (top to bottom) 90,000, 9,000, 900, 90 and 9 photo-isomerizations per rod per flash. (n = 5 wt, 8 SV2B−/− mice). B) Average b-wave amplitudes at different light intensities showing average intensity decrease in mice from SV2B knockouts (n = 5 wt, 8 SV2B−/− mice). Error bars represent S.E.M. C) Average a-wave amplitudes showing no difference in amplitude in wt and SV2B knockouts. D) The ratio of b- to a-wave amplitude at the two strongest stimulus intensities was ∼50% lower in SV2B−/− mice (p = 0.015 for 90,000, p = 0.026 for 9000, students t-test).
Mentions: To explore the function of SV2B, we compared neurotransmission in the retinas of wild-type and SV2B knockout mice by measuring the electroretinographic response to light flashes of varying intensity [22]. This procedure measures electric potential flux in the retina. The amplitudes of the a-wave component of the measure, which reflects closure of cGMP-gated ion channels in the outer segment membrane, were not significantly different in SV2B−/− retinas (Figure 3C), indicating that the channels regulating membrane conductance in photoreceptors function normally in the absence of SV2B. In contrast, b-wave amplitudes, which reflect synaptic transmission between photoreceptors and bipolar neurons, were reduced ∼30% in retinas of SV2B−/− mice compared to SV2B+/+ mice (Figure 3A–B). Decreased b-wave amplitudes were observed at stimulus intensities in which only rod photoreceptors were activated (9 and 900 photoisomerisations/sec) and those in which both rods and cones were activated (9000 and 90,000 photoisomerisations/sec) (Table 1). When b-wave amplitudes were normalized by calculating the b/a wave ratio, we observed that values from SV2B knockouts were ∼50% lower at the two highest stimulus intensities (Figure 3D). Examination of ribbon synapses in retinas from wild-type and SV2B −/− mice did not reveal obvious differences in photoreceptor synapse ultrastructure (Supplemental Figure S1). This contrasts with the striking change in ribbon morphology observed in Bassoon knockout mice, which demonstrate a similar neurotransmission phenotype [24]. Thus diminished transmission between photoreceptors and bipolar neurons does not appear to be due to gross changes in ribbon synapse development. Taken together, these observations indicate that SV2B, like SV2A [18], [25], is a positive modulator of synaptic transmission.

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