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Dysregulation of Ca(v)1.4 channels disrupts the maturation of photoreceptor synaptic ribbons in congenital stationary night blindness type 2.

Liu X, Kerov V, Haeseleer F, Majumder A, Artemyev N, Baker SA, Lee A - Channels (Austin) (2013)

Bottom Line: Using Cav 1.4-selective antibodies, we found that Cav 1.4 channels associate with ribbon precursors early in development and are concentrated at both rod and cone PR synapses in the mature retina.However, after postnatal day 13, many PR ribbons retain the immature morphology.Our results demonstrate the importance of proper Cav 1.4 function for efficient PR synapse maturation, and that dysregulation of Cav 1.4 channels in CSNB2 may have synaptopathic consequences.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Physiology and Biophysics; University of Iowa; Iowa City, IA USA; Departments of Otolaryngology-Head and Neck Surgery, and Neurology; University of Iowa; Iowa City, IA USA.

ABSTRACT
Mutations in the gene encoding Cav 1.4, CACNA1F, are associated with visual disorders including X-linked incomplete congenital stationary night blindness type 2 (CSNB2). In mice lacking Cav 1.4 channels, there are defects in the development of "ribbon" synapses formed between photoreceptors (PRs) and second-order neurons. However, many CSNB2 mutations disrupt the function rather than expression of Cav 1.4 channels. Whether defects in PR synapse development due to altered Cav 1.4 function are common features contributing to the pathogenesis of CSNB2 is unknown. To resolve this issue, we profiled changes in the subcellular distribution of Cav 1.4 channels and synapse morphology during development in wild-type (WT) mice and mouse models of CSNB2. Using Cav 1.4-selective antibodies, we found that Cav 1.4 channels associate with ribbon precursors early in development and are concentrated at both rod and cone PR synapses in the mature retina. In mouse models of CSNB2 in which the voltage-dependence of Cav 1.4 activation is either enhanced (Cav 1.4I756T) or inhibited (CaBP4 KO), the initial stages of PR synaptic ribbon formation are largely unaffected. However, after postnatal day 13, many PR ribbons retain the immature morphology. This synaptic abnormality corresponds in severity to the defect in synaptic transmission in the adult mutant mice, suggesting that lack of sufficient mature synapses contributes to vision impairment in Cav 1.4I756T and CaBP4 KO mice. Our results demonstrate the importance of proper Cav 1.4 function for efficient PR synapse maturation, and that dysregulation of Cav 1.4 channels in CSNB2 may have synaptopathic consequences.

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Figure 2. Cav1.4 antibodies label cone PR synapses. Double-labeling with antibodies against Cav1.4 (green) and PNA (red) in retina from mouse (A), macaque (B), and human (C). In (A and B), arrows and arrowheads indicate localization of PNA and Cav1.4, respectively, at elongated structures resembling cone synapses. In (C), arrowheads indicate Cav1.4 labeling clustered at PNA-labeled cone synapses. Inset in (C) shows high magnification view of boxed region. Scale bars: 2 μm. Results in (A) are representative of at least 3 independent experiments. Results in (B and C) are from 1 experiment.
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Figure 2: Figure 2. Cav1.4 antibodies label cone PR synapses. Double-labeling with antibodies against Cav1.4 (green) and PNA (red) in retina from mouse (A), macaque (B), and human (C). In (A and B), arrows and arrowheads indicate localization of PNA and Cav1.4, respectively, at elongated structures resembling cone synapses. In (C), arrowheads indicate Cav1.4 labeling clustered at PNA-labeled cone synapses. Inset in (C) shows high magnification view of boxed region. Scale bars: 2 μm. Results in (A) are representative of at least 3 independent experiments. Results in (B and C) are from 1 experiment.

Mentions: By immunofluorescence of WT mice, Cav1.4 antibodies labeled numerous horseshoe-shaped structures in the outer plexiform layer (OPL), which contains mostly rod PR terminals (spherules) in the mouse retina (Fig. 1D). These structures were also labeled with antibodies against RIBEYE, the major component of the ribbon,16 and resembled synapses formed between a single rod spherule and dendrites of bipolar neurons and horizontal cells.11 As in previous reports that used different Cav1.4 antibodies,15 Cav1.4 labeling was slightly shifted compared with that for RIBEYE (Fig. 1D), consistent with the localization of Cav1.4 at the arciform density, a subsynaptic structure adjacent to the ribbon.10,17 This pattern of labeling was absent in the OPL of Cav1.4 KO retina (Fig. 1D). Using fluorescently tagged peanut agglutinin (PNA) to label cones, we also observed Cav1.4 labeling in cone terminals (pedicles) in mouse retina (Fig. 2A). In macaque and human retinas, Cav1.4 antibody labeling closely aligned with that for PNA, and was associated with horseshoe-shaped structures resembling rod synapses throughout the OPL (Fig. 2B and C). Taken together, these results confirm the specificity of our antibodies, and show that Cav1.4 channels are localized to both rod and cone PR synapses in the mammalian retina.


Dysregulation of Ca(v)1.4 channels disrupts the maturation of photoreceptor synaptic ribbons in congenital stationary night blindness type 2.

Liu X, Kerov V, Haeseleer F, Majumder A, Artemyev N, Baker SA, Lee A - Channels (Austin) (2013)

Figure 2. Cav1.4 antibodies label cone PR synapses. Double-labeling with antibodies against Cav1.4 (green) and PNA (red) in retina from mouse (A), macaque (B), and human (C). In (A and B), arrows and arrowheads indicate localization of PNA and Cav1.4, respectively, at elongated structures resembling cone synapses. In (C), arrowheads indicate Cav1.4 labeling clustered at PNA-labeled cone synapses. Inset in (C) shows high magnification view of boxed region. Scale bars: 2 μm. Results in (A) are representative of at least 3 independent experiments. Results in (B and C) are from 1 experiment.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4042486&req=5

Figure 2: Figure 2. Cav1.4 antibodies label cone PR synapses. Double-labeling with antibodies against Cav1.4 (green) and PNA (red) in retina from mouse (A), macaque (B), and human (C). In (A and B), arrows and arrowheads indicate localization of PNA and Cav1.4, respectively, at elongated structures resembling cone synapses. In (C), arrowheads indicate Cav1.4 labeling clustered at PNA-labeled cone synapses. Inset in (C) shows high magnification view of boxed region. Scale bars: 2 μm. Results in (A) are representative of at least 3 independent experiments. Results in (B and C) are from 1 experiment.
Mentions: By immunofluorescence of WT mice, Cav1.4 antibodies labeled numerous horseshoe-shaped structures in the outer plexiform layer (OPL), which contains mostly rod PR terminals (spherules) in the mouse retina (Fig. 1D). These structures were also labeled with antibodies against RIBEYE, the major component of the ribbon,16 and resembled synapses formed between a single rod spherule and dendrites of bipolar neurons and horizontal cells.11 As in previous reports that used different Cav1.4 antibodies,15 Cav1.4 labeling was slightly shifted compared with that for RIBEYE (Fig. 1D), consistent with the localization of Cav1.4 at the arciform density, a subsynaptic structure adjacent to the ribbon.10,17 This pattern of labeling was absent in the OPL of Cav1.4 KO retina (Fig. 1D). Using fluorescently tagged peanut agglutinin (PNA) to label cones, we also observed Cav1.4 labeling in cone terminals (pedicles) in mouse retina (Fig. 2A). In macaque and human retinas, Cav1.4 antibody labeling closely aligned with that for PNA, and was associated with horseshoe-shaped structures resembling rod synapses throughout the OPL (Fig. 2B and C). Taken together, these results confirm the specificity of our antibodies, and show that Cav1.4 channels are localized to both rod and cone PR synapses in the mammalian retina.

Bottom Line: Using Cav 1.4-selective antibodies, we found that Cav 1.4 channels associate with ribbon precursors early in development and are concentrated at both rod and cone PR synapses in the mature retina.However, after postnatal day 13, many PR ribbons retain the immature morphology.Our results demonstrate the importance of proper Cav 1.4 function for efficient PR synapse maturation, and that dysregulation of Cav 1.4 channels in CSNB2 may have synaptopathic consequences.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Physiology and Biophysics; University of Iowa; Iowa City, IA USA; Departments of Otolaryngology-Head and Neck Surgery, and Neurology; University of Iowa; Iowa City, IA USA.

ABSTRACT
Mutations in the gene encoding Cav 1.4, CACNA1F, are associated with visual disorders including X-linked incomplete congenital stationary night blindness type 2 (CSNB2). In mice lacking Cav 1.4 channels, there are defects in the development of "ribbon" synapses formed between photoreceptors (PRs) and second-order neurons. However, many CSNB2 mutations disrupt the function rather than expression of Cav 1.4 channels. Whether defects in PR synapse development due to altered Cav 1.4 function are common features contributing to the pathogenesis of CSNB2 is unknown. To resolve this issue, we profiled changes in the subcellular distribution of Cav 1.4 channels and synapse morphology during development in wild-type (WT) mice and mouse models of CSNB2. Using Cav 1.4-selective antibodies, we found that Cav 1.4 channels associate with ribbon precursors early in development and are concentrated at both rod and cone PR synapses in the mature retina. In mouse models of CSNB2 in which the voltage-dependence of Cav 1.4 activation is either enhanced (Cav 1.4I756T) or inhibited (CaBP4 KO), the initial stages of PR synaptic ribbon formation are largely unaffected. However, after postnatal day 13, many PR ribbons retain the immature morphology. This synaptic abnormality corresponds in severity to the defect in synaptic transmission in the adult mutant mice, suggesting that lack of sufficient mature synapses contributes to vision impairment in Cav 1.4I756T and CaBP4 KO mice. Our results demonstrate the importance of proper Cav 1.4 function for efficient PR synapse maturation, and that dysregulation of Cav 1.4 channels in CSNB2 may have synaptopathic consequences.

Show MeSH
Related in: MedlinePlus