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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 5. Postsynaptic remodeling and ectopic ribbons in mice with altered Cav1.4 function. Double-label immunofluorescence of PKCα (green) and RIBEYE (red) in retina from WT, Cav1.4 KO, CaBP4 KO, or Cav1.4I756T mice (P8-adult). In WT retina, bipolar dendrites labeled with PKCα antibodies ramify in the OPL where they form synapses with rod spherules. In Cav1.4 KO mice, bipolar dendrites (arrows) start extending into the outer nuclear layer (ONL) at P11, and ectopic ribbons labeled by RIBEYE antibodies are evident (arrowheads). Postsynaptic remodeling emerges later in CaBP4 KO and Cav1.4I756T mice (~P13), and is less severe in adulthood (2-mo old) compared with WT mice. Scale bars: 2 μm. Results shown are representative of at least 3 independent experiments.
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Figure 5: Figure 5. Postsynaptic remodeling and ectopic ribbons in mice with altered Cav1.4 function. Double-label immunofluorescence of PKCα (green) and RIBEYE (red) in retina from WT, Cav1.4 KO, CaBP4 KO, or Cav1.4I756T mice (P8-adult). In WT retina, bipolar dendrites labeled with PKCα antibodies ramify in the OPL where they form synapses with rod spherules. In Cav1.4 KO mice, bipolar dendrites (arrows) start extending into the outer nuclear layer (ONL) at P11, and ectopic ribbons labeled by RIBEYE antibodies are evident (arrowheads). Postsynaptic remodeling emerges later in CaBP4 KO and Cav1.4I756T mice (~P13), and is less severe in adulthood (2-mo old) compared with WT mice. Scale bars: 2 μm. Results shown are representative of at least 3 independent experiments.

Mentions: Structural remodeling of horizontal and bipolar cell dendrites and the formation of ectopic synapses in the outer nuclear layer (ONL) are common features of mice with PR synapse defects.25 If postsynaptic modeling results from altered PR ribbon maturation in CaBP4 KO and Cav1.4I756T mice, it should be evident between P13 and P15, when presynaptic defects in these mice are first apparent (Fig. 4B and C). To test this, we analyzed retinas from P8 to adulthood that were double-labeled with RIBEYE and PKCα, a marker for rod bipolar cells. As shown previously,7,19 bipolar dendrites extending into the ONL were found in adult retina of Cav1.4 KO and CaBP4 KO mice. RIBEYE-labeled puncta were associated with these processes, suggestive of ectopic ribbon synapses (Fig. 5). This pattern of labeling emerged earlier in Cav1.4 KO (~P11) than in CaBP4 KO and Cav1.4I756T retinas (~P13, Fig. 5), consistent with the more severe presynaptic defects in the Cav1.4 KO mice (Figs. 3B and4D).


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 5. Postsynaptic remodeling and ectopic ribbons in mice with altered Cav1.4 function. Double-label immunofluorescence of PKCα (green) and RIBEYE (red) in retina from WT, Cav1.4 KO, CaBP4 KO, or Cav1.4I756T mice (P8-adult). In WT retina, bipolar dendrites labeled with PKCα antibodies ramify in the OPL where they form synapses with rod spherules. In Cav1.4 KO mice, bipolar dendrites (arrows) start extending into the outer nuclear layer (ONL) at P11, and ectopic ribbons labeled by RIBEYE antibodies are evident (arrowheads). Postsynaptic remodeling emerges later in CaBP4 KO and Cav1.4I756T mice (~P13), and is less severe in adulthood (2-mo old) compared with WT mice. Scale bars: 2 μm. Results shown are representative of at least 3 independent experiments.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Figure 5: Figure 5. Postsynaptic remodeling and ectopic ribbons in mice with altered Cav1.4 function. Double-label immunofluorescence of PKCα (green) and RIBEYE (red) in retina from WT, Cav1.4 KO, CaBP4 KO, or Cav1.4I756T mice (P8-adult). In WT retina, bipolar dendrites labeled with PKCα antibodies ramify in the OPL where they form synapses with rod spherules. In Cav1.4 KO mice, bipolar dendrites (arrows) start extending into the outer nuclear layer (ONL) at P11, and ectopic ribbons labeled by RIBEYE antibodies are evident (arrowheads). Postsynaptic remodeling emerges later in CaBP4 KO and Cav1.4I756T mice (~P13), and is less severe in adulthood (2-mo old) compared with WT mice. Scale bars: 2 μm. Results shown are representative of at least 3 independent experiments.
Mentions: Structural remodeling of horizontal and bipolar cell dendrites and the formation of ectopic synapses in the outer nuclear layer (ONL) are common features of mice with PR synapse defects.25 If postsynaptic modeling results from altered PR ribbon maturation in CaBP4 KO and Cav1.4I756T mice, it should be evident between P13 and P15, when presynaptic defects in these mice are first apparent (Fig. 4B and C). To test this, we analyzed retinas from P8 to adulthood that were double-labeled with RIBEYE and PKCα, a marker for rod bipolar cells. As shown previously,7,19 bipolar dendrites extending into the ONL were found in adult retina of Cav1.4 KO and CaBP4 KO mice. RIBEYE-labeled puncta were associated with these processes, suggestive of ectopic ribbon synapses (Fig. 5). This pattern of labeling emerged earlier in Cav1.4 KO (~P11) than in CaBP4 KO and Cav1.4I756T retinas (~P13, Fig. 5), consistent with the more severe presynaptic defects in the Cav1.4 KO mice (Figs. 3B and4D).

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