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Cav1.4 IT mouse as model for vision impairment in human congenital stationary night blindness type 2.

Knoflach D, Kerov V, Sartori SB, Obermair GJ, Schmuckermair C, Liu X, Sothilingam V, Garcia Garrido M, Baker SA, Glösmann M, Schicker K, Seeliger M, Lee A, Koschak A - Channels (Austin) (2013)

Bottom Line: Despite the increasing knowledge about the functional behavior of mutated channels in heterologous systems, the pathophysiological mechanisms that result in vision impairment remain to be elucidated.Morphologically, the retinal outer nuclear layer in adult IT mutants was reduced in size and cone outer segments appeared shorter.The associated visual deficiency was substantiated in behavioral paradigms.

View Article: PubMed Central - PubMed

Affiliation: Medical University Vienna; Centre for Physiology and Pharmacology; Department of Neurophysiology and Pharmacology; Vienna, Austria.

ABSTRACT
Mutations in the CACNA1F gene encoding the Cav1.4 Ca (2+) channel are associated with X-linked congenital stationary night blindness type 2 (CSNB2). Despite the increasing knowledge about the functional behavior of mutated channels in heterologous systems, the pathophysiological mechanisms that result in vision impairment remain to be elucidated. This work provides a thorough functional characterization of the novel IT mouse line that harbors the gain-of-function mutation I745T reported in a New Zealand CSNB2 family. (1) Electroretinographic recordings in IT mice permitted a direct comparison with human data. Our data supported the hypothesis that a hyperpolarizing shift in the voltage-dependence of channel activation-as seen in the IT gain-of-function mutant (2)-may reduce the dynamic range of photoreceptor activity. Morphologically, the retinal outer nuclear layer in adult IT mutants was reduced in size and cone outer segments appeared shorter. The organization of the outer plexiform layer was disrupted, and synaptic structures of photoreceptors had a variable, partly immature, appearance. The associated visual deficiency was substantiated in behavioral paradigms. The IT mouse line serves as a specific model for the functional phenotype of human CSNB2 patients with gain-of-function mutations and may help to further understand the dysfunction in CSNB.

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Figure 4. Photoreceptor synapses in adult wt and IT mice. (A) Immunofluorescence double-labeling of Cav1.4 (green) and the synaptic protein RIBEYE (red) in wt (right) and IT (left) mice. Wt mice show mature horseshoe-shaped ribbons whereas IT synapses were variable in morphology. (B) Co-staining with the rod bipolar cell maker PKCα (green) and CtBP2/Ribeye (red). Ectopic synapses in the outer nuclear layer (ONL) were observed only in IT mice (right). (C) Similar PNA staining (red) of cone synapses together with RIBEYE (green) in wt (left) and IT (right) mice. Scale bar 2 µm.
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Figure 4: Figure 4. Photoreceptor synapses in adult wt and IT mice. (A) Immunofluorescence double-labeling of Cav1.4 (green) and the synaptic protein RIBEYE (red) in wt (right) and IT (left) mice. Wt mice show mature horseshoe-shaped ribbons whereas IT synapses were variable in morphology. (B) Co-staining with the rod bipolar cell maker PKCα (green) and CtBP2/Ribeye (red). Ectopic synapses in the outer nuclear layer (ONL) were observed only in IT mice (right). (C) Similar PNA staining (red) of cone synapses together with RIBEYE (green) in wt (left) and IT (right) mice. Scale bar 2 µm.

Mentions: We assessed potential aberrations in cone morphology by labeling with peanut agglutinin (PNA), a lectin preferentially binding cone-photoreceptor associated domains of the interphotoreceptor matrix30,31 and glycogen phosphorylase (glypho), which stains cones from their outer segments to their pedicles.32 PNA labeling demonstrated that outer segments were present and of normal appearance (Fig. 3A). However, and in accordance with the decreased thickness of the ONL, the overall length of cones was shorter in IT mice. PNA-positive pedicles were also observed in the IT retina (Fig. 3A, arrowheads), with no obvious dissimilarity to the wt retina. No decrease in the number of cones was evident (as also indicated in Fig. 4C). In the wt retina anti-glypho stained the inner segments of cone photoreceptors, known sites of high energy consumption, as well as cone pedicles (Fig. 3B, left). Cone photoreceptors in IT mice were shorter with shorter outer and inner segments and pedicles that appeared larger than in wt retina (Fig. 3B, right, arrowheads). Notably, glypho signal was consistently higher in the IT mutant, both in the inner and outer retina. Using the S-opsin marker sc14363 we found S-opsin expression clearly visible in the cone outer segments in the ventral wt retina as well as their pedicles (Fig. 3C, left). Consistent with our glypho staining cones were shorter in IT mice (Fig. 3C, right, arrowheads). As seen in the inset of Figure 3C, indeed we found a few cones that appeared to sprout, a phenomenon seen also in KO mice at different ages.33


Cav1.4 IT mouse as model for vision impairment in human congenital stationary night blindness type 2.

Knoflach D, Kerov V, Sartori SB, Obermair GJ, Schmuckermair C, Liu X, Sothilingam V, Garcia Garrido M, Baker SA, Glösmann M, Schicker K, Seeliger M, Lee A, Koschak A - Channels (Austin) (2013)

Figure 4. Photoreceptor synapses in adult wt and IT mice. (A) Immunofluorescence double-labeling of Cav1.4 (green) and the synaptic protein RIBEYE (red) in wt (right) and IT (left) mice. Wt mice show mature horseshoe-shaped ribbons whereas IT synapses were variable in morphology. (B) Co-staining with the rod bipolar cell maker PKCα (green) and CtBP2/Ribeye (red). Ectopic synapses in the outer nuclear layer (ONL) were observed only in IT mice (right). (C) Similar PNA staining (red) of cone synapses together with RIBEYE (green) in wt (left) and IT (right) mice. Scale bar 2 µm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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Figure 4: Figure 4. Photoreceptor synapses in adult wt and IT mice. (A) Immunofluorescence double-labeling of Cav1.4 (green) and the synaptic protein RIBEYE (red) in wt (right) and IT (left) mice. Wt mice show mature horseshoe-shaped ribbons whereas IT synapses were variable in morphology. (B) Co-staining with the rod bipolar cell maker PKCα (green) and CtBP2/Ribeye (red). Ectopic synapses in the outer nuclear layer (ONL) were observed only in IT mice (right). (C) Similar PNA staining (red) of cone synapses together with RIBEYE (green) in wt (left) and IT (right) mice. Scale bar 2 µm.
Mentions: We assessed potential aberrations in cone morphology by labeling with peanut agglutinin (PNA), a lectin preferentially binding cone-photoreceptor associated domains of the interphotoreceptor matrix30,31 and glycogen phosphorylase (glypho), which stains cones from their outer segments to their pedicles.32 PNA labeling demonstrated that outer segments were present and of normal appearance (Fig. 3A). However, and in accordance with the decreased thickness of the ONL, the overall length of cones was shorter in IT mice. PNA-positive pedicles were also observed in the IT retina (Fig. 3A, arrowheads), with no obvious dissimilarity to the wt retina. No decrease in the number of cones was evident (as also indicated in Fig. 4C). In the wt retina anti-glypho stained the inner segments of cone photoreceptors, known sites of high energy consumption, as well as cone pedicles (Fig. 3B, left). Cone photoreceptors in IT mice were shorter with shorter outer and inner segments and pedicles that appeared larger than in wt retina (Fig. 3B, right, arrowheads). Notably, glypho signal was consistently higher in the IT mutant, both in the inner and outer retina. Using the S-opsin marker sc14363 we found S-opsin expression clearly visible in the cone outer segments in the ventral wt retina as well as their pedicles (Fig. 3C, left). Consistent with our glypho staining cones were shorter in IT mice (Fig. 3C, right, arrowheads). As seen in the inset of Figure 3C, indeed we found a few cones that appeared to sprout, a phenomenon seen also in KO mice at different ages.33

Bottom Line: Despite the increasing knowledge about the functional behavior of mutated channels in heterologous systems, the pathophysiological mechanisms that result in vision impairment remain to be elucidated.Morphologically, the retinal outer nuclear layer in adult IT mutants was reduced in size and cone outer segments appeared shorter.The associated visual deficiency was substantiated in behavioral paradigms.

View Article: PubMed Central - PubMed

Affiliation: Medical University Vienna; Centre for Physiology and Pharmacology; Department of Neurophysiology and Pharmacology; Vienna, Austria.

ABSTRACT
Mutations in the CACNA1F gene encoding the Cav1.4 Ca (2+) channel are associated with X-linked congenital stationary night blindness type 2 (CSNB2). Despite the increasing knowledge about the functional behavior of mutated channels in heterologous systems, the pathophysiological mechanisms that result in vision impairment remain to be elucidated. This work provides a thorough functional characterization of the novel IT mouse line that harbors the gain-of-function mutation I745T reported in a New Zealand CSNB2 family. (1) Electroretinographic recordings in IT mice permitted a direct comparison with human data. Our data supported the hypothesis that a hyperpolarizing shift in the voltage-dependence of channel activation-as seen in the IT gain-of-function mutant (2)-may reduce the dynamic range of photoreceptor activity. Morphologically, the retinal outer nuclear layer in adult IT mutants was reduced in size and cone outer segments appeared shorter. The organization of the outer plexiform layer was disrupted, and synaptic structures of photoreceptors had a variable, partly immature, appearance. The associated visual deficiency was substantiated in behavioral paradigms. The IT mouse line serves as a specific model for the functional phenotype of human CSNB2 patients with gain-of-function mutations and may help to further understand the dysfunction in CSNB.

Show MeSH
Related in: MedlinePlus