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Variable phenotypic expressivity in inbred retinal degeneration mouse lines: A comparative study of C3H/HeOu and FVB/N rd1 mice.

van Wyk M, Schneider S, Kleinlogel S - Mol. Vis. (2015)

Bottom Line: Recent advances in optogenetics and gene therapy have led to promising new treatment strategies for blindness caused by retinal photoreceptor loss.The rd1 founder mutation is present in more than 100 actively used mouse lines.By postnatal week 4, the FVB/N mice expressed significantly less cone opsin and Pde6b mRNA and had neither ERG nor OKR responses.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of Bern, Bern, Switzerland.

ABSTRACT

Purpose: Recent advances in optogenetics and gene therapy have led to promising new treatment strategies for blindness caused by retinal photoreceptor loss. Preclinical studies often rely on the retinal degeneration 1 (rd1 or Pde6b(rd1)) retinitis pigmentosa (RP) mouse model. The rd1 founder mutation is present in more than 100 actively used mouse lines. Since secondary genetic traits are well-known to modify the phenotypic progression of photoreceptor degeneration in animal models and human patients with RP, negligence of the genetic background in the rd1 mouse model is unwarranted. Moreover, the success of various potential therapies, including optogenetic gene therapy and prosthetic implants, depends on the progress of retinal degeneration, which might differ between rd1 mice. To examine the prospect of phenotypic expressivity in the rd1 mouse model, we compared the progress of retinal degeneration in two common rd1 lines, C3H/HeOu and FVB/N.

Methods: We followed retinal degeneration over 24 weeks in FVB/N, C3H/HeOu, and congenic Pde6b(+) seeing mouse lines, using a range of experimental techniques including extracellular recordings from retinal ganglion cells, PCR quantification of cone opsin and Pde6b transcripts, in vivo flash electroretinogram (ERG), and behavioral optokinetic reflex (OKR) recordings.

Results: We demonstrated a substantial difference in the speed of retinal degeneration and accompanying loss of visual function between the two rd1 lines. Photoreceptor degeneration and loss of vision were faster with an earlier onset in the FVB/N mice compared to C3H/HeOu mice, whereas the performance of the Pde6b(+) mice did not differ significantly in any of the tests. By postnatal week 4, the FVB/N mice expressed significantly less cone opsin and Pde6b mRNA and had neither ERG nor OKR responses. At 12 weeks of age, the retinal ganglion cells of the FVB/N mice had lost all light responses. In contrast, 4-week-old C3H/HeOu mice still had ERG and OKR responses, and we still recorded light responses from C3H/HeOu retinal ganglion cells until the age of 24 weeks. These results show that genetic background plays an important role in the rd1 mouse pathology.

Conclusions: Analogous to human RP, the mouse genetic background strongly influences the rd1 phenotype. Thus, different rd1 mouse lines may follow different timelines of retinal degeneration, making exact knowledge of genetic background imperative in all studies that use rd1 models.

No MeSH data available.


Related in: MedlinePlus

Immunocytochemical detection of cone opsin. Images were always taken from the retinal area with the highest density of labeled cones, typically in the mid-periphery of the retina. A: Examples of S-opsin staining in C3H/HeOu retinas demonstrate the progressive loss of cone outer segments and a concomitant accumulation of S-opsin in the cell bodies. One misshaped outer segment (clear arrow) and one soma without outer segments (OS) are indicated (solid arrow). Age, in weeks, is indicated in the top right of every panel. Scale bar=50 µm. B, C: S-opsin staining in wild-type C3H-Pde6b+ (B) and FVB-Pde6b+ (C) retinas were similar. D: Summary graph of OS counts in rd1 C3H/HeOu and FVB/N mice relative to the Pde6b+ mouse lines. For each group, n=8 retinas from four mice. The fits are exponential with the R-square values for C3H/HeOu and FVB/N at 0.94 and 0.8, respectively.
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f4: Immunocytochemical detection of cone opsin. Images were always taken from the retinal area with the highest density of labeled cones, typically in the mid-periphery of the retina. A: Examples of S-opsin staining in C3H/HeOu retinas demonstrate the progressive loss of cone outer segments and a concomitant accumulation of S-opsin in the cell bodies. One misshaped outer segment (clear arrow) and one soma without outer segments (OS) are indicated (solid arrow). Age, in weeks, is indicated in the top right of every panel. Scale bar=50 µm. B, C: S-opsin staining in wild-type C3H-Pde6b+ (B) and FVB-Pde6b+ (C) retinas were similar. D: Summary graph of OS counts in rd1 C3H/HeOu and FVB/N mice relative to the Pde6b+ mouse lines. For each group, n=8 retinas from four mice. The fits are exponential with the R-square values for C3H/HeOu and FVB/N at 0.94 and 0.8, respectively.

Mentions: As degeneration of the cone OS ultimately determines the onset of blindness [58], we performed anti-S-opsin immunostaining on retinal whole mounts (Figure 4) at 4-week age intervals and in all four mouse lines. We chose S-opsin (Opn1sw), which is also expressed by most green cones [59], for immunocytochemistry to allow comparison with previous work in rd1 mice. In the 3- to 4-week-old C3H/HeOu mice, and more apparent in the 3- to 4-week-old FVB/N mice, the cone OS were relatively small and misshaped or lobular compared to those of the healthy FVB-Pde6b+ and C3H-Pde6b+ retinas (Figures 1 and 4). This is in good agreement with the literature, which states that photoreceptor outer and inner segments are never fully developed in rd1 mice [17,60]. We performed OS counts in the mid-peripheral retinas of 4-week-old rd1 mice, where cone density is the highest, and found similar numbers for C3H/HeOu (8.43±0.9 k/mm2, n=6) and FVB/N (7.08±0.54 k/mm2, n=6) mice that did not significantly differ from the counts of their seeing congenics (C3H-Pde6b+ (9.45±0.75 k/mm2, n=5; FVB-Pde6b+ 8.72±0.68 k/mm2, n=5). In both rd1 lines, the OS count decreased with age resulting in a synchronous rise in the number of labeled cone cell bodies (Figure 4). The latter is most likely a direct consequence of OS loss, where opsin naturally destined for the OS now accumulates in the soma. As described previously, cone cell bodies labeled with opsin staining form dendrite-like processes without any OS [13]. OS degeneration progressed at different speeds in the FVB/N and C3H/HeOu mice. Although the OS had virtually disappeared by 16 weeks of age in the FVB/N mice (0.77±0.77 k/mm2), they were lost only by week 24 in the C3H/HeOu mice (0.81±0.33 k/mm2).


Variable phenotypic expressivity in inbred retinal degeneration mouse lines: A comparative study of C3H/HeOu and FVB/N rd1 mice.

van Wyk M, Schneider S, Kleinlogel S - Mol. Vis. (2015)

Immunocytochemical detection of cone opsin. Images were always taken from the retinal area with the highest density of labeled cones, typically in the mid-periphery of the retina. A: Examples of S-opsin staining in C3H/HeOu retinas demonstrate the progressive loss of cone outer segments and a concomitant accumulation of S-opsin in the cell bodies. One misshaped outer segment (clear arrow) and one soma without outer segments (OS) are indicated (solid arrow). Age, in weeks, is indicated in the top right of every panel. Scale bar=50 µm. B, C: S-opsin staining in wild-type C3H-Pde6b+ (B) and FVB-Pde6b+ (C) retinas were similar. D: Summary graph of OS counts in rd1 C3H/HeOu and FVB/N mice relative to the Pde6b+ mouse lines. For each group, n=8 retinas from four mice. The fits are exponential with the R-square values for C3H/HeOu and FVB/N at 0.94 and 0.8, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4522243&req=5

f4: Immunocytochemical detection of cone opsin. Images were always taken from the retinal area with the highest density of labeled cones, typically in the mid-periphery of the retina. A: Examples of S-opsin staining in C3H/HeOu retinas demonstrate the progressive loss of cone outer segments and a concomitant accumulation of S-opsin in the cell bodies. One misshaped outer segment (clear arrow) and one soma without outer segments (OS) are indicated (solid arrow). Age, in weeks, is indicated in the top right of every panel. Scale bar=50 µm. B, C: S-opsin staining in wild-type C3H-Pde6b+ (B) and FVB-Pde6b+ (C) retinas were similar. D: Summary graph of OS counts in rd1 C3H/HeOu and FVB/N mice relative to the Pde6b+ mouse lines. For each group, n=8 retinas from four mice. The fits are exponential with the R-square values for C3H/HeOu and FVB/N at 0.94 and 0.8, respectively.
Mentions: As degeneration of the cone OS ultimately determines the onset of blindness [58], we performed anti-S-opsin immunostaining on retinal whole mounts (Figure 4) at 4-week age intervals and in all four mouse lines. We chose S-opsin (Opn1sw), which is also expressed by most green cones [59], for immunocytochemistry to allow comparison with previous work in rd1 mice. In the 3- to 4-week-old C3H/HeOu mice, and more apparent in the 3- to 4-week-old FVB/N mice, the cone OS were relatively small and misshaped or lobular compared to those of the healthy FVB-Pde6b+ and C3H-Pde6b+ retinas (Figures 1 and 4). This is in good agreement with the literature, which states that photoreceptor outer and inner segments are never fully developed in rd1 mice [17,60]. We performed OS counts in the mid-peripheral retinas of 4-week-old rd1 mice, where cone density is the highest, and found similar numbers for C3H/HeOu (8.43±0.9 k/mm2, n=6) and FVB/N (7.08±0.54 k/mm2, n=6) mice that did not significantly differ from the counts of their seeing congenics (C3H-Pde6b+ (9.45±0.75 k/mm2, n=5; FVB-Pde6b+ 8.72±0.68 k/mm2, n=5). In both rd1 lines, the OS count decreased with age resulting in a synchronous rise in the number of labeled cone cell bodies (Figure 4). The latter is most likely a direct consequence of OS loss, where opsin naturally destined for the OS now accumulates in the soma. As described previously, cone cell bodies labeled with opsin staining form dendrite-like processes without any OS [13]. OS degeneration progressed at different speeds in the FVB/N and C3H/HeOu mice. Although the OS had virtually disappeared by 16 weeks of age in the FVB/N mice (0.77±0.77 k/mm2), they were lost only by week 24 in the C3H/HeOu mice (0.81±0.33 k/mm2).

Bottom Line: Recent advances in optogenetics and gene therapy have led to promising new treatment strategies for blindness caused by retinal photoreceptor loss.The rd1 founder mutation is present in more than 100 actively used mouse lines.By postnatal week 4, the FVB/N mice expressed significantly less cone opsin and Pde6b mRNA and had neither ERG nor OKR responses.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology, University of Bern, Bern, Switzerland.

ABSTRACT

Purpose: Recent advances in optogenetics and gene therapy have led to promising new treatment strategies for blindness caused by retinal photoreceptor loss. Preclinical studies often rely on the retinal degeneration 1 (rd1 or Pde6b(rd1)) retinitis pigmentosa (RP) mouse model. The rd1 founder mutation is present in more than 100 actively used mouse lines. Since secondary genetic traits are well-known to modify the phenotypic progression of photoreceptor degeneration in animal models and human patients with RP, negligence of the genetic background in the rd1 mouse model is unwarranted. Moreover, the success of various potential therapies, including optogenetic gene therapy and prosthetic implants, depends on the progress of retinal degeneration, which might differ between rd1 mice. To examine the prospect of phenotypic expressivity in the rd1 mouse model, we compared the progress of retinal degeneration in two common rd1 lines, C3H/HeOu and FVB/N.

Methods: We followed retinal degeneration over 24 weeks in FVB/N, C3H/HeOu, and congenic Pde6b(+) seeing mouse lines, using a range of experimental techniques including extracellular recordings from retinal ganglion cells, PCR quantification of cone opsin and Pde6b transcripts, in vivo flash electroretinogram (ERG), and behavioral optokinetic reflex (OKR) recordings.

Results: We demonstrated a substantial difference in the speed of retinal degeneration and accompanying loss of visual function between the two rd1 lines. Photoreceptor degeneration and loss of vision were faster with an earlier onset in the FVB/N mice compared to C3H/HeOu mice, whereas the performance of the Pde6b(+) mice did not differ significantly in any of the tests. By postnatal week 4, the FVB/N mice expressed significantly less cone opsin and Pde6b mRNA and had neither ERG nor OKR responses. At 12 weeks of age, the retinal ganglion cells of the FVB/N mice had lost all light responses. In contrast, 4-week-old C3H/HeOu mice still had ERG and OKR responses, and we still recorded light responses from C3H/HeOu retinal ganglion cells until the age of 24 weeks. These results show that genetic background plays an important role in the rd1 mouse pathology.

Conclusions: Analogous to human RP, the mouse genetic background strongly influences the rd1 phenotype. Thus, different rd1 mouse lines may follow different timelines of retinal degeneration, making exact knowledge of genetic background imperative in all studies that use rd1 models.

No MeSH data available.


Related in: MedlinePlus