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Abnormal fiber end migration in Royal College of Surgeons rats during posterior subcapsular cataract formation.

Joy A, Mohammed TA, Al-Ghoul KJ - Mol. Vis. (2010)

Bottom Line: At all time points thereafter, F-actin was rearranged into a 'rosette' pattern of prominent foci at cell vertices.The data are consistent with the hypothesis that migration of basal fiber ends is altered in a two stage process wherein initially, migration patterns undergo a rapid shift resulting in abnormal suture sub-branch formation.Subsequent cytological alterations are consistent with an eventual cessation of migration, precluding proper targeting of basal ends to their sutural destinations and leading to cataract plaque formation.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy and Cell Biology, Rush University Medical Center, 600 S. Paulina St., Chicago, IL 60612, USA.

ABSTRACT

Purpose: Prior structural studies of posterior subcapsular cataract (PSC) development in Royal College of Surgeons (RCS) rats suggest that migration of basal fiber ends was disrupted, ultimately resulting in a PSC. Therefore the goal of this study was to assess the overall migration patterns as well as changes to the structure and cytoskeleton of basal fiber ends during PSC development.

Methods: Lenses from 48 RCS dystrophic rats (RCS/Lav) and 24 genetically matched control animals (RCS-rdy(+)/Lav) from 2 to 8 weeks old were examined. Equatorial diameters were measured and suture patterns were photographed immediately following enucleation/dissection. Right eye lenses were fixed and processed to visualize the actin cytoskeleton via laser scanning confocal microscopy (LSCM), left eye lenses were decapsulated, fixed and processed for scanning electron microscopy (SEM). Scaled 3D-computer assisted drawings (CADs) and animations were constructed from the data to depict the changes in suture patterns and fiber end architecture.

Results: At 2 weeks, dystrophic lenses displayed an inverted Y suture on the posterior, and by 3 weeks most lenses had at least one sub-branch. Additional sub-branches were observed with time, opacities being visible as early as 4 weeks and progressing into PSC plaques by 6 weeks. Control lenses displayed inverted Y sutures at all ages and were transparent. SEM of dystrophic lenses revealed fiber ends with normal size, shape, arrangement, and filopodia at 2 weeks; scattered areas of dome-shaped fiber ends and small filopodia were present at 3 weeks. At 4 weeks the irregularly arranged domed fiber ends had extremely long filopodia with 'boutons' at their tips. By 6 weeks all fiber ends within plaques displayed rounded or domed basal membranes and lacked filopodial extensions. Control lenses at all time points had comparable ultrastructure to the 2 week old dystrophic lenses. F-actin arrangement within the basal membrane complex (BMC) of control lenses showed the expected peripheral pattern of labeling at all ages. Dystrophic RCS lenses at 2 weeks were comparable to controls, however by 3-4 weeks they displayed scattered foci of F-actin within the BMC. At all time points thereafter, F-actin was rearranged into a 'rosette' pattern of prominent foci at cell vertices.

Conclusions: The data are consistent with the hypothesis that migration of basal fiber ends is altered in a two stage process wherein initially, migration patterns undergo a rapid shift resulting in abnormal suture sub-branch formation. Subsequent cytological alterations are consistent with an eventual cessation of migration, precluding proper targeting of basal ends to their sutural destinations and leading to cataract plaque formation.

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Scanning electron micrographs of RCS/Lav lenses showing the morphology and arrangement of the posterior fiber ends (2–6 weeks). A, B: Low and high magnification images showing the normal shape and arrangement of the basal ends at 2 weeks of age. Note the uniform size and orientation of the filopodia in panel B (arrows). C, D: Low and high magnification images at 3 weeks postnatal, showing some areas with domed ends (asterisks in panel D). For the most part, the ends continue to maintain their normal shape and arrangement as seen at 2 weeks of age. E, F: By 4 weeks postnatal, fiber ends show distinct changes in their shape, end to end adhesion and the filopodia. Panel E shows the border between ends within the forming opacity (left of the dotted line) and normal ends just outside the opacity. The disordered and lengthened filopodia, membrane blebbing and loss of end to end adhesion can be clearly seen in Panel F.
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f4: Scanning electron micrographs of RCS/Lav lenses showing the morphology and arrangement of the posterior fiber ends (2–6 weeks). A, B: Low and high magnification images showing the normal shape and arrangement of the basal ends at 2 weeks of age. Note the uniform size and orientation of the filopodia in panel B (arrows). C, D: Low and high magnification images at 3 weeks postnatal, showing some areas with domed ends (asterisks in panel D). For the most part, the ends continue to maintain their normal shape and arrangement as seen at 2 weeks of age. E, F: By 4 weeks postnatal, fiber ends show distinct changes in their shape, end to end adhesion and the filopodia. Panel E shows the border between ends within the forming opacity (left of the dotted line) and normal ends just outside the opacity. The disordered and lengthened filopodia, membrane blebbing and loss of end to end adhesion can be clearly seen in Panel F.

Mentions: At 2–3 weeks postnatal, posterior fiber ends showed a normal size, shape and packing, i.e., the ends were irregularly spheroidal in shape, tightly packed and exhibited small filopodia in the direction of fiber end migration (Figure 4A,B, arrows indicate filopodial uniformity). Some lenses at 3 weeks showed scattered areas where the ends had a ‘domed’ shape (Figure 4C,D) but overall the filopodia continued to be arranged unidirectionally toward the posterior suture. At 4 weeks postnatal, the organized arrangement of the fiber ends was lost. Notable changes included: disorganized arrangement of the posterior fiber ends with a loss of tight packing between fiber ends (extracellular space [ECS] dilations), elongated filopodia, filopodial tips taking on a ‘bouton-like’ appearance and random orientation of filopodia (Figure 4E,F). Figure 4E clearly shows the border (dotted line) between the normal arrangement (right) and the abnormal fiber ends situated within the confines of the PSC plaque (left). The majority of the changes observed took place between 4 and 6 weeks postnatal and corresponded with PSC formation and suture pattern changes that were observed in the gross lens at the same age. By 7–8 weeks postnatal, the PSC was fully formed and the fiber end segments exhibited the characteristic change of direction away from the polar axis toward the capsule (Figure 5A,C) as has been previously described [14,15]. SEM images of the fiber ends within the PSC plaque at 7–8 weeks postnatal revealed two distinct sets of features; the ends either exhibited ECS dilations, altered morphology and disordered filopodia (Figure 5A,B) or they assumed a distended or globular appearance in a tightly packed configuration with complete lack of filopodia (Figure 5C,D). A subset of the lenses (less than 1/4) showed discrete areas wherein fiber ends had a stellate appearance with an apparent degree of fiber end loss (Figure 5E,F). RCS lenses of all ages in the control group exhibited fiber end shape, size and arrangement consistent with that seen in other rodent strains (Figure 6A-C), specifically, the fiber ends were uniform in size shape and exhibited a normal filopodial anatomy and organization. Fiber end morphology of the 2 week old dystrophic lenses, were comparable to the controls.


Abnormal fiber end migration in Royal College of Surgeons rats during posterior subcapsular cataract formation.

Joy A, Mohammed TA, Al-Ghoul KJ - Mol. Vis. (2010)

Scanning electron micrographs of RCS/Lav lenses showing the morphology and arrangement of the posterior fiber ends (2–6 weeks). A, B: Low and high magnification images showing the normal shape and arrangement of the basal ends at 2 weeks of age. Note the uniform size and orientation of the filopodia in panel B (arrows). C, D: Low and high magnification images at 3 weeks postnatal, showing some areas with domed ends (asterisks in panel D). For the most part, the ends continue to maintain their normal shape and arrangement as seen at 2 weeks of age. E, F: By 4 weeks postnatal, fiber ends show distinct changes in their shape, end to end adhesion and the filopodia. Panel E shows the border between ends within the forming opacity (left of the dotted line) and normal ends just outside the opacity. The disordered and lengthened filopodia, membrane blebbing and loss of end to end adhesion can be clearly seen in Panel F.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2925909&req=5

f4: Scanning electron micrographs of RCS/Lav lenses showing the morphology and arrangement of the posterior fiber ends (2–6 weeks). A, B: Low and high magnification images showing the normal shape and arrangement of the basal ends at 2 weeks of age. Note the uniform size and orientation of the filopodia in panel B (arrows). C, D: Low and high magnification images at 3 weeks postnatal, showing some areas with domed ends (asterisks in panel D). For the most part, the ends continue to maintain their normal shape and arrangement as seen at 2 weeks of age. E, F: By 4 weeks postnatal, fiber ends show distinct changes in their shape, end to end adhesion and the filopodia. Panel E shows the border between ends within the forming opacity (left of the dotted line) and normal ends just outside the opacity. The disordered and lengthened filopodia, membrane blebbing and loss of end to end adhesion can be clearly seen in Panel F.
Mentions: At 2–3 weeks postnatal, posterior fiber ends showed a normal size, shape and packing, i.e., the ends were irregularly spheroidal in shape, tightly packed and exhibited small filopodia in the direction of fiber end migration (Figure 4A,B, arrows indicate filopodial uniformity). Some lenses at 3 weeks showed scattered areas where the ends had a ‘domed’ shape (Figure 4C,D) but overall the filopodia continued to be arranged unidirectionally toward the posterior suture. At 4 weeks postnatal, the organized arrangement of the fiber ends was lost. Notable changes included: disorganized arrangement of the posterior fiber ends with a loss of tight packing between fiber ends (extracellular space [ECS] dilations), elongated filopodia, filopodial tips taking on a ‘bouton-like’ appearance and random orientation of filopodia (Figure 4E,F). Figure 4E clearly shows the border (dotted line) between the normal arrangement (right) and the abnormal fiber ends situated within the confines of the PSC plaque (left). The majority of the changes observed took place between 4 and 6 weeks postnatal and corresponded with PSC formation and suture pattern changes that were observed in the gross lens at the same age. By 7–8 weeks postnatal, the PSC was fully formed and the fiber end segments exhibited the characteristic change of direction away from the polar axis toward the capsule (Figure 5A,C) as has been previously described [14,15]. SEM images of the fiber ends within the PSC plaque at 7–8 weeks postnatal revealed two distinct sets of features; the ends either exhibited ECS dilations, altered morphology and disordered filopodia (Figure 5A,B) or they assumed a distended or globular appearance in a tightly packed configuration with complete lack of filopodia (Figure 5C,D). A subset of the lenses (less than 1/4) showed discrete areas wherein fiber ends had a stellate appearance with an apparent degree of fiber end loss (Figure 5E,F). RCS lenses of all ages in the control group exhibited fiber end shape, size and arrangement consistent with that seen in other rodent strains (Figure 6A-C), specifically, the fiber ends were uniform in size shape and exhibited a normal filopodial anatomy and organization. Fiber end morphology of the 2 week old dystrophic lenses, were comparable to the controls.

Bottom Line: At all time points thereafter, F-actin was rearranged into a 'rosette' pattern of prominent foci at cell vertices.The data are consistent with the hypothesis that migration of basal fiber ends is altered in a two stage process wherein initially, migration patterns undergo a rapid shift resulting in abnormal suture sub-branch formation.Subsequent cytological alterations are consistent with an eventual cessation of migration, precluding proper targeting of basal ends to their sutural destinations and leading to cataract plaque formation.

View Article: PubMed Central - PubMed

Affiliation: Department of Anatomy and Cell Biology, Rush University Medical Center, 600 S. Paulina St., Chicago, IL 60612, USA.

ABSTRACT

Purpose: Prior structural studies of posterior subcapsular cataract (PSC) development in Royal College of Surgeons (RCS) rats suggest that migration of basal fiber ends was disrupted, ultimately resulting in a PSC. Therefore the goal of this study was to assess the overall migration patterns as well as changes to the structure and cytoskeleton of basal fiber ends during PSC development.

Methods: Lenses from 48 RCS dystrophic rats (RCS/Lav) and 24 genetically matched control animals (RCS-rdy(+)/Lav) from 2 to 8 weeks old were examined. Equatorial diameters were measured and suture patterns were photographed immediately following enucleation/dissection. Right eye lenses were fixed and processed to visualize the actin cytoskeleton via laser scanning confocal microscopy (LSCM), left eye lenses were decapsulated, fixed and processed for scanning electron microscopy (SEM). Scaled 3D-computer assisted drawings (CADs) and animations were constructed from the data to depict the changes in suture patterns and fiber end architecture.

Results: At 2 weeks, dystrophic lenses displayed an inverted Y suture on the posterior, and by 3 weeks most lenses had at least one sub-branch. Additional sub-branches were observed with time, opacities being visible as early as 4 weeks and progressing into PSC plaques by 6 weeks. Control lenses displayed inverted Y sutures at all ages and were transparent. SEM of dystrophic lenses revealed fiber ends with normal size, shape, arrangement, and filopodia at 2 weeks; scattered areas of dome-shaped fiber ends and small filopodia were present at 3 weeks. At 4 weeks the irregularly arranged domed fiber ends had extremely long filopodia with 'boutons' at their tips. By 6 weeks all fiber ends within plaques displayed rounded or domed basal membranes and lacked filopodial extensions. Control lenses at all time points had comparable ultrastructure to the 2 week old dystrophic lenses. F-actin arrangement within the basal membrane complex (BMC) of control lenses showed the expected peripheral pattern of labeling at all ages. Dystrophic RCS lenses at 2 weeks were comparable to controls, however by 3-4 weeks they displayed scattered foci of F-actin within the BMC. At all time points thereafter, F-actin was rearranged into a 'rosette' pattern of prominent foci at cell vertices.

Conclusions: The data are consistent with the hypothesis that migration of basal fiber ends is altered in a two stage process wherein initially, migration patterns undergo a rapid shift resulting in abnormal suture sub-branch formation. Subsequent cytological alterations are consistent with an eventual cessation of migration, precluding proper targeting of basal ends to their sutural destinations and leading to cataract plaque formation.

Show MeSH
Related in: MedlinePlus