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RH Kroeger, HJ Wagner; Distribution of Cytosceletal Components During Retinomotor Movements in the Cichlid Fish Aequidens Pulcher . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3743.
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Purpose: In many fishes, photoreceptor inner/outer segment complexes and melanosomes in retina pigment epithelium (RPE) cells move during light/dark adaptation. The rods of Aequidens pulcher have long (up to 100 µm) outer segments which necessitate particularly large excursions of melanosomes and cone inner/outer segments. We studied such retinomotor movements (RMM) in intact retinae. Methods:Retinae of fishes in various states of adaptation were fixed in eye-cup preparations with 4% paraformaldehyde and isolated. Key elements of the cytoskeleton were tagged with phalloidin (microfilaments) and an antibody against α-tubulin (microtubules and unpolymerized tubulin). For general morphology, melanin in RPE cells was bleached and the tissues stained with the fluorescent dyes Lucifer Yellow (hydrophilic) and DiD (lipophilic). The tissues were visualized by confocal microscopy. Results: RPE: The cells underwent profound changes in shape during RMM, including relocations of the nuclei by about 20 mm. Little phalloidin reactivity was detectable. Cone elongation (dark apaptation): The inner segments stretched to long tubes with strong phalloidin reactivity close to the cell membranes. A typical, thread-like myoid was first formed when the cone inner/outer segments had almost reached their maximally dark-adapted positions. During formation of the myoid, phalloidin reactivity decreased and α-tubulin immunoreactivity became more localized. Cone contraction (light adaptation): The myoids remained thin and showed little phalloidin reactivity. Conclusion: In A. pulcher, changes in cell shape are important for the role of RPE cells in light/dark adaptation. Those movements seem to be mainly based on microtubules. Microfilaments appear to have an important role in cone elongation, while the elongated shape is maintained mainly by microtubules.
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