Retinal morphology in Astyanax mexicanus during degeneration

The teleost Astyanax mexicanus is extant in two readily available forms. One that lives in Mexican rivers and various convergent forms that live in nearby caves. These fish are born with eyes but in the cavefish they degenerate during development. It is known that the lens of cavefish undergoes apoptosis and that some cells in the neuroretina also die. It has not been described, however, if glia and various components of the neuroretina form before complete eye degeneration. Here we examined the development of the retina of the closest living ancestor that lives in the rivers and members of two lineages of cavefish. We report that although the neuroretina is smaller and more compact, it has all cell types and layers including amacrine cells and Muller glia. While various makers for photoreceptors are present in the cavefish inner segments, the outer segments of the photoreceptors in cavefish are missing from the earliest stages examined. This shows that the machinery for visual transducing discs might still be present but not organized in one part of the cell. It is interesting to note that the deficiencies in Astyanax cavefish resemble retinal diseases, such as retinitis pigmentosa.