Lens apoptosis in the Astyanax blind cavefish is not triggered by its small size or defects in morphogenesis

Blindness is a convergent trait in many cave animals of various phyla. Astyanax mexicanus cavefish is one of the best studied cave animals; however the mechanisms underlying eye degeneration in this species are not yet completely understood. The lens seems to play a central role, but only relatively late differentiation defects have been implicated in the cavefish lens apoptosis phenotype so far. Here, we used genetic crosses between Astyanax cavefish and surface fish to confirm that during development, lens size is independent of retina size. We then investigated whether the small size of the cavefish lens could directly cause cell death. Laser ablation experiments of lens placode cells in surface fish embryos showed that a small lens size is not sufficient to trigger lens apoptosis. We further examined potential lens morphogenesis defects through classical histology and live-imaging microscopy. From lens placode to lens ball, we found that lens invagination and formation of the lens epithelium and fiber cells occur normally in cavefish. We conclude that the main and deleterious defect in the Astyanax cavefish lens must concern the molecular control of lens cell function.