A shared mechanism in eye optical development: Lens nucleus centralization in Xenopuslaevis

Developing eye optics, determined by the lens and cornea, must coordinate with the axial length of growing eyes to focus light onto the retina to form an image. It was found that the lens nucleus in zebrafish (Danio rerio)y initially localized anteriorly in the optical axis of larvae, then centralized at older stages. An anteriorly placed lens nucleus is thought to enable a functional optical system in larvae, where eye axial length is short. To determine if a similar mechanism occurs in other aquatic animals, we studied the clawed frog, Xenopus laevis, a fully aquatic species that similarly relies on vision for survival at stages where eyes are initially small. We found that the tadpole lens nucleus was initially located anteriorly in the optical axis. As development proceeded, it moved to a more centralized location by the prometamorphosis period. Similarly, in eyes regenerated after embryonic ablation, tadpole lens nuclei were anteriorly localized and then centralized before metamorphosis, recapitulating the same pattern as control developing eyes. Moreover, the localization of the lens nucleus in the optical axes in both, the developing and regenerated Xenopus eyes correlate with axial eye length. Our findings suggest this could be a shared mechanism for eye optical development in at least two aquatic species. Future studies examining how nucleus centralization modulates lens optical power may reveal key mechanisms that coordinate optical development with axial eye growth. These insights could ultimately inform strategies to prevent or delay refractive errors that arise when these processes become mismatched.