Histological analysis of retinal development and remodeling in the brown anole lizard (<i>Anolis sagrei</i>)

The fovea, a pit in the retina, is crucial for high-acuity vision in humans and is found in the eyes of other vertebrates, including certain primates, birds, lizards, and fish. Despite its importance for vision, our understanding of the mechanisms involved in fovea development remains limited. Widely used ocular research models lack a foveated retina, and studies on fovea development are mostly limited to histological and molecular studies in primates. As a first step toward elucidating fovea development in nonprimate vertebrates, we present a detailed histological atlas of retina and fovea development in the bifoveated Anolis sagrei lizard, a novel reptile model for fovea research. We test the hypothesis that retinal remodeling, leading to fovea formation and photoreceptor cell packing, is related to asymmetric changes in eye shape. Our findings show that anole retina development follows the typical spatiotemporal patterning observed in most vertebrates: retinal neurogenesis starts in the central retina, progresses through the temporal retina, and finishes in the nasal retina. However, the areas destined to become the central or temporal fovea differentiate earlier than the rest of the retina. We observe dynamic changes in retinal thickness during ocular elongation and retraction-thinning during elongation and thickening during retraction. Additionally, a transient localized thickening of the ganglion cell layer occurs in the temporal fovea region just before pit formation. Our data indicate that anole retina development is similar to that of humans, including the onset and progression of retinal neurogenesis, followed by changes in ocular shape and retinal remodeling leading to pit formation. We propose that anoles are an excellent model system for fovea development research.