2023 Volume 40 Issue 3 Pages 128-136
More than 500 million years ago, the common ancestor of vertebrates acquired daylight vision with four types of cone cells and dim light vision with rod cells. Each photoreceptor cell has its unique phototransduction system and exhibits a characteristic cell morphology. These features are highly conserved across species, making it possible to identify photoreceptor cells in the retina in each species despite large evolutionary distances. However, photoreceptor cells in each species have been uniquely adapted to their specific light environment, and the number of photoreceptor cell types can vary greatly. This article explores the molecular basis of cross-species cell-type homology comparing the transcriptional mechanisms of photoreceptor differentiation in three species: zebrafish, house mouse, and human. Finally, I addressed the evolutionary shift from the four-cone type photoreceptor differentiation network, which would have been maintained in the common ancestor of fish and mammals, to the two-cone type mammalian network.
