Tracking Satb2-positive retinal ganglion cells in zebrafish unveils developmental functional reorganization.

Retinal ganglion cells (RGCs) relay visual information to the brain, and their functional properties are crucial for visually guided behavior. However, functional maturation of RGCs across development remains elusive. Here, we investigated the developmental maturation of a genetically defined RGC type expressing Satb2 in zebrafish, which allowed single-layer-resolved analysis of the tectal neuropil. Using in vivo calcium imaging, we characterized visual response properties of Satb2-positive RGC axon terminals at two developmental stages: 6-7 and 10-11 days post-fertilization. At the early stage, responses segregated into seven functional clusters with diverse tuning profiles. By the later stage, these responses reorganized into five clusters, indicating developmental restructuring of functional identities. Longitudinal imaging of individual RGC axons revealed that while some response types remain stable across development, others exhibit pronounced plasticity. In particular, certain RGC clusters acquired additional tuning features and converged into a motion-sensitive cluster, coinciding with a marked expansion of a motion-responsive cluster and reflecting progressive functional specialization. Moreover, direction-selectivity in Satb2-positive RGCs was observed later during development. Visual deprivation experiments revealed that core visual tuning is genetically determined, whereas visual experience is crucial for fine-tuning of the particular functional type. Together, our findings provide a single-cell-resolved view of retinal circuit maturation and reveal how stable and flexible responses are integrated during the development of vertebrate vision.