Conservation of retinal direction-selective circuits across vertebrate species.

Retinal circuits extract visual features such as color, contrast, and motion. Direction-selective (DS) circuits provide a well-studied model for understanding how the brain builds feature-selective circuits. Recent work highlights the remarkable evolutionary conservation of DS circuit components. Across species, these circuits share common transcriptional programs that diversify DS cell types and molecular cues that help establish precise synaptic organization. Directional tuning emerges during development without visual input through gene regulatory networks, extracellular signaling, and activity-dependent mechanisms. Disruption of these processes can impair motion processing and contribute to visual and oculomotor deficits. Therefore, DS circuits provide a powerful system for dissecting the molecular programs involved in neuronal subtype diversification, neurite guidance, and synaptic development. In this review, we summarize recent advances in our understanding of DS circuits, their development, cell type composition, and tuning across species.