Hamilton, N. R.; Neckles, V. N.; Al-Khindi, T.; Donthi, N.; Mizutori, S.; Fu, R.; Kiraly, J. K.; Winship, B. C.; Kolodkin, A. L.; Chaudhari, K.

The optokinetic reflex (OKR) is an evolutionarily conserved reflexive behavior that ensures image stabilization on the retina during global motion. It consists of smooth eye tracking movements in the direction of the moving stimulus interspersed with rapid resetting saccades. This reflex is driven by retinal ON direction-selective ganglion cells (oDSGCs), which comprise distinct subtypes tuned either to vertical or horizontal motion. oDSGCs convey directional signals to the brain via precise axonal projections to specific accessory optic system (AOS) nuclei. However, the mechanisms that establish and maintain the specificity of these circuits remain poorly understood. Here, we identify a critical role for the mechanosensitive ion channel Piezo2 in refining AOS circuitry to ensure appropriate eye movement responses. Single-cell transcriptomic profiling revealed selective enrichment of Piezo2 in horizontally-tuned oDSGCs. We show that both loss and hyperactivation of Piezo2 in retinal neurons leads to cross-coupling of horizontal and vertical OKR responses, producing aberrant diagonal eye tracking movements during horizontal optokinetic stimulation. Mechanistically, Piezo2 regulates the developmental refinement of oDSGC axonal projections within the AOS, and disruption of this process results in persistent ectopic innervation that enables aberrant crosstalk between horizontal and vertical motion pathways. These findings reveal a channel activity-dependent mechanism that ensures the functional segregation of directional motion circuits underlying gaze stabilization.