Circadian clock gates retinal regeneration by orchestrating Cxcl12-dependent immune coordination

The circadian clock orchestrates tissue homeostasis and repair, yet its role in central nervous system (CNS) regeneration remains largely unexplored. Here, we identify the circadian clock as an essential regulator of adult zebrafish retinal regeneration, a CNS model. Retinal injuries induced at distinct circadian times elicit differential Muller glia (MG) reprogramming and progenitor proliferation, both of which exhibit robust diurnal fluctuations. Disrupting circadian rhythms--via constant darkness (DD) or day-night reversal (DL)--suppresses MG reprogramming, MG-derived progenitor cell (MGPC) formation and neuronal regeneration, concomitant with dampened retinal immune responses. Notably, intravitreal immune stimulation restores MGPC numbers in the retina under DD conditions, linking immune activation to circadian-regulated regeneration. Single-cell RNA-seq reveals that DD disrupts MG reprogramming trajectories while inducing unfolded protein response (UPR) and suppressing ATP/protein synthesis. Moreover, clock disruption alters microglia heterogeneity, and cell-cell communication analysis identifies the Cxcl12-Cxcr4 signaling as a key chemotactic axis between MG/endothelial cell and immune populations. Mechanistically, Bmal1b directly binds E-box motifs in the cxcl12a/12b promoters, driving their rhythmic transcription to orchestrate the immune response after injury. Importantly, exogenous Cxcl12a partially restores both immune and regenerative responses in clock-disrupted retinas, establishing the Cxcl12-Cxcr4 axis as a circadian-immune checkpoint for retinal repair. Collectively, our findings reveal a novel paradigm in which the circadian clock gates CNS regeneration through Cxcl12-mediated immune coordination, offering potential therapeutic insights for CNS repair in mammals.