• Circadian clock components directly regulate stem-cell signaling pathways (Wnt, Notch, Hedgehog) via transcriptional control, chromatin remodeling, and post-translational modifications.
• Reciprocal feedback from these pathways modulates circadian amplitude and phase within stem-cell niches, creating a bidirectional regulatory network.
• Disruption of circadian-stem cell crosstalk impairs tissue homeostasis, reduces regenerative capacity, and may contribute to tumorigenesis.
• Chronotherapeutic timing of stem-cell interventions could improve the efficacy and safety of regenerative therapies.