HES5 is a basic helix-loop-helix (bHLH) transcriptional repressor that functions downstream of Notch signaling to regulate cell fate decisions across multiple tissues. As a transcriptional repressor, HES5 suppresses the expression of tissue-specific transcriptional activators, thereby inhibiting cell differentiation and promoting stem cell maintenance 1. In neural development, HES5 acts as a negative regulator of neurogenesis, maintaining neuronal stem cell populations and preventing premature neural differentiation 2. During cartilage development, HES5 is coupled to Notch receptor signaling and its expression decreases during chondrogenic differentiation, with Notch pathway blockade reducing cell proliferation 3. HES5 operates within complex regulatory networks, including negative feedback loops with other Hes family members like HES1 4, and cooperates with genes like Atoh1 in inner ear hair cell specification 5. In pathological contexts, HES5 exhibits context-dependent roles. In hepatocellular carcinoma, HES5 both suppresses MYC-driven tumorigenesis while promoting AKT-dependent liver tumor formation 6. In pulmonary hypertension, Notch3/HES5 signaling induces vascular dysfunction through endoplasmic reticulum stress and oxidative pathways, promoting pulmonary vascular contraction 7. HES5 serves as a validated marker for ectodermal cell fate specification in pluripotent stem cell differentiation 8, making it clinically relevant for stem cell quality control and regenerative medicine applications.