TPH2 and colorectal carcinoma: In summary, Zhu and colleagues revealed that CRC-associated microbiota metabolite IVA promoted 5-HT production from serotonergic neurons by inhibiting NuRD complex onto Tph2 promoter to initiate Tph2 expression; by engaging 5-HT receptor HTR1B/1D/1F, 5-HT promoted colorectal CSCs self-renewal through activating Wnt/β-catenin signaling pathway and thus initiating CRC (Figure 1).