HOPX (HOP homeobox) is an atypical homeodomain transcription factor that plays diverse roles across multiple tissue types. In lung development, HOPX serves as a marker for type 1 alveolar epithelial cells (AEC1s), where it is expressed during the differentiation of type 2 alveolar cells into AEC1s in alveolar repair processes 1. During brain development, HOPX marks hippocampal progenitors and is involved in neuronal lineage specification, with its expression patterns helping define regional markers in CA1, CA3, and dentate gyrus neurons 2. HOPX also marks outer radial glia in the developing human neocortex, where it is associated with stemness and the maintenance of neural stem cell populations 3. In intestinal epithelium, HOPX-positive cells contribute to fecal microRNA production, which helps regulate gut microbiota composition 4. Recent studies have identified HOPX as a key mediator in cancer biology, where it acts downstream of β-hydroxybutyrate signaling through the Hcar2 receptor to suppress colorectal cancer proliferation 5. Additionally, HOPX enhances CD8+ T cell cytotoxicity against gastric cancer cells through GPR109A signaling pathways 6. In lung fibrosis models, loss of HOPX expression indicates alveolar epithelial reprogramming during fibrotic processes 7.