TMEM119 is a cell surface protein that serves as a specific marker for microglial cells in both mice and humans. It functions as an osteoblastic inductive factor, promoting the proliferation, migration, and invasion of osteosarcoma cells. TMEM119 also acts downstream of parathyroid hormone (PTH) and is similar to the similar to mothers against decapentaplegic-3 (Smad3) signaling pathway in osteoblasts. TMEM119 is also considered a potential microglial cell marker that can distinguish resident microglia from blood-derived macrophages in the human brain. It is crucial for identifying microglia in healthy tissue and distinguishing them from infiltrating macrophages and other cell types in neurodegenerative disease models.