Identity of Gli1⁺ cells in the bone marrow

Bone marrow fibrosis is a critical component of primary myelofibrosis in which normal bone marrow tissue and blood-forming cells are gradually replaced with scar tissue. The specific cellular and molecular mechanisms that cause bone marrow fibrosis are not understood. A recent study using state-of-the-art techniques, including in vivo lineage tracing, provides evidence that Gli1⁺ cells are the cells responsible for fibrotic disease in the bone marrow. Strikingly, genetic depletion of Gli1⁺ cells rescues bone marrow failure and abolishes myelofibrosis. This work introduces a new central cellular target for bone marrow fibrosis. The knowledge that emerges from this research will be important for the treatment of several malignant and nonmalignant disorders.