Differential expression of mouse Grem1+ Vs. Grem1- bone-marrow cells

The gene expression of bone marrow cells of mice enriched for Gremlin1 vs control was measured (n=3). It is not known if endogenous adult mesenchymal stem cells (MSCs) exist.Following culture,perisinusoidal mesenchymal cells can clonally recapitulate the skeletal microenvironment, but this fails to confirm their endogenous lineage repertoire. Multipotential MSCs in vitro may be fate-restricted in vivo and specific perisinusoidal recombination does not trace bone or cartilage Reconciling in vitro MSCs with their in vivo potential has been challenging and remains untested outside of the bone. We prove that expression of the bone morphogenetic protein (BMP)-antagonist gremlin 1 (Grem1) identifies a population of self-renewing, multipotent bone, cartilage and stromal-primed MSCs in both health and healing that are completely distinct from the established Nes-GFP niche-supporting mesenchymal cells. Grem1 recombination also identifies small intestinal MSCs (siMSCs) that can be transplanted and clonally trace the self-renewing, multilineage periepithelial mesenchymal sheath. Our findings prove the existence of adult MSCs that are regionally and functionally distinct from perisinusoidal Nes-GFP cells. We also established that the mesenchyme undergoes ordered turnover outside of the bone and may help to preserve regional niches. Grem1 MSCs provide a new focus for investigating mesenchymal renewal and repair.