Yu, Vionnie W.C.Lymperi, StefaniaOki, ToshihikoJones, AlexandraSwiatek, PeterVasic, RadovanFerraro, FrancescaScadden, David T.2016-10-112016Yu, Vionnie W.C., Stefania Lymperi, Toshihiko Oki, Alexandra Jones, Peter Swiatek, Radovan Vasic, Francesca Ferraro, and David T. Scadden. 2016. “Distinctive Mesenchymal-Parenchymal Cell Pairings Govern B Cell Differentiation in the Bone Marrow.” Stem Cell Reports 7 (2): 220-235. doi:10.1016/j.stemcr.2016.06.009. http://dx.doi.org/10.1016/j.stemcr.2016.06.009.2213-6711http://nrs.harvard.edu/urn-3:HUL.InstRepos:29002452Summary Bone marrow niches for hematopoietic progenitor cells are not well defined despite their critical role in blood homeostasis. We previously found that cells expressing osteocalcin, a marker of mature osteolineage cells, regulate the production of thymic-seeding T lymphoid progenitors. Here, using a selective cell deletion strategy, we demonstrate that a subset of mesenchymal cells expressing osterix, a marker of bone precursors in the adult, serve to regulate the maturation of early B lymphoid precursors by promoting pro-B to pre-B cell transition through insulin-like growth factor 1 (IGF-1) production. Loss of Osx+ cells or Osx-specific deletion of IGF-1 led to a failure of B cell maturation and the impaired adaptive immune response. These data highlight the notion that bone marrow is a composite of specialized niches formed by pairings of specific mesenchymal cells with parenchymal stem or lineage committed progenitor cells, thereby providing distinctive functional units to regulate hematopoiesis.en-USJournal Article2016-10-1110.1016/j.stemcr.2016.06.009