Fig 1. Functional identification of P-SSCs and BM-SSCs.

(A) Interferon inducible Mx1⁺ SSCs (red) are shown to contribute to majority osteoblasts (green, overlap yellow) in vivo. (B) Mx1⁺ SSCs represent long-term osteolineage progenitor cells in BM and periosteal tissues. In vivo imaging shows that Mx1⁺ SSCs reside in bone marrow, suture, and periosteum of calvarial bones. Immunofluorescent staining of tibial metaphysis of Mx1/Tomato/Ocn-GFP mice shows that Mx1⁺ SSCs (red, arrows) are abundant in periosteum (PO) (Tibia IHC). (C) P-SSCs from periosteal tissues are FACS-sorted by CD45⁻CD31⁻Ter119⁻CD105⁺CD140a⁺ and Mx1⁺Ocn⁻, which are referred to as Mx1⁺Ocn⁻ P-SSCs. (D) Mx1⁺Nestin⁺ BM-SSCs are perivascular cells in BM but are undetectable in periosteum and calvarial suture. (E) Mx1⁺Nes⁺ cells within CD45⁻CD31⁻Ter119⁻CD105⁺ CD140a⁺ SSC fraction in bone marrow are isolated by FACS-sorting and are referred to as Mx1⁺Nes⁺ BM-SSCs. Notably, CD105⁺CD140a⁺ progenitors are heterogeneous Mx1⁺ and Nestin⁺ cells.