Figure 7: Disruption of KITL production in Sca1⁺ progenitors suppressed hematopoiesis in the ectopic niche.

(a) Sca1⁺ progenitors were transduced with lentivirus as indicated and 1,000 sorted GFP⁺ Sca1⁺ progenitors were co-transplanted with unmarked fetal skeletal progenitors under the kidney capsule. (b) Representative cross sections of the engrafted ectopic bone stained with H&E (right) or GFP (left) to identify the donor origin, harvested 1 month after transplant. (c) Representative FACS profiles of LSK frequencies that were pre-gated for live, CD45⁺lineage⁻ cells. (d) Cellularity of the ectopic niche marrow (*P<0.05, n=5, student’s t-test). (e) Rescue of lethally irradiated mice with 2 × 10⁵ marrow cells from engrafted ectopic niche generated with either mixed Sca1⁺/shKITL progenitors (red) or with Sca1⁺/Scrambled shRNA progenitors (yellow) or control bone marrow from host tibia (black) (n=8). (f) The schematic summaries our findings such that Sca1+ cells are the most primative giving rise to CXCL12 producing stromal cells, CD146+ cells and CD166+ cells. CD146+ and CD166+ cells are osteo-progenitors. It is possible that CD146+ is an intermidiary cell fate between Sca1+ cells and CD166+ cells.