Figure 6: Replication of hematopoietic stem cell niche. Figure represents the major findings of gene expression profiling of HSPC supportive matrix producing cells and support the concept of extremely variable nature of mechanisms underlying stem cell niche functions. It points to O2 and osteogenic factors as significant variables in helping to define and alter the biological functions of niche ECM. The acellular matrices from MS-5 cells at low O2 (MX3) were closer to endosteal niche like conditions; expressed higher levels of ECM related genes and hence expanded more primitive CD34+CD38+ HSPCs. MX2 matrix, which was prepared at higher O2 with osteogenic induction resembled vascular niche like conditions and hence expanded more committed CD34+CD45+ and CD34+CD133+ HSPCs. Ang-2, a ligand for Tie-2, was upregulated in MX2 condition, whereas Cxcl-12, a secreted ligand for CXCR-4, was upregulated in MX3 condition. Genes regulating hematopoiesis related signaling pathways like Wnt and Jak/Stat were differentially regulated in MX3 vs MX2. Proteoglycan decorin (Dcn) was up regulated in MX3, whereas Gpc-3 and Prg-4 were upregulated in MX2 condition. Hematopoietic Stem Cells (HSC); Multipotent Progenitor Cells (MPP); Differentiated Cells (DC); Common Myeloid Progenitor Cells (CMP); Erythroid Cells (EC).