IL7 as a marker of a subset of bone marrow mesenchymal stromal cells

The organisation of a multitude of cellular niche components, their communication via many signalling pathways and their response to physical factors, protects and regulates haematopoietic stem cell (HSC) fate in adult bone marrow. Whilst the contribution of osteoblasts, endothelial cells and perivascular cells have been examined, the role of a second stem cell population in the bone marrow; mesenchymal stem cells, is not well understood due to the lack of distinctive markers to identify them in vivo. There is therefore a requirement to determine a characteristic that allows their prospective isolation. Under certain conditions, stromal cells and osteoblasts in the bone marrow express IL-7. The use of a novel IL7-Cre BAC transgenic mouse line has allowed more accurate IL 7 protein detection in situ and demonstrated IL-7 reporter expression in mesenchymal lineage cells in endosteal and vascular HSC niche locations. These cells were further characterised in this study in order to determine if IL-7 or nestin, an intermediate filament associated with a wide range of stem cell populations, is expressed by and could identify bone marrow derived MSCs.

YFP positive cells were analysed in sections of IL-7Cre Rosa26-eYFP mice. Interestingly, it was only a proportion of mesenchymal cells that expressed YFP, supporting the theory that subsets of MSCs exist and therefore, that they may have different roles in numerous bone marrow niches. IL-7 was not observed to have any effect on the proliferation or differentiation of human MSCs. Generation of MSC clones supported the suggestion that in vitro cultures of MSCs are a heterogeneous population and they displayed a wide range of IL-7 and nestin mRNA expression levels.