Comparing hematopoietic stem cells and early lymphoid progenitors (CBX73). unidentified

Hematopoietic stem cells (HSC) are an important cell type with the capacity for self-renewal as well as differentiation into multi-lineage blood cells, maintaining the immune system throughout life. Many studies have attempted to identify unique markers associated with these extremely rare cells. In bone marrow of adult mice, the Lin-c-kitHi Sca1+ CD34-/Lo Thy1.1Lo subset is known to include HSC with long-term repopulating capacity. However, several of these parameters differ between strains of mice, change dramatically during developmental age and/or are expressed on many non-HSC during inflammation. Efficient HSC-based therapies and the emerging field of regenerative medicine will benefit from learning more about what defines stem cells. We previously determined that the most primitive cells with lymphopoietic potential first develop in the paraaortic splanchnopleura / aorta-gonad-mesonephros (AGM) region of embryos using Rag1/GFP knock-in mice. We also reported that Rag1/GFP-c-kitHi Sca1+ cells derived from E14.5 fetal liver (FL) reconstituted lympho-hematopoiesis in lethally irradiated adults, while Rag1/GFPLo c-kitHi Sca1+ cells transiently contributed to T and B lymphopoiesis. To extend those findings, microarray analyses were conducted to search for genes that characterize the initial transition of fetal HSC to primitive lymphopoietic cells. The comparisons involved mRNA from Rag1Lo ckitHi Sca1+, early lymphoid progenitors (ELP) and the HSC-enriched Rag1- ckitHi Sca1+ fraction isolated from E14.5 FL. While genes potentially related to early lymphopoiesis were discovered, our screen also identified genes whose expression seemed to correlate with HSC.