Expression of oncostatin M in hematopoietic organs

Murine oncostatin M (OSM), a member of the interleukin-6 (IL-6) -related cytokine subfamily, stimulates definitive hematopoiesis and liver development. The OSM gene was cloned as a cytokine-inducible early response gene in some hematopoietic cell lines. In this study, we performed in situ hybridization to examine the tissue distribution of cells expressing OSM mRNA in the developing and the adult mice. Its gene expression was seen in hematopoietic cells of developing liver from 11.5 days postcoitum (dpc), and persisted to the neonates. From 17.5 dpc, OSM mRNA-positive cells were found in other hematopoietic organs, including bone marrow, thymus, and spleen. The highest levels of gene expression were observed in the adult bone marrow. Most OSM-expressing cells expressed IL-5 receptor alpha subunit, a marker for eosinophil lineage. In addition, some positive cells expressed neutrophil elastase, which was used as a polymorphonuclear neutrophil (PMN) marker. After birth, OSM mRNA was expressed in tissue eosinophils in nonhematopoietic organs, including small intestine, lung, and skin. Our data revealed that eosinophil progenitors and eosinophils as well as PMNs are also an important cellular source of OSM in mice.