PTPN11 and myeloproliferative disorder: In murine osteoprogenitors and MSCs, a mutation of the gene Ptpn11, causing activation of the protein tyrosine phosphatase SHP2, can lead to myeloproliferative neoplasm and subsequent leukemogenesis, and this effect was not seen if SHP2 was similarly activated in mature osteolineage cells.(47) As a result of this mutation in the progenitors, high levels of the protein CCL3, also called macrophage inflammatory protein‐1 alpha (MIP‐1α), are secreted to the BMME, altering the HSC niche by recruiting monocytes and elevating the levels of proinflammatory cytokines in the local microenvironment.