Characterization of mouse cl megakaryocyte progenitors

Although it has been shown that unfractionated bone marrow, ris hematopoietic stem cells, common myeloid progenitors, and bipotent by megakaryocyte/erythrocyte progenitors can give rise to megakaryoor cyte colonies in culture, monopotent megakaryocyte-committed proris genitors (MKP) have never been prospectively isolated from the bone pr marrow of adult mice. Here, we use a monoclonal antibody to the bu megakaryocyte-associated surface protein, CD9, to purify MKPs from ce the c-kit+Sca-l-IL7Ra-Thyl.l-Linfraction of adult C57BL/Kain Thyl.1 bone marrow. The CD9+ fraction contained a subset of pc CD41+FcyRIOCD34+CD38+ cells that represent -0.01% of the total nucleated bone marrow cells. They give rise mainly to colonypc forming unit-megakaryocytes and occasionally burst-forming unitgi' megakaryocytes, with a plating efficiency >60% at the single-cell an level. In vivo, MKPs do not have spleen colony-forming activity nor do to they contribute to long-term multilineage hematopoiesis; they give we rise only to platelets for =3 weeks. Common myeloid progenitors and us megakaryocyte/erythrocyte progenitors can differentiate into MKPs ml after 72 h in stromal cultures, indicating that MKPs are downstream su of these two progenitors. These isolatable MKPs will be very useful di: for further studies of megakaryopoiesis as well as the elucidation of fo their gene expression patterns. C] of