Immature megakaryocytes undergo apoptosis in the absence of thrombopoietin

We examined withdrawal effects of recombinant mouse Tpo (rm-Tpo) on the apo ptosis of mature and immature megakaryocytes in in vitro experiments, Apopt otic megakaryocytes were detected by double staining for acetylcholinestera se and by the TdT-mediated dUTP-biotin nick end labeling (TUNEL) method. Wh en the purified mature megakaryocytes were cultured with or without rm-Tpo, the numbers of viable megakaryocytes, apoptotic megakaryocytes, and megaka ryocytes with cytoplasmic processes were not significantly different betwee n the two groups. In contrast, purified immature megakaryocytes underwent a poptosis when rm-Tpo was absent from the culture system. Murine bone marrow cells were cultured with rm-Tpo (50 U/mL) on days 1-7 to generate immature megakaryocytes and subsequently were cultured with different concentration s of rm-Tpo (0-50 U/mL) on days 8-14, The number of viable megakaryocytes w as decreased and that of apoptotic megakaryocytes was increased by rm-Tpo i n a dose-dependent manner. These results indicated a clear relation between the rm-Tpo level and the apoptosis of immature megakaryocytes, (C) 1999 In ternational Society for Experimental Hematology, Published by Elsevier Scie nce Inc.