Figure 1.

CD34⁺CD42b⁺ cells have a restricted capacity of megakaryocyte differentiation in vitro and platelet production in vivo. (A): Identification of CD34⁺CD42b⁺ population in bone marrow cells (BMCs). Adult mouse BMCs were stained with antibodies for cKit, Sca1, lineage marker (Lin), CD34, CD16/32 (FccRII/III), CD42b, CD41, CD150, and CD9. Note that only CD34⁺ fraction of the Lin⁻ population expressed CD42b (3rd figure from the left in the upper panels) and that the CD34⁺CD42b⁺ population was confined to the Sca1⁻cKit⁺ population (right in the upper panels), mainly in the common myeloid progenitor (CMP) fraction (the lower panels). A representative result from five independent experiments is shown. (B): (i) The representative morphologies of the colonies derived from indicated cell types in 96-well-plate liquid culture. The number of cells seeded in one well was 500 for LSK/CMP (CD42b-), 2000 for megakaryocyte–erythroid progenitor (MEP)/megakaryocytic progenitor (MKP). Arrowheads indicate mature megakaryocytes. (ii) Frequencies of vWF⁺ and TER119⁺ cells in the liquid culture shown in (i). (C): Capacity of CD34⁺CD42b⁺ cells (MKP) and MEP to generate platelet in vivo. Sublethally irradiated (4.5 Gy) mice were transplanted with 1 × 10⁴ CD34⁺CD42b⁺ cells or MEP from green fluorescent protein transgenic mice. On days 4, 7, 11, and 14 after transplantation, peripheral blood was collected and analyzed for platelet differentiation using CD41⁺ platelet-sized cells (n 5 4). Abbreviations: CMP, common myeloid progenitor; FSC, forward scatter; GFP, green fluorescent protein; GMP, granulocyte–monocyte progenitor; LSK, lineage⁻Sca1⁺cKit⁺; MEP, megakaryocyte–erythroid progenitor; MKP, megakaryocytic progenitor; SSC, side scatter.