The frequency of megakaryocytes capable of forming proplatelets is decreased in BM cultures derived from BclxL transgenic mice.

BM cultures of Tg19 or WT mice were enriched for megakaryocytes by indirect immunomagnetic negative separation. Isolated megakaryocytes were cultured for 3 days as described in “Materials and methods” and subjected to examination by phase contrast microscopy (A-D). Note 3 different types of cytoplasmic extensions for WT megakaryocytes: beaded proplatelets (A), pseudopodialike (B), and long, thin extensions (C), whereas mainly one type was observed for Tg19—long, thin extensions (D). Original magnification, × 600 for panel A and × 400 for panels B, C, and D. (E).The frequency of megakaryocytes making proplatelets was monitored. The data are averages ± SD for 3 experiments, with 2 wells analyzed in each.