Increase of megakaryocytes and their progenitors in the bone marrow of double transgenic mice. CFU-MK assay with subsequent staining for megakaryocyte-specific acetylcholinesterase was performed on bone marrow cells from 1 BCR/ABL single transgenic, 1 hCD34tTA single transgenic, and 2 hCD34tTA-BCR/ABL double transgenic mice. Panel A shows the typical megakaryocytic morphology of the CFU in agar from a double transgenic animal (original magnification, × 100), and (B) shows the number of CFU-MKs per femur and tibia. The error bars indicate the standard deviation on the basis of counting duplicate wells. The number of colonies found in CD34tTA-BCR/ABL bone marrow cells was increased 7-fold.