Mesodermal and hematopoietic progenitor potentials of ES cells are increased in response to mMix.i-Mix EBs were cultured in the presence (▪) or absence (▦) of DOX, harvested on the indicated days, and dispersed to single-cell suspensions. Cells were plated in methylcellulose progenitor assays in triplicate, and colonies were scored as indicated. Colony counts are expressed as mean ± SEM per 10 000 cells plated. (A) Mesodermal progenitors (transitional and blast colonies). EBs were harvested on days 3 and 4 and plated in methylcellulose blast colony cultures. Colonies were scored after 4 days. (B) Primitive erythroid and megakaryocyte colonies. EBs were harvested on day 4 or 5, plated in primitive hematopoietic progenitor cultures, and colonies were scored after 4 or 6 days. (C) Definitive hematopoietic colonies. EBs were harvested on day 4 or 5, plated in Methocult, and scored on day 8 or 10.