Distribution of thromboblastic progenitors in embryonic bone marrow. (A) Thromboblastic colonies were scored from sorted GPIIb-IIIa positive (+) and negative (−) populations, and from total E14 bone marrow cells (unsorted) in thromboblastic differentiation medium. Data were normalized to 1,000 cultured cells. Mean ± SD is from eight experiments. (B) Morphology of colonies of thromboblasts (Tb), and (C) thrombocytes (Tc) (MGG staining). These cells were GPIIb-IIIa⁺ (not shown). Thromboblasts colonies are composed of several clusters. Bar = 12 μm.