Blast cell colonies seen in cultures of spleen cells from 5- fluorouracil-treated mice provide a highly enriched population of primitive hemopoietic progenitors. Our recent studies of the differentiation potentials of the paired daughter cells of these progenitors showed different patterns of differentiation in the colonies produced by the separated daughter cells. In this study, we carried out sequential micromanipulation of paired progenitors followed by cytologic examinations of the colonies derived from these progenitors. Of the total 94 evaluable cultures, consisting of three or more colonies, 52 consisted of macrophage colonies and one consisted of megakaryocyte colonies. In the remaining 41 cultures, diverse combinations of colonies revealing heterogeneous compositions of cell lineages were identified. Presumptive genealogic trees of the differentiation of hemopoietic progenitors constructed for the latter group of cultures suggested that monopotent progenitors may be derived from pluripotent progenitors in two ways: (1) directly during one cell division of pluripotent cells or (2) as a result of progressive lineage restriction during successive division of the pluripotent progenitors. The results also suggested that some of the oligopotent progenitors are capable of limited self-renewal.

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