Distinct Origins of Restricted Progenitors in Postnatal Mouse Blood

BACKGROUND: Most researchers have accepted that unipotent progenitors are the predominant components in bone marrow for tissue regeneration. However, the unipotent progenitors for blood components are still unclear. We previously found that erythrocytes are derived from a distinct unipotent progenitors, or erythrocyte sacs. METHODS: In the current study, we investigated if the other types of unipotent blood cell progenitors existed, what was their original morphologies, and the mechanism of their generation in mouse blood. RESULTS: We found two morphologically distinct structures that released spore-like small progenitors in mouse blood. One structure was filamentary-like, contained inclusions, widened due to differentiation of the inclusions, and eventually, released spore-like DNA+ and cluster of differentiation 34 (CD34)(+) spore-like small progenitors. Another structure was bud-like, contained inclusion, enlarged from less than 10 µm to more than 30 µm, and also released many spore-like small progenitors. Each type of these spore-like progenitors was approximately 1 µm in diameter and could continue to transdifferentiate in circulation. CONCLUSIONS: Our data provide evidence that two types of blood cell restricted progenitors are produced from either filamentary structures or bud-like structures. Both filamentary and bud-like structures were originally released from morphologically distinct, or lineage predetermined tube-shaped structures, or specific niches. Thus, distinct lineages of blood unipotent progenitors are newly produced.