Differential amplification of murine bipotent megakaryocytic/erythroid "progenitor" and "precursor" cells during recovery from acute and chronic erythroid stress

¹ Istituto Superiore Sanità, Rome, Italy
² Stanford University School of Medicine, Stanford, California
³ University of California at Merced, Merced, California
⁴ University of Florence, Florence, Italy

^* To whom correspondence should be addressed. E-mail: migliar{at}iss.it.

	Abstract

Two murine bipotent erythroid/megakaryocytic cells, the progenitor (MEP) and precursor(PEM) cells, have been recently identified on the basis of the phenotypes of lin^negc-kit^posSca-1^neg CD16/CD32^lowCD34^low and TER119^pos4A5^pos or 2D5^pos, respectively. However, the functional relationship between these two subpopulations and their placement in the hemopoietic hierarchy is incompletely understood. We compared the biological properties of these subpopulations in marrow and spleen of mice with and without acute or chronic erythroid stress. MEP, but not PEM, express c-kit, respond to SCF in vitro and form spleen colonies in vivo. PEM comprise up to 50-70% of the cells in BFU-E-derived colonies but are not present amongst the progeny of purified MEP cultured under erythroid and megakaryocytic permissive conditions. PEM increase 10 to 20 fold under acute and chronic stress, whereas MEP increases (21 to 84%) are only observed in acutely stressed animals. These data suggest that MEP and PEM represent distinct cell populations that may exist in an upstream-downstream differentiation relationship under conditions of stress. While the dynamics of both populations are altered by stress induction, the differential response to acute and chronic stress suggests different regulatory mechanisms. A model describing the relationship between MEP, PEM and CMP is presented.

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