Multipotential hematopoietic progenitor cells from embryos developed in vitro engraft unconditioned W41/W41 neonatal miceB.

BACKGROUND AND OBJECTIVES The first hematopoietic stem cells (HSC) in the mouse able to give rise to the adult hematopoietic system emerge at embryonic day (E) 10.5 in the intraembryonic aorta-gonads-mesonephros (AGM) region, as demonstrated by transplantation into irradiated adult recipients. It has been shown by transplantation into conditioned neonatal or hematopoietic mutant adult recipients that less potent multipotential hematopoietic progenitors exist in the mouse embryo at E9, one day earlier than the appearance of HSC. Studies of the lineage relationships of multipotential hematopoietic progenitors and HSC in the mouse embryo have been complicated by inaccessibility due to in utero development. Attempts are being made to create an in vitro whole mouse embryo culture system to access the developing mouse embryo for such studies of hematopoietic cell emergence during early and mid-gestational stages. The aim of this study was to compare the development of multipotential hematopoietic progenitors in early in utero and in vitro-developed mouse embryos. DESIGN AND METHODS To test hematopoietic progentior/stem cell activity in the mouse embryonic tissues obtained from genetically marked in utero and in vitro-developed embryos, transplantations were performed using unconditioned neonatal W41/W41 (c-kit hematopoietic mutant) recipients. Long-term donor-cell reconstitution in transplanted mice was measured by (i) semiquantitative polymerase chain reaction and (ii) flow cytometry on peripheral blood and hematopoietic organs. RESULTS Our experimental data show that multipotent hematopoietic progenitors from in utero-developed embryos engraft unconditioned W41/W41 neonates. Furthermore, in vitro-developed whole embryos also contain early multipotent hematopoietic progenitor cells that are able to yield high-level, long-term engraftment of W41/W41 neonates. INTERPRETATION AND CONCLUSIONS The in vitro culture of whole mouse embryos during mid-gestational stages allows for the normal growth of multipotential hematopoietic progenitors that can be assayed by transplantation into W41/W41 neonatal recipients. Thus, in vitro-developed whole embryos can be used with confidence in future studies to examine the lineage relationships of multipotential hematopoietic progenitors and HSC.