Inability of adult circulating haemopoietic stem cells to sustain haemopoiesis in mouse fetal liver microenvironment.

Liver rudiments were removed from mouse embryos at Day 9 of gestation, before the 28-somite stage, when they are still not colonized by extrinsic haemopoietic stem cells (HSC), and they were grafted under the kidney capsule of syngeneic adult mice. Hepatocytes differentiated normally, but no colonization by HSC occurred. As control, we used precolonized thymic rudiments taken at Day 10 of gestation, when they are still included in the third branchial arches. They were grafted in the same conditions as liver rudiments and they became colonized by extrinsic HSC that gave rise to lymphocytes. So, adult HSC are not able to colonize the fetal liver rudiment while they have the capacity to home the fetal thymus. We discuss these results in terms of an ontogenic maturation of HSC that could change their homing capacities around birth.