Marking of definitive HSC precursors in E7.5-E8.5 embryos using an Abcg2-CreER lineage-tracing mouse model.

Abcg2, a member of the ATP-binding cassette transporter family, is expressed in adult hematopoietic stem cells (HSCs) and is required for the side population phenotype of adult bone marrow HSCs and other adult tissue-specific stem cells. Lineage tracing in adult mice using the Abcg2-Cre mouse model showed that Abcg2 marks HSCs, intestinal stem cells, and spermatogonial stem cells. It is unclear whether definitive HSCs or their precursors in early embryonic development can be marked by Abcg2 expression. Here, we treated pregnant Abcg2 Cre/Cre RosaLSL-YFP mice with a single injection of 4-hydroxytamoxifen at embryonic day 7.5. Four months after birth, a small yellow fluorescent protein-positive (YFP+ ) cell population could be detected in all of the major white blood cell lineages and this was stable for 8 months. Transplant of bone marrow cells or Sca1+ YFP+ cells from these mice showed continued multilineage marking in recipient mice at 4 months. These results demonstrate that Abcg2 expression marks precursors to adult long-term repopulating HSCs at E7.5 to E8.5 and contributes to a stable subpopulation of HSCs well into adulthood.