ERG +85 enhancer targets HSCs. (A) CD45.1/45.2 mice were transplanted with Venus^high LSK cells from CD45.2 SV40/Erg +85/Venus transgenic mice. BM cells stained for CD45.1 and CD45.2 at 14 weeks post-transplant show a mix of donor-derived (2) and recipient (1) cells. Donor-derived CD45.2 BM cells continue to express the Venus reporter 14 weeks post-transplant (i-ii). The Erg +85 enhancer remains highly active (ie, high Venus expression) in donor-derived LSK cells 14 weeks post-transplant (iii-iv). Donor-derived Mac1⁺/Gr1⁺ myeloid cells in the recipient continue to express the Venus reporter 14 weeks post-transplant (v-vi). A proportion of donor-derived CD3⁺ T cells in the recipient continue to express the Venus reporter 14 weeks post-transplant (vii-viii). Donor derived B220⁺ B cells in the recipient continue to express the Venus reporter 14 weeks post-transplant (ix-x). (B) Transverse cryosections through the aorta-gonad-mesonephros of E10.5 SV40/Erg +85/Venus transgenic embryos stained with CD34 (endothelial, HSC) and CD41 (an early marker of definitive hematopoiesis). Venus-expressing cells in the dorsal aorta express CD41 (i). A cryosection through the fetal liver of an E11.5 SV40/Erg +85/Venus transgenic embryo. CD41-expressing fetal liver cells also express the Venus reporter (ii).