Endomucin, a CD34-like sialomucin, marks hematopoietic stem cells throughout development

Abstract

To detect as yet unidentified cell-surface molecules specific to hematopoietic stem cells (HSCs), a modified signal sequence trap was successfully applied to mouse bone marrow (BM) CD34−c-Kit+Sca-1+Lin− (CD34−KSL) HSCs. One of the identified molecules, Endomucin, is an endothelial sialomucin closely related to CD34. High-level expression of Endomucin was confined to the BM KSL HSCs and progenitor cells, and, importantly, long-term repopulating (LTR)–HSCs were exclusively present in the Endomucin+CD34−KSL population. Notably, in the yolk sac, Endomucin expression separated multipotential hematopoietic cells from committed erythroid progenitors in the cell fraction positive for CD41, an early embryonic hematopoietic marker. Furthermore, developing HSCs in the intraembryonic aorta-gonad-mesonephros (AGM) region were highly enriched in the CD45−CD41+Endomucin+ fraction at day 10.5 of gestation (E10.5) and in the CD45+CD41+Endomucin+ fraction at E11.5. Detailed analyses of these fractions uncovered drastic changes in their BM repopulating capacities as well as in vitro cytokine responsiveness within this narrow time frame. Our findings establish Endomucin as a novel cell-surface marker for LTR-HSCs throughout development and provide a powerful tool in understanding HSC ontogeny.

Gene-expression profiling of different arms of lymphatic vasculature identifies candidates for manipulation of cell traffic

“…MSR1 and Siglec-1 are well-known macrophage molecules and EMCN is an endothelial molecule also present on stem cells (9,10). It is difficult to unambiguously discriminate between macrophage and lymphatic endothelial positivity in the SS and occasionally between the lymphatics and blood vasculature using only immunohistochemistry.…”

The placenta as a haematopoietic organ

“…Despite the fact that haematopoietic clusters have been described in the umbilical artery, thus far they have not been detected within the placental vessels. CD41, an integrin of the α subunit family (α IIb ), has recently been suggested as a marker for nascent HSCs (Bertrand et al 2008;Corbel and Salaun, 2002;Ferkowicz et al 2003;Matsubara et al 2005;Mikkola et al 2003;Mitjavila-Garcia et al 2002). We found CD41 expression on approximately one third of E12 Ly-6A GFP + placental cells, and immunohistochemical staining revealed that CD41 + cells are located within the vessels of the labyrinth, with a few of them attached to the inner vessel wall (Ottersbach and Dzierzak, 2005).…”

Markers for Hematopoietic Stem Cells: Histories and Recent Achievements

“…CD34, PECAM-1/CD31, endoglin, Tie2 and VE-cadherin are well-known endothelial antigens that also mark HSC particularly at early developmental stages (Mikkola & Orkin 2006;Takakura et al, 1998;Yokota et al, 2006). In addition, recent studies have identified endomucin, endothelial protein-C receptor/CD201, and junctional adhesion molecule-A that are common to HSC and endothelial cells (Matsubara et al, 2005;Balazs et al, 2006;Sugano et al, 2008). Although, as discussed above, the expression level of some of these antigens declines or even diminishes at later stages of development (Mikkola & Orkin 2006), each of these advances offered the promise of learning more about how HSC arise de novo and function throughout life.…”

“…In addition, many of these parameters differ between strains of mice and change dramatically during developmental age. For example, Sca1, which has been a center in the canonical HSC marker "LSK", is not detectable on the emerging HSC in the aorta-gonad-mesonephros (AGM) area and only appears after day 11.5 of gestation on HSC in fetal liver (Matsubara et al, 2005; Our unpublished observation). Furthermore, the expression level of Sca1 on HSC differs between strains and is not very effective to enrich HSC from Balb/c mice (Spangrude & Brooks, 1993).…”