Cell‐surface N otch1 expression identifies a primitive phenotype within CD 34 + CD 38 − haematopoietic cells

Objective Notch signalling has been implicated in haematopoietic stem cell self‐renewal. Although several studies have tested the effect of activating or inhibiting the N otch signalling pathway in stem cells, no study has yet determined the functional differences associated with expressing N otch1. The aims of this study were to characterise the expression of human cell‐surface N otch1 in cord blood ( CB ) CD 34 + cells and to study the function of N otch in CD 34 + cells in vitro . Methods A monoclonal antibody against the extracellular domain of N otch1 was developed, and N otch1 expression in CB CD 34 + cells was assessed by flow cytometry. CB CD 34 + cells were sorted on the basis of their N otch1 expression and cultured in serum‐free media. Single sorted CD 34 + CD 38 − N otch1 + / − cells were cultured for 8 wks on murine stroma monolayers and assayed for stem cell activity and lineage potential using a cobblestone area‐forming cell ( CAFC ) assay. Results Cell‐surface N otch1 expression was characterised in various primitive CD 34 + cell compartments including a small subpopulation of CD 34 + CD 38 − cells. We found the CD 34 + CD 38 − N otch1 + population to be enriched for stem cell activity. Moreover, CD 34 + CD 38 − N otch1 + , but not N otch1 − cells, demonstrated multilineage potential. Conclusions These data show that N otch1 is expressed on a functionally distinct subpopulation of CD 34 + cells that is highly enriched for stem cell activity and multilineage potential and could suggest that N otch1 could be used as a novel stem cell marker.