Differentiating embryonal stem cells are a rich source of haemopoietic gene products and suggest erythroid preconditioning of primitive haemopoietic stem cells

The difficulties associated with studying molecular mechanisms important in hemopoietic stem cell (HSC) function such as the problems of purifying hom ogeneous stem cell populations, have prompted us to adapt the murine ES cel l system as an in vitro model of HSC generation and function. We now report that careful analysis of the time course of HSC generation in differentiat ing ES cells allows them to be used as a source of known and novel hemopoie tic gene products. We have generated a subtracted library using cDNA from E S cells collected just prior to and just following the emergence of HSCs. A nalysis of this library shows it to be a rich source of known hemopoietic a nd hemopoietic related gene products with 44% of identifiable cDNAs falling into these camps. We have demonstrated the value of this system as a sourc e of novel genes of relevance to HSC function by characterizing a novel mem brane protein encoding cDNA that is preferentially expressed in primitive h emopoietic cells. Intriguingly, further analysis of the known components of the subtracted library is suggestive of erythroid preconditioning of the E S cell-derived HSC. We have used dot-blot and in situ analysis to indicate that this erythroid preconditioning is probably restricted to primitive but not definitive HSC.