Characterisation of Wnt gene expression during the differentiation of murine embryonic stem cells in vitro: role of Wnt3 in enhancing haematopoietic differentiation

The first haematopoietic stem cells in mammalian and non-mammalian vertebra tes are derived from mesoderm, therefore genes that are important in mesode rm patterning and formation might also play an essential role in haematopoi etic stem cell commitment and differentiation. Several members of the Wnt g ene family are expressed in very specific patterns in embryonic mesoderm an d have previously been shown to act as haematopoietic growth factors. In or der to investigate in detail the role that such secreted proteins play in t he biology of early haematopoietic commitment we have used in vitro differe ntiation of murine embryonal stem (ES) as a model system. Using reverse-tra nscriptase polymerase chain reaction analysis we identified several candida te Wnt genes whose expression pattern was consistent with a role in generat ion, maintenance and/or differentiation of early haematopoietic progenitor cells including three genes previously shown to have a role in haematopoies is (Wnt5a, Wnt2b and Wnr10b). The most interesting candidate was Wnt3. beca use of its strong and regulated expression during in vitro differentiation of murine ES cells as well as its early embryonic expression in mesoderm. O verexpression of Wnt3 was sufficient to cause a consistent increase in the number of embryoid bodies committing to haematopoiesis further strengthenin g the evidence that this protein can enhance haematopoietic commitment duri ng in vitro differentiation of ES cells. In addition, overexpression of Wnt 3 caused a marked upregulation of Brachyury expression, thus providing some evidence that Brachyury may be one of the target genes for the Wnt3 signal ling pathway. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.