In vitro differentiation of c-myb(-/-) ES cells reveals that the colony forming capacity of unilineage macrophage precursors and myeloid progenitor commitment are c-Myb independent

Mice homozygous for an inactivated c-myb allele exhibit embryonic (primitiv e) blood formation but die at about day 15 of gestation because of a failur e to generate adult (definitive) haemopoiesis. Recently, it has been shown that commitment to definitive haemopoiesis does occur ill vivo, but that so me point in the subsequent development towards the differentiated lineages is compromised. Here we have asked whether it is possible to demonstrate th is same distinction between the development of primitive and definitive hae mopoiesis during the in vivo differentiation of c-myb null ES cells, and wh ether this can be used to define more precisely at which developmental stag e the absence of c-Myb blocks the adult haemopoietic lineages. We investiga ted the kinetics of progenitor formation and commitment to differentiation using a combination of colony forming assays and analysis of RNA and surfac e antigen expression. Primitive unilineage macrophage and erythroid precurs or commitment could develop in the absence of c-Myb. No precursors characte ristic of definitive haemopoiesis were detected; nevertheless, we could sho w the expression of programme of transcription and surface antigens which i s consistent with the appearance of definitive progenitors blocked at an ea rly multipotential stage.