Commitment to the B-lymphoid lineage depends on the transcription factor Pax5

The Pax5 gene encoding the B-cell-specific activator protein (BSAP) is expressed within the haematopoietic system exclusively in the B-lymphoid lineage, where it is required in vivo for progression beyond the pro-B-cell stage. However, Pax5 is not essential for in vitro propagation of pro-B cells in the presence of interleukin-7 and stromal cells. Here we show that pro-B cells lacking Pax5 are also incapable of in vitro B-cell differentiation...