Core binding factor in the early avian embryo: cloning of Cbfbeta and combinatorial expression patterns with Runx1.

We have isolated the avian ortholog for CBFβ, the common non-DNA binding subunit of the core binding factor (CBF) that has important regulatory roles in major developmental pathways. CBFβ forms heterodimers with the DNA-binding Runx proteins and increases their affinity for DNA and their protein stability. Here, we describe the Cbfβ expression pattern during the first 4 days of chick embryo development, with a special interest in the developing hematopoietic system. We have compared its expression pattern to that of Runx1, which is crucial for the generation of definitive hematopoietic cells, and to other hematopoietic- or endothelial-specific markers (c-Myb, Pu.1, CD45, c-Ets-1 and VE-Cadherin). Initially, Cbfβ is widely expressed in the early mesoderm in both the yolk sac and the embryo proper, but later its expression becomes restricted to specific organs or cell types. We have found that Cbfβ expression overlaps with Runx1 in the hematopoietic system and neural tube. The somitic and mesonephric structures, however, express Cbfβ in the absence of detectable Runx1. Finally, Cbfβ and Runx1 display multiple combinatorial patterns in the endoderm and in specific nerves or ganglia. Taken together, we show that Cbfβ exhibits a dynamic expression pattern that varies according to the organ, cell type or developmental stage. By revealing multiple combinatorial patterns between Cbfβ and Runx1, these data provide new insights into the role of CBF during early development.