Expression of the polycomb group gene bmi-1 in the early chick embryo.

Bmi-1 is a protooncogene of the polycomb group that has important functions in self-renewal of adult stem cells and maintenance of anterior identity along the embryonic body axis. Despite these important functions, surprisingly little is known about its distribution pattern in the embryo. Here, we have isolated the chick homologue of bmi-1 and examined its expression pattern from gastrulation through neurulation and establishment of organ rudiments. During gastrulation, bmi-1 transcripts were expressed in the epiblast cells adjacent to the primitive streak. During early nervous system development, robust expression was observed in the open neural plate and later in the dorsal neural tube and much of the brain. Bmi-1 expression was also present in the developing heart primordia and the sensory placodes. The data show that bmi-1 is present in, but not restricted to, tissue containing multipotent precursor cells.