Specifically expressed in the hematopoietic lineage during embryogenesis; first expressed at the late blastula stage around the blastoderm margin. During gastrulation, restricted to the ventral mesoderm, the presumptive prechordal plate and the dorso-marginal cells of the organizer. At the 3-somite stage, strongly expressed in a caudal domain (marking the erythroid lineage) and a cephalic domain of the lateral mesoderm. At the 8- to 10-somite stage, caudal expression is in two bands of lateral mesoderm which later converge at the midline. Anterior expression is also in two bands of lateral mesoderm which converge as two patches at the midline by the 15-somite stage, with increased scattering of single cells (macrophage precursors) away from the midline to the yolksac. Once at the yolksac, expression is lost. By 20-24 hours post-fertilization (hpf), expressed in proerythroblasts in the erythroid blood island centered above the uro-genital opening. Expression persists in circulating erythroblasts but is lost in mature erythrocytes.