m m s

iff po in co erythrocytes. Primitive erythropoiesis is a transient wave of hematopoiesis that specifically occurs in the yolk sac the vitelline and umbilical arteries (de Bruijn et al., 2000), matopoietic cells have a distinct tissue origin and support the view that these cells have distinct progenitor popula-the yolk sac provides a suitablemicroenvironment for both primitive and definitive hematopoiesis, although theparallel with the appearance of definitive lymphohemato- tive hematopoietic progenitor cells (Kennedy et al., 1997; opic trans-The ex vivo culture of embryonic and extraembryonic tissues revealed the embryonic origin of definitive hemato-plantation of hematopoietic tissues in Xenopus embryos also implied the presence of bipotential precursors (Turpenpoietic progenitors (Chen et al., 2011; Schulz et al., 2012). Perlingeiro et al., 2001). Orthotopic and heterot1997a),orplacenta (Gekas et al., 2005;OttersbachandDzier-zak, 2005). Multipotent hematopoietic progenitors pro-duced in an initial wave of definitive hematopoiesis lac