Cell-tracing experiments in chicken (Jaffredo et al., 2000; Jaffredo et al., 1998) and mouse (Chen et al., 2009; de Bruijn et al., 2002; Sugiyama et al., 2003; Zovein et al., 2008) species indicate that IAHCs derive from hemogenic ECs through an Endothelial-to-Hematopoietic Transition (EHT).