Transgenic analysis of multienhancer constructs reveals distinct combinations able to drive expression to circulating erythroid or FL cells. Whole-mount staining (WM) and histologic sections of FL, dorsal aorta (DA), heart (H), yolk sac (YS), and peripheral vessels (V) from transgenic embryos harvested between E11.5 and E12.5. X-Gal reporter expression driven by the LMO2 1.3-kb extended pP (pPexLacZ) combined with candidate hematopoietic enhancers. The +1 construct is characterized by reduced endothelial and hematopoietic activity compared with pPex alone (Figure 3A). Addition of 5 putative hematopoietic enhancer elements (−75/−70/−25/−12/+1) induce specific expression in circulating erythrocytes and enhanced staining of FL. Systematic exclusion of elements −70, −25, and −12 reveals that the erythroid-specific expression can be attributed to the element −75, possibly in combination with element +1 (see −75 pPexLacZ+1 and −75 pPexLacZ). Robust FL expression, on the other hand, is conferred by collaboration of elements −25 and −12 (see −25 pPexLacZ+1, −12 pPexLacZ+1, −25/−12 pPexLacZ+1, and −25/−12 pPexLacZ).