Mast cells originate from EMP at 28 to 48 hpf. Double WISH using digoxigenin-labeled RNA antisense probe to zebrafish cpa5 stained with Fast Red and fluorescein-labeled RNA antisense probe to zebrafish lmo2 demonstrate coexpression of the zebrafish EMP marker lmo2 with the mast cell specific marker cpa5 at the ALM and posterior blood island (PBI) at 28 hpf, and at both the ALM and the CHT at 48 hpf (40× objective, Z1 inverted stereo-microscope; Carl Zeiss).