Erythroid-specific enhancer activity of intron7 of L fluviatilis nprl3. (A) Diagram of the L fluviatilis nprl3 gene and GFP reporter vectors used in transgenic enhancer reporter assays in P marinus. (B) Diagram of a 17-dpf P marinus embryo showing the circulatory system (red dashed lines) of the head and branchial arches. Dashed box indicates the region shown in panels C and D. (C) Still from supplemental Movie 1 showing erythroid-specific GFP reporter expression in circulation when intron7 of L fluviatilis nprl3 is used to drive GFP expression from the L fluviatilis hb2 promoter. (D) Still from supplemental Movie 2 showing erythroid-specific GFP reporter expression in circulation when the zebrafish MCS-R2 hb enhancer is used to drive GFP expression from the L fluviatilis hb2 promoter. Dotted white line in panels C and D outlines the embryo; original magnification, ×60. ba, branchial arches; dpf, days postfertilization; Dr, Danio rerio; h, heart; Lf, L fluviatilis; m, mouth.