Optimization of hybridization and POD reaction by dextran sulfate. (A, C, E, G) Lateral views of 1-dpf zebrafish embryos hybridized with a digoxigenin-labeled antisense RNA probe specific for dbx1a are shown with anterior to the left. Above each panel signal-to-noise ratios (s/n) are indicated and whether dextran sulfate was added (+) or not (-) to the hybridization buffer (Hyb) and/or TSA reaction. (B, D, F, H) Embryos hybridized without probe were used as negative controls to assess background noise. Black-and-white pictures were recorded with identical exposure times using an Orca digital camera (Hamamatsu) on an Axioplan II microscope (Carl Zeiss). Images were false-colored with help of the ImageJ software and no further adjustments or other image processing was performed. Scale bar = 100 μm.