Fig. 1. Example of image processing for the analysis of nuclear signals: ß-catenin staining of a parasagittal section, stage 10.25. 25 consecutive images of ß-catenin signal (A, red channel) and of DAPI staining (B, blue channel) were collected and collated automatically. The two images were merged (C), and filtered through a mask (D) created from the DAPI image. Because nuclei are small and their intensity difficult to visualize at low magnification, the nuclear area was expanded (E). To obtain semi-quantitative information, the intensity of the ß-catenin signal was translated into pseudocolors (F). The intensities were divided into five categories and translated into a color code (red to white) used for our drawings (G). Note that pale yellow can represent very weak or inhomogeneous signals. An identical procedure was used to analyze signals for P-Smad2 (red channel), P-Smad1 and P-MAPK (green channel).