Figure 4.

Expression of nos genes in developing gills of sturgeon, bichir, and shark embryos. The expression of nos2 in the gills of sterlet sturgeon Acipenser ruthenus (14 mm stage, a–c) and bichir Polypterus senegalus (stage 31, d,e); nos1 in the shark Scyliorhinus torazame (stage 27, g–i). Higher magnification views of the gill structure of (a,d,g) are shown in (b,e,h), respectively. The arrowheads indicate sectioning plane (a,d,g): transversal sections (c,f, 50 µm) and frontal section (I, 10 µm). gi, gill; yo, yolk; pf, pectoral fin. Scale bar in (a,d,g) is 0.5 mm. (Online version in colour.)