Fig. 5. nNOS mRNA expression in skin and peripheral organs of the developing zebrafish. (A) Weak labelling of nNOS mRNA (arrows) in the skin of a 20 h.p.f. embryo, treated as a whole-mount preparation before clearing, compared to the strong labelling in the same region of a cryosection from another embryo (B). In the skin, labelling is preferentially present in epithelial cells of the tail (C) and around the yolk sac (D). (E) Absence of labelling after incubation with the sense probe. (F) The initial nNOS mRNA expression in body organs (at 55 h.p.f.), in cells located in the rostral portion of the forming gut (arrows). (G–I) Strong labelling of expression in transversal sections of nNOS mRNA in cells (arrows) located bilateral to the swim bladder (sb) and gut (gut), in relation to the pro-nephritic duct (asterisks in G and H) and to the nNOS-expressing cells in the medulla (arrowheads in G). Brownish structures are pigments. Scale bars: 50 µm (B,C,G); 5 µm (D); 10 µm (E,F,H,I).