Fig. 5. Location of NOS and NO production in Xenopus embryo skin. (A) Bright-field image of skin surface of wild-type embryo showing general topography of skin cells, some of which are pigmented. Small white spheres are yolk platelets. (B) Punctate pattern of NADPH-diaphorase labelling in wild-type skin cells (blue label). Note diffuse background pigmentation (darker, grey). (C) Similar pattern of NADPH-diaphorase labelling in skin of albino embryo, which lacks pigmentation. (D) nNOS immunofluorescence labels a similar proportion of skin cells. (E) Example of control nNOS experiment in which the primary antibody was omitted and no labeled cells were detectable. (F) DAF2 marks cells producing NO, with similar distribution in skin. White arrows indicate examples of strongly labeled cells (in B, C, D and F). Scale bars, 50 µm. See text and Materials and methods for further details.