Figure 4

Immunohistochemical micrographs of the gastrointestinal tract and different parts of swim bladder of Atlantic cod. (a) Pyloric caeca: epithelial cells of the caecal mucosal fold (MuFo; arrows) were Pis1-immunoreactive, and some positivity was also observed in the surrounding tissues (open arrow) and between each caecal portion (*). (b) Proximal intestine: cells in mucosal epithelium (thick arrows) and compound glands (thin arrows), cells in lamina propria (Lp) and mucosal epithelium (arrow heads) were also Pis1-immunoreactive. (c and d) Rectum: cytoplasm of mucosal epithelium (Ep) and cytoplasm of columnar cells in compound glands (Cg) shown in (c) and (d), respectively were Pis1-immunoreactive, while goblet cells (arrow heads) in both mucosal epithelium and compound glands were immunonegative. Some positive multi-granular cells (arrows) in submucosa tissue (Sm) shown in (d) were also Pis1-positive. (e) A weak immunoreactivity was observed in mucosal epithelial cells (thin arrow), while a stronger positive signal was observed in the neuronal cell bodies (thick arrows). (f) Gas gland (Gg) and the connective tissue of the submucosa (Sm) were Pis1-immunoreactive, while a weaker positive signal was observed in the rete mirabile (Rm). (g) Higher magnification of gas gland showing the immunoreactivity of the gas gland cells. Negative control (inset) of the serial sections treated with dilution buffer was Pis1-immunonegative (Larger images are seen in Additional file 1: Figure S4).