Fig. 4. Localization of carbonic anhydrase in trophosome lobules of Riftia pachyptila. (A—D) In situ hybridization of carbonic anhydrase mRNA with DIG-labeled riboprobe. (A) Negative control, showing the organization of the trophosome with numerous lobules (L) bathing in coelomic fluid (CF). (B—D) Section of a lobule composed of a central efferent vessel (EV), peripheral afferent vessels (AV), bacteriocytes (BC) and peritoneal cells (PC) in the extreme periphery of the lobule. Arrowheads indicate positive hybridization with the riboprobe in the bacteriocytes (C) and in the peritoneal cells (D). (E) Corresponding protein immunolocalization using rabbit anti-chick CA II antiserum with (F) a detailed portion (boxed area in E) focusing on CA labeling in the bacteriocytes filling the lobule. (G,H) Histochemical localization of CA with DNSA (G) and corresponding result of competition with Ethoxyzolamide (H). Scale bar, 150 µm (A); 50 µm (B,E,G,H); 15 µm (C,D,F).