| Summary: | 碩士 === 國立中興大學 === 生命科學系所 === 101 === Different morphologies and functions of gill ionocytes are illustrated in seawater (SW) and fresh water (FW) teleosts. In SW-type ionocytes, the apical membrane invaginates to form a pit exhibited ion secretion. In FW-type ionocytes exhibited ion absorption, the apical membrane is flat with microvilli. Brackish medaka, Oryzias dancena, used as a good species for studies of ionoregulatory mechanisms. In previous studies, the higher gene and protein expressions of VILL determined in the FW-acclimated medaka than in the SW fish. The VILL protein was localized to the apical region of FW-type ionocytes in the brackish medaka. The present study demonstrated that the expression of VILL associated with remodeling of morphologies in the ionocytes response to osmotic challenges. There were two chapters: The first chapter compared morphologies and characteristics between SW-type and FW-type ionocytes. Ultrastructures of ionocytes in the gill of SW- and FW-acclimated medaka were observed by transmission electron microscope. Apical surface morphologies of SW-type and FW-type ionocytes were hole-type and flat-type with microvilli, respectively. In addition, this study demonstrates that a good experimental tissue, inner opercular membrane, was easily observed ionocytes compared to the gill by the combined techniques of fluorescent staining and scanning electron microscopy. It was a reliable image showed that typical morphologies of apical surfaces of SW-type and FW-type ionocytes were investigated in the opercular membranes of the brackish medaka. The VILL was specifically localized to the apical region along with microvilli in the FW-type ionocytes of medaka. In the secondary chapter, differential expression of VILL associated with remodeling of apical morphologies in the ionocytes when fish response to hyperosmotic and hypoosmotic challenges. When the medaka transfer from FW to brackish water (BW) or SW, flat-type ionocytes were transformed into hole-type ionocytes in the inner opercular membrane. The changes in the apical morphologies correlated with the disappeared expression of the apical VILL by immunofluorescent staining. Meanwhile, immunoblots of gill VILL protein had a downward trend. On the other hand, two hypoosmotic transfer experiments were performed. Transformed types of ionocytes in the opercular membrane of VILL- group and VILL+ group from hole-type cell were compared when the fish exposed to FW for 1 day. The apical surfaces of medaka ionocytes in the VILL- group were bigger and more convex than VILL+ group. In addition, obvious microvilli were found in the apical openings of the VILL+ ionocytes rather than those of VILL- ionocytes. Taken together, the present study illustrated a new molecular marker, VILL antibody, to distinguish the FW-type ionocytes. The VILL was involved in the formation of apical microvilli and size of apical surface in the transformation of ionocytes when the medaka responsed to osmotic challenges.
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