Immunohistochemical evidence identifying the site of androgen production in the ovary of the protogynous grouper Epinephelus merra

Androgen plays an important role in the developing ovaries of female fish. However, little is known regarding either the sites of production of androgen or its functional roles. In the present study, we investigated immunohistochemically the localization of cholesterol-side-chain-cleavage (P450scc) and cytochrome P45011-hydroxylase (P45011) with antibodies P450scc and P45011 in the ovary of the female honeycomb grouper Epinephelus merra during its reproductive cycle. Clusters of strongly immunopositive cells, with 100–1000 cells in each cluster, against both P450scc and P45011, were observed throughout the annual reproductive cycle in tissue near blood vessels in the tunica ovary surrounding the outer periphery of the ovary. The ultrastructural characteristics of these cells showed that they were steroid-producing cells. In contrast, immunopositive cells against P450scc but not against P45011 were localized in the theca layer surrounding the outer periphery of oocytes. These results suggest that two distinct steroid biosynthesis sites exist in the ovary and that cells at the two sites differ functionally. The only cells that biosynthesize 11-ketotestosterone are found in clusters in the vicinity of blood vessels; they possibly play a physiological role in oocyte growth and gonadal restructuring during the sex change of individuals of this species. CREST, JST (Japan Science and Technology Corporation), and the Takeda Science Foundation provided grants supporting this work. This study was also partially supported by a grant for the 21st century COE project entitled, The Comprehensive Analyses of Biodiversity in Coral Reef and Island Ecosystems in Asian and Pacific Regions. We also gratefully acknowledge a Japanese Government (Monbukagakusho) Scholarship.