Effects of 11-ketotestosterone and temperature on inhibin subunit mRNA levels in the ovary of the shortfinned eel, Anguilla australis

Members of the transforming growth factor-b (TGFb) superfamily are important during early oogenesis in mammals. In this study, we tested whether documented effects of 11-ketotestosterone (11KT) on previtellogenic eel ovaries are mediated through affecting the expression of key ovarian TGFb genes. Furthermore, we investigated whether 11KT effects interacted with temperature. Accordingly, three thermal regimes were compared and their interaction with 11KT-mediated actions on expression of TGFb superfamily genes (chiefly inhibin subunits) evaluated in the eel (Anguilla australis). Inhibin subunit mRNA levels were also measured in ovarian explants cultured in vitro with 11KT and in ovaries from eels collected from the wild. In wild eels, inhibin-bA mRNA levels were higher in early than in previtellogenic eels; inhibin-a expression did not differ between stages, whereas that of inhibin-bB first decreased, then recovered with advanced developmental stage. Temperature was ineffective in modulating any of the end points, at least as long as a Q₁₀ adjustment was made to correct for 'metabolic dose'. However, 11KT affected the expression of inhibin-a compared to control fish, while those of inhibin-b subunit genes remained unaffected. In contrast, 11KT dramatically reduced mRNA levels of inhibin-b subunits in vitro, but had inconsistent effects on inhibin-a transcript abundance. We conclude that 11KT affects ovarian inhibin subunit gene expression, but effects are not in keeping with the changes seen during early oogenesis in eels from the wild. We further contend that in vivo temperature experiments are easily biased and that Q₁₀ corrections may be required to identify 'true' temperature effects.