In poikilothermic vertebrates, sex determination is sometimes influenced by environmental factors such as temperature. However, little is known about the molecular mechanisms underlying environmental sex determination. The medaka (Oryzias latipes) is a teleost fish with an XX/XY sex determination system. Recently, it was reported that XX medaka can be sex-reversed into phenotypic males by high water temperature (HT; 32-34 degrees C) treatment during the sex differentiation period. Here we report that cortisol caused female-to-male sex reversal and that metyrapone (an inhibitor of cortisol synthesis) inhibited HT-induced masculinization of XX medaka. HT treatment caused elevation of whole-body levels of cortisol, while metyrapone suppressed the elevation by HT treatment during sexual differentiation. Moreover, cortisol and 33 degrees C treatments inhibited female-type proliferation of germ cells as well as expression of follicle-stimulating hormone receptor (fshr) mRNA in XX medaka during sexual differentiation. These results strongly suggest that HT induces masculinization of XX medaka by elevation of cortisol level, which, in turn, causes suppression of germ cell proliferation and of fshr mRNA expression.
A homolog of the serinehhreonine protein kinase (~3 4~~~' ) , encoded by the cdcZf gene of the fission yeast (Schizosaccharomyces pombe), is a catalytic subunit of maturation-promoting factor and a key regulator of the cell cycle. We have raised a monoclonal antibody against the most conserved amino acid sequence, the PSTAIR sequence (EGVPSTAIREISLLKE) of ~3 4~~~' This antibody recognizes 31 -34 kDa proteins by immunoblotting in all species examined so far. The proteins recognized by the anti-PSTAIR antibody are probably either ~3 4~~~' itself or proteins highly homologous to ~3 4~~~' in the given species, since, in all species studies to date, they are all precipitated with p13suc1, the fission yeast S U C~+ gene product, which binds to ~3 4~~~' with high specificity. The anti-PSTAIR imrnunoprecipitate had no histone H1 kinase activity and did not contain cyclin 6, suggesting that the PSTAIR region is masked when ~34'~'' forms a complex with cyclin B as an active kinase. lmmunoblotting with the anti-PSTAIR antibody demonstrated that the fastest-migrating form of ~3 4~~~' homologues becomes abundant, when oocytes mature or the cell enters M phase. The possible significance of this observation is discussed in relation to the phosphorylation and activity state of p34cdc2 The observed broad cross-reactivity of the anti-PSTAIR antibody against ~34'~'' homologues in various species should permit us to examine the role of ~34'~'' homologues in the regulation of the cell cycle in a variety of organisms.
I analyzed stomach contents of the American bullfrog, Rana catesbeiana, in the Mizorogaike Pond of Kyoto, Japan. As a result, adult bullfrogs were found to feed predominantly on crayfish, and juveniles eat diverse arthropods. A wide variety of aquatic organisms occurred in the diet of both adult and juvenile bullfrogs.
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