Suppression of P450 aromatase gene expression in sex-reversed males produced by rearing genetically female larvae at a high water temperature during a period of sex differentiation in the Japanese flounder (Paralichthys olivaceus)

Abstract

The phenotypic sex of many teleost fishes including flounders can be experimentally altered by treating embryos or larvae with varied temperatures or sex-steroid hormones. To analyse the sex determination mechanism, especially the role of cytochrome P450 aromatase (P450arom), an enzyme that catalyses the conversion of androgens to estrogens, in temperature-dependent gonadal sex differentiation in the Japanese flounder, we generated two populations of larvae, both having XX (genetic females) but each growing up to display all phenotypic females or males, by rearing the larvae at normal (18 C) or high (27 C) water temperatures from days 30 to 100 after hatching respectively. The larvae (XX) were produced artificially by mating normal females (XX) with gynogenetic diploid males (XX) which had been sex-reversed to phenotypic males by 17 -methyltestosterone.To study the role of P450arom in sex determination in the flounder, we first isolated a P450arom cDNA containing the complete open reading frame from the ovary. RT-PCR showed that P450arom mRNA was highly expressed in the ovary and spleen but weakly in the testis and brain. Semi-quantitative analyses of P450arom mRNA in gonads during sex differentiation showed that there was no difference in the levels of P450arom mRNA between the female and male groups when the gonad was sexually indifferent (day 50 after hatching). However, after the initiation of sex differentiation (day 60), the mRNA levels increased rapidly in the female group, whereas they decreased slightly in the male group. Similarly, estradiol-17 levels rose remarkably in the female group, yet remained constant in the male group.These results suggest that induction of sex reversal of genetically female larvae to phenotypic males by rearing them at a high water temperature caused a suppression of P450arom gene expression. Furthermore, we suggest that the maintenance of P450arom mRNA at very low levels is a prerequisite for testicular differentiation, while the increased levels are indispensable for ovarian differentiation.

Up-regulation of P450arom and down-regulation of Dmrt-1 genes in the temperature-dependent sex reversal from genetic males to phenotypic females in a salamander

“…Similar suppression of aromatase gene expression was observed in the temperature-dependent sex reversal of genetic females to phenotypic males in Japanese flounder reared at high temperature (Kitano et al 1999). Contrary to these, the reverse scenario is expected in H.…”

“…It was reported to be involved in not only normal development of ovary, but also temperature-dependent sex reversal (Chardard et al 1995;Chardard and Dournon, 1999: Kuntz et al 2003 in urodeles, TSD in many reptiles (Desvages et al 1993;Murdock and Wibbels 2003a), and natural sex changes (Liu et al 2004) and temperature-sensitive sex reversal (Kitano et al 1999) in fishes. We have shown in H. retardatus that sexual dimorphism in the P450arom expression was observed as early as 15 days after hatching when the morphological differentiation of gonads had not been occurred (Sakata et al 2005).…”

Molecular cloning of doublesex and mab-3-related transcription factor 1, forkhead transcription factor gene 2, and two types of cytochrome P450 aromatase in Southern catfish and their possible roles in sex differentiation

“…Until now, two aromatase genes (Cyp19a and Cyp19b) have been identified in fish (Chiang et al 2001, Kwon et al 2001. Several reports have demonstrated the involvement of aromatase in fish gonad differentiation (Chang et al 1997, Kitano et al 1999 and oocyte maturation (Bobe et al 2006).…”

“…These results suggest that Cyp19b is also involved in fish sex differentiation. Since Cyp19a expression is mainly restricted to the gonads, this gene is probably directly involved in the sex differentiation of the gonads (Chang et al 1997, Guiguen et al 1999, Kitano et al 1999, Kwon et al 2001. On the other hand, since Cyp19b is mainly expressed in the brain, this gene is conceivably involved in sex differentiation in an indirect manner (Kwon et al 2001, Chang et al 2005, Kazeto & Trant 2005, Sawyer et al 2006, probably through the brainpituitary-gonad axis.…”

Aromatase activity in the ovary and brain of the eastern mosquitofish (Gambusia holbrooki) exposed to paper mill effluent.

“…At least two forms of aromatase have been reported in mammals and fishes, with gonadal and brain forms coded for on two separate genes (30)(31)(32). Aromatase expression is constitutive in some tissues, but aromatase expression and activity can be altered by temperature, season, and various hormones, such as steroids (33)(34)(35). Exposure of embryonic alligators to the herbicide atrazine induces a significant increase in aromatase activity in the gonadadrenal-mesonephros of neonates (21).…”