The sexual plasticity of the gonads is not retained after the completion of sex differentiation in vertebrates, except in some hermaphroditic species. Here, we report that the depletion of estradiol-17β (E2) by aromatase inhibitors (AI) for up to six months resulted in a functional female-to-male sex reversal in sexually-mature adults of two gonochoristic fish species, Nile tilapia and medaka. The sex-reversed fish showed a typical male pattern of E2 and androgen levels, secondary sexual characteristics, and male-like sex behavior, producing fertile sperm. Conversely, co-treatment of E2 inhibited AI-induced sex reversal. In situ hybridization of medaka gonads during AI-induced sex reversal indicated that cysts on the dorsal side of the adult ovaries are the origin of germ cells and Sertoli cells in the newly formed testicular tissue. Gonochoristic fish maintain their sexual plasticity until adulthood and E2 plays a critical role in maintaining the female phenotype.

Recent studies have suggested that the hypothalamic-pituitary-gonadal axis is involved in gonadal sex change in sex-changing teleosts. However, its underlying mechanism remains largely unknown. In this study, we focused on the distinct roles of two gonadotropins (GTHs), follicle-stimulating hormone (FSH) and luteinizing hormone (LH), in the protogynous hermaphrodite teleost, honeycomb grouper (Epinephelus merra). First, we investigated the expression pattern of mRNAs for GTH subunits (cga, fshb, and lhb) in the pituitaries from fish at the different sexual phases. Real-time RT-PCR analyses showed that fhsb mRNA levels in the female pituitary were low. However, fshb transcripts increased dramatically in association with testis development. In contrast, levels of cga and lhb mRNAs did not significantly vary during sex change. In addition, immunohistochemical observations of Fshb- and Lhb-producing cells in the pituitary, through the use of specific antibodies for detections of teleost GTH subunits, were consistent with sexually dimorphic expression of Fshb. In order to identify the role of GTH in gonad of honeycomb grouper, we treated females with bovine FSH (50 or 500 ng/fish) or LH (500 ng/fish) in vivo. After 3 wk, FSH treatments induced female-to-male sex change and up-regulated endogenous androgen levels and fshb transcripts, whereas LH treatment had no effect on sex change. These results suggest that FSH may trigger the female-to-male sex change in honeycomb grouper.

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Immediately before the transition from metaphase to anaphase, the protein kinase activity of maturation or M-phase promoting factor (MPF) is inactivated by a mechanism that involves the degradation of its regulatory subunit, cyclin B. The availability of biologically active goldfish cyclin B produced in Escherichia coli and purified goldfish proteasomes (a nonlysosomal large protease) has allowed the role of proteasomes in the regulation of cyclin degradation to be examined for the first time. The 26S, but not the 20S proteasome, digested recombinant 49-kD cyclin B at lysine 57 (K57), producing a 42-kD truncated form. The 42-kD cyclin was also produced by the digestion of native cyclin B forming a complex with cdc2, a catalytic subunit of MPF, and a fragment transiently appeared during cyclin degradation when eggs were released from metaphase II arrest by egg activation. Mutant cyclin at K57 was resistant to both digestion by the 26S proteasome and degradation at metaphase/anaphase transition in Xenopus egg extracts. The results of this study indicate that the destruction of cyclin B is initiated by the ATP-dependent and ubiquitin-independent proteolytic activity of 26S proteasome through the first cutting in the NH2 terminus of cyclin (at K57 in the case of goldfish cyclin B). We also surmise that this cut allows the cyclin to be ubiquitinated for further destruction by ubiquitin-dependent activity of the 26S proteasome that leads to MPF inactivation.

O ocyte maturation in lower vertebrates is triggered by maturation-inducing hormone (MIH), which acts on receptors located on the oocyte membrane and induces the activation of maturation-promoting factor in the oocyte cytoplasm (1-4). During the course of maturation, oocytes undergo drastic morphological changes associated with progression of the meiotic cell cycle, in which breakdown of the oocyte nuclear envelope [germinal vesicle breakdown (GVBD)] occurring at the prophase͞metaphase transition is usually regarded as a hallmark of the progress of oocyte maturation. Two MIHs, 17␣,20␤-dihydroxy-4-pregnen-3-one (17,20␤-DHP) and 17␣,20␤,21-trihydroxy-4-pregnen-3-one (20␤-S), have been identified in several fish species (5, 6). In goldfish, 17,20␤-DHP has been shown to induce oocyte maturation by stimulating the de novo synthesis of cyclin B, a regulatory subunit of maturationpromoting factor (7). Although progestins including 17,20␤-DHP and 20␤-S are the most potent steroid inducers of oocyte maturation in fish, other hormones such as deoxycorticosterone and testosterone, but not estradiol or its analogs, are also effective (8).Several endocrine-disrupting chemicals, Kepon and dichlorodiphenyldichloroethane, have been reported to antagonize MIH-induced meiotic maturation of fish oocytes in vitro (9). One of the environmental endocrine-disrupting chemicals (EEDCs), diethylstilbestrol (DES) is a nonsteroidal substance that was prescribed from the late 1940s to the early 1970s to pregnant women to prevent abortion, preeclampsia, and other complications of pregnancy. Male and female offspring exposed in utero to DES may develop multiple and neoplastic lesions of the reproductive tract, along with other changes, during development (10). Here we show that exposing fish oocytes to DES at a dose within a range similar to that used in experimental exposure to 17,20␤-DHP induces oocyte maturation. Estradiol-17␤ has been reported to be ineffective in inducing fish oocyte maturation (11, 12) and even inhibitory in several teleost species (13-15). Thus, the stimulatory effect of DES to induce fish oocyte maturation observed in this study has not been published previously. This report shows that EEDC can potentially induce oocyte maturation like an endogenous MIH, 17,20␤-DHP. Materials and MethodsMaterials. Goldfish were purchased from a local supplier and maintained at 15°C until used. Zebrafish were maintained at 28.5°C on a 14-h light͞10-h dark cycle (16). 17,20␤-DHP, DES, DES dimethyl ether (DM-DES), DES dipropionate (DP-DES), and 17␤-estradiol were purchased from Sigma. Dimethylstilbestrol (DMS) was a generous gift from J. Katzenellenbogen (University of Illinois, Urbana). 17␣-Estradiol, ethynylestradiol, butyl benzyl phthalate, di(2-ethylhexyl)-phthalate, and pentachlorophenol were obtained from Wako Pure Chemical (Osaka). Other chemicals were purchased as follows: hexestrol (HEX; ICN); trans,trans-dienestrol(␣-dienestrol) (DIES; U.S. Pharmacopeia, Rockville, MD); resveratorol (Calbiochem); DDTs (AccuStandard, New Haven, ...

Background: Sex change in fishes provides a good experimental model for understanding the mechanisms and plasticity of sex determination and differentiation. The three-spot wrasse, Halichoeres trimaculatus is a protogynous hermaphrodite. During sex change from female to male, the ovary is replaced by the testis through the degeneration of oocytes and subsequent spermatogenesis. In the present study, we cloned a cDNA-encoding gonadal soma-derived factor (GSDF) from protogynous wrasse and examined its expression pattern in the sexually mature gonads and the sex-changing gonad induced experimentally by aromatase inhibition. Results: Expression of gsdf was predominantly observed in the testis, and it was mainly localized to the supporting cells surrounding the spermatogonia. In the ovary, only slight expression of gsdf was observed in morphologically undifferentiated supporting cells in contact with oogonia. During sex change, strong expression of gsdf appeared first in the supporting cells surrounding the gonial germ cells before the onset of spermatogenesis. Thereafter, the expression of gsdf continually increased in the supporting cells surrounding the proliferating spermatogonia throughout the sex change. Conclusions: These results suggest that gsdf is involved in the proliferation of spermatogonia and subsequent spermatogenesis in both the testis and the gonad in the early stages of sex change. Developmental Dynamics 242:388-399, 2013. V C 2013 Wiley Periodicals, Inc.Key words: gsdf; sex change; protogyny; sexual plasticity; three-spot wrasse Key findings:Gsdf is predominantly expressed in the testis of protogynous wrasse and is mainly localized to the supporting cells surrounding the spermatogonia. Only slight expression of gsdf was observed in most of the supporting cells in the neighboring ovarian oogonia. Strong expression of gsdf appeared in the supporting cells surrounding the gonial germ cells, which are the originators of spermatogenic cells in the ovary, during sex change induced by aromatase inhibition. These results suggest that gsdf is involved in the proliferation of spermatogonia and subsequent spermatogenesis in the early stages of sex change.

HBO1, a histone acetyl transferase, is a co-activator of DNA pre-replication complex formation. We recently reported that HBO1 is phosphorylated by ATM and/or ATR and binds to DDB2 after ultraviolet irradiation. Here, we show that phosphorylated HBO1 at cyclobutane pyrimidine dimer (CPD) sites mediates histone acetylation to facilitate recruitment of XPC at the damaged DNA sites. Furthermore, HBO1 facilitates accumulation of SNF2H and ACF1, an ATP-dependent chromatin remodelling complex, to CPD sites. Depletion of HBO1 inhibited repair of CPDs and sensitized cells to ultraviolet irradiation. However, depletion of HBO1 in cells derived from xeroderma pigmentosum patient complementation groups, XPE, XPC and XPA, did not lead to additional sensitivity towards ultraviolet irradiation. Our findings suggest that HBO1 acts in concert with SNF2H–ACF1 to make the chromosome structure more accessible to canonical nucleotide excision repair factors.

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