http://aerg.canberra.edu.au/library/sex_general/2002_Devlin_Nagahama_sex_determination_in_fish_review.pdf

Sex determination and sex differentiation in fish: an overview of genetic, physiological, and environmental influences

A period of oocyte growth is followed by a process called oocyte maturation (the resumption of meiosis) which occurs prior to ovulation and is a prerequisite for successful fertilization. Our studies using fish models have revealed that oocyte maturation is a three-step induction process involving gonadotropin (LH), maturation-inducing hormone (MIH), and maturation-promoting factor (MPF). LH acts on the ovarian follicle layer to produce MIH (17α, 20β-dihydroxy-4-pregnen-3-one, 17α, 20β-DP, in most fishes). The interaction of ovarian thecal and granulosa cell layers (two-cell type model), is required for the synthesis of 17α,20β-DP. The dramatic increase in the capacity of postvitellogenic follicles to produce 17α,20β-DP in response to LH is correlated with decreases in P450c17 (P450c17-I) and P450 aromatase (oP450arom) mRNA and increases in the novel form of P450c17 (P450c17-II) and 20β-hydroxysteroid dehydrogenase (20β-HSD) mRNA. Transcription factors such as Ad4BP/SF-1, Foxl2, and CREB may be involved in the regulation of expression of these steroidogenic enzymes. A distinct family of G-protein-coupled membrane-bound MIH receptors has been shown to mediate non-genomic actions of 17α, 20β-DP. The MIH signal induces the de novo synthesis of cyclin B from the stored mRNA, which activates a preexisting 35 kDa cdc2 kinase via phosphorylation of its threonine 161 by cyclin-dependent kinase activating kinase, thus producing the 34 kDa active cdc2 (active MPF). Upon egg activation, MPF is inactivated by degradation of cyclin B. This process is initiated by the 26S proteasome through the first cut in its NH2 terminus at lysine 57.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1440-169X.2008.01019.x

Regulation of oocyte maturation in fish.

http://digital.csic.es/bitstream/10261/44729/1/Taranger%20et%20al_%2c%20GCE.pdf

Control of puberty in farmed fish

https://digital.csic.es/bitstream/10261/44722/1/Mylonas_Fostier_Zanuy-GCE.pdf

Broodstock management and hormonal manipulations of fish reproduction

https://digital.csic.es/bitstream/10261/44879/1/Perspectives%20on%20fish%20gonadotropins%20and%20their%20receptors%20Levavi%20Sivan%20et%20al%202010%20Gen%20Comp%20Endocrinol.pdf

Perspectives on fish gonadotropins and their receptors.

Receptors for two salmon gonadotropins, GTH I and GTH II, were localized by use of in vitro ligand autoradiography of coho salmon gonads at various stages of sexual maturation. The results in both sexes revealed the presence of two types of GTH receptors: type I (GTH-RI), which interacts with both GTHs, and type II (GTH-RII), which interacts specifically with GTH II. GTH-RI was found at all stages of spermatogenesis examined and was localized on cells that were most likely Sertoli cells; however, it could not be determined whether GTH-RI was also localized on Leydig cells. In contrast, GTH-RII was found only in Leydig cells in the testis from a spermiating fish. In the vitellogenic ovary, GTH-RI was localized in the thecal layer and intensely on granulosa cells; in the preovulatory follicle, in contrast, GTH-RI was found in the thecal layer and in interstitial connective tissue, but not in the granulosa layer. Among all the stages of oogenesis examined, only granulosa cells of the preovulatory follicle exhibited GTH-RII. The appearance of GTH-RII coincides well with the increase in plasma levels of GTH II that occurs during final oocyte maturation and spermiation in coho salmon. The nature, distribution, and timing of appearance of these two receptors can explain, at least in part, the results of previous studies on steroidogenic activities of the two GTHs. The present study also suggests the functional homology of salmon GTH I and GTH II to mammalian FSH and LH, respectively, during gonadal development.

/pdf/localization-of-two-gonadotropin-receptors-in-the-salmon-4t46a27rqv.pdf

Localization of two gonadotropin receptors in the salmon gonad by in vitro ligand autoradiography.

The possible existence of distinct receptors for salmon gonadotropins (GTH I and GTh II) and the distribution of the receptor(s) were studied through examination of the binding of coho salmon (Oncorbynchus kistuch) GTh I and GTH II to membranes from thecal layers and granulosa cells of salmon ovaries. Purified coho salmon gonadotropins were iodinated by the lactoperoxidase method. Crude membrane preparations were obtained from thecal layers, granulosa cells, and whole ovaries of coho salmon in the postvitdllogenic/preovulatory phase. Binding of “5I-GTH I to membranes from thecal layers, granulosa cells, and whole ovaries, and binding of “51-GTh II to thecal layer cell membranes could be inhibited by both GTHs, but GTh I was more potent than GTh II. In contrast, GTh II was more potent than GTh I in inhibiting “5I.GTH II binding to membranes from granulosa cells and whole ovaries, but the inhibition curves were not parallel. Scatchard plot analysis suggested that there was a single type of receptor in the thecal layers for both GTHs, whereas in the granulosa cells there was more than one type of receptor for both GTHs. Based on these results, a two-receptor model for the postvitdllogenic/preovulatory salmon ovary is proposed with the following features: 1) there are two types of gonadotropin receptors in the salmon ovary, type I and type IL; 2) the type I receptor binds both GTHs, but with higher affinity for GTh I, whereas the type II receptor is highly specific for GTh II and may have only limited interaction with GTh I; and 3) the type I receptor is present in both thecal cells and granulosa cells, whereas the type II receptor is present in granulosa cells.

/pdf/a-two-receptor-model-for-salmon-gonadotropins-gth-i-and-gth-xppurv9qso.pdf

A two-receptor model for salmon gonadotropins (GTH I and GTH II).

Circulating concentrations of estradiol (E2), vitellogenin (VTG), thyroxine (T4), triiodothyronine (T3) and insulin were measured in reproductively maturing four and five year-old Atlantic salmon. Blood samples were collected from the fish in seawater for one year prior to their spawning in November in fresh water. In females, E2 and VTG were low but detectable from December to July, and then increased to peak levels in September and October. Plasma levels of T4 and T3 were relatively constant in winter and spring, and decreased in July. Plasma concentration of T4 increased in November when the fish returned to fresh water. Plasma T3 levels remained low during the autumn. Both T4 and T3 levels tended to be higher in males than in females during September through November. Plasma insulin concentrations increased during the spring to peak values in May, and then decreased in June and July in fish of both sexes. There was a significant elevation of plasma insulin in males during October, and the levels in males tended to be higher than those found in females during final maturation.

Relationship between metabolic and reproductive hormones in salmonid fish.

This study was designed to optimize binding conditions of salmon gonadotropins (GTH I and GTH II) to membrane preparations of salmon gonadal tissues. Coho salmon (Oncorhynchus kisutch) GTH I and GTH II were radioiodinated by lactoperoxidase method. Binding conditions were characterized using membrane preparations from coho salmon postovulatory ovaries. The optimal conditions for specific binding were the following: pH 7.5, 20–40 mM MgCl2, 15°C, ⩾ 24 hr incubation time. Specific binding of 125I-GTH I or 125I-GTH II can be displaced by (in order of relative potency from high to low) GTH I, GTH II, GTH I β-subunit, and GTH II β-subunit. GTH α-subunit did not displace labeled GTHs, but the mixture of α- and β-subunits. GTH but the mixture of α- and β-subunits was more potent than the β-subunits alone, indicating that recombination of subunits probably occurred. In membranes of postovulatory ovaries, the affinity of the receptor(s) for GTH I was higher, Kd = 0.87 ± 0.12 nM (mean ± SEM), than that for GTH II, Kd = 2.76 ± 0.33 nM; but the receptor density (capacity) was lower for GTH I (31.02 ± 3.72 fmol/mg protein) than that for GTH II (47.01 ± 4.77 fmol/mg protein). Specific binding for both GTH I and GTH II was also detected in membranes of ovaries and testes of immature coho salmon. These resuls suggest the presence of some shared and some separate binding sites for the two gonadotropins.

Liguang Yan

Papers

Localization of two gonadotropin receptors in the salmon gonad by in vitro ligand autoradiography.

A two-receptor model for salmon gonadotropins (GTH I and GTH II).

Relationship between metabolic and reproductive hormones in salmonid fish.

Binding of gonadotropins (GTH I and GTH II) to coho salmon gonadal membrane preparations

AbstractAn overview of the biological activities and receptors for salmon gonadotropin I and gonadotropin II