M. N. Skoblina

Aquaporins in gametogenesis of vertebrate animals

A review of the data on the presence, localization, and supposed role of aquaporin water channels in oocytes of Xenopus laevis, oogenesis and maturation of teleosts Sparus auratus and Oncorhynchus mykiss, oogenesis and oocyte maturation of rats and mice, and spermatogenesis of several mammalians.

Hydration of oocytes in teleost fishes

Data on the hydration of oocytes in teleost fishes during maturation stimulated by gonadotropic or steroid hormones in vivo and in vitro are reviewed. The cause of hydration, its dynamics, and some mechanisms ensuring uptake of water and ions by the oocyte are considered.

In vitro stimulation of oocyte ovulation in teleosts by gonadotropic and steroid hormones

Published data on in vitro stimulation of oocyte maturation and ovulation by gonadotropic and steroid hormones in different teleost species are reviewed. The involvement of meiosis-inducing steroids, eicosanoids, and nuclear progestogen receptor in the mechanism of ovulation induction is considered.

Stimulation of in vitro Oocyte Ovulation by Progesterone and Homologous Pituitary Gonadotropic Hormone in Sturgeons

We showed that the percentage of sturgeon oocytes ovulating in vitro in Ringer solution modified for sturgeons (RMS) considerably depends on the concentration of sodium bicarbonate and the concentration of progesterone. Under optimal conditions (0.5 g/L of sodium bicarbonate and 30 ng/mL of progesterone), it can be higher than 80. Oocytes that matured and ovulated under such conditions are capable of normal development. In the best case, approximately 70% of developing embryos (of the number of ovulated oocytes) reach the stage of hatching (dead-line of observation). This method of producing offspring based on the insemination of oocytes that have matured and ovulated in vitro can be used in work with single females of rare and disappearing sturgeon species.

Involvement of Gap Junctions in Stimulation of in vitroMaturation of the Common Frog Oocytes by Low Progesterone Concentrations

The inhibitor of gap junctions 18α-glycerretinic acid inhibits the maturation of follicle-enclosed common frog oocytes stimulated by low progesterone concentrations. The inhibitory effect of 18α-glycyrrhetinic acid does not depend on concentrations within the limits of 5–40 μM. The progesterone concentrations, at which oocyte maturation can be inhibited, differed markedly in different females. The inhibitory effects of actinomycin D (5 μg/ml) and 18α-glycyrrhetinic acid (5 μg/ml) were expressed when the same progesterone concentrations were used. When injected in an intact oocyte, Lucifer yellow was transferred into the follicle cells, thus suggesting the presence of gap junction between these latter and the oocyte. The data obtained suggest that the previously described transcription-dependent factor formed in the follicle cells under the influence of low progesterone concentrations and stimulating oocyte maturation is transferred in the oocyte via gap junctions.

Hormonal induction of in vitro maturation and ovulation of loach oocytes and obtaining egg cells capable of fertilization and development

Loach oocytes that have reached a definitive size and are surrounded by follicular envelopes are capable of maturation and ovulating under the effect of 1 μg/mL progesterone in 75% Leibovitz medium with 1 g/L sodium bicarbonate or with pH adjustment to 9.0 by 1 N sodium hydroxide. Inseminated eggs are developed until the stage of prelarvae when adding 20% bovine serum to the incubation medium. Substitution of the bovine serum with 10–20% loach ovarian fluid or 20% carp ovarian fluid provides more complete development of inseminated eggs until the stage of larva that pass to active feeding.

Maturation of the Follicle-Enclosed Common Frog Oocytes Stimulated by Low Progesterone Concentrations Depends on Transcription

The maturation of follicle-enclosed common frog oocytes stimulated by low progesterone concentration is inhibited by actinomycin D (5 μg/ml).The concentrations of progesterone, at which oocyte maturation was inhibited by actinomycin D, varied with the season and were different in different females. The inhibitor of steroidogenesis aminogluthetimide (100 μg/ml) did not suppress the maturation of follicle-enclosed oocytes in most experiments, which was induced by both high and low progesterone concentrations. The induction of maturation of the defolliculated (“denuded”) oocytes required lower progesterone concentrations than of the follicle-enclosed oocytes and, in addition, the maturation of denuded oocytes was not suppressed by actinomycin D. Thus, it was shown for the first time that low doses of progesterone induced the maturation of amphibian oocytes while acting on the follicle wall cells and this process depended on transcription. The factor inducing or enhancing maturation, which is formed in the follicle cells in the presence of low progesterone concentrations, remains as yet unknown.

Hormone-induced in vitro maturation and ovulation of Danio rerio oocytes and production of eggs capable of fertilization and futher development

It is common knowledge that zebrafish, Danio rerio, oocytes in their follicular envelope that have reached definitive size undergo in vitro maturation in 90% Leibovitz’s medium, pH 9.0, when treated with 17α, 20β-dihydroxyprogesterone and acquire developmental competence but do not ovulate (Seki et al., 2008). We have demonstrated that zebrafish oocytes that have undergone maturation under the indicated conditions ovulate when treated with prostaglandin F2α (5 μg/mL) and/or 20% carp ovarial fluid and are capable of development towards the actively feeding larvae upon fertilization (the maximum follow-up period).

Role of hydration in ovulation of common frog oocytes in vitro

Stimulation of ovulation of the common frog Rana temporaria oocytes with homologous pituitary extract caused an increase in their volume. Factors that are known to inhibit hydration in teleostean oocytes (potassium-free Ringer solution and inhibitor of Na+,K+-ATPase—ouabain), as well as aquaporin inhibitors (mercuric chloride and methylmethanethiosulphonate) inhibited also homologous pituitary extract-induced volume increase in follicle-enclosed oocytes and led to reduced percentage of ovulated oocytes. Volume of denuded oocytes remained unchanged in the course of maturation when exposed to progesterone or other treatments. The data obtained suggest that stimulation of oocyte ovulation in the common frog caused an increase in their hydration that is necessary for their ovulation but this did not occur in denuded cells.

Influence of culture medium osmolality on maturation and ovulation of common frog oocytes stimulated in vitro by pituitary extract or progesterone

The influence of diluted Ringer solution on ovulation and maturation of common frog oocytes stimulated in vitro by homologous pituitary extract (0.005 pit/ml) or progesterone (1 μg/ml) was studied. During hibernation, the dilution of Ringer solution led to a decreased percentage of oocytes ovulated and matured under the influence of both inducers. As the season of reproduction approached, the dependence of oocyte maturation and ovulation on the Ringer solution dilution was reduced. Possible causes of different dependence of the ovulation of amphibian and sturgeon oocytes stimulated by gonadotropic hormones or progesterone on the culture medium osmolality is discussed.