Stage of the estrous cycle at the time of pregnant mare's serum gonadotropin injection affects pre-implantation embryo development in vitro in the mouse

C57BL/6J mouse superovulation: schedule and age optimization to increase oocyte yield and reduce animal use

Superovulation protocols have been described for different mouse strains, however the numbers of animals used are still high and still little information is known about hormone administration schedules and estrous cycle phases. In this study, we aimed to optimize a superovulation protocol by injecting 5 IU of pregnant mare serum gonadotropin followed by 5 IU of hCG 48 h later, using three different schedules related to the beginning of the dark cycle (3, 5 and 7 pm) in a light cycle of 7 am to 7 pm, with light on at 7 am. C57BL/6J mice at 3, 4 and 5 weeks of age were used and the estrous cycle phase for times of PMSG and hCG injections was also analyzed. Total oocyte number was counted in the morning after hCG injection. Hormones given at 3 weeks of age at 3 pm (59 ± 15 oocytes) and 7 pm (61 ± 10 oocytes) produced a significantly higher oocyte number compared with oocytes numbers collected from females at the same age at 5 pm (P = 0.0004 and <0.0001 respectively). Females at 4 and 5 weeks of age produced higher numbers of oocytes when superovulated at 7 pm. No statistical differences between females at different phases of the estrous cycle were found. These results showed that in C57BL/6J mice, hormones should be given at 3 or 7 pm for females at 3 weeks of age, however older females should be superovulated closer to the beginning of the dark cycle to reduce female mouse use and increase the numbers of oocytes produced per female.

Ovum pick-up and in vitro maturation in spotted paca (Cuniculus paca-Linnaeus, 1766)

We tested FSHp, eCG and FSHp + eCG to establish ovum pick-up (OPU) and in vitro maturation method in spotted paca. Eight healthy adult females were subjected to each of four treatments to stimulate ovarian follicular growth. All females were subjected to a hormonal protocol using a single dose of 45 mg of injectable progesterone and single intramuscular injection of 0.075 mg d-cloprostenol on day 6. Ovarian stimulation was carried out as follows: in Group TFE (FSHp and eCG), animals were treated with a single dose of 80 mg of FSHp and 200 IU of eCG intramuscularly on day 6 after the application of progesterone; in Group TF (FSHp), they were treated with a single dose of 80 mg of FSHp intramuscularly on day 6 after application of progesterone; in Group treatment eCG, they were treated with 200 IU of eCG intramuscularly on day 6 after application of progesterone; and in Group TC (saline solution), 1 ml of saline solution was administered to control does. The OPU was performed between 22 and 26 hr after gonadotropin treatments. All recovered oocytes were placed into maturation media and incubated for 24 hr. There were no differences among the mean number of observed follicles, aspirated follicles and oocytes recovered per treatment. Oocyte maturation rates did not differ among groups, except, TF and treatment eCG oocytes had greater maturation rates than TC oocytes. In this study, gonadotropin administration failed to superovulate treated does and increase oocyte retrieval efficiency. Despite the feasibility of the procedure, further studies are needed to develop and refine hormonal protocols for oocyte recovery and in vitro maturation in this species.

Quality of Preovulatory (GV) Oocytes in Mice after Injection of eCG at Various Stages of the Estrous Cycle

We studied the influence of the estrous cycle on the morphology of preovulatory (germinal vesicle, GV) oocytes in mice and their capacity to meiotic maturation in vitro. After standard injections of eCG gonadotropin (PMSG, Follimag) to females at different stages of the estrous cycle, the maximum levels of GV oocytes (26±1/mouse) were isolated from the ovaries of animals injected with the hormone during estrus. The capacity of isolated GV oocytes to meiotic maturation in vitro decreased in the following order: estrus (75.5±2.3%), metestrus (67.9±3.4%), proestrus (57.8±4.4%), and diestrus (50.6±5.6%); the differences between estrus and diestrus/proestrus were significant (p<0.05). After eCG injections during estrus, GV oocytes differed from other oocytes by lesser total diameter, lesser diameter of cytoplasm, lesser thickness of zona pellucida, and moderately dilated perivitelline space. These signs reflected higher competence of the "estrous" GV oocytes for meiotic maturation in vitro. Hormone stimulation of females with eCG, with consideration for the stage of the estrous cycle, seems to be an effective method for improving the quality of GV oocytes isolated from mouse ovaries.

A rapid and efficient method for the collection of highly developmental murine immature oocytes using cilostazol, a phosphodiesterase 3A inhibitor

AIMS

The present study aims to define maturation, yield, health, and ease of collection of murine immature oocytes recovered using the conventional method or from mice treated with cilostazol.

MAIN METHODS

The conventional method included the superovulation of mice and the recovery of germinal vesicle (GV) or metaphase (MI) oocytes from preovulatory follicles. The cilostazol method included the oral treatment of superovulated mice with 7.5 mg cilostazol once or twice to result in the ovulation of MI or GV oocytes, respectively.

KEY FINDINGS

The cilostazol method resulted in >95% of GV or MI oocytes with a diameter range of 60-90 μm or 50.1-70 μm in comparison to <60.0% of GV or MI oocytes resulting from the conventional method, respectively (P < 0.0001). The cilostazol method resulted in GV oocytes having higher levels of co-occurrence of peripheral cortical granules (CG) and chromatin configuration of surrounded nucleolus and MI oocytes having higher levels of co-occurrence of normally organized spindles/chromosomes and peripheral CG with free domains than did the conventional method (P < 0.001). The cilostazol method was more time and labor efficient and resulted in higher oocyte yields of normal morphology than did the conventional method (P < 0.01).

SIGNIFICANCE

The presented method provides not only oocytes with uniform size and synchronized developmental maturation but also a technique of oocyte collection that is efficient and resourceful. It is possible that not all immature oocytes resulting from the conventional method are from preovulatory follicles nor have been developed adequately and consequently ovulated as opposed to the presented method.

Long-term exposure to very low doses of bisphenol S affects female reproduction

Bisphenols belong to the endocrine disruptors, affecting reproduction even in extremely low doses. Bisphenol S (BPS) has become widely used as a substitute for the earlier-used bisphenol A; however, its harmlessness is questionable. The aim of this study was to evaluate the effect of BPS on folliculogenesis and oocyte quality after in vivo exposure to low doses of BPS. Four-week-old ICR females (n = 16 in each experimental group) were exposed to vehicle control (VC), BPS1 (0.001 ng BPS.g/bw/day), BPS2 (0.1 ng.g/bw/day), BPS3 (10 ng.g/bw/day) and BPS4 (100 ng.g/bw/day) for 4 weeks. Ovaries were subjected to stereology and nano liquid chromatography-mass spectrometry (LC/MS). Simultaneously, metaphase II oocytes were obtained after pregnant mare serum gonadotrophin and human chorionic gonadotrophin administration, followed by immunostaining. In particular, mating and two-cell embryo flushing were performed. We observed that BPS decreases the amount of ovarian follicles and BPS2 (0.1 ng.g/bw/day) affects the volume of antral follicles. Accordingly, ovarian proteome is affected after BPS2 treatment. While BPS2 dosing results mainly in cytoskeletal damage in matured oocytes, the effects of BPS3 and BPS4 seem to be due instead to epigenetic alterations in oocytes. Arguably, these changes lead to observed affection of in vivo fertilization rate after BPS3 and BPS4 treatment. BPS significantly affects female reproduction astoundingly in extremely low doses. These findings underline the necessity to assess the risk of ongoing BPS exposure for public health.

Administration of Gonadotropins for Superovulation in Mice

For experiments that require large numbers of preimplantation mouse embryos, such as microinjection of zygotes, gonadotropins are administered to females before mating to increase the number of oocytes that are ovulated (i.e., to induce superovulation). Pregnant mare serum gonadotropin (PMSG) is used to mimic the oocyte maturation effect of the endogenous follicle-stimulating hormone (FSH), and human chorionic gonadotropin (hCG) is used to mimic the ovulation induction effect of luteinizing hormone (LH).

Removal of mouse ovary fat pad affects sex hormones, folliculogenesis and fertility

As a fat storage organ, adipose tissue is distributed widely all over the body and is important for energy supply, body temperature maintenance, organ protection, immune regulation and so on. In humans, both underweight and overweight women find it hard to become pregnant, which suggests that appropriate fat storage can guarantee the female reproductive capacity. In fact, a large mass of adipose tissue distributes around the reproductive system both in the male and female. However, the functions of ovary fat pad (the nearest adipose tissue to ovary) are not known. In our study, we found that the ovary fat pad-removed female mice showed decreased fertility and less ovulated mature eggs. We further identified that only a small proportion of follicles developed to antral follicle, and many follicles were blocked at the secondary follicle stage. The overall secretion levels of estrogen and FSH were lower in the whole estrus cycle (especially at proestrus); however, the LH level was higher in ovary fat pad-removed mice than that in control groups. Moreover, the estrus cycle of ovary fat pad-removed mice showed significant disorder. Besides, the expression of FSH receptor decreased, but the LH receptor increased in ovary fat pad-removed mice. These results suggest that ovary fat pad is important for mouse reproduction.

Superovulatory response, oocyte spontaneous activation, and embryo development in WMN/Nrs inbred rats

WMN/Nrs inbred rats have been widely used in radiation biology for years. However, their reproductive profile has never been examined. We examined various reproductive characteristics of WMN/Nrs inbred rats such as superovulatory response, oocytes spontaneous activation (OSA), and embryo development in vitro and in vivo. Superovulation was induced in 3- to 9-week-old females by injection of 150 IU/kg PMSG and 150 IU/Kg hCG by 48 h apart. Only 8- and 9-week-old animals superovulated averaging 31.4 and 43.9 oocytes, respectively, and superovulation did not depend on estrous cycle. Animals 3-7 weeks of age did not superovulate. Because Wistar strains have been known to show a high incidence of OSA, factors expected to affect OSA in WMN/Nrs, including the time interval of various steps from euthanasia to oocyte recovery, incubation media, estrous cycle, and anesthetic treatments, were examined. The time from animal euthanasia to oviduct excision was the only factor shown to affect OSA. We also compared in vitro and in vivo embryo developmental competence between embryos obtained by natural ovulation and superovulation. Although percent in vitro development of 2-cell embryos to blastocysts was similar for embryos obtained by natural ovulation (63.7%) and superovulation (69.7%), fetus development after oviductal transfer of 2-cell embryos was significantly lower in embryos obtained by superovulation than in those obtained by natural ovulation (60.2% vs. 87.5%, P=0.02). Our results provide important normative data regarding future applications of rat assisted reproductive technologies (ARTs) such as in vitro fertilization and cryopreservation in WMN/Nrs strain and may be applicable to other strains of laboratory rats.

Enhancement of histone acetylation by trichostatin A during in vitro fertilization of bovine oocytes affects cell number of the inner cell mass of the resulting blastocysts

Histone acetylation is one of the major mechanisms of epigenetic reprogramming of gamete genomes after fertilization to establish a totipotent state for normal development. In the present study, the effects of trichostatin A (TSA), an inhibitor of histone deacetylase, during in vitro fertilization (IVF) of bovine oocytes on subsequent embryonic development were investigated. Cumulus-enclosed oocytes obtained from slaughterhouse bovine ovaries were matured in vitro and subjected to IVF in a defined medium supplemented with 0 (control), 5, 50, and 500 nM TSA for 18 h. After IVF, presumptive zygotes were cultured in modified synthetic oviductal fluid (mSOF) medium until 168 h postinsemination (hpi). Some oocytes were immunostained using antibody specific for histone H4-acetylated lysine 5 at 10 hpi. Cleavage, blastocyst development and cell number of inner cell mass (ICM) and trophectoderm (TE) of blastocysts were assessed. TSA treatment enhanced histone acetylation that was prominent in decondensed sperm nuclei. TSA did not affect the postfertilization cleavage, blastocyst rates, and TE cell number. However, it significantly enhanced ICM cell number (p < 0.05). These results indicate that TSA treatment during IVF of bovine oocytes does not affect blastocyst development but alters the cell number of ICM, suggesting that overriding epigenetic modification of the genome during fertilization has a carryover effect on cell proliferation and differentiation in preimplantation embryos. Thus, further environmental quality controls in assisted reproductive technologies are needed in terms of factors which affect chromatin remodelling.

Human menopausal and pregnant mare serum gonadotrophins in murine superovulation regimens for transgenic applications

Superovulation is a fundamental procedure for generating transgenic rodents. While various methods exist, zygote yield/quality remain suboptimal, making these techniques open to refinement. All require a follicle stimulating and a luteinising effect. The former can be induced by pregnant mare serum gonadotrophin (PMSG) or other compounds like human menopausal gonadotrophin (HMG). While HMG can double zygote yield compared to PMSG, no study has compared their effects on embryo quality. Embryo yield could also be increased with PMSG: timing administration at estrus may further improve follicular recruitment. This study compared: (i) the efficacy of HMG/PMSG for producing viable embryos for microinjection; and (ii) the effect of HMG/PMSG administration at estrus on embryo yield. Whitten effect-induced estrous C57/Bl6xCBA F(1) hybrid mice were superovulated as follows: PMSG (day 1; 5 IU intraperitoneally) or HMG (days 1 and 2; 1 IU intramuscularly); all received human chorionic gonadotrophin (hCG) on day 3 (5 IU, intraperitoneally). Zygotes were retrieved following mating, morphologically assessed and microinjected with innocuous ZhAT1R construct (expressing LacZ reporter and human angiotensin II type 1 receptor) before transfer to pseudopregnant recipients. Pups were tested for the transgene by Southern blot. Neither HMG nor PMSG proved superior in improving embryo yield, morphology and short-term post-microinjection survival. However, HMG group micromanipulated embryos all failed to establish a pregnancy/generate transgenic pups, unlike their PMSG counterparts. While HMG can be used for superovulation, it appears to increase embryo vulnerability to the long-term effects of microinjection. Furthermore, the embryo yields associated with HMG can be replicated by timing PMSG injection to coincide with Whitten effect-induced estrus.

Beneficial effects of dithiothreitol on relative levels of glutathione S-transferase activity and thiols in oocytes, and cell number, DNA fragmentation and allocation at the blastocyst stage in the mouse

We analyzed the effect of in vitro aging of mouse oocytes in the presence of dithiothreitol (DTT) on relative levels of glutathione S-transferase (GST) activity and thiols in oocytes, and cell number, DNA fragmentation and cellular allocation to the inner cell mass (ICM) and trophectoderm (TE) lineage at the blastocyst stage. Ovulated oocytes from gonadotropin primed hybrid female mice of 6-8 weeks of age were aged in vitro in the presence of 0, 5, 50, or 500 microM DTT for 6 hr prior to insemination. Relative levels of GST activity and thiols in oocytes were determined by confocal laser scanning microscopy, DNA fragmentation using a single-step TUNEL method, and cell allocation to the ICM and TE lineage by blastocyst staining with propidium iodide and Hoechst 33258. Non-aged oocytes exhibited higher relative levels of GST activity and thiols when compared to oocytes aged in the presence of 0, 5, and 50 microM DTT. Day 5 blastocysts from the 5, 50, and 500 microM DTT groups exhibited higher total number of cells, number of ICM cells, and ICM/TE ratio, but lower percentage of number of nuclei with DNA fragmentation/number of ICM cells than blastocyst from the 0 microM DTT group. These data show that DTT counteracts the negative effects of a post-ovulatory aging of mouse oocytes in vitro on relative levels of GST activity and thiols in oocytes, and percentage of number of nuclei with DNA fragmentation/number of ICM cells, total number of cells, number of ICM cells and ICM/TE ratio in Day 5 blastocysts.

Association of female aging with decreased parthenogenetic activation, raised MPF, and MAPKs activities and reduced levels of glutathione S-transferases activity and thiols in mouse oocytes

This study aims to determine in the mouse whether oocytes from reproductively old females exhibit a different susceptibility to be parthenogenetically activated when compared to oocytes from young females. At the age of 10-12 (young-female group) or 60-62 (old-female group) weeks, hybrid female mice were superovulated using pregnant mare's serum gonadotropin (PMSG) followed by human chorionic gonadotropin (hCG) 48 hr later. After removing the cumulus cells, oocytes were exposed to any of two different activating protocols: (a) 6-min exposure to 8% ethanol; and (b) treatment with 200 microM thimerosal for 15 min followed by 8 mM dithiothreitol (DTT) for 30 min. Oocytes from old female mice displayed (1) lower total percentage of parthenogenetic activation and extrusion of the second polar body after treatment with either thimerosal + DTT or ethanol; (2) higher M-phase-promoting factor (MPF) and mitogen-activated protein kinases (MAPKs) activities; and (3) lower intracytoplasmic levels of glutathione S-transferases (GSTs) activity and thiols than oocytes from young females. These data show that female aging is associated with higher resistance of oocytes to be parthenogenetically activated, higher MPF and MAPKs activities and lower intracytoplasmic levels of GSTs activity and thiols.