Establishment of a basic method for manipulating preantral follicles: effects of retrieval method on in vitro growth of preantral follicles and intrafollicular oocytes

Culture of preantral follicles in poly(ethylene) glycol-based, three-dimensional hydrogel: a relationship between swelling ratio and follicular developments

This study was undertaken to examine how the softness of poly(ethylene) glycol (PEG)-based hydrogels, creating a three-dimensional (3D) microenvironment, influences the in vitro growth of mouse ovarian follicles. Early secondary, preantral follicles of 2 week-old mice were cultured in a crosslinked four-arm PEG hydrogel. The hydrogel swelling ratio, which relates to softness, was modified within the range 25.7-15.5 by increasing the reactive PEG concentration in the precursor solution from 5% to 15% w/v, but it did not influence follicular growth to form the pseudoantrum (60-80%; p = 0.76). Significant (p < 0.04) model effects, however, were detected in the maturation and developmental competence of the follicle-derived oocytes. A swelling ratio of > 21.4 yielded better oocyte maturation than other levels, while the highest competence to develop pronuclear and blastocyst formation was detected at 20.6. In conclusion, gel softness, as reflected in swelling ratio, was one of the essential factors for supporting folliculogenesis in vivo within a hydrogel-based, 3D microenvironment.

In vitro culture of early secondary preantral follicles in hanging drop of ovarian cell-conditioned medium to obtain MII oocytes from outbred deer mice

The ovarian follicle (each contains a single oocyte) is the fundamental functional tissue unit of mammalian ovaries. In humans, it has been long held true that females are born with a maximum number of follicles (or oocytes) that are not only nonrenewable, but also undergoing degeneration with time with a sharply decreased oocyte quality after the age of ∼35. Therefore, it is of importance to isolate and bank ovarian follicles for in vitro culture to obtain fertilizable oocytes later, to preserve the fertility of professional women who may want to delay childbearing, young and unmarried women who may lose gonadal function because of exposure to environmental/occupational hazards or aggressive medical treatments, such as radiation and chemotherapy, and even endangered species and breeds. Although they contributed significantly to the understanding of follicle science and biology, most studies reported to date on this topic were done using the man-made, unnatural inbred animal species. It was found in this study that the conventional two-dimensional microliter drop and three-dimensional hanging drop (HD) methods, reported to be effective for in vitro culture of preantral follicles from inbred mice, are not directly transferrable to outbred deer mice. Therefore, a modified HD method was developed in this study to achieve a much higher (>5 times compared to the best conventional methods) percentage of developing early secondary preantral follicles from the outbred mice to the antral stage, for which, the use of an ovarian cell-conditioned medium and multiple follicles per HD were identified to be crucial. It was further found that the method for in vitro maturation of oocytes in antral follicles obtained by in vitro culture of preantral follicles could be very different from that for oocytes in antral follicles obtained by hormone stimulation in vivo. Therefore, this study should provide important guidance for establishing effective protocols of in vitro follicle culture to preserve the fertility of wildlife and humans outbred by nature.

Development of a serum-free defined system employing growth factors for preantral follicle culture

This study was conducted to evaluate if mouse preantral follicles can yield developmentally competent oocytes following culture in serum-free, defined medium. Donor follicles were obtained from 14-day-old B6CBAF1 mice, and cultured in α-MEM-Glutamax medium. The replacement of fetal bovine serum with knockout serum replacement (KSR) did not significantly reduce follicle growth or oocyte maturation in vitro, although it significantly reduced the development of oocytes after activation. Regardless of the replacement medium, follicle growth was not influenced by the addition of leukemia inhibitory factor (LIF). The addition of 100 ng/ml stem cell factor (SCF) to the KSR-supplemented serum-free medium significantly stimulated follicle development, which further improved blastocyst formation after oocyte activation. On Day 3 of culture, a significant increase in Bmp7 expression was detected in the SCF-containing medium compared with the serum-containing medium, whereas Gdf9 and Amh were increased in the serum-containing medium. A significant increase in estradiol production was detected under serum-free conditions, but minimal progesterone secretion was detected throughout the culture period. In conclusion, serum-free media can be used to optimize ovarian follicle cultures, and the addition of SCF is beneficial for deriving developmentally competent oocytes through follicle culture.

Growth of Ovarian Primary Follicles Retrieved from Neonates of Different Ages and Derivation of Mature Oocytes Following In vitro-Culture

This study was conducted to improve the yield of mature oocytes from in vitro-culture of ovarian primary follicles by optimizing follicle retrieval from neonatal mice of different ages. Primary follicles of 75 to 99 μm in diameter were collected daily from 7- to 14-day-old neonatal mice, and subsequently cultured in α-MEM medium. Number of primary follicles isolated, growth of the follicle during in vitro-culture and maturation of intrafollicular oocytes were monitored. Overall, mean number of preantral follicles per animal was improved from 10.7 to 88.7 as the age of follicle donors was increased from 7 to 14-day-old. Number of primary follicles was increased gradually up to 11-day-old (35.7 follicle per an animal), then reduced to 29 in 14-day-old (p = 0.0013). More follicles retrieved from 10-day-old or 11-day-old females maintained their morphological normality at the end of primary culture than the follicles retrieved from 9-day-old. Of those cultured, primary follicles retrieved from 11-day-old mice yielded largest larger number of early secondary follicles than the follicles retrieved from in the other ages (39 vs. 13 to 29%). More than 3.3-times increase (0.86 to 2.86; p<0.05) in an average number of mature oocytes per animal was observed in the group of 11-day-old, compared with 9-day-old. However, no difference was found in the percentage of primary follicles developing into the pseudoantral stage (21 to 30%; p = 0.5222) and in the percentage of oocytes mucified (32 to 39%; p = 0.5792). In conclusion, a positive correlation between retrieval time and follicle growth was detected, which influences the efficiency to derive mature oocytes by follicle culture.

Genetic and cellular aspects of the establishment of histocompatible stem cells: information gained from an animal model

The establishment of patient-specific histocompatible stem cells may be an alternative for overcoming current limitations in stem cell engineering. We are developing an animal model to assist the establishment of histocompatible, autologous stem cells. In this process, we obtained valuable information on establishing and characterizing stem cells. As an initial step, we succeeded in establishing histocompatible stem cells using preantral follicle cultures and subsequent parthenogenetic activation. The gene expression profile of the established stem cells was similar to that of embryonic stem cells (ESCs) derived from normal fertilization. On the other hand, we propose a way to derive histocompatible, ESC-like cells by co-culturing ovarian stromal cells with feeder fibroblasts, which may allow the derivation of stem cells from somatic tissue. However, more progress regarding the establishment and elucidation on origination of established cell lines is necessary to use this genetic manipulation-free procedure. Nevertheless, relevant information on the process will help to stimulate preclinical research on cell transformation into differentiated, undifferentiated, and even cancerous cells, as well as clinical studies on the application of induced pluripotent cells.

Derivation of developmentally competent oocytes by in vitro culture of preantral follicles retrieved from aged mice

Mature oocytes were derived from cultured preantral follicles retrieved from aged (63-67 weeks old) mice with decreased fecundity; IVF of the oocytes resulted in cleaving embryos. There was no difference in developmental competence of 4-cell embryos to the blastocyst stage between the adult and the aged groups, although general retardation of follicle development and oocyte maturation and development after IVF was detected.

Effectiveness of slow freezing and vitrification for long-term preservation of mouse ovarian tissue

This study was conducted to evaluate the interaction between cryo-damage and ART outcome after cryopreservation of mouse ovarian tissues with different methods. Either a vitrification or a slow freezing was employed for the cryopreservation of B6CBAF1 mouse ovaries and follicle growth and the preimplantation development of intrafollicular oocytes following parthenogenesis or IVF were monitored. Both cryopreservation protocols caused significant damage to follicle components, including vacuole formation and mitochondrial deformities. Regardless of the cryopreservation protocols employed, a sharp (P < 0.0001) decrease in follicle viability and post-thaw growth was detected. When IVF program was employed, significant (P < 0.05) decrease in cleavage and blastocyst formation was notable in both modes of cryopreservation. However, such retardation was not found when oocytes were parthenogenetically activated. In the IVF oocytes, slow freezing led to better development than vitrification. In conclusion, a close relationship between cryopreservation and ART methods should be considered for the selection of cryopreservation program.

Derivation of histocompatible stem cells from ovarian tissue

Somatic cell nuclear transfer, the first established technique for producing patient-specific autologous stem cells, inevitably requires the sacrifice of viable embryos. To circumvent the serious ethical issues associated with this use of embryos, researchers have developed several alternative methods for the production of histocompatible stem cells. In our research, we have used two methods to derive histocompatible stem cells from murine ovarian tissue. First, we have established autologous stem cells by culturing degeneration-fated preantral follicles to produce developmentally competent, mature oocytes and then parthenogenetically activating these mature oocytes to acquire genetic homogeneity. Second, we have used cell-to-cell interactions to derive stem cells from ovarian stromal cells without undertaking genetic modification. We have successfully derived autologous murine stem cells by manipulating primary and early secondary follicles in vitro, and this method has proved successful even for follicles retrieved from aged ovaries. Furthermore, we believe that it will be possible to isolate stem cells directly from non-germline ovarian tissue or to derive stem cells by culturing the ovarian cells with other somatic cells. If achieved, these aims will greatly advance the development of induced pluripotent stem cell technology, as well as tissue-specific stem cell research. In this review, we introduce the relevant technologies for establishing histocompatible stem cells from ovarian tissue cells without undertaking genetic manipulation and review the current limitations of, and future research directions in, stem cell biology.

The rate of in vitro maturation of primary follicles from adult mice and the quality of oocytes is improved in the absence of anti-mullerian hormone

Anti-Müllerian hormone (AMH) inhibits the recruitment of primordial follicles into the growing pool, but its role in primary and secondary follicles is not clear. We isolated primary follicles from the ovaries of 9- to 10-week old mice and examined whether AMH affected follicular development. Follicles were matured in media that was prepared using unsexed fetal bovine serum (FBS) or female FBS (FFBS) with or without added AMH for approximately 2 weeks and maturation rates to secondary follicles and metaphase II (MII) oocytes were measured by standard morphological criteria. Rates of parthenogenetic activation and in vitro fertilization (IVF) were assessed by cleavage and blastocyst development, respectively. Whereas addition of AMH blocked primary to secondary follicle transition, the primary to secondary and secondary to MII follicle maturation rates was significantly improved with FFBS. Folliculogenesis resumed once AMH was removed from the media of the arrested primary follicles. The rates of IVF and parthenogenesis of oocytes after in vitro maturation (IVM) without AMH were also improved compared to controls. The results indicate that removal of AMH from culture conditions during IVM from primary follicular stages should be considered to improve outcome.

Histone deacetylase inhibition improves meiotic competence but not developmental competence in growing pig oocytes

In fully grown pig oocytes, meiotic maturation in vitro is retarded by inhibition of histone deacetylases by trichostatin A (TSA). In growing oocytes with partial meiotic competence, culture with TSA has no significant effect on the meiotic maturation. Growing oocytes treated with TSA mature mainly to metaphase I. The ratio of oocytes that mature to metaphase II is very limited. After transient exposure to TSA, the maturation of growing oocytes with partial meiotic competence takes a different course. When these oocytes are first cultured in a TSA-free medium, then cultured for another 24 h with 100 nM TSA and finally again in a TSA-free medium for 24 h, the ratio of oocytes that mature to metaphase II significantly increases reaching 59%. When oocytes were cultured for the same length of time without transient exposure to TSA, only 19% matured to metaphase II. Those oocytes that matured to metaphase II after transient exposure to TSA were successfully activated using calcium ionophore. However, the subsequent cleavage was very limited. We can conclude that transient exposure of growing pig oocytes with partial meiotic competence to TSA increases oocyte meiotic competence, but it does not enhance developmental competence after parthenogenetic activation.

Improved establishment of autologous stem cells derived from preantral follicle culture and oocyte parthenogenesis

This study was conducted to improve establishing autologous embryonic stem cells (ESCs) by culture of preantral follicles and parthenogenetic activation of oocytes. First, paternal inheritance of the follicle donor was changed without altering maternal heredity by employing B6CBAF1 instead of B6D2F1 mice. A significant increase in the establishment of parthenogenetic ESCs was detected after the change, and a different gene expression pro-file was detected in the ESCs established. Among 62 stemness-related genes showing different expression level between two strains, 35 (56.5%) were lower in the rarely established ESCs (B6D2F1) than in the easily established ESCs (B6CBAF1). Several paternally expressed genes were aberrantly expressed in the rarely established ESCs. Second, the establishment of parthenogenetic ESCs in B6D2F1 was significantly improved when preantral follicles were cultured in glutathione (GSH)-containing medium. In the ESCs derived from GSH-treated follicles, 77% of the 62 genes showing the difference increased their expression. Translation of several proteins related to stemness (Wnt-1, beta-catenin, p-p44/42, and smad) was similar between the parthenogenetic ESCs established after GSH treatment and the control E14 ESCs. We concluded that change in genetic inheritance and exposure of in vitro-growing ovarian follicles to GSH contributes to improving establishment of parthenogenetic ESCs, which may help increase the feasibility of the established lines for patient-specific, stem cell therapy.