The activin-follistatin system and in vitro early follicle development in goats

Changes in surfactant protein A and D in ovine ovaries related to follicle development

Surfactant protein A (SP-A) and Surfactant protein D (SP-D) glycoproteins play a crucial role in maintaining lung homeostasis and lung host defense. Interestingly, these proteins are also expressed in extra-pulmonary tissues, including the female genital tract. The ovarian tissue, where SP-A and SP-D expression increases with follicular development, may serve as the primary site of defense for this tissue. However, their functions in these tissues are not well understood and are currently an active area of research. Therefore, the objective of this study is to investigate the expression of SP-A and SP-D in the ovine ovary throughout the ovarian cycle using immunohistochemistry by semiquantitative intensity classification and Western blotting techniques. These findings revealed the presence of SP-A and SP-D in various compartments of the ovary, such as the follicular epithelium, granulosa cells, cumulus cells, theca cells, oocyte I, follicular fluid, and luteal cells of Graafian follicles, excluding the corpus albicans. SP-A and SP-D likely act as a first line of defense against potential pathogens that infiltrate the ovaries. Further investigation of the differential expression of SP-A and SP-D proteins in ovarian follicles will provide a basis for understanding their interactions with key proteins involved in oogenesis.

Making a good egg: human oocyte health, aging, and in vitro development

Mammalian eggs (oocytes) are formed during fetal life and establish associations with somatic cells to form primordial follicles that create a store of germ cells (the primordial pool). The size of this pool is influenced by key events during the formation of germ cells and by factors that influence the subsequent activation of follicle growth. These regulatory pathways must ensure that the reserve of oocytes within primordial follicles in humans lasts for up to 50 years, yet only approximately 0.1% will ever be ovulated with the rest undergoing degeneration. This review outlines the mechanisms and regulatory pathways that govern the processes of oocyte and follicle formation and later growth, within the ovarian stroma, through to ovulation with particular reference to human oocytes/follicles. In addition, the effects of aging on female reproductive capacity through changes in oocyte number and quality are emphasized, with both the cellular mechanisms and clinical implications discussed. Finally, the details of current developments in culture systems that support all stages of follicle growth to generate mature oocytes in vitro and emerging prospects for making new oocytes from stem cells are outlined.

Eugenol Improves Follicular Survival and Development During in vitro Culture of Goat Ovarian Tissue

This study evaluated the effects of different concentrations (10, 20, or 40 μM) of eugenol (EUG 10, EUG 20, or EUG 40), ascorbic acid (50 μg/mL; AA) or anethole (300 μg/mL; ANE 300) on the in-vitro survival and development of goat preantral follicles and oxidative stress in the cultured ovarian tissue. Ovarian fragments from five goats were cultured for 1 or 7 days in Alpha Minimum Essential Medium (α-MEM+) supplemented or not with AA, ANE 300, EUG 10, EUG 20 or EUG 40. On day 7 of culture, when compared to MEM, the addition of EUG 40 had increased the rate of follicular development, as observed by a decrease in the proportion of primordial follicles alongside with an increase in the rate of normally developing follicles. Furthermore, EUG 40 significantly increased both follicular and oocyte diameters. Subsequently, ovarian fragments from three goats were cultured for 1 or 7 days in α-MEM+ supplemented or not with AA, ANE 300 or EUG 40. All tested antioxidants, except ANE 300, were able to significantly decrease the levels of reactive oxygen species in the ovarian tissue, but EUG 40 could most efficiently neutralize free radicals. All ovarian tissues cultured in the presence of antioxidants, especially EUG 40, presented a significant decrease in H3K4me3 labeling, indicating a silencing of genes that play a role in the inhibition of follicular activation and apoptosis induction. When compared to cultured control tissues, both EUG 40 and ANE 300 significantly increased the intensity of calreticulin labeling in growing follicles. The mRNA relative expression of ERP29 and KDM3A was significantly increased when the culture medium was supplemented with EUG 40, indicating a response to ER stress experienced during culture. In conclusion, EUG 40 improved in-vitro follicle survival, activation and development and decreased ROS production, ER stress and histone lysine methylation in goat ovarian tissue.

A functional polymorphism of inhibin alpha subunit at miR-181b-1-3p-binding site regulates proliferation and apoptosis of chicken ovarian granular cells

INHA, the gene encoding the inhibin alpha subunit, was involved in folliculogenesis in mammals, but no study was reported for its working pathway in birds. Here we hypothesize that gene polymorphism in INHA 3'UTR might influence miRNAs binding efficiency and further affect the function of this gene. Thus, we investigated the association between the 3'UTR single-nucleotide polymorphisms (SNPs) in INHA and the laying performance in chickens and further explore their possible molecular cascades in granulosa cells (GC). Five SNPs were detected in Tianfu green-shell layers and g. 22,178,975 G > A was significantly associated with total egg numbers at the age of 300 days (EN, n = 286). Birds carrying the AA genotype laid more EN than those with GG (P < 0.05). The allele transition from G to A in the 3'UTR of INHA gene destroyed a binding site which was targeted by miR-181b-1-3p. The expression abundances of INHA mRNA increased firstly and then decreased with follicle growing, and reached the top in the sixth largest pre-ovulation follicle, whereas miR-181b-1-3p levels in chicken pre-hierarchical follicles had the contrary tendency. Further studies indicated that high levels of miR-181b-1-3p increased apoptosis and reduced GC proliferation while miR-181b-1-3p inhibitors decreased apoptosis and promoted GC proliferation. Additionally, depression of INHA increased apoptosis and reduced GC proliferation via a caspase-3-dependent mitochondrial pathway. Generally, the mutation in INHA 3'UTR was tightly correlated with egg production in chickens, and blocked a binding site of miR-181b-1-3p. miR-181b-1-3p inhibited GC proliferation and promoted apoptosis by targeting INHA.

Inhibin A regulates follicular development via hormone secretion and granulosa cell behaviors in laying hens

Inhibin A regulates follicular development, and its expression level is related to physiological activities, such as the recruitment, selection, and predominance during follicular development. Therefore, examining inhibin A and its regulatory effects on the reproductive performance of poultry is crucial. In this study, we measured the mRNA and protein abundances of INHA and INHBA in the chicken reproductive system and determined the hormone secretion and apoptosis of follicular granulosa cells (GCs) after being treated with inhibin A protein, and flow cytometry was performed to analyze GC apoptosis in INHA-specific small RNA interference (siRNA). We detected that INHA and INHBA were mainly expressed in chicken follicles. The highest INHA mRNA abundance was found in the fifth largest preovulatory follicle (F5) (P < 0.05). INHBA mRNA expression in the largest preovulatory follicle (F1) was significantly higher than those in other follicles (P < 0.05). Similar results were found for INHA and INHBA protein expression in those follicles (P < 0.05). Treatment with inhibin A protein increased the activity of GCs in a dose-dependent manner (P < 0.05), which was characterized by decreased gene expression of pro-apoptotic factors Bax and Caspase-3 (P < 0.05) and increased expression of proliferation genes Bcl-2 and PCNA (P < 0.05). Additionally, inhibin A significantly increased the secretion of progesterone and estradiol (P < 0.05). RNAi-mediated knockdown of INHA increased apoptosis in GCs via a Caspase-3-dependent mitochondrial pathway.

The transcriptional regulator CBX2 and ovarian function: A whole genome and whole transcriptome approach

The chromobox homolog 2 (CBX2) was found to be important for human testis development, but its role in the human ovary remains elusive. We conducted a genome-wide analysis based on DNA adenine methyltransferase identification (DamID) and RNA sequencing strategies to investigate CBX2 in the human granulosa cells. Functional analysis revealed that CBX2 was upstream of genes contributing to ovarian function like folliculogenesis and steroidogenesis (i.e. ESR1, NRG1, AKR1C1, PTGER2, BMP15, BMP2, FSHR and NTRK1/2). We identified CBX2 regulated genes associated with polycystic ovary syndrome (PCOS) such as TGFβ, MAP3K15 and DKK1, as well as genes implicated in premature ovarian failure (POF) (i.e. POF1B, BMP15 and HOXA13) and the pituitary deficiency (i.e. LHX4 and KISS1). Our study provided an excellent opportunity to identify genes surrounding CBX2 in the ovary and might contribute to the understanding of ovarian physiopathology causing infertility in women.

Activin-A receptor expression patterns in prepubertal goat oocytes and derived embryos

This study examines the presence of activin IIA and IIB receptors (ActR-IIA and ActR-IIB) by Western blotting and immunocytochemistry in immature and IVM-oocytes, 2 to 8-cells embryos and blastocysts from prepubertal goats. Western blotting revealed that activin receptors are synthesized during oocyte maturation and embryo development. In the immunocytochemistry experiments, no immunostaining for either receptor was detected in oocytes while both receptors were immunolabelled in all the cells of cleaved embryos. In blastocysts, while ActR-IIA expression appeared evenly distributed in the two cell lineages, inner cell mass and trophectoderm, the ActR-IIB immunosignal was restricted mainly to the inner cell mass. Our findings reveal the presence of activin type II receptors (ActR-IIA and ActR-IIB) in in vitro matured prepubertal goat oocytes and blastocyst-stage embryos. The expression of these receptors could be a key factor in understanding differences between competent and incompetent oocytes.

Stroma cell-derived factor 1 and connexins (37 and 43) are preserved after vitrification and in vitro culture of goat ovarian cortex

This study aimed to evaluate the follicular morphology and development (follicular activation, cell proliferation, and hormone production), as well as the distribution pattern of Connexins 37 and 43 and SDF-1α after vitrification and in vitro culture of goat ovarian tissue. The study involved four experimental groups: fresh control, vitrified control, fresh culture and vitrified culture. The ovarian fragments were vitrified by a solid surface technique using the Ovarian Tissue Cryosystem and subsequently in vitro cultured for 7 days. The percentage of normal preantral follicles was similar between vitrified control and vitrified culture. However, both vitrified control and vitrified culture treatments showed a significant reduction of morphologically normal follicles in comparison to fresh control. A higher percentage of developing follicles (transition, primary and secondary) was observed in both fresh culture and vitrified culture treatments. Progesterone and estradiol production decreased (P < 0.05) during in vitro culture. SDF-1α and Cx37 proteins were detected in oocytes and granulosa cells from all the treatments. However, in vitrified cultured tissue, only granulosa cells were labeled with Cx37. Connexin 43 was detected in the granulosa, theca cells and zona pellucida in all the treatments. In conclusion, in vitro culture of vitrified goat ovarian cortex was able to promote follicle survival and did not alter the expression of SDF-1α and 43. However, the expression of Cx 37 was modified after in vitro culture of vitrified tissue.

Expression of kit ligand and insulin-like growth factor binding protein 3 during in vivo or in vitro development of ovarian follicles in sheep

Expression of Kit ligand (KL) and insulin-like growth factor binding protein (IGFBP3) genes was studied at different in vivo and corresponding in vitro stages of development of the ovarian follicles in sheep. The expression of both KL and IGFBP3 was significantly higher in the primordial follicles relative to any other stage of development. Compared to the other stages, the KL expression in the cumulus cells from in vivo grown large antral follicles and that of IGFBP3 in COCs' isolated from large antral follicles matured in vitro for 24 hr were significantly higher. In the oocytes from in vivo grown ovarian follicles, the expression of KL was the same at all the stages of development. Insulin-like growth factor binding protein 3 expression was also the same in the oocytes at all the stages of the development except for a significantly lower expression in those from antral follicles. The expression of KL in the cumulus cells decreased significantly in the in vitro grown early antral follicles but did not change further as the development progressed. The expression of IGFBP3 in the cumulus cells from in vitro grown ovarian follicles appeared to increase as the development progressed although the increase was not significant between any two consecutive stages of development. In the oocytes in in vitro grown ovarian follicles, the expression levels of KL and IGFBP3 genes did not change with development. It is concluded that (i) KL and IGFBP3 genes follow specific patterns of expression during ovarian folliculogenesis and (ii) in vitro culture of preantral follicles compromises the development potential through alterations in the stage-specific patterns of expression of these and other developmentally important genes.

The spatiotemporal hormonal orchestration of human folliculogenesis, early embryogenesis and blastocyst implantation

The early reproductive events starting with folliculogenesis and ending with blastocyst implantation into the uterine endometrium are regulated by a complex interplay among endocrine, paracrine and autocrine factors. This review examines the spatiotemporal integration of these maternal and embryonic signals that are required for successful reproduction. In coordination with hypothalamic-pituitary-gonadal (HPG) hormones, an intraovarian HPG-like axis regulates folliculogenesis, follicular quiescence, ovulation, follicular atresia, and corpus luteal functions. Upon conception and passage of the zygote through the fallopian tube, the contribution of maternal hormones in the form of paracrine secretions from the endosalpinx to embryonic development declines, with autocrine and paracrine signaling becoming increasingly important as instructional signals for the differentiation of the early zygote/morula into a blastocyst. These maternal and embryonic signals include activin and gonadotropin-releasing hormone 1 (GnRH1) that are crucial for the synthesis and secretion of the 'pregnancy' hormone human chorionic gonadotropin (hCG). hCG in turn signals pre-implantation embryonic cell division and sex steroid production required for stem cell differentiation, and subsequent blastulation, gastrulation, cavitation and blastocyst formation. Upon reaching the uterus, blastocyst hatching occurs under the influence of decreased activin signaling, while the attachment and invasion of the trophoblast into the endometrium appears to be driven by a decrease in activin signaling, and by increased GnRH1 and hCG signaling that allows for tissue remodeling and the controlled invasion of the blastocyst into the uterine endometrium. This review demonstrates the importance of integrative endocrine, paracrine, and autocrine signaling for successful human reproduction.

Ovarian follicle development in vitro and oocyte competence: advances and challenges for farm animals

During the last 2 decades, research on in vitro preantral follicle growth and oocyte maturation has delivered fascinating advances concerning the knowledge of processes regulating follicle growth and the developmental competence of oocytes. These advances include (1) information about the role of several hormones and growth factors on in vitro activation of primordial follicles; (2) increased understanding of the intracellular pathway involved in the initiation of primordial follicle growth; (3) the growth of primary and secondary follicles up to antral stages; and (4) production of embryos from oocytes from in vitro grown preantral follicles. This review article describes these advances, especially in regard farm animals, and discusses the reasons that limit embryo production from oocytes derived from preantral follicles cultured in vitro.

Cooperative Effects of FOXL2 with the Members of TGF-β Superfamily on FSH Receptor mRNA Expression and Granulosa Cell Proliferation from Hen Prehierarchical Follicles

Forkhead box L2 (FOXL2) is a member of the forkhead nuclear factor 3 gene family and plays an essential role in ovarian growth and maturation in mammals. However, its potential effects and regulative mechanism in development of chicken ovarian prehierarchical follicles remain unexplored. In this study, the cooperative effects of FOXL2 with activin A, growth differentiation factor-9 (GDF9) and follistatin, three members of the transforming growth factor beta (TGF-β) superfamily that were previously suggested to exert a critical role in follicle development was investigated. We demonstrated herein, using in-situ hybridization, Northern blot and immunohistochemical analyses of oocytes and granulosa cells in various sizes of prehierarchical follicles that both FOXL2 transcripts and FOXL2 proteins are predominantly expressed in a highly similar expression pattern to that of GDF9 gene. In addition, the FOXL2 transcript was found at lower levels in theca cells in the absence of GDF9. Furthermore, culture of granulosa cells (GCs) from the prehierarchical follicles (6–8 mm) in conditioned medium revealed that in the pcDNA3.0-FOXL2 transfected GCs, there was a more dramatic increase in FSHR mRNA expression after treatment with activin A (10 ng/ml) or GDF9 (100 ng/ml) for 24 h which caused a stimulatory effect on the GC proliferation. In contrast, a significant decrease of FSHR mRNA was detected after treatment with follistatin (50 ng/ml) and resulted in an inhibitory effect on the cell proliferation. The results of this suggested that FOXL2 plays a bidirectional modulating role involved in the intracellular FSHR transcription and GC proliferation via an autocrine regulatory mechanism in a positive or negative manner through cooperation with activin A and/or GDF9, and follistatin in the hen follicle development. This cooperative action may be mediated by the examined Smad signals and simultaneously implicated in modulation of the StAR, CCND2, and CYP11A1 expression.

New insights into implication of the SLIT/ROBO pathway in the prehierarchical follicle development of hen ovary

The SLIT/Roundabout (ROBO) pathway is involved in follicle development of mammalian ovary, and 2 secreted hormones activin A and inhibin A have potential roles in modulation of the SLIT/ROBO system, but the related actions remain poorly understood in bird. The aims of the present study were to examine the spatial and temporal expression of the SLIT ligand genes (SLIT1, SLIT2, and SLIT3) and their receptor ROBO1, ROBO2, ROBO3, and ROBO4 genes in various-sized prehierarchical follicles during hen ovary development and the effects of activin A and inhibin A on the expression of these genes in the cultured hen follicles. Our result demonstrated that the transcripts of the 3 SLIT genes were highly expressed in the developing follicles and expression patterns of the SLIT transcripts were different from those of ROBO genes detected by real-time quantitative reverse transcriptase PCR. Both SLIT and ROBO transcripts were predominantly expressed in oocytes and granulosa cells from the prehierarchichal follicles examined by in situ hybridization. The localization for SLIT and ROBO proteins was revealed by immunohistochemistry similar to the spatial distribution of their transcript. In cultured follicles (4 to 8 mm in diameter), the expression levels of SLIT and ROBO members are hormonally regulated by activin A (10 ng/mL) and/or inhibin A (20 ng/mL) after treatment for 24 h. However, the expression of only SLIT2, SLIT3, and ROBO3 mRNA presented a directly opposite response to activin A and inhibin A hormones. These results indicate that SLIT/ROBO pathway is implicated in the prehierarchical follicular development of the hen ovary by an intrafollicular autocrine and/or paracrine action, and is influenced by activin A and inhibin A hormones.

Influence of Insulin-like Growth Factor I (IGF-I) on the survival and the in vitro development of caprine preantral follicles

The aim of this study was to investigate the effects of the insulin-like growth factor -I (IGF-I) on survival, activation (transition from primordial to primary follicles) and growth of caprine preantral follicles cultured in vitro. Fragments of ovarian cortex were cultured for one and seven days in the absence or presence of IGF-I (0, 50 and 100ng/ml). The non-cultured and cultured tissues were processed and analyzed by histology and transmission electron microscopy. The culture for one day in a medium with 100ng/ml of IGF-I showed 86.7% of morphologically normal follicles. These results were similar (P>0.05) to the percentage of normal follicles found in the control (96.7%). It was also found that this medium increased the percentage of follicular activation (developing follicles) with one day of culture. The oocyte and follicular diameters remained similar to the control by culturing for one day in a medium containing 100ng/ml of IGF-I. The ultrastructural analysis did not confirm the integrity of the follicular fragments in a medium containing IGF-I (100ng/ml) after one and seven days of culture. In conclusion, this study demonstrated that the addition of 100 ng/ml of IGF-I in the culture medium enables the development of preantral follicles of goats with one day of culture. However, it is not sufficient to maintain the follicular integrity and the follicular survival rate after seven days of culture.

In vitro developmental competence of prepubertal goat oocytes cultured with recombinant activin-A

The present study was designed to evaluate the effect of activin-A during the in vitro oocyte maturation (IVM) and in vitro embryo culture (IVC) on nuclear maturation, blastocyst yield and blastocyst quality of prepubertal goat oocytes. In Experiment 1, three groups of oocytes were used during the IVM of prepubertal goat oocytes to determine the optimal concentration of recombinant human activin-A added to the maturation medium. Cumulus-oocyte complexes were matured in an IVM medium containing 0, 10 and 100 ng/ml (groups A0, A10 and A100), fertilized and in vitro cultured using standard procedures. In Experiment 2, the addition of 10 ng/ml activin-A at IVM (A10A0), IVC (A0A10) or IVM+IVC (A10A10) was studied and compared with the control group (A0A0). Results of the first experiment demonstrated that the addition of activin-A yielded similar percentages of maturation (⩽71.0%) and blastocyst formation rates (⩽24.9%) than the control group (A0). Experiment 2 showed that exposure of prepubertal goat oocytes to an IVC medium containing 10 ng/ml activin-A (A0A10) significantly increased the rates of development to the blastocyst stage, as compared with the control group (A0A0) (19.5±2.21% v. 13.1±2.37%, respectively; P<0.05). With regard to the blastocyst quality, total number of cells, inner cell mass (ICM) and trophectoderm of prepubertal goat embryos produced in the presence of activin-A did not differ significantly among experimental groups. In summary, these results indicate that supplementation of the IVC medium with activin-A enhances embryo development of prepubertal goat oocytes.

Intra-ovarian roles of activins and inhibins

Granulosa cells are the main ovarian source of inhibins, activins and activin-binding protein (follistatin) while germ (oogonia, oocytes) and somatic (theca, granulosa, luteal) cells express activin receptors, signaling components and inhibin co-receptor (betaglycan). Activins are implicated in various intra-ovarian roles including germ cell survival and primordial follicle assembly; follicle growth from preantral to mid-antral stages; suppression of thecal androgen production; promotion of granulosa cell proliferation, FSHR and CYP19A1 expression; enhancement of oocyte developmental competence; retardation of follicle luteinization and/or atresia and involvement in luteolysis. Inhibins (primarily inhibin A) are produced in greatest amounts by preovulatory follicles (and corpus luteum in primates) and suppress FSH secretion through endocrine negative feedback. Together with follistatin, inhibins act locally to oppose auto-/paracrine activin (and BMP) signaling thus modulating many of the above processes. The balance between activin-inhibin shifts during follicle development with activin signalling prevailing at earlier stages but declining as inhibin and betaglycan expression rise.

Growth of mouse oocytes to maturity from premeiotic germ cells in vitro

In the present study, we established an in vitro culture system suitable for generating fertilizable oocytes from premeiotic mouse female germ cells. These results were achieved after first establishing an in vitro culture system allowing immature oocytes from 12–14 day- old mice to reach meiotic maturation through culture onto preantral granulosa cell (PAGC) monolayers in the presence of Activin A (ActA). To generate mature oocytes from premeiotic germ cells, pieces of ovaries from 12.5 days post coitum (dpc) embryos were cultured in medium supplemented with ActA for 28 days and the oocytes formed within the explants were isolated and cocultured onto PAGC monolayers in the presence of ActA for 6–7 days. The oocytes were then subjected to a final meiotic maturation assay to evaluate their capability to undergo germinal vesicle break down (GVBD) and reach the metaphase II (MII) stage. We found that during the first 28 days of culture, a significant number of oocytes within the ovarian explants reached nearly full growth and formed preantral follicle-like structures with the surrounding somatic cells. GSH level and Cx37 expression in the oocytes within the explants were indicative of proper developmental conditions. Moreover, the imprinting of Igf2r and Peg3 genes in these oocytes was correctly established. Further culture onto PAGCs in the presence of ActA allowed about 16% of the oocytes to undergo GVBD, among which 17% reached the MII stage during the final 16–18 hr maturation culture. These MII oocytes showed normal spindle and chromosome assembly and a correct ERK1/2 activity. About 35% of the in vitro matured oocytes were fertilized and 53.44% of them were able to reach the 2-cell stage. Finally, around 7% of the 2-cell embryos developed to the morula/blastocyst stage.

Activin B is produced early in antral follicular development and suppresses thecal androgen production

Little is known about the role of activin B during folliculogenesis. This study investigated the expression levels of activin/inhibin subunits (βA, βB, and α), steroid enzyme, and gonadotrophin receptors in theca (TC) and granulosa cells (GC) by QPCR and activin A and B and inhibin A protein levels in follicular fluid (FF) of developing sheep follicles during estrus and anestrus. The effect of activin B on androgen production from primary TC cultures in vitro was also assessed. During folliculogenesis, in anestrus and estrus, FF activin B concentrations and thecal and GC activin βB mRNA levels decreased as follicle diameter increased from 1–3 to >6 mm regardless of estrogenic status. Estrogenic preovulatory follicles had reduced concentrations of FF activins B and A, and TC and GCs expressed higher levels of activin βA mRNA at 3–4 mm, and TCs more inhibin α mRNA at >4 mm stages of development compared with nonestrogenic follicles. Activin B decreased androstenedione production from primary TCs in vitro, an effect blocked by inhibin A. Thus, sheep follicles 1–3 mm in diameter contained high FF levels of activin B, which decreased as the follicle size increased, and, like activin A, suppressed thecal androgen production in vitro, an effect blocked by inhibin. Furthermore, the theca of large estrogenic follicles expressed high levels of inhibin α and activin βA mRNA suggesting local thecal derived inhibin A production. This would inhibit the negative effects of thecal activins B and A ensuring maximum androgen production for enhanced estradiol production by the preovulatory follicle(s).

The effects of FSH and activin A on follicle development in vitro

Numerous studies have reported on the roles of activins in gonadal regulation; however, little is known about their specific roles in early folliculogenesis. Ovarian follicular growth was investigated in 10-day cultures of day 4 postnatal whole ovaries treated with activin A (ActA; 50 ng/ml), with or without FSH (100 ng/ml) in vitro. We hypothesized that treatment with ActA±FSH would affect rates of growth and atresia in follicles. None of the treatments affected primordial follicle activation, and antral follicles were not observed after 10 days in culture. Primordial follicle numbers from all treatment groups were ∼20% of those in day 4 fresh ovaries, indicating that activation had occurred. In the presence of ActA, preantral follicle numbers increased significantly (P<0.0001). ActA alone decreased the proportion of atretic follicles in the primary and preantral classes, whereas the combined treatment of ActA+FSH increased the proportion of atretic preantral oocytes. Real-time PCR analysis revealed that follistatin, FSH receptor, and activin βA and βB subunits were all expressed at significantly higher levels in the ActA-only treated group but not in the ActA+FSH group. Here, we report novel findings supporting the role of FSH in primordial follicle survival through an action on apoptosis and a stimulatory role of ActA in the primordial to primary and preantral stages of follicle development, suggesting an inhibitory action of activin on oocyte apoptosis.

Expression of keratinocyte growth factor in goat ovaries and its effects on preantral follicles within cultured ovarian cortex

The aims of this study were to evaluate the expression of keratinocyte growth factor (KGF) in goat ovaries and to study its effects on preantral follicle survival and development. The ovaries were used for immunohistochemistry or for in vitro culture for 1 or 7 days with KGF (0, 1, 10, 50, 100, 150, or 200 ng/mL). Noncultured (fresh control) and cultured ovarian slices were processed for histological analysis and transmission electron microscopy (TEM). The results showed that after 7 days of in vitro culture, all treatments had a significant reduction in the percentage of normal follicles compared with the fresh control. After 7 days of culture, the highest KGF concentrations (150 and 200 ng/mL) induced a significant reduction in the percentage of normal follicles compared with the tissues cultured in the absence (α-MEM(+) alone) or presence of 1, 10, and 50 ng/mL KGF. Transmission electron microscopy confirmed follicular integrity after 7 days of culture in 1 ng/mL KGF. In addition, compared with the fresh control, the percentage of growing follicles was significantly increased in all treatments after 1 or 7 days of culture. Immunohistochemical analyses showed the expression of KGF in oocytes and granulosa cells in all follicle developmental stages as well as in thecal and stromal cells. In conclusion, this study demonstrated that, at the lowest concentration (1 ng/mL), KGF maintained the ultrastructure of goat preantral follicles cultured in vitro for up to 7 days. Furthermore, the KGF protein was widely distributed in goat ovaries, especially in ovarian follicles.

Steady-state level of bone morphogenetic protein-15 in goat ovaries and its influence on in vitro development and survival of preantral follicles

This study investigates steady-state level of bone morphogenetic protein-15 (BMP-15) mRNA in caprine follicles, and the effects of BMP-15 on in vitro development of preantral follicles. Ovarian fragments were cultured for one or seven days in Minimal Essential Medium (MEM(+)) with BMP-15 (0, 1, 10, 50, 100 or 200 ng/mL), and further analyzed by histology, transmission electron and fluorescent microscopy. BMP-15 mRNA in secondary follicles was higher than in primordial and primary follicles. After seven days, 10, 50 or 100 ng/mL of BMP-15 maintained the percentage of normal follicles similar to the control (non-cultured), and increased the oocyte and follicle diameters when compared to the control and MEM(+). BMP-15 at 100 ng/mL increased the secondary follicles and maintained their ultrastructural integrity. In conclusion, the BMP-15 mRNAs were detected in all follicular categories. BMP-15 (100 ng/mL) maintained the integrity and promoted the growth of caprine preantral follicles cultured for seven days.

Cryopreservation and in vitro culture of caprine preantral follicles

Preantral follicles (PFs) form a far larger oocyte reservoir (~90% of the follicular population) than antral follicles. Several laboratories have focussed efforts on cryopreservation and in vitro culture (IVC) of PFs to obtain large numbers of fertilisable oocytes. This technology could be used to improve the reproductive potential of economically important animals, including goats, to preserve endangered species and breeds and improve fertility after chemotherapy in young women. Caprine PFs have been successfully cryopreserved using either vitrification or slow freezing. In addition, in vitro embryo production from oocytes enclosed in caprine PFs grown and matured in vitro was also achieved. The present paper selectively reviews the published studies on cryopreservation and IVC of caprine PFs to highlight advances, limitations and prospects.

Ultrastructure of isolated mouse ovarian follicles cultured in vitro

BACKGROUND

In vitro maturation of ovarian follicles, in combination with cryopreservation, might be a valuable method for preserving and/or restoring fertility in mammals with impaired reproductive function. Several culture systems capable of sustaining mammalian follicle growth in vitro have been developed and many studies exist on factors influencing the development of in vitro grown oocytes. However, a very few reports concern the ultrastructural morphology of in vitro grown follicles.

METHODS

The present study was designed to evaluate, by transmission and scanning electron microscopy, the ultrastructural features of isolated mouse preantral follicles cultured in vitro for 6 days in a standard medium containing fetal calf serum (FCS). The culture was supplemented or not with FSH.

RESULTS

The follicles cultured in FCS alone, without FSH supplementation (FCS follicles), did not form the antral cavity. They displayed low differentiation (juxta-nuclear aggregates of organelles in the ooplasm, a variable amount of microvilli on the oolemma, numerous granulosa cell-oolemma contacts, signs of degeneration in granulosa cell compartment). Eighty (80)% of FSH-treated follicles formed the antral cavity (FSH antral follicles). These follicles showed various ultrastructural markers of maturity (spreading of organelles in ooplasm, abundant microvilli on the oolemma, scarce granulosa cell-oolemma contacts, granulosa cell proliferation). Areas of detachment of the innermost granulosa cell layer from the oocyte were also found, along with a diffuse granulosa cell loosening compatible with the antral formation. Theca cells showed an immature morphology for the stage reached. Twenty (20)% of FSH-treated follicles did not develop the antral cavity (FSH non-antral follicles) and displayed morphological differentiation features intermediate between those shown by FCS and FSH antral follicles (spreading of organelles in the ooplasm, variable amount of microvilli, scattered granulosa cell-oolemma contacts, signs of degeneration in granulosa cell compartment).

CONCLUSIONS

It is concluded that FSH supports the in vitro growth of follicles, but the presence of a diffuse structural granulosa cell-oocyte uncoupling and the absence of theca development unveil the incomplete efficiency of the system. The present study contributes to explain, from a morphological point of view, the effects of culture conditions on the development of mouse in vitro grown follicles and to highlight the necessity of maintaining efficient intercellular communications to obtain large numbers of fully-grown mature germ cells.

Fibroblast growth factor-10 maintains the survival and promotes the growth of cultured goat preantral follicles

The aim of the present study was to investigate the effects of fibroblast growth factor-10 (FGF-10) on the survival, activation (transition from primordial to primary follicles), and growth of goat preantral follicles cultured in vitro. Pieces of ovarian cortex were cultured for 1 and 7 d in the absence or presence of FGF-10 (0, 1, 10, 50, 100, and 200 ng/mL). Noncultured and cultured tissues were processed and analyzed by histology, transmission electron microscopy, and viability testing. Results showed that after 7 d, a greater percentage (79.9%) of morphologically normal follicles (containing an oocyte with regular shape and uniform cytoplasm, and organized layers of granulosa cells without a pyknotic nucleus) was observed when cultured with 50 ng/mL of FGF-10 when compared with other concentrations of FGF-10 (0 ng/mL, 67.3%; 1 ng/mL, 68.2%; 10 ng/mL, 63.3%; 100 ng/mL, 64.4%; 200 ng/mL, 52.7%). Ultrastructural analyses and viability testing using fluorescent markers confirmed the follicular integrity of FGF-10 (50 ng/mL)-treated fragments after 7 d of culture. After 7 d, all FGF-10 concentrations reduced the percentage of primordial follicles and increased the percentage of developing follicles. In the presence of 50 ng/mL of FGF-10, follicles increased in diameter after 7 d of culture when compared with other concentrations tested. In conclusion, this study demonstrates that FGF-10 maintains the morphological integrity of goat preantral follicles and stimulates the growth of activated follicles in culture. The culture conditions identified here contribute to the understanding of the factors involved in goat early follicular development.

Bone Morphogenetic Protein-6 (BMP-6) induces atresia in goat primordial follicles cultured in vitro

This study investigated the effects of bone morphogenetic protein 6 (BMP-6) on in vitro primordial follicle development in goats. Samples of goat ovarian cortex were cultured in vitro for 1 or 7 days in Minimum Essential Medium (control medium) supplemented with different concentrations of BMP-6. Follicle survival, activation and growth were evaluated through histology and transmission electron microscopy (TEM). After 7 days of culture, histological analysis demonstrated that BMP-6 enhanced the percentages of atretic primordial follicles when compared to fresh control (day 0). Nevertheless, BMP-6 increased follicular and oocyte diameter during both culture periods. As the culture period progressed from day 1 to day 7, a significant increase in follicle diameter was observed with 1 or 50ng/ml BMP-6. However, on the contrary to that observed with the control medium TEM revealed that follicles cultured for up to 7 days with 1 or 50ng/ml BMP-6 had evident signs of atresia. In conclusion, this study demonstrated that BMP-6 negatively affects the survival and ultrastructure of goat primordial follicles.

Oocyte development in bovine primordial follicles is promoted by activin and FSH within a two-step serum-free culture system

Quiescent follicles of large mammals initiate growth within cultured pieces of ovarian cortex. Systems capable of sustaining in vitro development from this early stage until oocyte maturation would allow investigation of mechanisms regulating oocyte development in its entirety. The aims of this study were 1) to determine whether bovine follicles initiated to grow in vitro could be isolated from the cortical environment, and could undergo further development and 2) to evaluate the effect of activin and FSH on the development of secondary follicles derived from primordial follicles. Fragments of bovine ovarian cortex were cultured in serum-free medium for 6 days; thereafter, secondary follicles were isolated for further culture. After a maximum total of 21 days in vitro, follicles were either processed for histological assessment or opened to release the oocyte-cumulus complexes for inspection by light microscopy. Compared with control, significant follicle and oocyte growth were observed in activin-exposed follicles, with or without FSH, with some oocyte diameters measuring over 100 microns following a total in vitro period of 15 days. Significant oestradiol secretion was observed in follicles cultured in activin alone after a total of 9 days in vitro compared with other treatment groups; however, this effect was not sustained. In summary, this study demonstrates the promotion of primordial bovine follicle development within a two-step serum-free culture system with oocyte diameters >100 mum achieved over 15 days in vitro. Further development of this system is needed to support complete oocyte growth and thereafter in vitro maturation.

Activin promotes follicular integrity and oogenesis in cultured pre-antral bovine follicles

The aim of this study was to determine the individual and combined effect of activin and follicle stimulating hormone (FSH) on somatic and germ cell development in cultured pre-antral follicles. Pre-antral bovine follicles (mean diameter 157 +/- 3, range 132-199 microm) were cultured for 8 days in serum-free medium in the presence of either 100 ng/ml of recombinant human activin A (rhAct A), 100 ng/ml rhAct A combined with a high (100 ng/ml) or low (50 ng/ml) concentration of recombinant FSH (rFSH) or 50 ng/ml rFSH alone. Intrafollicular connexin 43 expression and actin-based cell adhesion were assessed on Day 2 and 4 of culture. Steroidogenesis was evaluated after Day 4 and 8. Follicles exposed to 100 ng/ml activin maintained expression of connexin 43 at the follicular periphery. In the presence of activin, with or without 100 ng/ml or 50 ng/ml FSH, follicles were steroidogenic undergoing significant growth (P < 0.01), granulosa cell proliferation (P < 0.01) and antral cavity formation (P < 0.05) compared with cultured controls. Maximum oocyte growth occurred in the presence of 100 ng/ml activin alone with a significant percentage of these oocytes maintaining normal morphology over controls (P < 0.05). These results are consistent with a role for activin in maintaining oocyte granulosa cell interactions due to increased peripheral granulosa cell adhesion to the basement membrane and retention of adhesion at the surface of the zona pellucida. Thus, the polarized expression of cell contact interactions promoted by activin supports ongoing folliculogenesis.

The current knowledge on radiosensitivity of ovarian follicle development stages

BACKGROUND

The aim of this paper is to review the available information on ovarian radiation sensitivity and the genetic hazard of ionizing radiation in female mammals including humans.

METHODS

The literature present in the author's laboratories (international papers from the 1970s) was complemented by a Medline literature search using the keywords 'ionizing radiation genetic effects', 'oocyte radiosensitivity' and 'oocyte DNA repair' (1990-2008). Further articles were acquired from citations in the research papers and reports.

RESULTS

Animal data show that oocyte radiosensitivity varies widely according to the follicle/oocyte stage and the species. Oocytes near ovulation show the highest susceptibility to radiation induction of mutational events. Congenital anomalies have been observed after exposure to high doses (1-5 Gy), but extrapolation of these data to humans requires caution. In humans, the dose required to induce permanent ovarian failure would vary from 20.3 Gy at birth to 14.3 Gy at 30 years. Most epidemiological studies found little evidence of genetic diseases at the doses at which medical, occupational or accidental exposure occurred.

CONCLUSIONS

The fact that genetic effects were observed in irradiated animals suggests that these could also occur in humans. The probability of such events remains low compared with the 'spontaneous' risks of genetic effects.

A two-step serum-free culture system supports development of human oocytes from primordial follicles in the presence of activin

BACKGROUND

The objective of this study was to determine whether follicles grown within human ovarian cortical strip culture for 6 days in serum-free medium could be isolated at the secondary stage of pre-antral development and grown in vitro to the late pre-antral/early antral stage during a 4 day culture period.

METHODS

Ovarian cortical biopsies were obtained from six women aged 26-40 years, with informed consent, during elective Caesarean section. Small tissue slices of ovarian cortex, with underlying stromal tissue removed, were cultured in serum-free medium for 6 days and at the end of this period pre-antral (secondary) follicles were dissected from the strips. Seventy-four intact pre-antral follicles ranging in size (66-132 microm) (mean size 100 microm +/- 3.4) were selected for further culture. Follicles were placed individually within V-shaped microwell culture plates in serum-free medium in the presence (n = 38) or absence (n = 36) of 100 ng/ml of human recombinant activin A.

RESULTS

Pre-antral follicles grown for 4 days in the presence of activin A grew to a larger size (mean diameter 143 microm +/- 7.4) than those grown in control medium (mean diameter 111 microm +/- 8) (P < 0.005). Ninety percent of follicles cultured in the presence of activin A increased in size during the first 2 days of culture compared with only 36% of follicles in control medium (P > 0.005). Of the follicles surviving the entire culture period, 30% of those cultured in the presence of activin A showed normal morphology with intact oocytes and antral formation. None of the follicles grown in control medium developed antral cavities and >90% of those follicles collected at the end of the culture period showed signs of oocyte degeneration.

CONCLUSIONS

The results reported here demonstrate that under certain conditions, it is possible to achieve accelerated oocyte/follicle development from human primordial/primary follicles. This provides the first encouraging step towards achieving full in vitro growth of human oocytes.

Growth and differentiation factor-9 stimulates activation of goat primordial follicles in vitro and their progression to secondary follicles

The aim of the present study was to investigate the effects of growth and differentiation factor-9 (GDF-9) on the survival and activation of preantral follicles, as well as their subsequent progression to secondary follicles, using goat ovarian cortical culture in vitro. Pieces of ovarian cortex were cultured for 1 and 7 days in minimum essential medium (MEM) with or without different concentrations of GDF-9 (1–200 ng mL–1). On Day 0 and after 1 and 7 days of culture, cortical pieces were fixed for histological and transmission electron microscopy evaluation. Preantral follicles were classified according to their development stage (primordial, intermediate, primary and secondary) and on the basis of morphological features (normal or degenerated). In addition, follicular and oocyte diameters were determined before and after culture. The results showed that, compared with non-cultured cortical tissue (Day 0), the culture of ovarian tissue significantly reduced (P < 0.05) the percentage of normal follicles in all media tested, except for tissue cultured in the presence of 200 ng mL–1 GDF-9. Furthermore, in all media tested, the percentage of primordial follicles was significantly reduced (P < 0.05), with a concomitant increase in the percentage of developing follicles. The highest percentage of secondary follicles was observed after 7 days of culture in MEM plus 200 ng mL–1 GDF-9. At all concentrations of GDF-9 tested, follicular diameter increased significantly after 7 days of culture compared with non-cultured cortical tissue. In conclusion, the results of the present study indicate that 200 ng mL–1 GDF-9 maintains the survival of preantral follicles and promotes activation of primordial follicles. Furthermore, GDF-9 stimulates the transition from primary to secondary follicles, maintaining ultrastructural integrity of the follicles.