Formation of mammalian oocytes and their growth, differentiation and maturation within ovarian follicles

Cell-specific expression and immunolocalization of nitric oxide synthase isoforms and the related nitric oxide/cyclic GMP signaling pathway in the ovaries of neonatal and immature rats

OBJECTIVE

The present study is designed to investigate the cellular expressions and immunolocalizations of three different nitric oxide synthase (NOS) isoforms and the related nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) signaling pathway in the ovaries of neonatal and immature rats.

METHODS

The ovaries were obtained from ICR (Institute for Cancer Research) female Sprague-Dawley rats at postnatal days 1, 5, 7, 10, and 19. Then we carried out the histologic examination, immunohistochemistry, measurement of NOS activity, and modifications within the NO/cGMP pathway.

RESULTS

During postnatal days 1, 5, 7, 10, and 19, all three isoforms of NOS were mainly localized to the oocytes and expressed as a gradual increase in granulosa cells and theca cells within the growing follicle. The ovarian total NOS activities and NO levels were increased at postnatal days 7 and 10 compared with other days.

CONCLUSIONS

Our findings suggest that the locally produced NO and the NO/NOS signaling systems are involved in the follicular development to puberty.

In vitro growth and steroidogenesis of dog follicles are influenced by the physical and hormonal microenvironment

The present study examined the influences of the physical and hormonal microenvironment on in vitro growth and steroidogenesis of dog follicles. Follicles were enzymatically isolated and individually encapsulated in 0.5% (w/v; n=17) or 1.5% (n=10) alginate and cultured with 0.5 IU/ml equine chorionic gonadotropin for 192 h. In a separate experiment, follicles were encapsulated in 0.5% alginate and cultured with 0 (n=22), 1 (n=23), 10 (n=20) or 100 (n=21) μg/ml FSH for 240 h. Follicle diameter and steroid production were assessed every 48 h in both studies. Follicles encapsulated in the 0.5% alginate grew faster (P<0.05) than those cultured in the 1.5% concentration. Oestradiol (E(2)) and progesterone (P(4)) increased consistently (P<0.05) over time, and follicles in the 1.5% alginate produced more (P<0.05) P(4) than those in the 0.5% solution. Follicles cultured in the highest FSH concentration (100 μg/ml) increased 100% in size after 240 h compared with 50 to 70% in lower dosages. E(2) concentration remained unchanged over time (P>0.05) across FSH dosages. However, P(4) increased (P<0.05) as culture progressed and with increasing FSH concentration. Results demonstrate that dog follicles cultured in alginate retain structural integrity, grow in size and are hormonally active. Lower alginate and increasing FSH concentrations promote in vitro follicle growth. However, the absence of an E(2) rise in follicles cultured in FSH alone suggests the need for LH supplementation to support theca cell differentiation and granulosa cell function.

Leukemia inhibitory factor stimulates the transition of primordial to primary follicle and supports the goat primordial follicle viability in vitro

The aim of this study was to evaluate the effect of leukemia inhibitory factor (LIF) on the activation and survival of preantral follicles cultured in vitro enclosed in ovarian fragments (in situ). Goat ovarian cortex was divided into fragments to be used in this study. One fragment was immediately fixed (fresh control - FC) and the remaining fragments were cultured in supplemented minimum essential medium (MEM) without (cultured control - CC) or with different concentrations of LIF (1, 10, 50, 100 or 200 ng/ml) for 1 or 7 days, at 39°C in air with 5% CO2. Fresh control, CC and treated ovarian fragments were processed for histological and fluorescence analysis. The percentage of histological normal preantral follicles cultured for 7 days with 1 ng/ml (49.3%), 10 ng/ml (58.6%) and 50 ng/ml (58%) of LIF was higher than in the CC (32.6%; p < 0.05). After 7 days of culture, the percentage of primordial follicles in situ cultured with LIF decreased and primary follicles increased in all LIF concentrations compared with FC and CC (p < 0.05). In conclusion, LIF induced primordial follicle activation and supported preantral follicle viability of goat ovarian tissues cultured for 7 days.

Expression of follicle-stimulating hormone receptor (FSHR) in goat ovarian follicles and the impact of sequential culture medium on in vitro development of caprine preantral follicles

This study evaluated the expression of FSH receptors (FSHR) in the different stages of goat follicle development and investigated whether the addition of increasing concentrations of FSH throughout the culture period influences the survival, growth and antral formation of in vitro-cultured caprine preantral follicles. The expression of FSHR was analysed before and after culturing follicles using real-time RT-PCR. For the culture, preantral follicles (≥150 μm) were isolated from ovarian fragments and cultured for 18 days in α-MEM+ alone or associated with recombinant FSH (rFSH: 100 or 1000 ng/ml), or in α-MEM+ supplemented with increasing concentrations of FSH throughout culture periods as follows: (a) sequential medium 1: FSH 100 ng/ml (from day 0 to 6), FSH 500 ng/ml (from day 6 to 12) and FSH 1000 ng/ml (from day 12 to 18); and (b) sequential medium 2: FSH 500 ng/ml (from day 0 to 9) and 1000 ng/ml (from day 9 to 18). Follicle development was evaluated on the basis of antral cavity formation, follicular and oocyte growth, and cumulus-oocyte complex health. The expression of FSHR in isolated caprine follicles increased from the preantral to antral phase. Regarding the culture, after 18 days, sequential medium 1 promoted follicular survival, antrum formation and a reduction in oocyte extrusion. Both sequential media promoted a higher rate of meiotic resumption compared with the other treatments. In conclusion, the addition of increased concentrations of FSH (sequential medium) has a significant impact on the in vitro development of caprine preantral follicles.

Newborn pig ovarian tissue xenografted into Severe Combined Immunodeficient (SCID) mice acquires limited responsiveness to gonadotropins

In the pig ovary, the transition from primordial to primary and secondary ovarian follicles begins before birth, but antral follicles can be observed, for the first time, at approximately 60-90 d of age. At approximately the same time, secondary follicles become responsive to gonadotropins, leading to the formation of antral follicles. Placing pieces of ovarian tissue under the kidney capsule of immunodeficient (SCID) mice allows the requirements for follicular recruitment and development to be studied. The objective of this study was to investigate if primordial follicles contained in ovarian fragments isolated from newborn piglets (36 +/- 12 h old) and immediately transplanted under the kidney capsule of SCID mice, are able to become responsive to gonadotropins after 60 d (as in an unaltered animal). Ovarian fragments were transplanted under the kidney capsule of three groups of four female and four male SCID mice. The first group did not receive any hormonal treatment for 12 wk. The second group was treated from the 9th week with 1 IU of FSH/LH on alternating days for 3 wk, and the third group was treated with 5 IU Pregnant Mare Serum Ganadotropin (PMSG) 48 h before euthanasia. Primordial follicles contained in ovarian fragments isolated from newborn piglets developed only to the secondary stage. Therefore, development of gonadotropin responsiveness in ovarian fragments xenotransplanted in SCID mice was delayed compared to what occurs in the unaltered animal, and there was minimal response to exogenous gonadotropins.

Mouse TRIP13/PCH2 is required for recombination and normal higher-order chromosome structure during meiosis

Accurate chromosome segregation during meiosis requires that homologous chromosomes pair and become physically connected so that they can orient properly on the meiosis I spindle. These connections are formed by homologous recombination closely integrated with the development of meiosis-specific, higher-order chromosome structures. The yeast Pch2 protein has emerged as an important factor with roles in both recombination and chromosome structure formation, but recent analysis suggested that TRIP13, the mouse Pch2 ortholog, is not required for the same processes. Using distinct Trip13 alleles with moderate and severe impairment of TRIP13 function, we report here that TRIP13 is required for proper synaptonemal complex formation, such that autosomal bivalents in Trip13-deficient meiocytes frequently displayed pericentric synaptic forks and other defects. In males, TRIP13 is required for efficient synapsis of the sex chromosomes and for sex body formation. Furthermore, the numbers of crossovers and chiasmata are reduced in the absence of TRIP13, and their distribution along the chromosomes is altered, suggesting a role for TRIP13 in aspects of crossover formation and/or control. Recombination defects are evident very early in meiotic prophase, soon after DSB formation. These findings provide evidence for evolutionarily conserved functions for TRIP13/Pch2 in both recombination and formation of higher order chromosome structures, and they support the hypothesis that TRIP13/Pch2 participates in coordinating these key aspects of meiotic chromosome behavior.

Meiosis is the specialized cell division that gives rise to reproductive cells such as sperm and eggs. During meiosis in most organisms, genetic information is exchanged between homologous maternal and paternal chromosomes through the process of homologous recombination. This recombination forms connections between homologous chromosomes that allow them to segregate accurately when the meiotic cell divides. Recombination defects can result in reproductive cells with abnormal chromosome numbers, which are a major cause of developmental disorders and spontaneous abortions in humans. Meiotic recombination is tightly controlled such that each pair of chromosomes undergoes at least one crossover recombination event despite a low average number of crossovers per chromosome. Recombination is coordinated with the development of specialized, meiosis-specific chromosome structures that stabilize pairing interactions between homologous maternal and paternal chromosomes. We show here that the mouse TRIP13 protein is required for normal execution of many aspects of meiotic recombination and chromosome structure development that it was not previously known to influence. Intriguingly, many of these new roles appear to parallel known functions of a homologous protein from budding yeast, called Pch2. These findings thus indicate that TRIP13/Pch2 functions are more widely conserved throughout evolution than thought before.

Real-time qRT-PCR analysis of EGF receptor in cumulus-oocyte complexes recovered by laparoscopy in hormonally treated goats

Ovarian stimulation with exogenous follicle stimulating hormone (FSH) has been used to increase the number of viable oocytes for laparoscopic oocyte recovery (LOR) in goats. The aim of this study was to evaluate the effect of two FSH protocols for ovarian stimulation in goats on the expression pattern of epidermal growth factor (EGF) receptor (EGFR) in cumulus–oocyte complexes (COCs) recovered by LOR. After real-time qRT-PCR analysis, expression profiles of morphologically graded COCs were compared prior to and after in vitro maturation (IVM) on a FSH protocol basis. The use of a protocol with higher number of FSH injections at a shorter interval resulted in GI/GII COCs with a higher level of EGFR expression in cumulus cells, but not in the oocyte, which was correlated with an elevated meiotic competence following IVM. Based on the maturation profile and EGFR expression patterns observed between groups, the morphological selection of COCs prior to IVM was not a good predictor of oocyte meiotic competence. Therefore, EGFR may be a good candidate marker for indirect prediction of goat oocyte quality. The IVM process of goat COCs increased the EGFR expression in oocytes and cumulus cells, which seemed to be strongly associated with the resumption of meiosis. In summary, differential EGFR expression in goat cumulus cells was associated with the in vivo prematuration process, and in turn, the upregulation in the entire COC was associated with IVM. Cause-and-effect relationships between such increased expression levels, particularly in the oocyte, and oocyte competence itself still need to be further investigated.

Current achievements and future research directions in ovarian tissue culture, in vitro follicle development and transplantation: implications for fertility preservation

BACKGROUND Female cancer patients are offered 'banking' of gametes before starting fertility-threatening cancer therapy. Transplants of fresh and frozen ovarian tissue between healthy fertile and infertile women have demonstrated the utility of the tissue banked for restoration of endocrine and fertility function. Additional methods, like follicle culture and isolated follicle transplantation, are in development. METHODS Specialist reproductive medicine scientists and clinicians with complementary expertise in ovarian tissue culture and transplantation presented relevant published literature in their field of expertise and also unpublished promising data for discussion. As the major aims were to identify the current gaps prohibiting advancement, to share technical experience and to orient new research, contributors were allowed to provide their opinioned expert views on future research. RESULTS Normal healthy children have been born in cancer survivors after orthotopic transplantation of their cryopreserved ovarian tissue. Longevity of the graft might be optimized by using new vitrification techniques and by promoting rapid revascularization of the graft. For the in vitro culture of follicles, a successive battery of culture methods including the use of defined media, growth factors and three-dimensional extracellular matrix support might overcome growth arrest of the follicles. Molecular methods and immunoassay can evaluate stage of maturation and guide adequate differentiation. Large animals, including non-human primates, are essential working models. CONCLUSIONS Experiments on ovarian tissue from non-human primate models and from consenting fertile and infertile patients benefit from a multidisciplinary approach. The new discipline of oncofertility requires professionalization, multidisciplinarity and mobilization of funding for basic and translational research.

Stability of housekeeping genes and expression of locally produced growth factors and hormone receptors in goat preantral follicles

The aim of the present study was to investigate the stability of six housekeeping genes, and the relative expression of growth factors (EGF, GDF-9, BMP-15, VEGF, FGF-2, BMP-6, IGF-1 and KL) and hormone receptors (FSH, LH and GH) in goat preantral follicles. To evaluate to stability of housekeeping genes micro-dissected fresh follicles (150–200 μm) as well as follicles that have been in vitro cultured for 12 days were used. In addition, isolated fresh follicles were used to compare expression of various growth factors and hormone receptors before culture. Both fresh and cultured follicles were subjected to total RNA extraction and synthesis of cDNA. After amplification of cDNA by real-time PCR, the geNorm software program was used to evaluate the stability of glyceraldehyde-2-phosphate dehydrogenase (GAPDH), β-tubulin, β-actin, phosphoglycerokinase (PGK), 18S rRNA, ubiquitin (UBQ) and ribosomal protein 19 (RPL-19). In addition, follicular steady-state levels of mRNA from the various growth factors under study were compared. Results demonstrated that, in goat preantral follicles, UBQ and β-actin were the most suitable reference genes and thus could be used as parameters to normalize data from future in vitro studies. In contrast, 18S RNA appeared the least stable gene among the tested housekeeping genes. Analysis of mRNA for several hypophyseal hormone receptors in fresh preantral follicles showed significantly higher FSH-R mRNA levels than those of LH-R and GH-R, and no difference between GH-R and LH-R mRNA levels. In regard growth factor mRNA expression in goat preantral follicles, EGF mRNA levels appeared significantly lower than those of the other studied growth factors. Increasingly higher relative mRNA levels were observed for GDF-9, BMP-15, BMP-6, FGF-2, VEGF, Kl and IGF-1, successively. In conclusion, UBQ and β-actin are the most stable housekeeping genes in fresh and 12-days cultured caprine preantral follicles. Furthermore, in fresh follicles, high levels of FSH-R mRNA are detected while among eight growth factors, IGF-1 is the most highly expressed and EGF the weakest expressed compound.

Follicular morphology, oocyte diameter and localisation of fibroblast growth factors in the domestic dog ovary

Remarkably little is known about folliculogenesis in the dog. Objectives were to characterise (1) changes in follicle/oocyte diameter and granulosa cell number and (2) localisation of fibroblast growth factor (FGF)-2 and FGF-7 during dog ovarian follicle development. Fourteen ovarian pairs were excised and processed for histological evaluation. Two to four serial sections/bitch were stained with hematoxylin, and follicle/oocyte diameters and granulosa cell number were determined at each developmental stage. Mean follicle and oocyte size were compared among stages by one-way analysis of variance. Relationships between follicle and oocyte size and granulosa cell number were determined using correlation and regression analysis, respectively. Another eight serial sections/bitch were processed for immunostaining to determine FGF-2 and FGF-7 localisation. Primordial and primary follicles were similar in size, but smaller than the progressively increasing (p < 0.05) diameter of the later stages. Oocyte diameter gradually increased (p < 0.05) among oocytes derived from primordial, primary, secondary and early antral follicles with no difference (p > 0.05) thereafter. Oocyte size and granulosa cell number increased (p < 0.01) with follicular diameter. Except during anoestrus, FGF-2 occurred in oocytes and granulosa cells of primordial to secondary follicles. In adult bitches, FGF-7 was localised in granulosa cells of primary and secondary follicles and also occurred in the theca layer of antral follicles during prooestrus and oestrus. In summary, folliculogenesis in the domestic dog occurs in two phases: pre-antral phase characterised by increasing follicle size in association with oocyte growth and granulosa cell proliferation and antral phase linked with marked granulosa cell proliferation and accumulation of antral cavity fluid. Finally, the temporal localisation pattern of FGF-2 implies its role in follicular activation, whereas FGF-7 activities appear related to later folliculogenesis.

Oogenesis specific genes (Nobox, Oct4, Bmp15, Gdf9, Oogenesin1 and Oogenesin2) are differentially expressed during natural and gonadotropin-induced mouse follicular development

Using a semi-quantitative, single-cell sensitive RT-PCR method, we studied the expression of oogenesis specific genes (Nobox, Oct4, Bmp15, Gdf9, Oogenesin1 and Oogenesin2) in single oocytes collected from primordial, primary, secondary, preantral and antral follicles during natural and gonadotropin-induced mouse follicular development. We compared the number of transcripts of these genes, showing that they are differentially expressed, both in natural conditions and under gonadotropin-induction throughout the assessed developmental stages. Our data show a clear increase in the number of transcripts between the primordial until the preantral stages, with the exception of the Oogenesin1 transcripts under gonadotropin-induction. The number of transcripts starts decreasing at the antral stage and proceeds until the metaphase II stage, with values very similar to those obtained for the primordial oocytes in both analyzed conditions. Under exogenous gonadotropin-induction, oocyte recruitment to ovulation at the preantral stage is marked by an increase in Nobox and Oogenesin2 gene expression that is concomitant with a decrease in Oogenesin1 gene expression. Oocytes that are able to proceed into whole embryo development show a tight regulation of Nobox and Oct4 expression at the antral stage. A parallel immunocytochemical study at the protein level corroborates these findings.

Primordial germ cell-like cells differentiated in vitro from skin-derived stem cells

Background

We have previously demonstrated that stem cells isolated from fetal porcine skin have the potential to form oocyte-like cells (OLCs) in vitro. However, primordial germ cells (PGCs), which must also be specified during the stem cell differentiation to give rise to these putative oocytes at more advanced stages of culture, were not systematically characterized. The current study tested the hypothesis that a morphologically distinct population of cells derived from skin stem cells prior to OLC formation corresponds to putative PGCs, which differentiate further into more mature gametes.

Methodology/Principal Findings

When induced to differentiate in an appropriate microenvironment, a subpopulation of morphologically distinct cells, some of which are alkaline phosphatase (AP)-positive, also express Oct4, Fragilis, Stella, Dazl, and Vasa, which are markers indicative of germ cell formation. A known differentially methylated region (DMR) within the H19 gene locus, which is demethylated in oocytes after establishment of the maternal imprint, is hypomethylated in PGC-like cells compared to undifferentiated skin-derived stem cells, suggesting that the putative germ cell population undergoes imprint erasure. Additional evidence supporting the germ cell identity of in vitro-generated PGC-like cells is that, when labeled with a Dazl-GFP reporter, these cells further differentiate into GFP-positive OLCs.

Significance

The ability to generate germ cell precursors from somatic stem cells may provide an in vitro model to study some of the unanswered questions surrounding early germ cell formation.

Identification and characterization of miRNAs expressed in the bovine ovary

Background

MicroRNAs are the major class of gene-regulating molecules playing diverse roles through sequence complementarity to target mRNAs at post-transcriptional level. Tightly regulated expression and interaction of a multitude of genes for ovarian folliculogenesis could be regulated by these miRNAs. Identification of them is the first step towards understanding miRNA-guided gene regulation in different biological functions. Despite increasing efforts in miRNAs identification across various species and diverse tissue types, little is known about bovine ovarian miRNAs. Here, we report the identification and characterization of miRNAs expressed in the bovine ovary through cloning, expression analysis and target prediction.

Results

The miRNA library (5'-independent ligation cloning method), which was constructed from bovine ovary in this study, revealed cloning of 50 known and 24 novel miRNAs. Among all identified miRNAs, 38 were found to be new for bovine and were derived from 43 distinct loci showing characteristic secondary structure. While 22 miRNAs precursor loci were found to be well conserved in more than one species, 16 were found to be bovine specific. Most of the miRNAs were cloned multiple times, in which let-7a, let-7b, let-7c, miR-21, miR-23b, miR-24, miR-27a, miR-126 and miR-143 were cloned 10, 28, 13, 4, 11, 7, 6, 4 and 11 times, respectively. Expression analysis of all new and some annotated miRNAs in different intra-ovarian structures and in other multiple tissues showed that some were present ubiquitously while others were differentially expressed among different tissue types. Bta-miR-29a was localized in the follicular cells at different developmental stages in the cyclic ovary. Bio-informatics prediction, screening and Gene Ontology analysis of miRNAs targets identified several biological processes and pathways underlying the ovarian function.

Conclusion

Results of this study suggest the presence of miRNAs in the bovine ovary, thereby elucidate their potential role in regulating diverse molecular and physiological pathways underlying the ovarian functionality. This information will give insights into bovine ovarian miRNAs, which can be further characterized for their role in follicular development and female fertility as well.

Interaction between ascorbic acid and follicle-stimulating hormone maintains follicular viability after long-term in vitro culture of caprine preantral follicles

This study evaluates the effects of ascorbic acid and its interaction with follicle-stimulating hormone (FSH) on the morphology, activation, and in vitro growth of caprine preantral follicles. Ovarian fragments were cultured for 1, 7, or 14 d in minimum essential medium (MEM) containing ascorbic acid (50 or 100microg/mL), FSH (50ng/mL), or both of these substances. Ovarian tissue that was either fresh (control) or cultured for 1, 7, or 14 d was processed for histological and ultrastructural evaluation. The results showed that after 14 d of culture, medium supplemented with 50microg/mL of ascorbic acid alone or combined with FSH showed higher rates of follicular survival compared with MEM. After 7 d of culture, FSH, ascorbic acid at 50microg/mL with or without FSH, and ascorbic acid at 100microg/mL increased the percentage of follicular activation compared to fresh control. In addition, FSH alone significantly increased the percentage of growing follicles after 14 d. The combination of 50microg/mL of ascorbic acid and FSH promoted a significant increase in oocyte and follicular diameter after 7 d of culture. Ultrastructural and fluorescent analysis confirmed the integrity of follicles cultured with 50microg/mL of ascorbic acid and FSH after 14 d. In conclusion, the combination of 50microg/mL of ascorbic acid and FSH maintained follicular integrity and promoted follicular activation and growth after long-term in vitro culture of caprine preantral follicles.

Maternal imprinting during mouse oocyte growth in vivo and in vitro

Epigenetic regulation of gene expression is critical for oogenesis in mammals. In this study, a simple and efficient method was used to obtain the oocytes from cultured fetal mouse ovaries of 12.5dpc. The methylation pattern of these oocytes was examined. The results showed that the establishment of imprinting of Igf2r and Peg3 in oocytes derived from cultured fetal mouse germ cells in vitro follows a slower time course than that of oocytes in vivo. However, oocytes in vitro and in vivo share similar methylation patterns. Igf2r was gradually de novo methylated, and the methylation covers 80% CpG sites in oocytes cultured for 28days. However, only 45% of the CpG sites is methylated in Peg3 at the same stage. Furthermore, it demonstrated that the degree of DNA methylation is positively correlated with the size of oocytes in vitro and in vivo, indicating a progressive methylation process during oocyte growth.

Highly sensitive saturation labeling reveals changes in abundance of cell cycle-associated proteins and redox enzyme variants during oocyte maturation in vitro

Oocyte maturation is a complex process and a critical issue in assisted reproduction techniques (ART) in humans and other mammals. We used a sensitive 2-D DIGE saturation labeling approach including an internal pooled standard for quantitative proteome profiling of immature versus in vitro matured bovine oocytes in six independent samples. The study comprised 48 2D gel images representing 24 DIGE experiments. From 250 ng sample analyzed per gel, quantitative analysis revealed an average of 2244 spots in pH 4-7 images and 1291 spots in pH 6-9 images. Thirty-eight spots with different intensities were detected in total. Spots of a preparative gel from 2200 oocytes were identified by nano-LC-MS/MS analysis. The ten spots which could be unambiguously identified include the Ca2+-binding protein translationally controlled tumor protein, enzymes of the Krebs and pentose phosphate cycles, clusterin, 14-3-3 epsilon, elongation factor-1 gamma, and redox enzymes such as polymorphic forms of GST Mu 5 and peroxiredoxin-3. The cellular distribution of two proteins was determined by confocal laser scanning microscopy. The interesting protein candidates identified by this study may help to improve the in vitro maturation process in order to increase the rate of successful in vitro fertilization and other ART in cattle and other mammals.

Potential regulatory functions of microRNAs in the ovary

The interactions between ovarian germ and somatic cells and expression of several intraovarian autocrine/paracrine regulators are major contributing factors in the ovary. These intraovarian mediators regulate various ovarian cellular activities including cell growth, differentiation, and apoptosis, which are critical in follicular development. MicroRNAs (miRNAs) have emerged as key components of posttranscriptional gene expression. Recent evidence generated in mice implicates the regulatory function of miRNAs in oocyte maturation and ovarian follicular development. In the human, miRNAs may target specific gene expression in granulosa cells and participate in establishment and progression of ovarian cancer. Here, we review the currently available information on the expression and potential regulatory functions of miRNAs in the ovary under normal and pathologic conditions. Understanding the underlying mechanisms of how ovarian germ cell and somatic cell miRNAs are regulated and identifying their specific target genes and their functions may lead to the development of strategies to achieve target-specific gene regulation for the prevention and treatment of various ovarian disorders.

Essential role of follicle stimulating hormone in the maintenance of caprine preantral follicle viability in vitro

The aims of the present study were to investigate the effects of follicle-stimulating hormone (FSH) on survival, activation and growth of caprine primordial follicles using histological and ultrastructural studies. Pieces of caprine ovarian cortex were cultured for 1 or 7 days in minimum essential medium (MEM - control medium) supplemented with different concentrations of FSH (0, 10, 50 or 100 ng/ml). Small fragments from non-cultured ovarian tissue and from those cultured for 1 or 7 days in a specific medium were processed for classical histology and transmission electron microscopy (TEM). Additionally, effects of FSH on oocyte and follicle diameter of cultured follicles were evaluated. The results showed that the lowest percentage of normal follicles was observed after 7 days of culture in control medium. After 1 day of culture, a higher percentage of growing follicles was observed in the medium supplemented with 50 ng/ml of FSH. In the presence of 10 and 50 ng/ml of FSH, an increase in diameter of both oocyte and follicle on day 7 of culture was observed. TEM showed ultrastructural integrity of follicles after 1 day of culture in MEM and after 7 days in MEM plus 50 ng/ml FSH, but did not confirm the integrity of those follicles cultured for 7 days in MEM. In conclusion, this study demonstrated that FSH at concentration of 50 ng/ml not only maintains the morphological integrity of 7 days cultured caprine preantral follicles, but also stimulate the activation of primordial follicles and the growth of activated follicles.

Reduced fertility in high-yielding dairy cows: are the oocyte and embryo in danger? Part I. The importance of negative energy balance and altered corpus luteum function to the reduction of oocyte and embryo quality in high-yielding dairy cows

Fertility in high yielding dairy cows is declining, and there is increasing evidence to presume that oocyte and embryo quality are major factors in the complex pathogenesis of reproductive failure. In this report we present an overview of possible mechanisms linking negative energy balance (NEB) and deficiencies in oocyte and embryo developmental competence; specifically, in the high producing dairy cow. Changes in follicular growth patterns during a period of NEB can indirectly affect oocyte quality. The endocrine and biochemical changes, which are associated with NEB, are reflected in the microenvironment of the growing and maturing female gamete, and likely result in the ovulation of a developmentally incompetent oocyte. Even after an oocyte is successfully ovulated and fertilized, a full-term pregnancy is still not guaranteed. Inadequate corpus luteum function, associated with reduced progesterone, and probably also low insulin-like growth factor concentrations, can cause a suboptimal microenvironment in the uterus that is incapable of sustaining early embryonic life. This may partly account for the low conception rates and the high incidence of early embryonic mortality in high yielding dairy cows.

Spatio-Temporal Expression Patterns of Aurora Kinases A, B, and C and Cytoplasmic Polyadenylation-Element-Binding Protein in Bovine Oocytes During Meiotic Maturation1

Maturation of immature bovine oocytes requires cytoplasmic polyadenylation and synthesis of a number of proteins involved in meiotic progression and metaphase-II arrest. Aurora serine-threonine kinases--localized in centrosomes, chromosomes, and midbody--regulate chromosome segregation and cytokinesis in somatic cells. In frog and mouse oocytes, Aurora A regulates polyadenylation-dependent translation of several mRNAs such as MOS and CCNB1, presumably by phosphorylating CPEB, and Aurora B phosphorylates histone H3 during meiosis. We analyzed the expression of three Aurora kinase genes--AURKA, AURKB, and AURKC--in bovine oocytes during meiosis by reverse transcription followed by quantitative real-time PCR and immunodetection. Aurora A was the most abundant form in oocytes, both at mRNA and protein levels. AURKA protein progressively accumulated in the oocyte cytoplasm during antral follicle growth and in vitro maturation. AURKB associated with metaphase chromosomes. AURKB, AURKC, and Thr-phosphorylated AURKA were detected at a contractile ring/midbody during the first polar body extrusion. CPEB, localized in oocyte cytoplasm, was hyperphosphorylated during prophase/metaphase-I transition. Most CPEB degraded in metaphase-II oocytes and remnants remained localized in a contractile ring. Roscovitine, U0126, and metformin inhibited meiotic divisions; they all induced a decrease of CCNB1 and phospho-MAPK3/1 levels and prevented CPEB degradation. However, only metformin depleted AURKA. The Aurora kinase inhibitor VX680 at 100 nmol/L did not inhibit meiosis but led to multinuclear oocytes due to the failure of the polar body extrusion. Thus, in bovine oocyte meiosis, massive destruction of CPEB accompanies metaphase-I/II transition, and Aurora kinases participate in regulating segregation of the chromosomes, maintenance of metaphase-II, and formation of the first polar body.

Leukemia inhibitory factor induces cumulus expansion in immature human and mouse oocytes and improves mouse two-cell rate and delivery rates when it is present during mouse in vitro oocyte maturation

OBJECTIVE

To examine the role of leukemia inhibitory factor (LIF) during in vitro maturation (IVM) on human and mice cumulus expansion and mice oocyte competence by in vitro fertilization (IVF), culture, and embryo transfer (ET).

DESIGN

Prospective animal and human study.

SETTING

Serono laboratories and IVF clinic.

PATIENT(S)

Healthy women volunteers and 8-week-old female mice.

INTERVENTION(S)

Cumulus compacted human and mice oocytes were matured in IVM media with and without recombinant follicle-stimulating hormone (FSH) and with and without LIF. Mice IVM oocytes with and without 0.2 IU/mL of recombinant FSH; or with and without recombinant FSH + LIF (0.1, 1.0, 1000.0 ng/mL) and ovulated oocytes were in vitro fertilized and cultured. We transferred 395 blastocysts to the uterine horn of 2.5-day pseudopregnant female mice.

MAIN OUTCOME MEASURE(S)

Cumulus expansion in human and mice oocytes, and two-cell rate, blastocyst rate, and delivered rate of live pups in mice.

RESULT(S)

In human and mouse oocytes, LIF induced cumulus expansion. When 1000 ng/mL of LIF was added in combination with recombinant FSH, a statistically significant increase in cleavage rate, embryo development rate, and birth rate was observed when compared with oocytes matured with FSH alone.

CONCLUSION(S)

Leukemia inhibitory factor induced cumulus expansion similarly in human and mouse cumulus-oocyte complexes, and recombinant FSH plus LIF supplementation during mouse IVM significantly improved oocyte competence as measured by cleavage rate, blastocyst development, and birth rate.

Effect of sodium nitroprusside, a nitric oxide donor, on the in vitro maturation of bovine oocytes

Nitric oxide (NO) is a highly reactive free radical involved in intra- and intercellular signaling in various stages of reproduction. The objective of the present study was to evaluate the effect of the addition of sodium nitroprusside (SNP), a NO donor, on nuclear and cytoplasmic in vitro maturation of bovine oocytes. Analysis of variance was conducted and the means were compared by t test at a level of 5%. Low (10(-7) and 10(-9)M) and intermediate (10(-5)M) concentrations of SNP had no significant effect on nuclear maturation, however, when a greater concentration of SNP (10(-3)M) was added, oocytes remained in metaphase I (MI) after 24 h culture (P<0.05) and did not show cumulus expansion. To evaluate if this effect was reversible and if a retardation or inhibition had occurred in the progression from MI to MII, oocytes were cultured in presence of 10(-3)M of SNP for 24 h followed by culture for an additional 24 h in medium with or without SNP. After 48 h, the oocytes remained in MI even when the medium was changed at 24 h with or without SNP. The kinetics of nuclear maturation was assessed to evaluate if there had been or not a retardation in the progression of meiosis with the concentration of 10(-3)M SNP. This concentration delayed germinal vesicle breakdown (VGBD) at 8 h of culture (P<0.05), and at 12 h there was no significant difference between the control and the treated group. The concentrations that did not induce alterations in nuclear maturation were evaluated for cytoplasmic maturation. The concentration of 10(-5)M improved the percentage of peripheral cortical granules (P<0.05), and significantly increased the percentage of blastocysts. These results demonstrate that SNP at greater concentrations (10(-3)M) has a cytotoxic effect, but at intermediate (10(-5)M) concentrations it increases blastocyst rates. NO exhibits a dual effect on bovine oocytes, inhibits (10(-3)M of SNP) nuclear and cytoplasmic maturation or stimulates (10(-5)M of SNP) cytoplasmic maturation, depending on concentration in the culture medium.

Isolation, characterization, and in vitro and in vivo differentiation of putative thecal stem cells

Although ovarian theca cells play an indispensable role in folliculogenesis by providing follicular structural integrity and steroid substrates for estrogen production, little information is available about their recruitment, growth, and differentiation because their immature forms have not been identified. We have isolated putative thecal stem cells with the ability to self-renew and differentiate in vivo and in vitro. They are similar to fibroblasts in morphology and proliferate in vitro as round colonies with a homogenous cell population. They were induced to differentiate into early precursors and steroidogenic cells in a stepwise manner after treatment with serum, luteinizing hormone, and paracrine factors from granulosa cells. At each differentiation step, these cells displayed appropriate gene expression and morphological markers and later secreted androstenedione. The fully mature morphology was achieved by coculture with isolated granulosa cells. When transplanted into the ovaries, the putative thecal stem cells colonized exclusively in the ovarian interstitium and the thecal layer of follicles as differentiated cells. Thus, thecal stem cells appear to be present in neonatal ovaries and can be isolated, purified, and induced to differentiate in vitro. Thecal stem cells could provide an invaluable in vitro experimental system to study interactions among the oocytes, granulosa cells, and theca cells during normal folliculogenesis and to study ovarian pathology caused by theca cell dysfunction.

ISWI chromatin remodeling in ovarian somatic and germ cells: revenge of the NURFs

Chromatin has emerged as an important regulator of gene expression, interposed between cell signaling pathways and transcriptional machinery. It participates in transmitting extra- and intra-cellular signals that coordinate ovarian events: ovarian follicle development, the meiotic maturation of the oocyte that precedes ovulation, and the ovulatory process and consequent luteinization. Recent evidence from model organisms and mammals suggests that chromatin signaling is achieved, in part, by imitation switch (ISWI) ATP-dependent chromatin-remodeling complexes. This review highlights a role for complexes containing the ISWI ATPase sucrose nonfermenting-2h (Snf2h) in proliferation in somatic and germ cells and also in meiosis in germ cells. Moreover, complexes containing the Snf2l ATPase dictate the differentiation of somatic cells and act in the induction of the terminal phases of meiosis in the oocyte.

Age, FSH Dose and Follicular Aspiration Frequency Affect Oocyte Yield from Juvenile Donor Lambs

Experiments were conducted to determine the effects of lamb age, frequency of follicular aspirations, and hormone stimulation by fixed or variable FSH dose, on the number of collected oocytes and their maturational competence. In trial 1, the characteristics of follicular population (number and diameter of follicles) were studied in 40 lambs which were slaughtered at the age of 30 days (S1), 42 days (S2), 60 days (S3) and 5-6 months (S4), each n = 10. In trial 2, 27 lambs were divided into four groups. group MF lambs (n = 6) had follicular aspiration (OPU) in four monthly intervals commencing from the age of 8-9 weeks (sessions MF1, MF2, MF3 and MF4). In groups SF2, SF3 and SF4 (each n = 6), OPU was conducted once during the 12-13, 16-17 and 20-21 week of age, respectively. Ovarian stimulation was conducted with fixed FSH dose (3.52 mg/animal). In trial 3, 10 lambs (group MV) were treated as those of group MF apart from the FSH dose, which was administered according to the body weight in a dose of 0.27 mg/kg. The number and the size of follicles, the number and the quality of collected oocytes and the maturational competence of the oocytes were compared between and within groups. In trial 1, the total number and the number of small follicles were greater in groups S1 and S2 compared with those of S3 and S4 (p < 0.01). Similarly, the follicular population was greater in group MF1 than in group SF3 (p < 0.01). In sessions MF2, MF3, MV2, MV3 and MV4, more oocytes were collected in comparison with those from the respective once-aspirated age mates (groups SF2, SF3 and SF4). In total, more (p = 0.02) oocytes per donor were collected from group MV (15.2 +/- 5.5) than from group MF (9.0 +/- 3.2). An absolute maturational failure was observed in oocytes collected from groups SF2 and SF3. Maturational competence varied between 16.7% and 58.3% (p = 0.017) among sessions of group MF, but it was more uniform among sessions of group MV (range 12.5-42.9%, p > 0.05). Our results indicate that firstly, the number and the quality of harvested oocytes from juvenile lambs can be much improved if follicular stimulation regime is adjusted to the body weight. Secondly, in terms of follicular population and oocyte quality, 3 and 4-month-old lambs are naturally bad oocyte donors, but this characteristic can be reversed by a previous follicular ablation.

Effects of fibroblast growth factor-2 on the in vitro culture of caprine preantral follicles

The aims of the present study were to evaluate the effects of fibroblast growth factor-2 (FGF-2) on survival, activation and growth of caprine early-staged (preantral) follicles using histological and ultrastructural studies. Fragments of caprine ovarian cortex were cultured for 1 or 5 days in an enriched minimum essential medium, supplemented or not with different concentrations of FGF-2 (10, 50 or 100 ng/ml). Fragments from non-cultured ovarian tissue (control) and from tissues cultured for 1 or 5 days in a specific medium were processed for transmission electron microscopy (TEM) or classical histology to evaluate the morphological quality of caprine preantral follicles and to calculate the percentages of normal follicles. Additionally, effects of FGF-2 on oocyte and follicle diameter of cultured preantral follicles were investigated. Our results showed that, although the percentages of histologically normal follicles were lower in cultured than in non-cultured ovarian tissue fragments, there were no differences in this regard among treatments, neither on day 1 nor on day 5 of culture. After 1 and 5 days of culture, a significantly higher percentage of growing follicles was observed in the medium supplemented with 50 ng/ml of FGF-2. This FGF-2 treatment furthermore resulted in an increase in diameter of both oocytes and follicles that were cultured for 5 days. TEM showed that the ultrastructural integrity of caprine preantral follicles was maintained during their 5-day culture in the presence of 50 ng/ml FGF-2. In conclusion, this study demonstrated that at a concentration of 50 ng/ml FGF-2 not only maintains the morphological integrity of caprine preantral follicles cultured for 5 days, but also stimulates the activation of primordial follicles and the growth of activated follicles.

Cystathionine beta synthase participates in murine oocyte maturation mediated by homocysteine

Our previous study demonstrated that cystathionine beta synthase (CBS) is highly expressed in the cumulus-oocyte complex during ovulation. However, the role of CBS during oocyte maturation remains uncertain. In this study, a small-interfering (si) RNA interference (siRNA) approach was used to investigate the potential role of CBS during oocyte maturation. Accompanied with a gradual increase of homocysteine, the introduction of CBS-siRNA into murine granulosa cells selectively depleted the corresponding target mRNA and protein for CBS as assessed by semi-quantitative reverse-transcriptase PCR (RT-PCR) and immunofluorescence staining. When fully grown, germinal vesicle (GV) oocytes matured in vitro for 16 h using medium from transfected granulosa cells, the functional suppression of CBS resulted in a significant increase in the rate of GV-arrested oocytes. The results of this study provide evidence that CBS participates in the process of oocyte maturation. Furthermore, this effect may be fulfilled by conditioning the level of homocysteine in the microenvironment of the oocyte.

The Kit ligand/c-Kit receptor system in goat ovaries: gene expression and protein localization

Relatively little information is available on the local factors that regulate folliculogenesis in goats. To examine the possibility that the Kit ligand (KL) system is expressed throughout the folliculogenesis, we studied the presence and distribution of KL and its receptor, c-Kit, in goat ovaries. Ovaries of goats were collected and either fixed in paraformaldehyde for immunohistochemical localization of KL and c-Kit proteins, or used for the isolation of follicles, luteal cells, surface epithelium and medullary samples to study mRNA expression for KL and c-Kit, using the reverse transcriptase polymerase chain reaction (RT-PCR). KL protein and mRNA were found in follicles at all stages of development, i.e. primordial, primary, secondary, small and large antral follicles, as well as in corpora lutea, surface epithelium and medullary tissue. Antral follicles expressed both KL-1 and KL-2 mRNAs, while earlier staged follicles expressed KL-1 transcript only. KL protein was demonstrated in granulosa cells from the primordial follicle onward. Its mRNA could be detected in granulosa cells isolated from antral follicles and occasionally in their theca cells. c-Kit mRNA was expressed in all antral follicular compartments and at all stages of follicular development. c-Kit protein was predominantly found in oocytes from the primordial follicle stage onwards, in theca cells of antral follicles, as well as in corpora lutea, surface epithelium and medullary tissue, particularly in the wall of blood vessels, which may indicate these cells as the main sites of action of KL. It is concluded that the KL/c-Kit system, in goat ovaries, is widespread and that it may be involved in the regulation of various local processes, including folliculogenesis and luteal activity.

In vitro maturation and early developmental capacity of bovine oocytes cultured in pure follicular fluid and supplementation with follicular wall

Mammalian oocytes mature in follicular fluid (FF), surrounded by follicular cells. In the present study, in vitro maturation of bovine oocytes cultured in FF from dominant follicles 15-17mm in diameter (with various forms of heat pretreatment) and supplementation with follicular wall from follicles 3-5mm in diameter (FW1) were examined. Heat pretreatment of FF was as follows: (1) no treatment (FF1); (2) 56 degrees C for 30min (FF2); and (3) 100 degrees C for 20s (FF3). After IVM in FF1, oocytes underwent IVF and IVC and embryo development was assessed (up to the morula stage). The rate of oocyte maturation was decreased in pure FF1 versus control (44.5% versus 62.8%, P<0.001). In the control medium, FW1 did not significantly affect nuclear maturation. By contrast, the addition of FW1 to FF1 increased the rate of matured oocytes approximately two-fold (85.9% versus 45.6%, P<0.001). Furthermore, the maturation rate in the FF+FW1 system declined (from 85.9 to 71.0%, P<0.001), whereas that in the FF system increased (from 45.6 to 71.6%, P<0.001) with increased temperature of the FF treatment. Supplementation of the control medium with FW1 increased the yield of morulae (42.6% versus 13.7%, P<0.001). However, the stimulatory effect of FW1 on the morula rate was much higher in pure FF1 (72.5% versus 31.7%, P<0.001). These findings indicated, for the first time, the stimulatory impact of FW1 on in vitro maturation and early developmental capacity of bovine oocytes cultured in pure FF from dominant follicles. We also inferred that bovine FF constituents affecting bovine oocyte maturation and the meiosis-promoting ability of the FW were heat-labile.

Ultrastructural and morphometric characterization of buffalo (Bubalus bubalis) ovarian preantral follicles

The main objective of the present study was to characterize buffalo preantral ovarian follicles. Parts of ovarian cortex, collected from postpubertal buffalo females that were having estrous cycles at regular intervals, were selected under stereomicroscopy and processed for optic and transmission electron microscopy. Primordial follicles were characterized as an oocyte encircled by one layer of flattened cells. The buffalo primordial follicle has a mean diameter of 35 microm and the oocyte diameter is 24.9 microm. The oocyte nucleus is relatively large and eccentric; and in the cytoplasm a large amount of mitochondria, vesicles and endoplasmic reticulum cistern, mainly of the smooth type is observed. The primordial follicles cells are rich in plasma membrane invaginations, which are observed within the cell and between the cell and the oocyte. The primary follicles (mean diameter of 41.8 microm) consist of an oocyte, with a medium diameter of 26.9 microm, surrounded by one layer of cubical granulosa cells. At this follicular stage, the beginning of zona pellucida deposition can also be seen in areas between the oocyte and follicular cells. The secondary follicles, which are surrounded by more than one layer of cubical cells, have a diameter of 53.3 microm, and the oocyte has a mean diameter of 29.4 microm. The ultrastructural analysis showed a large amount of coalescent vesicles, more evident in the oocyte periphery. The zona pellucida (ZP) is thicker at this stage and contains a large quantity of glycoproteins. In general, the ultrastructure of buffalo preantral follicles was similar to that of other mammalian species, but some differences were observed, which indicate species specific characteristics. The main differences observed were cytoplasmic vesicles quantity, mitochondria shape and inner content, ZP deposition and granulosa cell-oocyte junctions. In conclusion, the morphological differences described in this paper, could be responsible for some functional differences observed in Bubalus bubalis in vitro embryo production and follicular dynamics, when compared with Bos taurus or Bos indicus species.

Reproductive ageing in women

The traditional view in respect to female reproduction is that the number of oocytes at birth is fixed and continuously declines towards the point when no more oocytes are available after menopause. In this review we briefly discuss the embryonic development of female germ cells and ovarian follicles. The ontogeny of the hypothalamic-pituitary-gonadal axis is then discussed, with a focus on pubertal transition and normal ovulatory menstrual cycles during female adult life. Biochemical markers of menopausal transition are briefly examined. We also examine the effects of age on female fertility, the contribution of chromosomal abnormalities of the oocyte to the observed decline in female fertility with age and the possible biological basis for the occurrence of such abnormalities. Finally, we consider the effects of maternal age on obstetric complications and perinatal outcome. New data that have the potential to revolutionize our understanding of mammalian oogenesis and follicular formation, and of the female reproductive ageing process, are also briefly considered.

Follicle stimulating hormone and fibroblast growth factor-2 interact and promote goat primordial follicle development in vitro

The aims of the present study were to investigate the effects of the interaction between follicle stimulating hormone (FSH) and fibroblast growth factor-2 (FGF-2) on survival, follicular growth initiation and further growth of caprine preantral follicles. Pieces of caprine ovarian cortex were cultured for 1 or 7 days in minimum essential medium (MEM) supplemented with FSH, FGF-2 or FSH + FGF-2. Small fragments from non-cultured ovarian tissue and from those cultured for 1 or 7 days were processed for classical histology and transmission electron microscopy (TEM) to verify follicular morphology and growth. The results showed that, after 7 days culture, the highest percentages of normal follicles were observed in medium supplemented with FSH. After 7 days culture, the interaction between FSH and FGF-2 was most effective to promote the initiation of primordial follicles growth and oocyte growth. TEM showed ultrastructural integrity of follicles after 1 day of culture in MEM and after 7 days in all treatments, except in those follicles cultured for 7 days in MEM. In conclusion, this study demonstrated that the interaction between FSH and FGF-2 stimulates the initiation of primordial follicles growth and the subsequent growth of developing follicles. Furthermore, these data showed that FSH is important to maintain follicular integrity after 7 days culture.

Caspase-2 involvement during ionizing radiation-induced oocyte death in the mouse ovary

In mammals, the pool of primordial follicles at birth is determinant for female fertility. Exposure to IR during oogonia proliferation and the diplotene stages of ovarian development induced the virtual disappearance of primordial follicles in the postnatal ovary, while half the follicular reserve remained present after irradiation during the zygotene/pachytene stages. This sensitivity difference was correlated with the level of caspase-2 expression evaluated by immunohistochemistry. At the diplotene stage, Western blot and caspase activity analysis revealed that caspase-2 was activated 2 h after irradiation and a significant increase in the number of oocytes expressing cleaved caspase-9 and -3 occurred 6 h after treatment. Inhibition of caspase-2 activity prevented the cleavage of caspase-9 and partially prevented the loss of oocytes in response to irradiation. Taken together, our results show that caspase-2-dependent activation of the mitochondrial apoptotic pathway is one of the mechanisms involved in the genotoxic stress-induced depletion of the primordial follicle pool.

Detection of ovine lentivirus in the cumulus cells, but not in the oocytes or follicular fluid, of naturally infected sheep

The aim of this study was to examine the Maedi-Visna virus (MVV) infection status of oocytes, cumulus cells, and follicular fluid taken from 140 ewes from breeding flocks. MVV proviral-DNA and MVV RNA were detected using nested-PCR and RT-PCR MVV gene amplification, respectively in the gag gene. Nested-PCR analysis for MVV proviral-DNA was positive in peripheral blood mononuclear cells in 37.1% (52/140) of ewes and in 44.6% (125/280) of ovarian cortex samples. The examination of samples taken from ovarian follicles demonstrated that 8/280 batches of cumulus cells contained MVV proviral-DNA, whereas none of the 280 batches of oocytes taken from the same ovaries and whose cumulus cells has been removed, was found to be PCR positive. This was confirmed by RT-PCR analysis showing no MVV-viral RNA detection in all batches of oocytes without cumulus cells (0/280) and follicular fluid samples taken from the last 88 ovaries (0/88). The purity of the oocyte fraction and the efficacy of cumulus cell removal from oocytes was proved by absence of granulosa cell-specific mRNA in all batches of oocytes lacking the cumulus cells, using RT-PCR. This is the first demonstration that ewe cumulus cells harbor MVV genome and despite being in contact with these infected-cumulus cells, the oocytes and follicular fluid remain free from infection. In addition, the enzymatic and mechanical procedures we used to remove infected-cumulus cells surrounding the oocytes, are effective to generate MVV free-oocytes from MVV-infected ewes.

Analysis of transcription factor AP-2 expression and function during mouse preimplantation development

The activating protein 2 (AP-2) transcription factor family is required for multiple aspects of mouse postimplantation development, but much less is known about the expression and possible function of these genes during the preimplantation period. In the present study, we have examined the expression of all five members of the mouse AP-2 gene family in the unfertilized oocyte and from zygote formation to the blastocyst stage of development. Four AP-2 genes are differentially expressed during the preimplantation period,Tcfap2a, Tcfap2b, Tcfap2c, and Tcfap2e. Furthermore, with the exception of Tcfap2a, these genes are also expressed in unfertilized oocytes, indicating that they may be important for oogenesis, maternal-effect functions, or both. Given these findings, we have initiated studies to assess how various combinations of maternal and zygotic AP-2 gene expression might function together to regulate pre- and peri-implantation development. The present study focuses on the interplay between the expression of zygotic Tcfap2aand maternal and zygoticTcfap2c. These studies indicate that zygotic, but not maternal, Tcfap2cexpression is required for normal embryogenesis. In addition, the combined loss of both Tcfap2a and Tcfap2caccelerates embryonic lethality compared to the loss of either gene alone, demonstrating that genetic redundancy exists between these two AP-2 family members during the peri-implantation period of embryogenesis.

Expression of mRNA and protein localization of epidermal growth factor and its receptor in goat ovaries

To examine the possibility that epidermal growth factor (EGF) and its receptor (EGF-R) are expressed throughout folliculogenesis, we studied the presence and distribution of EGF and EGF-R in goat ovaries. Ovaries of goats were collected and either fixed in paraformaldehyde for immunohistochemical localization of proteins, or used for the isolation of follicles, luteal cells and ovarian surface epithelium to study mRNA expression for EGF and EGF-R, using the reverse transcriptase polymerase chain reaction. EGF protein and mRNA were found in primordial, primary and secondary follicles as well as in small and large antral follicles and in surface epithelium, but in corpora lutea only the protein could be detected. Antral follicles expressed EGF mRNA in oocyte, cumulus, mural granulosa and theca cells. For EGF-R, both protein and mRNA were present at all stages of follicular development and in all antral follicular compartments. EGF-R protein and mRNA were also found in corpora lutea and surface epithelium. It is concluded that EGF and its receptor are expressed in goat ovarian follicles at all stages of follicle development, in corpora lutea, and in ovarian surface epithelium.

Smad signalling in the ovary

It has now been a decade since the first discovery of the intracellular Smad proteins, the downstream signalling molecules of one of the most important growth factor families in the animal kingdom, the transforming growth factor beta (TGF-beta) superfamily. In the ovary, several TGF-beta superfamily members are expressed by the oocyte, granulosa and thecal cells at different stages of folliculogenesis, and they signal mainly through two different Smad pathways in an autocrine/paracrine manner. Defects in the upstream signalling cascade molecules, the ligands and receptors, are known to have adverse effects on ovarian organogenesis and folliculogenesis, but the role of the individual Smad proteins in the proper function of the ovary is just beginning to be understood for example through the use of Smad knockout models. Although most of the different Smad knockouts are embryonic lethal, it is known, however, that in Smad1 and Smad5 knockout mice primordial germ cell development is impaired and that Smad3 deficient mice harbouring a deletion in exon 8 exhibit impaired folliculogenesis and reduced fertility. In this minireview we discuss the role of Smad structure and function in the ovarian context.

Ovum Pick-up in Sheep: a Comparison between Different Aspiration Devices for Optimal Oocyte Retrieval

In vivo ovum pick-up (OPU) in sheep may be improved with a proper choice of aspiration elements (needle and tubing) and aspiration vacuum pressure. In the present study, two experiments were carried out. In Expt 1, visible follicles in ovaries of slaughtered ewes (treated separately according to their diameters: small<3 mm, medium 3-5 mm and large>5 mm) were aspirated using different combinations of the three studied factors such as aspiration flow rate (10, 20, 30, 40 and 50 ml water/min), needle gauge (18 and 20 G) and tubing inner diameter (1, 2 or 3 mm internal diameter). In Expt 2, a study with two 18 G needles of different lengths (18 G: 82 mm; 18 GL: 600 mm) was carried out, using ovaries obtained post-mortem, and performing in vivo laparoscopic follicular aspiration on ewes. We considered good quality oocytes as those with both complete compact cumulus and a homogeneous cytoplasm. Recovery rate, proportion of good quality oocytes (good quality oocytes/100 oocytes recovered) and overall efficiency (good quality oocytes/100 follicles aspirated) were noted. In Expt 1, aspiration flow rate affect remarkable proportion of good quality oocytes (69.5%, 50.5%, 44.8%, 36.5% and 28.3% for flows from 10 to 50 ml/min respectively, p<0.05). Needle gauge did not affect aspiration device efficiency. Thin and intermediate tubings were more effective (overall efficiency rates: 34.9%, 32.3% and 28.1% for 1, 2 and 3 mm respectively, p<0.05). Follicle size did not affect recovery rate, but proportion of good quality oocytes was higher for large (77.9%) and medium (64.4%) follicles (p<0.05). Finally, some combinations of the aspiration device showed greater effectiveness. In Expt 2, needle length did not influence recovery rate, but good quality oocytes rate was significantly modified both post-mortem and in vivo (good quality rate for 18 G vs 18 GL needles: 69.5% vs 47.7% and 58.1% vs 25.4%, post-mortem and in vivo respectively, p<0.05). We conclude that low-aspiration flow rates (10 and 20 ml/min) with thin or intermediate tubings (1 and 2 mm), and any short needle (18 G or 20 G) are the most adequate aspiration factors for OPU in sheep.

Comparative analysis of follicle morphology and oocyte diameter in four mammalian species (mouse, hamster, pig, and human)

Background

Laboratory animals are commonly used for evaluating the physiological properties of the mammalian ovarian follicle and the enclosed oocyte. The use of different species to determine the morphological relationship between the follicle and oocyte has led to a recognizable pattern of follicular stages, but differences in follicle size, oocyte diameter and granulosa cell proliferation are not consistent across the different species. In an effort to better understand how these differences are expressed across multiple species, this investigation evaluates oocyte and follicle diameters and granulosa cell proliferation in the mouse, hamster, pig, and human.

Methods

Histological sections of ovaries from the mouse, hamster, pig, and human were used to calculate the diameter of the oocyte and follicle and the number of granulosa cells present at pre-determined stages of follicular development. A statistical analysis of these data was performed to determine the relationship of follicular growth and development within and between the species tested.

Results

These data have revealed that the relationships of the features listed are tightly regulated within each species, but they vary between the species studied.

Conclusion

This information may be useful for comparative studies conducted in different animal models and the human.