Characterization of oviduct epithelial spheroids for the study of embryo-maternal communication in cattle

Most in vitro models of oviduct epithelial cells (OEC) used thus far to gain insights into embryo-maternal communication induce cell dedifferentiation or are technically challenging. Moreover, although the presence of developing embryos has been shown to alter gene expression in OEC, the effect of embryos on OEC physiology remains largely unknown. Here, we propose a model based on bovine oviduct epithelial spheroids (OES) with specific shape and diameter (100-200 μm) criteria. The aims of this study were to i) determine the appropriate culture conditions of bovine OES cultured in suspension by evaluating their morphology, total cell number, viability, and activity of ciliated cells; ii) monitor gene expression in OES at the time of their formation (day 0) and over the 10 days of culture; and iii) test whether the vicinity of developing embryos affects OES quality criteria. On day 10, the proportions of vesicle-shaped OES (V-OES) were higher in M199/500 (500 μl of HEPES-buffered TCM-199) and synthetic oviduct fluid (SOF)/25 (25-μL droplet of SOF medium under mineral oil) than in M199/25 (25-μL droplet of M199 under mineral oil). The proportion of viable cells in V-OES was not affected by culture conditions and remained high (>80%) through day 10. The total number of cells per V-OES decreased over time except in SOF/25, while the proportions of ciliated cells increased over time in M199/500 but decreased in M199/25 and SOF/25. The movement amplitude of OES in suspension decreased over time under all culture conditions. Moreover, the gene expression of ANXA1, ESR1, HSPA8, and HSPA1A in OES remained stable during culture, while that of PGR and OVGP1 decreased from day 0 to day 10. Last, the co-culture of developing embryos with OES in SOF/25 increased the rates of blastocysts on days 7 and 8 compared to embryos cultured alone, and increased the proportion of V-OES compared to OES cultured alone. In conclusion, M199/500 and SOF/25 provided the optimal conditions for the long-time culture of OES. The supporting effect of OES on embryo development and of developing embryos on OES morphology was evidenced for the first time. Altogether, these results point OES as an easy-to-use, standardizable, and physiological model to study embryo-maternal interactions in cattle.

Cumulative and potential synergistic effects of seven different bisphenols on human granulosa cells in vitro?

Bisphenol (BP) structural analogues of BPA are widely used. Previous studies showed similar effects of BPA and BPS on reproduction in several species including human. We hypothesised that the similar effects of several bisphenols (BPs) could accumulate in granulosa cells (GCs) and affects steroidogenesis. This study investigated the effects of seven BP analogues and their equimolar cocktail on human granulosa cells (hGC) and assessed BPA, BPS, BPF and BPAF level exposures in the follicular fluid of 277 women undergoing Assisted Reproductive Technology. The hGCs were recovered after women oocyte punctures and treated with the seven BP analogues (BPS, BPA, BPAF, BPF, BPAP, BPE and BPB) or their equimolar cocktail of 7 × 1.43 or 7 × 7.14 μM for each of the seven BPs, the sum of BPs reaching 10 ("∑BPs 10 μM"), or 50 μM ("∑BPs 50 μM"), respectively. Oestradiol and progesterone secretion, cell proliferation, viability and expression of steroidogenic enzymes were investigated. Progesterone secretion was decreased by 6 BPs 10 μM and the cocktail "∑BPs 10 μM", (-17.8 to -41.3%) and by all seven BPs 50 μM and "∑BPs 50 μM" (-21.8 to -84.2%). Oestradiol secretion was decreased only by 50 μM BPAF and BPAP (-37.8% and -44%, respectively), with corresponding decreases in CYP17A1 and CYP19A1 gene expression. Cellular proliferation was decreased after treatment with 50 μM BPAF (-32.2%), BPAP (-29%), BPB (-24%) and the equimolar cocktail "∑BPs 50 μM" (-33.1%). BPB (50 μM) and the cocktail "∑BPs 50 μM" increased HSD3B2 mRNA expression. At least one BP was detected in 64 of 277 (23.1%) women follicular fluids. Similar effects of the seven BPs or their cocktail were observed on progesterone secretion and/or on cell proliferation, suggesting cumulative effects of BPs. Our results highlight the urge to consider all BPs simultaneously and to further investigate the potential additive or synergistic effects of several BPs.

Bisphenol A and bisphenol S both disrupt ovine granulosa cell steroidogenesis but through different molecular pathways

BACKGROUND

Ovarian granulosa cells (GC) are essential for the development and maturation of a proper oocyte. GC are sensitive to endocrine disruptors, including bisphenol A (BPA) and its analogue bisphenol S (BPS), plasticisers present in everyday consumer products. BPA exhibits greater binding affinity for the membrane oestrogen receptor (GPER) than for the nuclear oestrogen receptors (ERα and ERβ). Here, we analysed the effects of BPA and BPS on the steroidogenesis of ovine GC in vitro, as well as their early mechanisms of action, the ovine being a relevant model to study human reproductive impairment. Disruption of GC steroidogenesis might alter oocyte quality and consequently fertility rate. In addition, we compared the effects of a specific GPER agonist (G-1) and antagonist (G-15) to those of BPA and BPS. Ewe GC were cultured with BPA or BPS (10 or 50 µM) or G-1 (1 µM) and/or G-15 (10 µM) for 48 h to study steroidogenesis.

RESULTS

Both BPA and BPS (10 µM) altered the secretion of progesterone, however, only BPS (10 µM) affected oestradiol secretion. RNA-seq was performed on GC after 1 h of culture with BPA or BPS (50 µM) or G-1 (10 µM), followed by real-time PCR analyses of differentially expressed genes after 12, 24 and 48 h of culture. The absence of induced GPER target genes showed that BPA and BPS did not activate GPER in GC after 1 h of treatment. These molecules exhibited mainly independent early mechanisms of action. Gene ontology analysis showed that after 1 h of treatment, BPA mainly disrupted the expression of the genes involved in metabolism and transcription, while BPS had a smaller effect and impaired cellular communications. BPA had a transient effect on the expression of CHAC1 (NOTCH signalling and oxidative balance), JUN (linked to MAPK pathway), NR4A1 (oestradiol secretion inhibition), ARRDC4 (endocytose of GPCR) and KLF10 (cell growth, differentiation and apoptosis), while expression changes were maintained over time for the genes LSMEM1 (linked to MAPK pathway), TXNIP (oxidative stress) and LIF (cell cycle regulation) after 12 and 48 h, respectively.

CONCLUSION

In conclusion, although they exhibited similar effects, BPA and BPS impaired different molecular pathways in GC in vitro. New investigations will be necessary to follow the temporal changes of these genes over time, as well as the biological processes involved.

Bisphenol S Impairs Oestradiol Secretion during In Vitro Basal Folliculogenesis in a Mono-Ovulatory Species Model

Bisphenol S (BPS) affects terminal folliculogenesis by impairing steroidogenesis in granulosa cells from different species. Nevertheless, limited data are available on its effects during basal folliculogenesis. In this study, we evaluate in vitro the effects of a long-term BPS exposure on a model of basal follicular development in a mono-ovulatory species. We cultured ovine preantral follicles (180−240 μm, n = 168) with BPS (0.1 μM (possible human exposure dose) or 10 μM (high dose)) and monitored antrum appearance and follicular survival and growth for 15 days. We measured hormonal secretions (oestradiol (at day 13 [D13]), progesterone and anti-Müllerian hormone [D15]) and expression of key follicular development and redox status genes (D15) in medium and whole follicles, respectively. BPS (0.1 µM) decreased oestradiol secretion compared with the control (−48.8%, p < 0.001), without significantly impairing antrum appearance, follicular survival and growth, anti-Müllerian hormone and progesterone secretion and target gene expression. Thus, BPS could also impair oestradiol secretion during basal folliculogenesis as it is the case during terminal folliculogenesis. It questions the use of BPS as a safe BPA substitute in the human environment. More studies are required to elucidate mechanisms of action of BPS and its effects throughout basal follicular development.

Bisphenol S Alters the Steroidome in the Preovulatory Follicle, Oviduct Fluid and Plasma in Ewes With Contrasted Metabolic Status

Bisphenol A (BPA), a plasticizer and endocrine disruptor, has been substituted by bisphenol S (BPS), a structural analogue that had already shown adverse effects on granulosa cell steroidogenesis. The objective of this study was to assess the effect of chronic exposure to BPS, a possible endocrine disruptor, on steroid hormones in the ovary, oviduct and plasma using the ewe as a model. Given the interaction between steroidogenesis and the metabolic status, the BPS effect was tested according to two diet groups. Eighty adult ewes were allotted to restricted (R) and well-fed (WF) groups, that were further subdivided into two subgroups. Ewes were exposed to 50 µg BPS/kg/day in their diet (R50 and WF50 groups) or were unexposed controls (R0 and WF0 groups). After at least 3 months of BPS exposure, preovulatory follicular fluid, oviduct fluid and plasma were collected and steroid hormones were analyzed by gas chromatography coupled with tandem mass spectrometry (GC-MS/MS). A deleterious effect of restricted diet on the volume of oviduct fluid and numbers of pre-ovulatory follicles was observed. Exposure to BPS impaired estradiol concentrations in both follicular and oviduct fluids of well-fed ewes and progesterone, estradiol and estrone concentrations in plasma of restricted ewes. In addition, a significant interaction between metabolic status and BPS exposure was observed for seven steroids, including estradiol. In conclusion, BPS acts in ewes as an endocrine disruptor with differential actions according to metabolic status.

Chronic low BPS exposure through diet impairs in vitro embryo production parameters according to metabolic status in the ewe

Bisphenol A (BPA), an endocrine disruptor, has been replaced by structural analogues including bisphenol S (BPS). BPA and BPS exhibited similar effects regarding reproductive functions. Moreover, metabolic status and lipid metabolism are related to female fertility and could worsen BPS effects. The objective was to determine BPS in vivo effects on folliculogenesis and embryo production after chronic exposure through diet, and the influence of metabolic status in adult ewes. Sixty primiparous 2.5 year-old ewes, undergoing a restricted or well fed diet, were exposed to BPS (0, 4 or 50 µg/kg/day) for at least three months. After hormonal oestrus synchronisation and ovarian stimulation, ewes were subjected to ovum pick-up (OPU) procedures to collect immature oocytes, that underwent in vitro maturation, fertilisation and embryo production. Body weight, body condition score and plasma glucose were higher in well-fed compared to restricted ewes, while plasma NEFA was lower during the 4-5 months after the beginning of the diets. Plasma progesterone levels increased on day 5 before OPU session in well-fed compared to restricted ewes. No effect of BPS dose was observed on follicle population, plasma AMH levels and embryo production numbers and rates. However, a significant diet x BPS dose interaction was reported for cleaved embryos, > 4-cell embryos, blastocyst and early blastocyst numbers, and plasma triiodothyronine levels. Our study showed that a contrasted diet did not affect follicle population nor embryo production in adult ewes but could affect the quality and progesterone secretion of the corpus luteum. Chronic low BPS exposure had no effect on follicular population and oocyte competence. Nevertheless, the significant diet x dose interactions observed on embryo production suggest that BPS effect is modulated by metabolic status. Further studies are required to assess the risk of BPS exposure for public reproductive health.

Protein Palmitoylation in Bovine Ovarian Follicle

Protein palmitoylation is a reversible post-translational modification by fatty acids (FA), mainly a palmitate (C16:0). Palmitoylation allows protein shuttling between the plasma membrane and cytosol to regulate protein stability, sorting and signaling activity and its deficiency leads to diseases. We aimed to characterize the palmitoyl-proteome of ovarian follicular cells and molecular machinery regulating protein palmitoylation within the follicle. For the first time, 84 palmitoylated proteins were identified from bovine granulosa cells (GC), cumulus cells (CC) and oocytes by acyl-biotin exchange proteomics. Of these, 32 were transmembrane proteins and 27 proteins were detected in bovine follicular fluid extracellular vesicles (ffEVs). Expression of palmitoylation and depalmitoylation enzymes as palmitoyltransferases (ZDHHCs), acylthioesterases (LYPLA1 and LYPLA2) and palmitoylthioesterases (PPT1 and PPT2) were analysed using transcriptome and proteome data in oocytes, CC and GC. By immunofluorescence, ZDHHC16, PPT1, PPT2 and LYPLA2 proteins were localized in GC, CC and oocyte. In oocyte and CC, abundance of palmitoylation-related enzymes significantly varied during oocyte maturation. These variations and the involvement of identified palmitoyl-proteins in oxidation-reduction processes, energy metabolism, protein localization, vesicle-mediated transport, response to stress, G-protein mediated and other signaling pathways suggests that protein palmitoylation may play important roles in oocyte maturation and ffEV-mediated communications within the follicle.

Leukaemia inhibitory factor modulates the differentiation of granulosa cells during sheep in vitro preantral to antral follicle development and improves oocyte meiotic competence

In vitro follicle development from cryopreserved ovarian tissue could become an invaluable assisted reproduction technology for women with early ovarian failure. The challenge lies in producing, from small follicles present in the ovarian cortex, high-quality mature oocytes able to sustain embryo development. In vivo, an optimal combination of hormones and other factors coordinates the development of follicles and their enclosed oocyte. We have investigated the effect of the leukaemia inhibitory factor (LIF) cytokine, alone or in combination with FSH, on sheep in vitro follicle development from the preantral stage onwards. LIF did not alter follicle growth or antrum formation, but it modulated the differentiation of granulosa cells, as revealed by decreased production of anti-Müllerian hormone and abolished FSH-induced stimulation of oestradiol secretion. This modulatory role was also reflected in the abundance of mRNA from 35 genes, analysed by reverse-transcription coupled to microfluidic quantitative PCR. LIF stimulated or at least maintained the expression of genes involved in the dialogue between the oocyte and granulosa cells, through gap junctions (GJA4 encoding connexin 37) or paracrine signalling (Bone morphogenetic protein 15, KIT ligand and their receptors). Finally, the presence of both LIF and FSH during follicle growth strongly improved oocyte meiotic competence: most oocytes (56%) underwent subsequent nuclear maturation, a significant increase compared with their counterparts from follicles of similar size (550-900 µm) cultured with FSH only (28%) or developed in vivo (9%). Their ability to sustain embryo development remains to be evaluated. Combined supplementation with FSH and LIF certainly merits investigation with human follicles.

MALDI-TOF Mass Spectrometry Revealed Significant Lipid Variations in Follicular Fluid and Somatic Follicular Cells but Not in Enclosed Oocytes between the Large Dominant and Small Subordinate Follicles in Bovine Ovary

Lipid metabolism in ovarian follicular cells supports the preparation of an enclosed oocyte to ovulation. We aimed to compare lipid composition of a dominant large follicle (LF) and subordinated small follicles (SFs) within the same ovaries. Mass spectrometry imaging displayed the differences in the distribution of several lipid features between the different follicles. Comparison of lipid fingerprints between LF and SF by Matrix Assisted Laser Desorption/Ionisation Time-Of-Flight (MALDI-TOF) mass spectrometry revealed that in the oocytes, only 8 out of 468 detected lipids (1.7%) significantly changed their abundance (p < 0.05, fold change > 2). In contrast, follicular fluid (FF), granulosa, theca and cumulus cells demonstrated 55.5%, 14.9%, 5.3% and 9.8% of significantly varied features between LF and SF, respectively. In total, 25.2% of differential lipids were identified and indicated potential changes in membrane and signaling lipids. Tremendous changes in FF lipid composition were likely due to the stage specific secretions from somatic follicular cells that was in line with the differences observed from FF extracellular vesicles and gene expression of candidate genes in granulosa and theca cells between LF and SF. In addition, lipid storage in granulosa and theca cells varied in relation to follicular size and atresia. Differences in follicular cells lipid profiles between LF and SF may probably reflect follicle atresia degree and/or accumulation of appropriate lipids for post-ovulation processes as formation of corpus luteum. In contrast, the enclosed oocyte seems to be protected during final follicular growth, likely due in part to significant lipid transformations in surrounding cumulus cells. Therefore, the enclosed oocyte could likely keep lipid building blocks and energy resources to support further maturation and early embryo development.

Bisphenol A and S impaired ovine granulosa cell steroidogenesis

Bisphenols, plasticisers used in food containers, can transfer to food. Bisphenol A (BPA) has been described as an endocrine disruptor and consequently banned from the food industry in several countries. It was replaced by a structural analogue, Bisphenol S (BPS). BPA action on the steroidogenesis is one of the mechanisms underlying its adverse effects on the efficiency of female reproduction. This study aimed to determine whether BPS is a safe alternative to BPA regarding GC functions. Antral follicles (2–6 mm), of approximatively 1000 adult ewe ovaries, were aspired and GC purified. For 48 h, ovine GC were treated with BPA or BPS (from 1 nM to 200 µM) and the effects on cell viability, proliferation, steroid production, steroidogenic enzyme expression and signalling pathways were investigated. Dosages at and greater than 100 μM BPA and 10 µM BPS decreased progesterone secretion by 39% (P < 0.001) and 22% (P = 0.040), respectively. BPA and BPS 10 μM and previously mentioned concentrations increased oestradiol secretion two-fold (P < 0.001 and P = 0.082, respectively). Only 100 µM BPA induced a decrease (P < 0.001) in gene expression of the enzymes of steroidogenesis involved in the production of progesterone. BPA reduced MAPK3/1 phosphorylation and ESR1 and ESR2 gene expression, effects that were not observed with BPS. BPA and BPS altered steroidogenesis of ovine GC. Thus, BPS does not appear to be a safe alternative for BPA. Further investigations are required to elucidate BPA and BPS mechanisms of action.

Bisphenol S Impaired Human Granulosa Cell Steroidogenesis in Vitro

Bisphenol S (BPS) is a structural analog of the endocrine disruptor bisphenol A (BPA); it is the main BPA replacement in the plastics industry. Previous studies have shown that BPA and BPS exhibit similar effects on reproduction in fish and rodent species. BPS reportedly alters steroidogenesis in bovine granulosa cells. Luteinised granulosa cells collected from 59 women who were undergoing an in vitro fertilization procedure were cultured for 48 h in the presence or absence of BPS (10 nM, 100 nM, 1 µM, 10 µM or 50 µM). BPS exposure was investigated by assessing follicular fluids from these 59 women for their BPS content. Culture medium, cells, total messenger RNA (mRNA) and total protein extracted from the luteinised granulosa cells were examined for oestradiol and progesterone secretion, cellular proliferation, viability, gene expression, steroidogenic enzyme expression and cell signaling. BPS was measured in follicular fluids using mass spectrometry. Exposure of granulosa cells to 10 or 50 µM BPS for 48 h induced a 16% (p = 0.0059) and 64% (p < 0.0001) decrease, respectively, in progesterone secretion; 50 µM BPS decreased oestradiol secretion by 46% (p < 0.0001). Ten µM BPS also tended to reduce CYP11A1 protein expression by 37% (p = 0.0947) without affecting HSD3B1 and CYP19A1 expression. Fifty µM BPS increased ERRγ expression. Environmental levels of BPS (nanomolar range) did not induce changes in steroidogenesis in human granulosa cells. The effects of BPS were observed after only 48 h of BPS exposure. These acute effects might be similar to chronic effects of physiological BPS levels.

Bisphenol S Impaired In Vitro Ovine Early Developmental Oocyte Competence

INTRODUCTION

Bisphenol A (BPA) is a widespread compound in the plastic industry that is especially used to produce baby bottles, food packaging and metal cans. BPA, an endocrine disruptor, leads to alterations in reproductive function and therefore has been banned from the food industry. Unregulated BPA analogues, particularly Bisphenol S (BPS), have emerged and are now used in the plastic industry. Thus, this study aimed to examine the acute effects of low and environmental doses of BPS on ewe oocyte quality and developmental competence, and its mechanism of action, during in vitro maturation.

METHODS

Ewe cumulus-oocyte complexes underwent in vitro maturation in the presence or absence of BPS (1 nM, 10 nM, 100 nM, 1 µM or 10 µM). Oocytes were then subjected to in vitro fertilisation and development.

RESULTS

1 µM BPS induced a 12.7% decrease in the cleavage rate (p = 0.004) and a 42.6% decrease in the blastocyst rate (p = 0.017) compared to control. The blastocyst rate reduction was also observed with 10 nM BPS. Furthermore, 10 µM BPS reduced the oocyte maturation rate, and 1 µM BPS decreased cumulus cell progesterone secretion. PR and AMH gene expression were reduced in cumulus cells. BPS induced a 5-fold increase in MAPK 3/1 activation (p = 0.04).

CONCLUSIONS

BPS impaired ewe oocyte developmental competence. The data suggest that BPS might not be a safe BPA analogue. Further studies are required to elucidate its detailed mechanism of action.

179 Bisphenol S affects invitro early developmental oocyte competence in ewes

In the plastics industry, bisphenol S (BPS) replaces sisphenol A reported to be an oestrogen mimetic endocrine disruptor damaging oocyte meiosis and maturation (Machtinger 2014 Reprod. Biomed. Online 29, 404). Studies on fish and rodents reported that BPS affects reproduction similarly to BPA (Uzumcu 2007 Reprod. Toxicol. 23, 337; Giulivo 2016 Environ. Res. 151, 251; Ullah 2016 Chemosphere 152, 353). Bisphenol S is detected in human urine at nanomolar concentrations (Liao 2012 Environ. Sci. Technol 46, 6860) and in some laboratory supplies (tips and tubes; unpublished data). Therefore, in this study, we assessed effects of BPS at low doses during invitro maturation (IVM) on oocyte developmental competence in ewes. Cumulus-oocyte complexes (COC) collected from ovine follicles &gt;2mm underwent 24-h IVM, in the absence or presence of BPS at 1, 10, and 100 nM and 1 and 10 µM (Sigma Chemical Co.). Nuclear oocyte maturation rate was evaluated by MII oocyte count after chromatin Hoechst staining [n=3 replicates (R), 1159 oocytes]. At 6h of IVM, BPS effects on mRNA expression of oestrogen (E2) and progesterone (P4) receptors in cumulus cells (CC) were assessed by real-time quantitative PCR. After 24h of IVM, The effect of BPS on P4 level was assessed in spent medium by enzyme-linked immunosorbent assay (n=6 R, 40 COC/condition). Transcript expression level and P4 concentration were analysed using nonparametric one-way ANOVA, with Tukey post hoc test (Rcmdr, R version 3.5.3). After 24h of IVM, matured COC underwent IVF and invitro culture (IVC) for 7 days. Cleavage and blastocyst rates were assessed on Days 2 and 7, respectively, after IVF (8 experiments, 300 COC/condition). Data were analysed using logistic regression and linear model (R version 3.5.3). Our results showed a decreased oocyte maturation rate with 10 µM BPS (76.6%, n=171; P=0.0008) compared with control (88%, n=152), with no effect on cell viability. The concentration of P4 decreased with 1 µM BPS (0.02ngmL−1 per COC) compared with control (0.034ngmL−1 per COC; P&lt;0.001). At 6h IVM, BPS had no significant effect on oestrogen receptors (ESR1, ESR2, GPER) transcripts in CC but 10 nM BPS decreased mRNA expression of P4 receptor (PR) (0.00647±0.00145; P=0,005) compared with control (0.01165±0.00196). Within fertilized COC, 1 µM BPS decreased cleavage rate (47.6%, n=152) compared with control (54.6%; P=0.004). Among cleaved embryos, blastocyst rate decreased to 14.2% and 12.5% with 10 nM and 1 µM BPS respectively (n=26, P=0.046; and n=19, P=0.017), compared with control (21.8%, n=44). Bisphenol S at a low dose during ovine IVM reduced COC P4 secretion, PR transcript in CC, and cleavage and blastocyst rates. Our data suggest that BPS at an environmental dose (10 nM) negatively affects early developmental oocyte competence. Studies are ongoing to investigate the effect of BPS on Day 6 embryo cell number and on the ERK1/2 signalling pathway in oocyte. This study was supported by INRA, Region Val-de-Loire (BEMOL) and the French National Research Agency (ANR-18-CE34-0011-01 MAMBO). We thank A. Arnould and T. Delpuech for ovine ovary collection and Endocrinology and Phenotyping laboratory for P4 assay.

Prenatal programming by testosterone of follicular theca cell functions in ovary

In mammalian ovaries, the theca layers of growing follicles are critical for maintaining their structural integrity and supporting androgen synthesis. Through combining the postnatal monitoring of ovaries by abdominal magnetic resonance imaging, endocrine profiling, hormonal analysis of the follicular fluid of growing follicles, and transcriptomic analysis of follicular theca cells, we provide evidence that the exposure of ovine fetuses to testosterone excess activates postnatal follicular growth and strongly affects the functions of follicular theca in adulthood. Prenatal exposure to testosterone impaired androgen synthesis in the small antral follicles of adults and affected the expression in their theca cells of a wide array of genes encoding extracellular matrix components, their membrane receptors, and signaling pathways. Most expression changes were uncorrelated with the concentrations of gonadotropins, steroids, and anti-Müllerian hormone in the recent hormonal environment of theca cells, suggesting that these changes rather result from the long-term developmental effects of testosterone on theca cell precursors in fetal ovaries. Disruptions of the extracellular matrix structure and signaling in the follicular theca and ovarian cortex can explain the acceleration of follicle growth through altering the stiffness of ovarian tissue. We propose that these mechanisms participate in the etiology of the polycystic ovarian syndrome, a major reproductive pathology in woman.

An evolutionary approach to recover genes predominantly expressed in the testes of the zebrafish, chicken and mouse

Background

Previously, we have demonstrated that genes involved in ovarian function are highly conserved throughout evolution. In this study, we aimed to document the conservation of genes involved in spermatogenesis from flies to vertebrates and their expression profiles in vertebrates.

Results

We retrieved 379 Drosophila melanogaster genes that are functionally involved in male reproduction according to their mutant phenotypes and listed their vertebrate orthologs. 83% of the fly genes have at least one vertebrate ortholog for a total of 625 mouse orthologs. This conservation percentage is almost twice as high as the 42% rate for the whole fly genome and is similar to that previously found for genes preferentially expressed in ovaries. Of the 625 mouse orthologs, we selected 68 mouse genes of interest, 42 of which exhibited a predominant relative expression in testes and 26 were their paralogs. These 68 mouse genes exhibited 144 and 60 orthologs in chicken and zebrafish, respectively, gathered in 28 groups of paralogs. Almost two thirds of the chicken orthologs and half of the zebrafish orthologs exhibited a relative expression ≥50% in testis. Finally, our focus on functional in silico data demonstrated that most of these genes were involved in the germ cell process, primarily in structure elaboration/maintenance and in acid nucleic metabolism.

Conclusion

Our work confirms that the genes involved in germ cell development are highly conserved across evolution in vertebrates and invertebrates and display a high rate of conservation of preferential testicular expression among vertebrates. Among the genes highlighted in this study, three mouse genes (Lrrc46, Pabpc6 and Pkd2l1) have not previously been described in the testes, neither their zebrafish nor chicken orthologs. The phylogenetic approach developed in this study finally allows considering new testicular genes for further fundamental studies in vertebrates, including model species (mouse and zebrafish).

Electronic supplementary material

The online version of this article (10.1186/s12862-019-1462-8) contains supplementary material, which is available to authorized users.

Genes Involved in Drosophila melanogaster Ovarian Function Are Highly Conserved Throughout Evolution

This work presents a systematic approach to study the conservation of genes between fruit flies and mammals. We have listed 971 Drosophila genes involved in female reproduction at the ovarian level and systematically looked for orthologs in the Ciona, zebrafish, coelacanth, lizard, chicken, and mouse. Depending on the species, the percentage of these Drosophila genes with at least one ortholog varies between 69% and 78%. In comparison, only 42% of all the Drosophila genes have an ortholog in the mouse genome (P < 0.0001), suggesting a dramatically higher evolutionary conservation of ovarian genes. The 177 Drosophila genes that have no ortholog in mice and other vertebrates correspond to genes that are involved in mechanisms of oogenesis that are specific to the fruit fly or the insects. Among 759 genes with at least one ortholog in the zebrafish, 73 have an expression enriched in the ovary in this species (RNA-seq data). Among 760 genes that have at least one ortholog in the mouse; 76 and 11 orthologs are reported to be preferentially and exclusively expressed in the mouse ovary, respectively (based on the UniGene expressed sequence tag database). Several of them are already known to play a key role in murine oogenesis and/or to be enriched in the mouse/zebrafish oocyte, whereas others have remained unreported. We have investigated, by RNA-seq and real-time quantitative PCR, the exclusive ovarian expression of 10 genes in fish and mammals. Overall, we have found several novel candidates potentially involved in mammalian oogenesis by an evolutionary approach and using the fruit fly as an animal model.

In vitro maturation affects chromosome segregation, spindle morphology and acetylation of lysine 16 on histone H4 in horse oocytes

Implantation failure and genetic developmental disabilities in mammals are caused by errors in chromosome segregation originating mainly in the oocyte during meiosis I. Some conditions, like maternal ageing or in vitro maturation (IVM), increase the incidence of oocyte aneuploidy. Here oocytes from adult mares were used to investigate oocyte maturation in a monovulatory species. Experiments were conducted to compare: (1) the incidence of aneuploidy, (2) the morphology of the spindle, (3) the acetylation of lysine 16 on histone H4 (H4K16) and (4) the relative amount of histone acetyltransferase 1 (HAT1), K(lysine) acetyltransferase 8 (KAT8, also known as MYST1), histone deacetylase 1 (HDAC1) and NAD-dependent protein deacetylase sirtuin 1 (SIRT1) mRNA in metaphase II stage oocytes that were in vitro matured or collected from peri-ovulatory follicles. The frequency of aneuploidy and anomalies in spindle morphology was increased following IVM, along with a decrease in H4K16 acetylation that was in agreement with our previous observations. However, differences in the amount of the transcripts investigated were not detected. These results suggest that the degradation of transcripts encoding for histone deacetylases and acetyltransferases is not involved in the changes of H4K16 acetylation observed following IVM, while translational or post-translational mechanisms might have a role. Our study also suggests that epigenetic instabilities introduced by IVM may affect the oocyte and embryo genetic stability.

161 Cumulus Cell Luteinization is Enhanced During Aging of Bovine Oocytes Matured In Vitro

Maturing mammalian oocytes can prevent luteinization of cumulus cells (CC) both in vivo and in vitro by regulating CC steroidogenesis (Gilchrist et al. 2004 Anim. Reprod. Sci. 82-83, 431-446; Ramirez et al. 2016 Anim. Reprod. 14, 280). However, when the oocyte attains the metaphase II stage, aging processes are accelerated and may impair protective abilities of CC. The aim of the present research was to study the luteinization of CC surrounding aging bovine oocytes and its susceptibility to prolactin (PRL), which performs a luteotropic function in mammals. We analysed (1) the steroidogenic activity of CC during the prolonged culture of cumulus–oocyte complexes (COC), and (2) the expression of genes related to luteinization in CC. Bovine COC were matured in TCM-199 containing 10% fetal calf serum (FCS), 10 μg mL−1 porcine FSH, and 10 μg mL−1 ovine LH. After 22 h of IVM, COC were transferred to the aging medium consisting of TCM-199 supplemented with 10% FCS and cultured for 0, 12, or 24 h in the absence (Control) or presence of 50 ng mL−1 bovine PRL. Progesterone (P4) and oestradiol-17β (E2) levels in spent media were determined by ELISA. The expression of luteinization-related genes STAR (steroidogenic acute regulatory protein), HSD3B1 (3β-hydroxysteroid dehydrogenase type 1), PGR (genomic P4 receptor), and PGRMC1 and PGRMC2 (P4 receptor membrane components 1 and 2) was analysed by real-time RT-PCR. The data from 6 to 8 replicates (at least 170 oocytes for each condition) were analysed by ANOVA following by Tukey’s (steroidogenesis) or Dunn’s (gene expression) tests. In the control group, the level of P4 production exhibited by COC during 24-h aging was 5.5-fold higher than the level observed during in vitro maturation (1.50 ± 0.15 ng v. 0.27 ± 0.02 ng of P4/COC; P < 0.001). Conversely, E2 production by aging COC was 2.7 times lower than that by maturing COC (0.39 ± 0.05 pg v. 1.04 ± 0.05 pg of E2/COC; P < 0.001). The CC expression of genes responsible for P4 synthesis, STAR and HSD3B1, increased progressively by 24 h of aging (7.1- and 34.6-fold, respectively; P < 0.001). Meanwhile, the steroid secretion and expression of STAR and HSD3B1 genes were unaffected by PRL. The relative mRNA abundance of PGRMC1 increased 2.3-fold (P < 0.05) in the control (at 24 h) and PRL groups (at 12 h), while that of PGRMC2 did not change significantly in both groups. In addition, PGR transcript level decreased (P < 0.01) 9.9-fold at 12 h and 18.3-fold at 24 h aging of PRL-treated COC, whereas this decrease was only 5-fold (P < 0.05) at 24 h in Control. The findings indicate that aging of bovine oocytes matured in vitro enhances luteinization of surrounding CC. Prolactin does not affect steroidogenesis but may modulate the expression of P4 receptors in cumulus cells. This research was supported partly by FASO Russia and INRA (France).

Analysis of Chromosome Segregation, Histone Acetylation, and Spindle Morphology in Horse Oocytes

The field of assisted reproduction has been developed to treat infertility in women, companion animals, and endangered species. In the horse, assisted reproduction also allows for the production of embryos from high performers without interrupting their sports career and contributes to an increase in the number of foals from mares of high genetic value. The present manuscript describes the procedures used for collecting immature and mature oocytes from horse ovaries using ovum pick-up (OPU). These oocytes were then used to investigate the incidence of aneuploidy by adapting a protocol previously developed in mice. Specifically, the chromosomes and the centromeres of metaphase II (MII) oocytes were fluorescently labeled and counted on sequential focal plans after confocal laser microscope scanning. This analysis revealed a higher incidence in the aneuploidy rate when immature oocytes were collected from the follicles and matured in vitro compared to in vivo. Immunostaining for tubulin and the acetylated form of histone four at specific lysine residues also revealed differences in the morphology of the meiotic spindle and in the global pattern of histone acetylation. Finally, the expression of mRNAs coding for histone deacetylases (HDACs) and acetyl-transferases (HATs) was investigated by reverse transcription and quantitative-PCR (q-PCR). No differences in the relative expression of transcripts were observed between in vitro and in vivo matured oocytes. In agreement with a general silencing of the transcriptional activity during oocyte maturation, the analysis of the total transcript amount can only reveal mRNA stability or degradation. Therefore, these findings indicate that other translational and post-translational regulations might be affected. Overall, the present study describes an experimental approach to morphologically and biochemically characterize the horse oocyte, a cell type that is extremely challenging to study due to low sample availability. However, it can expand our knowledge on the reproductive biology and infertility in monovulatory species.

An integrated approach to bovine oocyte quality: from phenotype to genes

In cattle, early embryonic failure plays a major role in the limitation of reproductive performance and is influenced by genetic effects. Suboptimal oocyte quality, including an inadequate store of maternal factors, is suspected to contribute to this phenomenon. In the present study, 13 Montbeliarde cows were phenotyped on oocyte quality, based on their ability to produce viable embryos after in vitro maturation, fertilisation and culture for 7 days. This discriminated two groups of animals, exhibiting developmental rates below 18.8% or above 40.9% (relative to cleaved embryos). Using microarrays, transcriptomic profiles were compared between oocytes collected in vivo from these two groups of animals. The difference in oocyte development potential was associated with changes in transcripts from 60 genes in immature oocytes and 135 genes in mature oocytes (following Bonferroni 5% correction). Of these, 16 and 32 genes were located in previously identified fertility quantitative trait loci. A subset of differential genes was investigated on distinct samples by reverse transcription-quantitative polymerase chain reaction. For SLC25A16, PPP1R14C, ROBO1, AMDHD1 and MEAF6 transcripts, differential expression was confirmed between high and low oocyte potential animals. Further sequencing and searches for polymorphisms will pave the way for implementing their use in genomic selection.

Progesterone improves the maturation of male-induced preovulatory follicles in anoestrous ewes

The first ovulation induced by male effect in sheep during seasonal anoestrus usually results in the development of a short cycle that can be avoided by progesterone priming before ram introduction. In elucidating the involvement of the hypothalamic–pituitary–gonadal axis in the occurrence of short cycles, the effects of progesterone and the time of anoestrus on the development of male-induced preovulatory follicles were investigated in anoestrous ewes using morphological, endocrine and molecular approaches. Ewes were primed with progesterone for 2 (CIDR2) or 12 days (CIDR12) and untreated ewes used as controls during early (April) and late (June) anoestrus. The duration of follicular growth and the lifespan of the male-induced preovulatory follicles were prolonged by ∼1.6 days in CIDR12 ewes compared with the controls. These changes were accompanied by a delay in the preovulatory LH and FSH surges and ovulation. Intra-follicular oestradiol concentration and mRNA levels ofLHCGRandSTARin the granulosa and theca cells of the preovulatory follicles were higher in CIDR12 ewes than the control ewes. The expression of mRNA levels ofCYP11A1andCYP17A1also increased in theca cells of CIDR12 ewes. CIDR2 ewes gave intermediate results. Moreover, ewes ovulated earlier in June than in April, without changes in the duration of follicular growth, but these effects were unrelated to the lifespan of corpus luteum. Our results give the first evidence supporting the positive effect of progesterone priming on the completion of growth and maturation of preovulatory follicles induced by male effect in seasonal anoestrous ewes, thereby preventing short cycles.

Fatty acid synthesis and oxidation in cumulus cells support oocyte maturation in bovine

Oocyte meiotic maturation requires energy from various substrates including glucose, amino acids, and lipids. Mitochondrial fatty acid (FA) β-oxidation (FAO) in the oocyte is required for meiotic maturation, which is accompanied by differential expression of numerous genes involved in FAs metabolism in surrounding cumulus cells (CCs) in vivo. The objective was to elucidate components involved in FAs metabolism in CCs during oocyte maturation. Twenty-seven genes related to lipogenesis, lipolysis, FA transport, and FAO were chosen from comparative transcriptome analysis of bovine CCs before and after maturation in vivo. Using real-time PCR, 22 were significantly upregulated at different times of in vitro maturation (IVM) in relation to oocyte meiosis progression from germinal vesicle breakdown to metaphase-II. Proteins FA synthase, acetyl-coenzyme-A carboxylase, carnitine palmitoyltransferase, perilipin 2, and FA binding protein 3 were detected by Western blot and immunolocalized to CCs and oocyte cytoplasm, with FA binding protein 3 concentrated around oocyte chromatin. By mass spectrometry, CCs lipid profiling was shown to be different before and after IVM. FAO inhibitors etomoxir and mildronate dose-dependently decreased the oocyte maturation rate in vitro. In terms of viability, cumulus enclosed oocytes were more sensitive to etomoxir than denuded oocytes. In CCs, etomoxir (150 μM) led to downregulation of lipogenesis genes and upregulated lipolysis and FAO genes. Moreover, the number of lipid droplets decreased, whereas several lipid species were more abundant compared with nontreated CCs after IVM. In conclusion, FAs metabolism in CCs is important to maintain metabolic homeostasis and may influence meiosis progression and survival of enclosed oocytes.

Breast-cancer anti-estrogen resistance 4 (BCAR4) encodes a novel maternal-effect protein in bovine and is expressed in the oocyte of humans and other non-rodent mammals

STUDY QUESTION

Does BCAR4 have a role in mammalian embryo development?

SUMMARY ANSWER

Expression, localization and functional data support that BCAR4 is a maternal-effect protein in non-rodent mammals.

WHAT IS KNOWN ALREADY

BCAR4 was previously identified as an oocyte-specific gene in cattle, and as a marker of certain breast tumors in humans.

STUDY DESIGN, SIZE, DURATION

Human oocytes were obtained from patients undergoing IVF, but had failed to mature after ovarian stimulation. Dog oocytes were obtained from ovariectomized bitches. Pig, horse and bovine ovaries were obtained from commercial slaughterhouses for extraction of immature oocyte-cumulus complexes. In vivo matured bovine matured oocytes were obtained after ovulation induction and ovulation inducing treatment of Montbeliard heifers.

MATERIALS, SETTING AND METHODS

Expression at the RNA level was analyzed by reverse transcription coupled to polymerase chain reaction. Western blot and immunolabeling coupled to confocal or electronic microscopy were used to analyze bovine protein expression and intracellular localization. For the functional approach, short-interfering RNA were microinjected into mature bovine oocytes, followed by IVF; cleavage and embryo development were recorded.

MAIN RESULTS AND THE ROLE OF CHANCE

The BCAR4 gene is conserved in mammalian species from various orders and has been lost in rodents after divergence with lagomorphs. The transcript is expressed in the oocytes of humans and domestic species. We bring the first experimental evidence of the BCAR4 protein in mammals. In cattle, the protein is not detected in immature oocytes but starts to be synthesized during maturation, increases in the zygote and persists until the morula stage. The protein is detected throughout the cytoplasm in mature oocytes, concentrates in and around the pronuclei in the zygote, and appears to shuttle in and out of the nuclei starting in the 2-cell embryo; BCAR4 is also present at the junctions between blastomeres from 2-cell to morula. In our functional approach, targeting the BCAR4 transcript by small-interfering RNA significantly compromised development to the morula or/and blastocyst stages (P < 0.05, logistic regression).

LIMITATIONS, REASONS FOR CAUTION

As indicated above, protein expression and function were investigated in cattle and mostly in vitro matured oocytes were used.

WIDER IMPLICATIONS OF THE FINDINGS

This study provides a novel candidate gene whose mutation or deregulation may underlie certain cases of unexplained female infertility.

Brilliant Cresyl Blue stain selects largest oocytes with highest mitochondrial activity, maturation-promoting factor activity and embryo developmental competence in prepubertal sheep

The aim of this study was to test the Brilliant Cresyl Blue (BCB) stain to select prepubertal sheep oocytes for in vitro blastocyst production. Oocyte diameter, mitochondrial activity, maturation-promoting factor (MPF) activity and mRNA relative expression (RE) of genes related to metabolism (ATPase Na(+)/K(+) transporting α 1 (ATP1A1) and cytochrome c oxidase subunit 1 (COX1)) and constitutive function of the cell (cytoplasmic polyadenylation-element-binding protein (CPEB) and S100A10) were assessed. Immature oocytes were exposed to different BCB concentrations (13, 26, 39 and 52  μM) and classified according to their cytoplasm colouration as grown BCB+ (blue cytoplasm) and growing BCB- (colourless cytoplasm). Staining oocytes with 13  μM BCB during 60  min allows selection of (BCB+) the largest (123.66  μm) and most competent oocytes to develop to the blastocyst stage (21%) with a higher number of cells (69.71 ± 6.19 s.e.m.) compared with non-stained BCB- oocytes (106.82  μm, 9% and 45.91 ± 3.35 s.e.m. respectively). Mitochondrial activity, assessed by MitoTracker Orange CMTMRos probe, was significantly higher in BCB+ than in BCB- oocytes after in vitro maturation (3369 and 1565  AU respectively). MPF activity was assessed by CDC2 kinase activity assay showing significantly higher activity at metaphase II stage in BCB+ than in BCB- oocytes (1.479 ± 0.09 and 1.184 ± 0.05 optical density respectively). The genes analysed in this work, ATP1A1, COX1, CPEB and S100A 10, did not show significant effect in mRNA RE between BCB selected oocytes. In conclusion, BCB stains larger and more competent oocytes to develop to the blastocyst stage with more active mitochondria and MPF activity and higher blastocyst cell number.

Expression of maternal transcripts during bovine oocyte in vitro maturation is affected by donor age

The primary objective of this study was to compare expression of maternal transcripts in bovine oocyte populations with differential developmental competence: oocytes from prepubertal and pubertal animals; and oocytes from small (3-4 mm) and large (6-10 mm) follicles from pubertal animals. All transcripts were examined in oocytes prior to and after in vitro maturation (IVM). Genes were selected based on their known maternal effect in mouse (ZAR1, STELLA, HSF1, MATER/NLRP5 and its paralogue NLRP9), or their identification as markers of oocyte maturation, either involved in redox metabolism (PRDX1, PRDX2) or meiotic progression (AURKA). Total or polyadenylated forms of the transcripts were followed by reverse transcription coupled to real-time PCR. Six polyadenylated transcripts were found significantly reduced after maturation irrespective of donor age or follicle diameter (p<0.05). Within these six polyadenylated transcripts, ZAR1, NLRP9, HSF1, PRDX1 and PRDX2 were significantly reduced in oocytes from prepubertal animals compared to adult animals (p<0.05). A younger age was also associated with lower abundance (total form) of PRDX2/PRDX1 irrespective of maturation. Total HSF1, PRDX1 and polyadenylated NLRP9 showed a tendency (p values from 0.053 to 0.08) for a higher detection in oocytes from small follicles, thus encouraging further investigation of the follicle diameter model. However, at the present time, follicle size did not significantly affect expression of transcripts examined. In conclusion, this study demonstrates differences in the maternal store of RNA and its regulation during IVM which is dependent on donor age.

Thymosins β-4 and β-10 are expressed in bovine ovarian follicles and upregulated in cumulus cells during meiotic maturation

β-Thymosins are small proteins that regulate the actin cytoskeleton and are involved in cell motility, differentiation, the induction of metalloproteinases, in anti-inflammatory processes and tumourigenesis. However, their roles in the ovary have not yet been elucidated. Using transcriptomics and real time reverse transcription-polymerase chain reaction validation, the present study demonstrates that thymosin β-4 (TMSB4) and thymosin β-10 (TMSB10) are upregulated in bovine cumulus cells (CCs) during in vitro maturation of cumulus-oocyte complexes (COCs) in parallel with an increase in mRNA expression of HAS2, COX2 and PGR genes. Using immunocytochemistry, both proteins were found to be localised mainly in granulosa cells, CCs and oocytes, in both the cytoplasm and nucleus, as well as being colocalised with F-actin stress fibres in CCs. Using different maturation mediums, we showed that the expression of TMSB10, but not TMSB4, was positively correlated with COC expansion and progesterone secretion and negatively correlated with apoptosis. Immunofluorescence, coupled with terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end-labelling (TUNEL), demonstrated the absence of TMSB4 and/or TMSB10 in apoptotic cells. TMSB10 expression was higher in COCs matured in vivo than in vitro, and differences related to the age of the animal were observed. TMSB4 and/or TMSB10 expression was unchanged, whereas HAS2 overexpressed in CCs from oocytes that developed to the blastocyst stage in vitro compared with those that did not. Thus, TMSB4 and/or TMSB10 ovarian expression patterns suggest that these two thymosins may be involved in cumulus modifications during maturation.

Regulation of bovine oocyte-specific transcripts during in vitro oocyte maturation and after maternal-embryonic transition analyzed using a transcriptomic approach

Oocyte/embryo genomics in mammals faces specific challenges due to limited biological material, to the comparison of models with different total RNA contents, and to expression of a specific set of genes often absent from commercially available microarrays. Here, we report experimental validation of a RNA amplification protocol for bovine oocytes and blastocysts. Using real-time PCR, we have confirmed that the profile of both abundant and scarce polyadenylated transcripts was conserved after RNA amplification. Next, amplified probes generated from immature oocytes, in vitro matured oocytes, and in vitro produced hatched blastocysts were hybridized onto a macroarray that included oocyte-specific genes. Following an original approach, we have compared two normalization procedures, based on the median signal or an exogenous standard. We have evidenced the expected difference in sets of differential genes depending on the normalization procedure. Using a 1.5-fold threshold, no transcript was found to be upregulated when data were normalized to an exogenous standard, which reflects the absence of transcription during in vitro oocyte maturation. In blastocysts, the majority of oocyte-preferentially expressed genes were not activated, as previously observed in mouse. Finally, microarray data were validated by real-time PCR on a random subset of genes. Our study sheds new light on and complements previous transcriptomic analyses of bovine oocyte to embryo transition using commercial platforms.

Factors affecting oocyte quality: who is driving the follicle?

Mammalian ovaries contain a large stock of oocytes enclosed in primordial follicles. Ovarian cyclic activity induces some of these follicles to initiate growth towards a possible ovulation. However, most of these follicles terminate their growth at any moment and degenerate through atresia. In growing follicles, only a subset of oocytes are capable to support meiosis, fertilization and early embryo development to the blastocyst stage, as shown through embryo in vitro production experiments. This proportion of competent oocytes is increasing along with follicular size. Growing lines of evidence suggest that oocyte competence relies on the storage of gene products (messenger RNA or protein) that will be determinant to support early stages of embryo development, before full activation of embryonic genome. Given these facts, the question is: are these gene products stored in oocytes during late folliculogenesis, allowing an increasing proportion of them to become competent? Alternatively, these transcripts may be stored during early folliculogenesis as the oocyte grows and displays high transcription activity. Several arguments support this latter hypothesis and are discussed in this review: (i) many attempts at prolonged culture of oocytes from antral follicles have failed to increase developmental competence, suggesting that developmental competence may be acquired before antral formation; (ii) the recent discovery of oocyte secreted factors and of their ability to regulate many parameters of surrounding somatic cells, possibly influencing the fate of follicles between ovulation or atresia, suggests a central role of oocyte quality in the success of folliculogenesis. Finally, in addition to their role in interfollicular regulation of ovulation rate, late folliculogenesis regulation and atresia could also be seen as a selective process aimed at the elimination through follicular atresia of oocytes that did not succeed to store proper gene products set during their growth.

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.

Differential regulation of abundance and deadenylation of maternal transcripts during bovine oocyte maturation in vitro and in vivo

Background

In bovine maturing oocytes and cleavage stage embryos, gene expression is mostly controlled at the post-transcriptional level, through degradation and deadenylation/polyadenylation. We have investigated how post transcriptional control of maternal transcripts was affected during in vitro and in vivo maturation, as a model of differential developmental competence.

Results

Using real time PCR, we have analyzed variation of maternal transcripts, in terms of abundance and polyadenylation, during in vitro or in vivo oocyte maturation and in vitro embryo development. Four genes are characterized here for the first time in bovine: ring finger protein 18 (RNF18) and breast cancer anti-estrogen resistance 4 (BCAR4), whose oocyte preferential expression was not previously reported in any species, as well as Maternal embryonic leucine zipper kinase (MELK) and STELLA. We included three known oocyte marker genes (Maternal antigen that embryos require (MATER), Zygote arrest 1 (ZAR1), NACHT, leucine rich repeat and PYD containing 9 (NALP9)). In addition, we selected transcripts previously identified as differentially regulated during maturation, peroxiredoxin 1 and 2 (PRDX1, PRDX2), inhibitor of DNA binding 2 and 3 (ID2, ID3), cyclin B1 (CCNB1), cell division cycle 2 (CDC2), as well as Aurora A (AURKA). Most transcripts underwent a moderate degradation during maturation. But they displayed sharply contrasted deadenylation patterns that account for variations observed previously by DNA array and correlated with the presence of a putative cytoplasmic polyadenylation element in their 3' untranslated region. Similar variations in abundance and polyadenylation status were observed during in vitro maturation or in vivo maturation, except for PRDX1, that appears as a marker of in vivo maturation. Throughout in vitro development, oocyte restricted transcripts were progressively degraded until the morula stage, except for MELK ; and the corresponding genes remained silent after major embryonic genome activation.

Conclusion

Altogether, our data emphasize the extent of post-transcriptional regulation during oocyte maturation. They do not evidence a general alteration of this phenomenon after in vitro maturation as compared to in vivo maturation, but indicate that some individual messenger RNA can be affected.

Zygote arrest 1 gene in pig, cattle and human: evidence of different transcript variants in male and female germ cells

BACKGROUND

Zygote arrest 1 (ZAR1) is one of the few known oocyte-specific maternal-effect genes essential for the beginning of embryo development discovered in mice. This gene is evolutionary conserved in vertebrates and ZAR1 protein is characterized by the presence of atypical plant homeobox zing finger domain, suggesting its role in transcription regulation. This work was aimed at the study of this gene, which could be one of the key regulators of successful preimplantation development of domestic animals, in pig and cattle, as compared with human.

METHODS

Screenings of somatic cell hybrid panels and in silico research were performed to characterize ZAR1 chromosome localization and sequences. Rapid amplification of cDNA ends was used to obtain full-length cDNAs. Spatio-temporal mRNA expression patterns were studied using Northern blot, reverse transcription coupled to polymerase chain reaction and in situ hybridization.

RESULTS

We demonstrated that ZAR1 is a single copy gene, positioned on chromosome 8 in pig and 6 in cattle, and several variants of correspondent cDNA were cloned from oocytes. Sequence analysis of ZAR1 cDNAs evidenced numerous short inverted repeats within the coding sequences and putative Pumilio-binding and embryo-deadenylation elements within the 3'-untranslated regions, indicating the potential regulation ways. We showed that ZAR1 expressed exclusively in oocytes in pig ovary, persisted during first cleavages in embryos developed in vivo and declined sharply in morulae and blastocysts. ZAR1 mRNA was also detected in testis, and, at lower level, in hypothalamus and pituitary in both species. For the first time, ZAR1 was localized in testicular germ cells, notably in round spermatids. In addition, in pig, cattle and human only shorter ZAR1 transcript variants resulting from alternative splicing were found in testis as compared to oocyte.

CONCLUSION

Our data suggest that in addition to its role in early embryo development highlighted by expression pattern of full-length transcript in oocytes and early embryos, ZAR1 could also be implicated in the regulation of meiosis and post meiotic differentiation of male and female germ cells through expression of shorter splicing variants. Species conservation of ZAR1 expression and regulation underlines the central role of this gene in early reproductive processes.

Bovine mater-like NALP9 is an oocyte marker gene

We have cloned and sequenced the bovine NALP9 cDNA, which contains a 2991 bp long open reading frame with 76% homology to its human counterpart. The putative 996 amino acids protein presents the domain organization typical of the Nacht, Leucine rich repeat and Pyrin domain containing (NALP) family that includes the maternal effect factor MATER. By reverse transcription coupled to polymerase chain reaction, we have analyzed expression of NALP9 in a panel of somatic and gonadic tissues and during in vitro preimplantation development. The transcript was detected exclusively in testis and ovary, and at a remarkably high level in the oocyte from antral follicles. NALP9 mRNA remained present after in vitro maturation and fertilization, and was detected in embryos, but transcription was not reactivated at the maternal to embryo transition. Thus NALP9 is characterized as a novel oocyte marker gene in cattle.

Spatio-Temporal Expression of the Germ Cell Marker Genes MATER, ZAR1, GDF9, BMP15,andVASA in Adult Bovine Tissues, Oocytes, and Preimplantation Embryos1

We have cloned the bovine homologue of Mater (maternal antigen that embryos require) cDNA, potentially the first germ cell-specific maternal-effect gene in this species. The 3297 base-pair longest open reading frame encodes a putative protein of 1098 amino acids with a domain organization similar to its human counterpart. By reverse transcription coupled to polymerase chain reaction, we have analyzed the spatiotemporal expression of MATER, along with other potential markers of germ cells or oocytes: ZAR1 (zygotic arrest 1), GDF9 (growth and differentiation factor 9), BMP15 (bone morphogenetic protein 15), and VASA. In agreement with a preferential oocyte origin, MATER, ZAR1, GDF9, and BMP15 transcripts were detected in the oocyte itself at a much higher level than in the gonads, while no significant expression was detected in our panel of somatic tissues (uterus, heart, spleen, intestine, liver, lung, mammary gland, muscle). In situ hybridization confirmed oocyte-restricted expression of MATER and ZAR1 within the ovary, as early as preantral follicle stages. VASA was highly represented in the testis and the ovary, and still present in the oocyte from antral follicles. Maternal MATER, ZAR1, GDF9, and BMP15 transcripts persisted during oocyte in vitro maturation and fertilization and in preimplantation embryo until the five- to eight-cell or morula stage, but transcription was not reactivated at the time of embryonic genome activation.