Steroidome and metabolome analysis in gilt saliva to identify potential biomarkers of boar effect receptivity

Optimal management of gilt reproduction requires oestrus synchronization. Hormonal treatments are used for this purpose, but there is a growing demand for non-hormonal alternatives, especially in organic farms. The boar effect is an important alternative opportunity to induce and synchronize oestrus without hormones. Before puberty, gilts exhibit a 'waiting period' during which boar exposure could induce and synchronize the first ovulation. We searched for salivary biomarkers of this period of boar effect receptivity to improve detection of the gilts to stimulate with the perspective of enhancing the efficacy of the boar effect. Saliva samples were collected from 30 Large-White×Landrace crossbred gilts between 140 and 175 days of age. Gilts were exposed twice a day to a boar and subjected to oestrus detection from 150 to 175 days of age. Among the 30 gilts, 10 were detected in oestrus 4 to 7 days after the first introduction of the boar and were considered receptive to the boar effect, 14 were detected in oestrus more than 8 days after first boar contact, and six did not show oestrus and were considered non-receptive. Saliva samples from six receptive and six non-receptive gilts were analyzed for steroidome and for metabolome using gas chromatography coupled to tandem mass spectrometry and ¹H nuclear magnetic resonance spectroscopy, respectively. Four saliva samples per gilt were analyzed: 25 days and 11 days before boar introduction, the day of boar introduction, 3 days later for receptive gilts or 7 days later for non-receptive gilts. Twenty-nine steroids and 31 metabolites were detected in gilt saliva. Salivary concentrations of six steroids and three metabolites were significantly different between receptive and non-receptive gilts: progesterone and glycolate 25 days before boar introduction, 3α5β20α- and 3β5α20β-hexahydroprogesterone, dehydroepiandrosterone, androstenediol, succinate, and butyrate 11 days before boar introduction, and 3β5α-tetrahydroprogesterone on the day of boar introduction. Thus, nine potential salivary biomarkers of boar effect receptivity were identified in our experimental conditions. Further studies with higher numbers of gilts and salivary sampling points are necessary to ascertain their reliability.

249 AN EFFICIENT AND REPEATABLE IN VITRO FERTILIZATION TECHNIQUE IN THE EQUINE FOR PRESERVATION OF ENDANGERED SPECIES

Most wild equids are currently endangered or threatened, as mentioned in the International Union for the Conservation of Nature Red List, and several domestic horse breeds are at risk of extinction. Genome resource banking requires cryoconservation of semen, oocytes, and/or embryos. Embryo production in equids is limited in vivo because routine induction of multiple ovulation is still ineffective. Embryo production in vitro allows the production of several embryos per cycle that could easily be frozen because of their small size. Intracytoplasmic sperm injection has been widely adopted to generate horse embryos in vitro; however, intracytoplasmic sperm injection is time-consuming and requires expensive equipment and expertise in micromanipulation. Several attempts to establish an efficient IVF technique in the equine were performed, but reported IVF rates remain quite low and no repeatable equine IVF technique was available. Our objective was to develop an efficient and repeatable IVF technique in the equine. Immature cumulus-oocyte complexes (COC) were collected either from slaughtered mares in a local slaughterhouse or from our experimental mares by ovum pick up (OPU). The COC were cultured for 26 h in an in vitro maturation (IVM) medium or in preovulatory follicular fluid (FF) collected by OPU, pre-incubated for 30 min in oviducal fluid collected from slaughtered females, co-incubated for 18 h with fresh spermatozoa treated with procain, and cultured in SOF for 30 h. They were fixed and analysed either after 18 h IVF (experiment 1) or after 30 h in vitro development (experiment 2). In experiment 1, COC were collected from slaughtered mares and analysed after 18 h IVF. Zygotes with 2 pronuclei were observed. The IVF rate was similar for oocytes matured in IVM medium (22/33, 67%) or FF (24/42, 57%; chi-square test, P > 0.05). In experiment 2, COC were collected from slaughtered mares and from experimental mares and analysed after 30 h of in vitro development. We observed zygotes with 2 highly decondensed pronuclei, pronuclei decondensation being the first step of embryo development. For oocytes collected from slaughtered mares, the percentage of zygotes was similar for oocytes matured in IVM medium (8/11, 73%) or FF (10/15, 67%). For oocytes collected by ovum pickup, the percentage was similar for IVM medium (3/5, 60%) or FF (6/8, 75%). We also observed some embryonic structures with several nuclei, but the quality of these embryos was poor. In conclusion, we have established an efficient IVM-IVF technique that allows the first step of embryo development. Because we obtained similar results for 4 years, we consider that this efficient technique is repeatable. Further experiments are in progress to improve the quality of the embryos.

A hybrid characterization framework to determine the visco-hyperelastic properties of a porcine zona pellucida

The zona pellucida (ZP) is a specialized extracellular matrix surrounding the developing oocyte. This thick matrix consists of various types of glycoprotein that play different roles in the fertilization process. Nowadays, several techniques are available for assessing ZP's mechanical response. The basic assumption behind these methods is that the ZP behaves like an elastic body: hence, dissipative forces are neglected and Young's modulus remains unaffected by probe dynamics. However, dissipative forces are strongly regulated by the slippage of ZP chains past one another while reaction forces related to elastic deformations (driven by the ability of each chain to stretch) depend on the ZP structure (i.e. number of cross-links and distances between knots). Although viscous reaction forces generated by the ZP are one of the main factors regulating sperm transit, their peculiar behaviour along the ZP structure remains poorly understood and rarely investigated. In order to overcome this limitation, a novel visco-hyperelastic model describing the porcine ZP reaction forces generated by nanoindentations at different probe rates is developed and verified in this study. Visco-hyperelastic parameters of porcine ZP membranes are determined by means of a hybrid characterization framework combining atomic force microscopy nanoindentation measurements, nonlinear finite-element analysis and nonlinear optimization. Remarkably, it is possible to separate the contributions of hyperelastic and viscous terms to ZP mechanical response and evaluate the error made in the determination of ZP mechanical properties if viscous effects were not considered.

Efficiency of embryonic development after intrafollicular and intraoviductal transfer of in vitro and in vivo matured horse oocytes

In vivo techniques, such as intraoviductal oocyte transfer (OT) and intrafollicular oocyte transfer (IFOT), can be considered as alternatives to bypass the lack of efficient superovulation treatments and the inadequacy of conventional in vitro fertilization techniques in the horse. We compared embryo production after transfer of in vivo recovered oocytes (1) into a recipient's oviduct or (2) into her preovulatory follicle either immediately after ovum pick-up or (3) after in vitro maturation (IVM). Recipients were inseminated with fresh semen of a stallion with a known normal fertility. Ten days after surgery, rates of embryos collected in excess to the number of ovulations were calculated and compared for each group. Embryo collection rates were 32.5% (13 of 40), 5.5% (3 of 55), and 12.8% (6 of 47) for OT, post-IVM IFOT, and immediate IFOT, respectively. Oocyte transfer significantly yielded more embryos than did immediate IFOT and post-IVM IFOT. We also showed that in vitro matured oocytes could successfully be used for IFOT. Our results also suggest that improvement of the IFOT technique could turn it into an inexpensive and easy-to-perform procedure that could be an answer to the inefficiency of superovulation treatments in the mare.

Cytoplasmic lipid droplets and mitochondrial distribution in equine oocytes: Implications on oocyte maturation, fertilization and developmental competence after ICSI

Lipid droplets (LDs) and mitochondria in the ooplasm are essential for energy production required for maturation, fertilization and embryo development. This study investigates the correlations between cytoplasmic LDs polar aggregation and: (1) nuclear maturation (Experiment 1); (2) mitochondrial (mt) distribution pattern and localization (Experiment 2); (3) fertilization and embryonic development after intracytoplasmic sperm injection (ICSI; Experiment 3) in equine oocytes recovered from slaughtered mares and matured in vitro. Morphologically normal oocytes were selected after culture and categorized as having polar (P) aggregation or uniform (U) distribution of LDs. In Experiment 1, the maturation rate was significantly higher in P compared with U oocytes (69%, 40/58 vs. 32%, 13/41; P<0.001). In Experiment 2, it was observed that P and U oocytes showed heterogeneous mt distribution at comparable rates (68%, 25/37 vs. 50%, 2/4 for P and U respectively; NS). Moreover, only in 8/25 (32%) of P oocytes, LDs overlapped with mt aggregates in the area containing meiotic spindle. In Experiment 3, normal fertilization (51%, 19/37 vs. 60%, 6/10, for P and U) and cleavage rates (83%, 20/24 vs. 67%, 4/6, for P and U) did not differ between groups, also in oocytes with LDs located nearby the polar body. Overall, P aggregation of LDs was related to cumulus expansion at collection. In conclusion, in equine matured oocytes, P aggregation of LDs is related with cumulus expansion and nuclear maturation. However, it is not related with heterogeneous mt distribution and cannot be considered a predictive indicator for normal fertilization and embryo development.

Influence of cysteamine on in vitro maturation, in vitro and in vivo fertilization of equine oocytes

Contents The effect of cysteamine on in vitro nuclear and cytoplasmic maturation of equine oocytes collected by transvaginal ultrasound guided follicular aspiration was assessed. Oocytes were matured in vitro with (cysteamine group) or without (control group) cysteamine. The nuclear stage after DNA Hoechst staining, penetration rates after two different in vitro fertilization (IVF) techniques (IVF media with ionophore and Hepes buffer with heparin) and the embryo yield following oocyte intra-oviductal transfer were used as a criterion for assessing nuclear and cytoplasmic maturation, respectively. Contrary to the data described in other domestic species, there was no effect of cysteamine on in vitro nuclear maturation, IVF or in vivo embryonic development under our conditions. Ovum pick up yields (52%) and maturation rates (control group: 47% and cysteamine group: 55%) were similar to those previously reported. From 57 oocytes transferred to the oviduct in each group, the number of embryos collected was 10 (17%) in the control group and five in the cysteamine group (9%). Those two percentages were not statistically different (p > 0.05). No effect of IVF technique was seen on the success rate (6%) in each group.

In vitro equine oocyte maturation in pure follicular fluid plus interleukin-1 and fertilization following ICSI

The interleukin-1 (IL-1) system is thought to be involved in periovulatory events in the mare. Previous in vivo studies have demonstrated that IL-1beta induces oocyte maturation, but depresses the pregnancy rate 14 days after ovulation. To better understand the role of IL-1 in oocyte maturation and fertilization, the effects of IL-1 on the in vitro maturation rate of equine oocytes in pure follicular fluid were evaluated and fertilization rate assessed following intracytoplasmic sperm injection (ICSI). Oocytes collected from slaughterhouse ovaries were cultured in four different media for 30 h prior to fertilization. Two experiments were performed, each using three maturation media as the experimental treatments. Medium 1 was pure follicular fluid from subordinate follicles. Medium 2 was medium 1 plus 50 ng/ml recombinant human IL-1beta. Medium 3 was pure follicular fluid collected from mares administered crude equine gonadotropin (CEG). Medium 4 was medium 2 plus 50 ng/ml of recombinant human IL-1 receptor antagonist. Media 1, 2 and 3 were compared in experiment 1. In experiment 2, media 1, 2 and 4 were compared. After maturation, metaphase II oocytes were submitted to microinjection and assessed for signs of fertilization. In experiment 1, 101 oocytes were evaluated. The rate of polar body extrusion was 66, 51 and 68% and the proportions of normally fertilized oocytes after ICSI were 40, 18 and 38% for media 1, 2 and 3, respectively. In experiment 2, 122 oocytes were evaluated. The rate of polar body extrusion was 55, 48 and 42% and the proportions showing normal fertilization after ICSI were 14, 25 and 29% for media 1, 2 and 4, respectively. There was no positive effect of IL-1beta on maturation in both experiments, but the fertilization rate and percentage of embryos reaching four-cell were low in the presence of IL-1beta, indicating that this cytokine may interfere with fertilization and early embryo development.

294 EFFECT OF CYSTEAMINE ADMINISTRATION DURING EQUINE OOCYTE MATURATION ON GLUTATHIONE CONTENT, NUCLEAR MATURATION, AND DEVELOPMENTAL CAPABILITY AFTER INTRACYTOPLASMIC SPERM INJECTION

In the recent years, assisted reproduction methods have produced only limited success in equine species in comparison with other domestic mammals. A major factor affecting oocyte viability during in vitro culture is oxidative stress. Oxidative modifications could be responsible for oocyte-defective in vitro maturation and consequently compromise subsequent fertilization and embryonic development. Low-molecular-weight thiol compounds such as cysteamine, added during in vitro culture of bovine, porcine, and ovine oocytes, increase intracellular glutathione (GSH) synthesis, which prevents oxidative damages and consequently improves in vitro maturation and embryo development. The present study was aimed at investigating whether equine oocyte maturation efficiency and embryonic developmental capability following ICSI benefit from the addition of cysteamine during in vitro maturation (IVM). Cumulus oocyte complexes (COCs) were collected from slaughtered ovaries and cultured for 30 h at 38.5°C in 500 μL of control medium (TCM199 + 0.4% BSA + 0.1 IU/mL rhFSH + 50 ng/mL EGF) either supplemented with 100 μM cysteamine or not. After culture, nuclear stage was assessed by Hoechst 33342 staining after cumulus cell removal, and MII oocytes were analyzed for GSH content (Baker MA et al. 1990 Anal. Biochem. 190, 360–365). Groups of COCs matured under the same conditions were denuded with hyaluronidase and only oocytes with a visible polar body were fertilized by ICSI. The number of embryos that reached the 2–4 cell stage was assessed by nuclear staining with propidium iodide after 72 h of culture in SOF supplemented with 5% calf serum at 38.5°C in a modified atmosphere (5% CO2, 5% O2, and 90% N2). Our data indicated that oocytes cultured in the presence of cysteamine had a nuclear maturation rate similar to those cultured in control medium (Table 1). Intraoocyte GSH content increased during IVM, and the addition of cysteamine induced a significant GSH accumulation in matured oocytes. After ICSI, a similar proportion of zygotes in each group developed beyond the two-cell stage after 72 h of culture. The results of this study demonstrate that the addition of cysteamine to the IVM medium increases GSH content in equine oocytes. However, this affects neither the maturation rate nor the capability to reach the early embryonic development after ICSI. We hypothesize that factor(s) other than GSH content are responsible for the limited in vitro developmental capability of equine oocyte. Table 1. Effect of cysteamine administration on maturation rate, oocyte GSH content (pmol/oocyte), and early embryonic development after ICSI This work was supported by a 2003 UniMi Grant.

The interleukin-1 system and female reproduction

Interleukins (ILs) are known best for their involvement in the immune system and their role during inflammation. In the ovary, a growing body of evidence suggests that the ovarian follicle is a site of inflammatory reactions. Thus ovarian cells could represent sources and targets of ILs. Since then, the IL-1 system components (IL-1alpha, IL-1beta, IL-1 receptor antagonist, IL-1 receptors) have been demonstrated to have several sites of synthesis in the ovary. These factors have been localized in the various ovarian cell types, such as the oocyte, granulosa and theca cells, in several mammalian species. IL-1-like bioactivity has been reported in human and porcine follicular fluid at the time of ovulation. The role of IL-1 in local processes is still poorly known, although there is evidence for involvement in the ovulation process, and in oocyte maturation. More precisely, IL-1 may be involved in several ovulation-associated events such as the synthesis of proteases, regulation of plasminogen activator activity, prostaglandin and nitric oxide production. IL-1 also regulates ovarian steroidogenesis. These different aspects of the involvement of the IL-1 system in important aspects of female reproduction are discussed.

Inhibition of in vitro maturation of equine oocytes by interleukin 1 beta via specific IL-1 receptors

Interleukin 1 beta (IL-1 beta) inhibits the LH-induced resumption of meiosis of equine oocytes in vitro. The present study was performed to clarify this inhibitory effect of IL-1 beta by testing increasing concentrations of IL-1 beta, and by measuring the effect of addition of IL-1 receptor antagonist (IL-1RA) to the culture medium. The effect of IL-1 beta on epidermal growth factor (EGF)-induced resumption of meiosis was also studied. Cumulus-oocyte complexes (COCs) were collected from subordinate follicles on ovaries obtained from an abattoir. In five distinct experiments, COCs were cultured for 30 h and nuclear maturation of oocytes was evaluated by DNA staining. In Expt 1, seven different media were tested: medium 1 (TCM199+BSA); medium 2 (medium 1+50 ng IL-1 beta ml(-1)); medium 3 (medium 1+eLH); and media 4, 5, 6 and 7 (medium 3 containing 0.1, 1.0, 10.0 and 50.0 ng IL-1 beta ml(-1), respectively). In Expt 2, four different media were tested: medium 1 (TCM199+BSA+eLH); medium 2 (medium 1+50 ng IL-1 beta ml(-1)); and media 3 and 4 (medium 2+IL-1RA at 50 and 100 ng ml(-1), respectively). In Expt 3, three different media were tested: medium 1 (TCM199+BSA+eLH); medium 2 (medium 1+50 ng IL-1RA ml(-1)); and medium 3 (medium 2+50 ng IL-1 beta ml(-1)). In Expt 4, four different media were tested: medium 1 (TCM199+BSA+eLH); and media 2, 3 and 4 (medium 1+IL-1RA at 50, 100 and 150 ng ml(-1), respectively). In Expt 5, three different media were tested: medium 1 (TCM199+BSA+EGF); medium 2 (medium 1+50 ng IL-1 beta ml(-1)); and medium 3 (medium 2+50 ng IL-1RA ml(-1)). In Expt 1, LH alone induced an increase in the rate of in vitro maturation (IVM) of equine oocytes (P<0.05), whereas IL-1 beta alone did not have any effect compared with medium 1. IL-1 beta (50 ng ml(-1)) significantly inhibited the eLH-induced IVM of oocytes (P<0.05) compared with medium 3. A decrease in rate of maturation was observed from a concentration of 10 ng IL-1 beta ml(-1) onwards. In Expt 2, the presence of IL-1RA in the culture medium inhibited the effect of IL-1 beta and restored the rate of oocyte maturation (P<0.05) observed in the presence of LH alone. In Expts 3 and 4 it was demonstrated that IL-1RA alone had no positive effect on the eLH-induced rate of maturation. In Expt 5, IL-1 beta inhibited the EGF-induced resumption of meiosis (P<0.05). The addition of IL-1RA inhibited this effect and restored the rate of oocyte maturation (P<0.05) observed with EGF alone. In conclusion, the present data confirm the inhibitory effect of IL-1 beta on IVM of equine oocytes induced by eLH and demonstrate its inhibitory effect on EGF-induced oocyte maturation. The rate of maturation decreased in a dose-dependent way and the lowest rate of maturation was observed at 50 ng IL-1 beta ml(-1) (P<0.05). The use of IL-1RA inhibited these effects, demonstrating that the action of IL-1 beta is receptor-mediated. Moreover, the results clearly show that, in equine species, IL-1 beta is involved in the physiology of COCs by regulating resumption of meiosis.

Intrafollicular concentrations of steroids and steroidogenic enzymes in relation to follicular development in the mare

The objective of the present study was to determine the changes in follicular fluid steroid concentrations and in granulosa cell steroidogenic enzyme expression during the follicular phase, in relation to follicular size and physiological status in the mare. Follicular fluid and follicular cells were recovered by ultrasound-guided follicular punctures either around the time of emergence of the dominant follicle, at the end of the dominant follicle growth, or at the preovulatory stage, after injection of gonadotropin to induce ovulation. Cellular relative amounts of steroidogenic acute regulatory protein (StAR), P450-side chain cleavage (P450(scc)), 3beta-hydroxysteroid dehydrogenase (3betaHSD), 17alpha-hydroxylase, and aromatase were assessed by semiquantitative Western blot and densitometry. Follicular fluid was assayed for cholesterol concentrations by colorimetric assay and for progesterone, testosterone, and estradiol-17beta concentrations by RIA. Intrafollicular concentrations of progesterone and estradiol-17beta significantly increased in the dominant follicle during growth. After injection of gonadotropin, follicular maturation was characterized by a decrease in estradiol-17beta concentrations and a further increase in progesterone concentrations. Granulosa cells from dominant follicles had increased levels of StAR, P450(scc), 3betaHSD, and aromatase during growth, but decreased levels during maturation. Levels of StAR, P450(scc), 3betaHSD, and aromatase, as well as progesterone and estradiol-17beta, were lower in granulosa cells from subordinate than from dominant follicles. We did not observe a relationship between the steroidogenic activity of follicles and the capacity of their enclosed oocytes to complete meiosis in vitro.

Influence of epidermal growth factor on in vitro maturation of equine oocytes

The effect of epidermal growth factor (EGF) on the in vitro maturation rate of equine oocytes was examined. Oocytes were collected from an abattoir (Expt 1) or using ultrasound-guided follicular puncture in vivo (Expt 2). All oocytes with a compact or expanded cumulus at recovery were cultured for 30 h in: medium 1 (TCM199 + fetal calf serum (FCS) + crude equine gonadotrophin (CEG) + oestradiol + antibiotics); medium 2 (TCM199 + EGF); medium 3 (medium 1 without FCS + EGF); or medium 4 (medium 1 without CEG + EGF). In Expt 1, 84% (37/44) and 87% (40/46) cumulus expansion (P > 0.05), and 39% (22/57) and 9% (5/57) (P < 0.01) nuclear maturation, were observed in medium 1 and 2, respectively. In Expt 2, cumulus expansion was observed after culture in medium 1, 3 and 4 (30/30, 31/31 and 29/29, respectively). The nuclear maturation rate was significantly lower in medium 3 (6%, 2/36) than in medium 1 (43%, 16/37) (P < 0.01) and was higher in medium 4 (64%, 25/39) than in medium 1, although the effect was not significant (P = 0.07). In conclusion, 50 ng EGF ml(-1) alone was an effective substitute for crude equine gonadotrophin and the presence of EGF improves the nuclear maturation rate of equine oocytes.

Intrafollicular content of luteinizing hormone receptor, alpha-inhibin, and aromatase in relation to follicular growth, estrous cycle stage, and oocyte competence for in vitro maturation in the mare

The intrafollicular content of LH receptor, alpha-inhibin, and aromatase are known good indicators of follicular status. We investigated the amounts of these proteins in granulosa and cumulus cells in relation to oocyte competence for in vitro maturation, follicular growth, and estrous cycle stage in the mare. Follicular punctures were performed 34 h after an injection of crude equine gonadotropins, either during the follicular phase, at the end of the follicular phase, or during the luteal phase. The cumulus-oocyte complex, granulosa cells, and follicular fluid of follicles larger than 5 mm were collected. The nuclear stage of the oocytes after in vitro culture was determined microscopically. Granulosa and cumulus cell amounts of LH receptor, alpha-inhibin, and aromatase were assessed by the semiquantitative Western blot method and image analysis. Follicular fluids were assayed for progesterone (P4) and estradiol-17beta (E2). The three factors were expressed in mural granulosa and cumulus cells from all follicles from the gonadotropin-independent growth period until the preovulatory stage. Considering all the follicles punctured, the amounts of LH receptor and alpha-inhibin in granulosa cells were not different for the three physiological stages studied. The amounts of aromatase in granulosa cells, as well as the E2:P4 ratios, were higher for follicles punctured during the follicular phase than for the two other groups (p < 0.05). Considering the data from the three groups, the E2:P4 ratio and the LH receptor and aromatase contents, but not alpha-inhibin, in granulosa cells increased with an increase in follicular diameter (p < 0.01). The E2:P4 ratios and the amounts of LH receptor, alpha-inhibin, and aromatase in granulosa cells were lower in follicles 5-9 mm in diameter than in larger ones (p < 0.05). In cumulus cells, the amounts of the three factors were different neither between the three groups nor between the follicular diameters. Although we could not establish any obvious relationship to oocyte competence for in vitro maturation, the influence of the follicle diameter on the content of LH receptors, alpha-inhibin, and aromatase in granulosa cells was similar to the influence of follicle diameter on oocyte competence. Therefore, one can hypothesize that, in the mare, there is a link between the acquisition of oocyte competence and the expression of these factors in the follicular cells.

Functional and cooperative interactions between the homeodomain PDX1, Pbx, and Prep1 factors on the somatostatin promoter

Expression of the somatostatin gene in endocrine pancreatic cells is controlled by several regulatory cis-elements located in the promoter region. Among these, the adjacent UE-A and TSEI elements, located from -113 to -85 relative to the transcription initiation site, function in combination and act as a pancreas-specific mini-enhancer. The TSEI element is recognized by the pancreatic homeodomain factor PDX1. In the present study, we show that the UE-A element binds a heterodimeric complex composed of a Pbx factor and the Prep1 protein, both belonging to the atypical three-amino acid loop extension homeodomain family. Recombinant Pbx1 and Prep1 proteins bind cooperatively to the UE-A site, whereas neither protein can bind this site alone. Transient transfection experiments reveal that both Pbx1 and Prep1 are required to generate a strong transcriptional activation from the UE-A element when this element is inserted close to the TATA box. In contrast, in the context of the intact somatostatin promoter or mini-enhancer, Pbx1 and Prep1 alone have no effect, but they produce a drastic activation when the pancreatic homeodomain factor PDX1 is also coexpressed. Thus, the activity of the somatostatin mini-enhancer is mediated by a cooperative interaction between the Pbx-Prep1 heterodimeric complex and the pancreatic factor PDX1.

Oocyte competence for in vitro maturation is associated with histone H1 kinase activity and is influenced by estrous cycle stage in the mare

The in vitro maturation rate of equine oocytes remains low, regardless of culture conditions. Our objective was to determine the reasons for failure of equine oocytes to resume meiosis during in vitro maturation and to ascertain the influence of the estrous cycle stage on meiotic competence. In 10 cyclic mares, 7 ultrasound-guided follicular punctures were performed alternately during the follicular phase (group DF; n = 3 punctures), at the end of the follicular phase (group EF; n = 2), and during the luteal phase (group DL; n = 2). We evaluated the competence of the oocytes for in vitro maturation and measured their maturation-promoting factor activity by histone H1 kinase assay. Puncturing once at the end of the follicular phase and once during the luteal phase, or three times during the follicular phase, yielded about 11 cumulus-oocyte complexes per 22 days. The maturation rate was different between the groups, 51% in group EF, 34% in group DL (p < 0.05), and 15% in group DF (p < 0.01), and it increased with an increase in follicular diameter (p < 0.05). After in vitro culture, the H1 kinase activity was lower in oocytes that remained in germinal vesicle or dense chromatin stages than in oocytes that reached metaphase I or metaphase II (p < 0.05). The H1 kinase activity was not different between oocytes in germinal vesicle stage after in vitro maturation and immature oocytes that were not cultured in vitro, and was higher in preovulatory oocytes that reached metaphase II in vivo than in the oocytes that reached metaphase II after in vitro maturation (p < 0.001). This is the first report on kinase activity in the equine oocyte.

Maturation-promoting factor (MPF) and mitogen activated protein kinase (MAPK) expression in relation to oocyte competence for in-vitro maturation in the mare

In the equine species, a large proportion of oocytes fail to complete meiosis during in-vitro culture. The biochemical and molecular basis of this failure is unknown. The meiotic cell cycle is controlled in part by the maturation-promoting factor (MPF) and the mitogen-activated protein kinase (MAPK). In this study, we evaluated the oocyte competence for in-vitro maturation and the expression of MPF components (p34cdc2 and cyclin B) and MAPK after in-vitro culture. The maturation rate was influenced by the culture medium and the physiological stage of the mare at the time of oocyte recovery. We showed that MAPK and the two subunits of MPF were present in equine oocytes whatever the nuclear stage they reached after in-vitro culture and whatever the culture medium used. In incompetent oocytes, MAPK remained in its non-phosphorylated form, supposed to be inactive. In conclusion, the incompetence of equine oocytes to resume and complete meiosis is not due to the absence of p34cdc2, cyclin B or MAPK. Our results suggest that it is more probably due to a deficiency of regulators of MPF and/or to an inability to phosphorylate MAPK.

Chorionic gonadotropin secretion is associated with an inhibition of follicular growth and an improvement in oocyte competence for in vitro maturation in the mare

This study reports the follicular growth and oocyte competence for in vitro maturation and fertilization under the influence of circulating eCG. Three to 7 successive ultrasound-guided follicular punctures were performed on 4 pregnant mares from Day 23 until Day 75 of pregnancy and on 5 control mares whose embryonic vesicle was crushed on Day 22. All follicles larger than 5 mm were punctured 24 h after the largest follicle reached 18 mm. Expanded cumulus oocyte complexes (COCs) were stained at recovery to analyze the nuclear stage. Compact COCs were cultured in vitro for 46 h and either stained or processed for in vitro fertilization (IVF) and stained 26 h after IVF. In the control group, no mares showed an increase in eCG levels, whereas all the pregnant mares had concentrations higher than 100 ng/ml from Day 37. The number of follicles flushed during each puncture attempt significantly decreased with time for 3 of 4 pregnant mares. No significant change in this number was observed for the 5 control mares. The maturation rate of the oocytes from follicles 10-14 mm was significantly higher in the pregnant vs. the control group (14 of 17, 82%, vs. 13 of 30, 43%). The difference was not significant for the oocytes from follicles smaller than 9 mm or larger than 15 mm. After IVF, no oocyte was fertilized. The results led us to conclude that eCG is associated with an inhibition of follicular growth and an improvement in oocyte competence for in vitro maturation.

A high-molecular-weight preovulatory stage-related protein in equine follicular fluid and granulosa cells

The high-molecular-weight proteins of equine follicular fluid were examined to determine whether some polypeptides are unique to certain physiological conditions. Fluids from ovarian follicles of various diameters and physiological stages during the follicular phase were recovered by ultrasound-guided follicular aspiration. Granulosa cells and cumulus-oocyte complexes (COC) were recovered by scraping the intrafollicular wall during puncture. Follicular fluids and corresponding serum, as well as granulosa cell lysates, were analyzed by one-dimensional SDS-PAGE and silver staining. COC morphology was assessed microscopically. A 200-kDa protein band was demonstrated in fluids from preovulatory follicles, in natural conditions or after induction of ovulation. This protein band was absent in fluids from follicles at earlier stages, subordinate follicles, and serum. The presence of this protein at the preovulatory (PO) stage was ascertained through recovery of the fluid from follicles twice during their growth. Its appearance was time dependent after induction of ovulation but was not induced by an intrafollicular injection of a physiological dose of progesterone. We also demonstrated the presence of this 200-kDa protein in granulosa cells lysates recovered from preovulatory follicles. The expression of this protein in the follicular fluid was related to the cumulus aspect and chromatin configuration of the enclosed COC. No relation was found between its presence in the follicular fluid at the PO stage and subsequent ovulation of the punctured follicle or embryo production. The identification of this molecule is approached and discussed. These results show a novel PO stage-related protein in equine follicular fluid, which may be involved in the differentiation and maturation mechanisms occurring in the follicle during the preovulatory period.

Transfer of immature oocytes to a preovulatory follicle: an alternative to in vitro maturation in the mare?

In the mare, success rates for the in vitro maturation of oocytes are low. Accordingly, we attempted to determine if immature oocytes could be matured in vivo by injecting them into a preovulatory follicle. Groups of 3-9 oocytes collected from donor mares were transferred under ultrasound control into the preovulatory follicle of a recipient mare that was treated with crude equine pituitary gonadotrophin (CEG) to induce ovulation. Just before ovulation (34 h post treatment) the preovulatory follicle of the recipient mare was punctured to collect both the transferred and the indigenous oocytes to analyse the stages of nuclear maturation. The transfer technique did not impair significantly the final maturation of the recipient preovulatory follicle. The indigenous oocytes within the recipient follicles were recognisable by their larger expanded cumulus of yellow colouration due to high hyaluronic acid content; 7/12 of these oocytes were mature (metaphase II). Around half (42/86; 49%) of the oocytes transferred to preovulatory follicles were recovered subsequently. Most of them showed cumulus expansion (41/42, 6 of which were rich in hyaluronic acid), 13 (32%) were mature, 15 (36%) were immature and 13 (32%) were degenerate. When the indigenous oocyte of the recipient mare was mature, 38% of the transferred oocytes were mature, this rate being no different from the in vitro maturation rate of 46%. This study showed that in vivo maturation of immature oocytes by transfer into a preovulatory follicle in a recipient mare is possible. The maturation rate is not different from the in vitro maturation rate. The technique allows the generation of mature oocytes that have an expanded cumulus rich in hyaluronic acid, similar to the situation in preovulatory oocytes. This result has not been obtained in vitro previously.

Timing of in vivo maturation of equine preovulatory oocytes and competence for in vitro maturation of immature oocytes collected simultaneously

The objects of this study were to monitor the development of the cumulus complex and nuclear maturation in oocytes recovered from preovulatory follicles following treatment to induce ovulation and to investigate the in vitro maturation competence of oocytes recovered from smaller nonpreovulatory follicles of varying size. All follicles > or =5 mm in pony mares were individually punctured at 0, 6, 12, 24 and 35 h after an injection of LH to induce ovulation. The recovery rates of oocytes were 64% from 55 preovulatory follicles, 22% from 32 subordinate follicles and 52% from 227 small follicles. Cumulus expansion of the preovulatory oocytes occurred at 12 h post LH treatment while the metaphase I and II components of nuclear maturation were not completed until 24 and 35 h post LH respectively. For nonpreovulatory follicles, the frequency of atresia and oocyte competence for in vitro nuclear maturation both increased with increasing follicular size.

Equine oocyte competence for nuclear and cytoplasmic in vitro maturation: effect of follicle size and hormonal environment

Equine oocyte competence after in vitro maturation (IVM) was investigated in terms of the diameter of the follicle of origin and the stage of the estrous cycle, with three criteria of maturation: nuclear stage after DNA Hoechst staining, meiotic spindle morphology after tubulin immunocytochemical staining, and cortical granule localization after lectin labeling. Seven successive in vivo ultrasound-guided follicular punctures were performed on 10 cyclic saddle mares, alternatively at the end of the follicular phase (after induction of ovulation with a gonadotropin injection) and in midluteal phase (with or without a gonadotropin injection). Expanded cumulus-oocyte complexes (COCs) were stained at collection, and compact COCs were stained after in vitro culture. They were observed under a confocal microscope. Successive punctures on one mare provided 0.9 preovulatory COCs and 8 immature COCs per 22 days. Among the preovulatory oocytes, 55% had completed nuclear and cytoplasmic maturation, 86% of which displayed a normal meiotic spindle. Of the 262 oocytes cultured in vitro, 37% completed nuclear maturation. The nuclear and cytoplasmic maturation rate significantly increased with follicle diameter. The IVM rate tended to be higher in follicular phase and tended to increase in luteal phase with the gonadotropin injection. The meiotic spindle morphology was not significantly different between the classes of follicular diameters. This study provided the opportunity to increase the number of characterized oocytes collected per cycle and per mare. This is the first report showing the progressive acquisition of meiotic competence in the equine oocyte during antral follicle growth and is the only description of the equine meiotic spindle.