Cellular responses and microRNA profiling in bovine spermatozoa under heat shock.

In brief: Elevated temperatures disturbed sperm physiology. Bovine sperm cells exposed to heat shock led to diminished mitochondrial activity, fertilizing ability, increased oxidative stress and caspase activity concomitant with a delay in embryonic developmental kinetics and modulation of sperm-borne microRNAsmiRNAs. Abstract: Sperm function is susceptible to adverse environmental conditions. It has been demonstrated that in vivo and in vitro exposure of bovine sperm to elevated temperature reduces sperm motility and fertilizing potential. However, the cascade of functional, cellular, and molecular events triggered by elevated temperature in the mature sperm cell remains not fully understood. Therefore, the aim of this study was to determine the effect of heat shock on mature sperm cells. Frozen-thawed Holstein sperm were evaluated immediately after Percoll purification (0 h non-incubation control) or after incubation at 35, 38.5, and 41°C for 4 h. Heat shock reduced sperm motility after 3-4 h at 41°C while mitochondrial activity was reduced by 38.5 and 41°C when compared to the control. Heat shock also increased sperm reactive oxygen species production and caspase activity. Heat-shocked sperm had lower fertilizing ability, which led to diminished cleavage and blastocyst rates. Preimplantation embryo developmental kinetics was also slowed and reduced by sperm heat shock. The microRNA (miR) profiling identified >300 miRs in bovine sperm. Among these, three and seven miRs were exclusively identified in sperm cells exposed to 35 and 41°C, respectively. Moreover, miR-181d was enriched in sperm cells exposed to higher temperatures. Hence, elevated temperature altered the physiology of mature sperm cells by perturbing cellular processes and the miR profile, which collectively led to lower fertilizing ability and preimplantation development.

Dissecting EPPIN protease inhibitor domains in sperm motility and fertilizing ability: repercussions for male contraceptive development.

EPPIN (epididymal protease inhibitor) is a mammalian conserved sperm-binding protein displaying an N-terminal WFDC (whey-acidic protein four-disulfide core) and a C-terminal Kunitz protease inhibitor domains. EPPIN plays a key role in regulating sperm motility after ejaculation via interaction with the seminal plasma protein SEMG1 (semenogelin-1). EPPIN ligands targeting the SEMG1 binding site in the Kunitz domain are under development as male contraceptive drugs. Nevertheless, the relative contributions of EPPIN WFDC and Kunitz domains to sperm function remain obscure. Here, we evaluated the effects of antibodies targeting specific epitopes in EPPIN's WFDC (Q20E antibody, Gln20-Glu39 epitope) and Kunitz (S21C and F21C antibodies, Ser103-Cys123 and Phe90-C110 epitopes, respectively) domains on mouse sperm motility and fertilizing ability. Computer-assisted sperm analysis showed that sperm co-incubation with S21C antibody (but not F21C antibody) lowered progressive and hyperactivated motilities and impaired kinematic parameters describing progressive (straight-line velocity; VSL, average path velocity; VAP and straightness; STR) and vigorous sperm movements (curvilinear velocity; VCL, amplitude of lateral head movement; ALH, and linearity; LIN) compared with control. Conversely, Q20E antibody-induced milder inhibition of progressive motility and kinematic parameters (VAP, VCL and ALH). Sperm co-incubation with S21C or Q20E antibodies affected in vitro fertilization as revealed by reduced cleavage rates, albeit without changes in capacitation-induced tyrosine phosphorylation. In conclusion, we show that targeting specific epitopes in EPPIN Kunitz and WFDC domains inhibits sperm motility and capacitation-associated events, which decrease their fertilizing ability; nevertheless, similar observations in vivo remain to be demonstrated. Simultaneously targeting residues in S21C and Q20E epitopes is a promising approach for the rational design of EPPIN-based ligands with spermostatic activity.

Contextualizing Autophagy during Gametogenesis and Preimplantation Embryonic Development.

Mammals face environmental stressors throughout their lifespan, which may jeopardize cellular homeostasis. Hence, these organisms have acquired mechanisms to cope with stressors by sensing, repairing the damage, and reallocating resources to increase the odds of long-term survival. Autophagy is a pro-survival lysosome-mediated cytoplasm degradation pathway for organelle and macromolecule recycling. Furthermore, autophagy efflux increases, and this pathway becomes idiosyncratic depending upon developmental and environmental contexts. Mammalian germ cells and preimplantation embryos are attractive models for dissecting autophagy due to their metastable phenotypes during differentiation and exposure to varying environmental cues. The aim of this review is to explore autophagy during mammalian gametogenesis, fertilization and preimplantation embryonic development by contemplating its physiological role during development, under key stressors, and within the scope of assisted reproduction technologies.

Cellular and epigenetic changes induced by heat stress in bovine preimplantation embryos.

Exposure of the preimplantation embryo to heat stress triggers a series of cellular, molecular, and adaptive changes preventing a normal embryonic development. Heat stress disrupts the embryo cytoskeleton, intracellular calcium levels, mitochondrial function, and induces apoptosis. Moreover, heat stress can act indirectly through induction of reactive oxygen species (ROS), leading to a variety of cellular damage. Embryonic resistance to heat shock is determined by factors such as genotype, developmental stage, apoptosis, redox status, and regulatory molecules. The early embryo is very susceptible to heat stress; it acquires resistance to elevated temperature as development advances. One of the mechanisms involved in the developmental acquisition of thermotolerance is heat-induced apoptosis, which acts as a quality control mechanism to remove damaged blastomeres allowing the embryo to survive after stress. Although embryos at >8-cell stage can activate the apoptotic cascade as an adaptive response to stress, embryos at the two-cell stage are resistant to proapoptotic signals. This lack of apoptotic response has been associated to mitochondrial resistance to depolarization and epigenetic regulations, such as DNA methylation and histone deacetylation. Even though the cellular mechanisms triggered by heat stress have been studied, very little attention has been paid to the vulnerability of the epigenome to drastic temperature changes during the preimplantation period. Therefore, this review aims to characterize the effects of elevated temperature on the bovine embryo, especially addresissing developmental, cellular, and epigenetic alterations triggered in response to temperature.

Role of insulin-like growth factor 1 on cross-bred Bos indicus cattle germinal vesicle oocytes exposed to heat shock.

Germinal vesicle (GV) oocytes are susceptible to heat stress. However, neither the cellular mechanisms triggered by elevated temperature nor the thermoprotective effects of insulin-like growth factor (IGF) on GV oocytes are completely understood. Therefore, a series of experiments was conducted to determine the direct effects of IGF1 (0, 12.5, 25, 50 and 100ng mL-1) on heat-treated GV oocytes. Butyrolactone-arrested GV oocytes were cultured at 38.5°C (control) or 41°C (heat shock; HS) for 14h in the presence of different concentrations of IGF1. Exposure of GV oocytes to 41°C increased (P<0.05) the number of terminal deoxyribonucleotidyl transferase-mediated fluorescein-dUTP nick end-labelling (TUNEL)-positive oocytes. At concentrations of 12.5 and 25ng mL-1, IGF1 tended to minimise these negative effect of HS (P=0.07). However, neither HS nor IGF1 had any effect on caspase activity. HS also decreased (P<0.05) GV oocyte mitochondrial activity and developmental competence to the blastocyst stage. These deleterious effects of HS were alleviated (P<0.05) by 12.5ng mL-1 IGF1. This concentration of IGF1 did not affect cleavage rate, the percentage of TUNEL-positive blastomeres and total blastocyst cell number regardless of temperature. In conclusion, exposure of GV oocytes to HS triggered the apoptotic cascade and compromised oocyte developmental competence. Physiological concentrations of IGF1 had a beneficial effect on heat-shocked GV oocytes.

Influence of bovine sperm DNA fragmentation and oxidative stress on early embryo in vitro development outcome.

Sperm chromatin fragmentation may be caused by a number of factors, the most significant of which is reactive oxygen species. However, little is known about the effect of sperm oxidative stress (OS) on DNA integrity, fertilization, and embryonic development in cattle. Therefore, the goal of this study was to evaluate the influence of sperm OS susceptibility on the DNA fragmentation rate and in vitro embryo production (IVP) in a population of bulls. Groups of cryopreserved sperm samples were divided into four groups, based on their susceptibility to OS (G1, low OS; G2, average OS; G3, high OS; and G4, highest OS). Our results demonstrated that the sperm DNA integrity was compromised in response to increased OS susceptibility. Furthermore, semen samples with lower susceptibility to OS were also less susceptible to DNA damage (G1, 4.06%; G2, 6.09%; G3, 6.19%; and G4, 6.20%). In addition, embryo IVP provided evidence that the embryo cleavage rate decreased as the OS increased (G1, 70.18%; G2, 62.24%; G3, 55.85%; and G4, 50.93%), but no significant difference in the blastocyst rate or the number of blastomeres was observed among the groups. The groups with greater sensitivity to OS were also associated with a greater percentage of apoptotic cells (G1, 2.6%; G2, 2.76%; G3, 5.59%; and G4, 4.49%). In conclusion, we demonstrated that an increased susceptibility to OS compromises sperm DNA integrity and consequently reduces embryo quality.

Sperm-mediated gene transfer: effect on bovine in vitro embryo production.

The technique of sperm-mediated gene transfer (SMGT) can be used to delivery exogenous DNA into the oocyte. However, it has low repeatability and produces inconsistent results. In order to optimize this technique, it is necessary to study the mechanism by which DNA enters the sperm cell and integrates in the sperm genome. Furthermore, studies must focus in the maintenance of sperm cell viability and function. The aim of this study was to evaluate different SMGT protocols of sperm electroporation or capacitation (CaI) aiming to maintain sperm viability in the production of bovine embryos in vitro. Frozen-thawed semen was divided in two experimental groups (electroporation or CaI) and one control group (non-treated cells). For the electroporation method, five different voltages (100, 500, 750, 1000 or 1500 V) with 25 µF capacitance were used. For CaI treatment, combinations of two CaI concentrations (250 nM or 500 nM), two incubation periods of sperm cells with CaI (1 or 5 min) and two incubation periods that mimicked time of sperm cell interaction with exogenous DNA molecules (1 or 2 h) were evaluated. According to our data, electroporation and CaI treatments do not prevent sperm penetration and oocyte fertilization and can be an alternative method to achieve satisfactory DNA delivery in SMGT protocols.

Use of retinyl acetate, retinoic acid and insulin-like growth factor-I (IGF-I) to enhance goat embryo production.

Experiments were carried out to investigate the beneficial effects of retinyl acetate (RAc) and retinoic acid (RA) on goat oocyte maturation as well as the effects of insulin-like growth factor-I (IGF-I), RAc and RA during embryo culture under chemically defined conditions. In Experiment 1, in vitro maturation (IVM) was performed in a chemically defined basic maturation medium (bMM) supplemented with 0.3 µM RAc or 0.5 µM RA. Presumptive zygotes and embryos (2-4 cells) were cultured in droplets of potassium simplex optimised medium (KSOM); however, none of the embryos reached the blastocyst stage. In Experiment 2, oocytes were matured in bMM + RAc or bMM + RA. Presumptive zygotes and 2- to 4-cell embryos were placed in fresh KSOM droplets supplemented with RAc, RA, IGF-I, RAc+IGF-I or RA+IGF-I. In Experiment 1, addition of RAc and RA to bMM increased (P < 0.05) the proportion of 2- to 4-cell embryos reaching the morula stage as compared to the control. In Experiment 2, supplementation of embryo culture media with retinoids and IGF-I increased (P < 0.05) the proportion of 2- to 4-cell stage embryos developing to the morula and blastocyst stage. Our data demonstrate that goat embryo production in chemically defined media could be improved by exogenous RAc or RA and by the interaction between retinoids and IGF-I, and that goat embryos can be produced in vitro from oocytes following protocols similar to those currently used for cattle.

Effects of different cryopreservation methods on post-thaw culture conditions of in vitro produced bovine embryos.

The aim of this work was to evaluate the effect of cryopreservation protocols on subsequent development of in vitro produced bovine embryos under different culture conditions. Expanded in vitro produced blastocysts (n = 600) harvested on days 7-9 were submitted to controlled freezing [slow freezing group: 10% ethylene glycol (EG) for 10 min and 1.2°C/min cryopreservation]; quick-freezing [rapid freezing group: 10% EG for 10 min, 20% EG + 20% glycerol (Gly) for 30 s]; or vitrification [vitrification group: 10% EG for 10 min, 25% EG + 25% Gly for 30 s] protocols. Control group embryos were not exposed to cryoprotectant or cryopreservation protocols and the hatching rate was evaluated on day 12 post-insemination. In order to evaluate development, frozen-thawed embryos were subjected to granulosa cell co-culture in TCM199 or SOFaa for 4 days. Data were analyzed by PROC MIXED model using SAS Systems for Windows®. Values were significant at p < 0.05. The hatching rate of the control group was 46.09%. In embryos cultured in TCM199, slow freezing and vitrification group hatching rates were 44.65 ± 5.94% and 9.43 ± 6.77%, respectively. In embryos cultured in SOFaa, slow freezing and vitrification groups showed hatching rates of 11.65 ± 3.37 and 8.67 ± 4.47%, respectively. In contrast, the rapid freezing group embryos did not hatch, regardless of culture medium. The slow freezing group showed higher hatching rates than other cryopreservation groups. Under such conditions, controlled freezing (1.2°C/min) can be an alternative to cryopreservation of in vitro produced bovine embryos.

Treatment of in vitro-Matured Bovine Oocytes With Tauroursodeoxycholic Acid Modulates the Oxidative Stress Signaling Pathway.

In several species, oocyte and embryo competence are improved by the addition of endoplasmic reticulum (ER) stress inhibitors to in vitro maturation (IVM) medium and/or in vitro culture (IVC) medium. This study aimed to evaluate the effects of three concentrations of tauroursodeoxycholic acid (TUDCA; 50, 200, and 1,000 µM), a chemical chaperone for relieving ER stress, during IVM of bovine cumulus-oocyte complexes (COCs) for 24 h. Treated oocytes were analyzed for nuclear maturation, reactive oxygen species (ROS) production, mitochondrial activity, and abundance of target transcripts. In addition, the number of pronuclei in oocytes was evaluated after 18-20 h of insemination, and the rates of blastocyst and hatched blastocyst formation were evaluated after 7 and 8/9 days of culture, respectively. We further evaluated the transcript abundance of embryonic quality markers. Our findings showed that supplementation of IVM medium with 200 µM of TUDCA decreased ROS production and increased abundance of transcripts related to antioxidant activity in oocytes (CAT, GPX1, and HMOX1) and embryos (GPX1 and PRDX3). Interestingly, high concentration of TUDCA (1,000 µM) was toxic to oocytes, reducing the nuclear maturation rate, decreasing mitochondrial activity, and increasing the abundance of ER stress (HSPA5) and cellular apoptosis (CASP3 and CD40) related transcripts. The results of this study suggest that treatment with 200 µM of TUDCA is associated with a greater resistance to oxidative stress and indirectly with ER stress relief in bovine oocytes.

Applicability of Raman spectroscopy on porcine parvovirus and porcine circovirus type 2 detection.

Porcine parvovirus (PPV) is one of the major infectious causes of reproductive failure of swine. This disease is characterized by embryonic and fetal infection and death, responsible for important economic losses. PPV is also implicated as a trigger in the development of post-weaning multisystemic wasting syndrome (PMWS) caused by Porcine circovirus type 2 (PCV2). Their detection is PCR-based, which is quite sensitive and specific, but laborious, costly and time-demanding. Therefore, this study aimed to assess Raman spectroscopy (RS) as a diagnostic tool for PPV and PCV2 due to its label-free properties and unique ability to search and identify molecular fingerprints. Briefly, swine testis (ST) cells were inoculated with PPV or PCV2 and in vitro cultured (37 °C, 5% CO2) for four days. Fixed cells were then submitted to RS investigation using a 633 nm laser. A total of 225 spectra centered at 1300 cm-1 was obtained for each sample (5 spectra/cell; 15 cells/replicate; 3 replicates) of PPV-, PCV2-infected and uninfected (control) ST cells. Clear statistical discrimination between samples from both virus-infected cells was achieved with a Principal Component - Linear Discriminant Analysis (PCA-LDA) model, reaching sensitivity rates from 95.55% to 97.77%, respectively to PCV2- and PPV-infected cells. These results were then submitted to a Leave-One-Out (LOO) validation algorithm resulting in 99.97% of accuracy. Extensive band assignment was analyzed and compiled for better understanding of PPV and PCV2 virus-cell interaction, demonstrating that specific protein, lipids and DNA/RNA bands are the most important assignments related to discrimination of virus-infected from uninfected cells. In conclusion, these results represent promising bases for RS application on PCV2 and PPV detection for future diagnostic applications.

Thermoprotective molecules to improve oocyte competence under elevated temperature.

Heat stress is an environmental factor that challenges livestock by disturbing animal homeostasis. Despite the broad detrimental effects of heat stress on reproductive function, the germline and the early preimplantation embryo are particularly prone. There is extensive evidence that elevated temperature reduces oocyte developmental competence through a series of cellular and molecular damages. Further research revealed that the oocyte respond to stress by activating cellular mechanisms such as heat shock response, unfolded protein response and autophagy to improve survival under heat shock. Such knowledge paved the way for the identification of thermoprotective molecules that alleviate heat-induced oocyte oxidative stress, organelle damage, and apoptosis. Therefore, this review depicts the deleterious effects of heat shock on oocyte developmental competence, heat-induced cellular and molecular changes, outlines pro-survival cellular mechanisms and explores thermoprotective molecules to improve oocyte competence.

Autophagy is a pro-survival adaptive response to heat shock in bovine cumulus-oocyte complexes.

Autophagy is a physiological mechanism that can be activated under stress conditions. However, the role of autophagy during oocyte maturation has been poorly investigated. Therefore, this study characterized the role of autophagy on developmental competence and gene expression of bovine oocytes exposed to heat shock (HS). Cumulus-oocyte-complexes (COCs) were matured at Control (38.5 °C) and HS (41 °C) temperatures in the presence of 0 and 10 mM 3-methyladenine (3MA; autophagy inhibitor). Western blotting analysis revealed that HS increased autophagy marker LC3-II/LC3-I ratio in oocytes. However, there was no effect of temperature for oocytes matured with 3MA. On cumulus cells, 3MA reduced LC3-II/LC3-I ratio regardless of temperature. Inhibition of autophagy during IVM of heat-shocked oocytes (3MA-41 °C) reduced cleavage and blastocyst rates compared to standard in vitro matured heat-shocked oocytes (IVM-41 °C). Therefore, the magnitude of HS detrimental effects was greater in the presence of autophagy inhibitor. Oocyte maturation under 3MA-41 °C reduced mRNA abundance for genes related to energy metabolism (MTIF3), heat shock response (HSF1), and oocyte maturation (HAS2 and GREM1). In conclusion, autophagy is a stress response induced on heat shocked oocytes. Inhibition of autophagy modulated key functional processes rendering the oocyte more susceptible to the deleterious effects of heat shock.

Time-dependent effects of heat shock on the zona pellucida ultrastructure and in vitro developmental competence of bovine oocytes.

The aim of this study was to determine the effects of different exposure lenght to heat shock (HS) during in vitro maturation (IVM) on zona pellucida (ZP) ultrastructure and developmental competence of bovine oocytes. Cumulus-oocyte complexes (COCs) were matured in vitro (IVM) at 38.5 °C for 24 h (control group, CG), or incubated at 41 °C (HS) for 6 h (HS-6h), 12 h (HS-12h), 18 h (HS-18h), and 22h (HS-22h) followed by incubation at 38.5 °C to complete a full 24-h period of maturation. After IVM, oocytes were subjected to scanning electron microscopy (SEM) or in vitro fertilization and culture until the blastocyst stage. For heat-shocked oocytes, with exception of those in the HS-6h group, SEM examinations revealed that ZP surfaces were rough and characterized by a presence of spongy network. Oocytes from the HS-22h group displayed an increase in the number of pores, as well as a higher proportion of oocytes with amorphous ZPs. The proportion of oocytes that reached metaphase II (MII) stage decreased in all HS groups, regardless of the duration of exposure to 41 °C. These results provide evidence that HS during IVM for 12-22 h reduces the developmental competence of bovine oocytes, increasing the percentage of oocytes with abnormal chromosomal organization, and reducing fertilization and blastocysts formation rate. The effects of HS were more pronounced for the 22-h exposure group. The damage induced by HS on oocyte function clearly increased upon exposure to elevated temperature.

Early fetal sexing of Saanen goats by use of transrectal ultrasonography to identify the genital tubercle and external genitalia.

OBJECTIVE: To define the optimum period for sexing of Saanen goat fetuses by use of transrectal ultrasonography. ANIMALS: 82 Saanen goats pregnant with 124 fetuses. PROCEDURES: Fetal sexing was performed on the basis of the final location of the genital tubercle or identification of external genitalia. In experiment 1, fetuses (n = 78) were monitored every 48 hours from days 40 to 60 of gestation, whereas for experiment 2, 46 fetuses were examined only once between days 47 and 77 of gestation. RESULTS: For experiment 1, accuracy of fetal sexing was 20 of 20 (100%) for a single fetus, 39 of 42 (92.8%) for twin fetuses, and 10 of 16 (62.5%) for triplet fetuses. Diagnostic accuracy was significantly lower for triplet fetuses than that for single or twin fetuses. Final location of the genital tubercle was detected between 45 and 55 days of gestation (mean +/- SEM, 48.9 +/- 1.8 days). For experiment 2, accuracy of fetal sexing for a single fetus (24/24 [100%]) was significantly higher than the accuracy for twin fetuses (16/22 [72.7%]). Considering all fetuses that were born, accuracy of diagnosis was 69 of 78 (88.4%) for experiment 1 and 40 of 46 (86.9%) for experiment 2. Accuracy did not differ significantly between experiments. CONCLUSIONS AND CLINICAL RELEVANCE: Real-time ultrasonography after day 55 of gestation is a suitable method for determination of sex of Saanen goat fetuses by observation of the genital tubercle or identification of external genitalia.

Thermoprotective effect of insulin-like growth factor 1 on in vitro matured bovine oocyte exposed to heat shock.

The role of insulin-like growth factor 1 (IGF1) on cellular function and developmental capacity of heat-shocked oocytes has not been completely understood. Therefore, the objective of this study was to determine the effect of IGF1 on apoptosis, mitochondrial activity, cytoskeletal changes, nuclear maturation, and developmental competence of bovine oocytes exposed to heat shock. Cumulus-oocyte complexes were submitted to control (38.5 °C for 22 hours) and heat shock (41 °C for 14 hours followed by 38.5 °C for 8 hours) in the presence of 0 or 100 ng/mL IGF1 during IVM. Heat shock increased the percentage of TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling)-positive oocyte and reduced oocyte mitochondrial activity. However, addition of 100 ng/mL IGF1 minimized these deleterious effects of temperature. Caspase activity was affected neither by heat shock nor IGF1. Exposure of bovine oocytes to 41 °C during the first 14-hour IVM affected cortical actin localization and microtubule organization at the meiotic spindle and reduced the percentage oocytes that reached the metaphase II stage. However, in the presence of IGF1, cortical actin and percentage of metaphase II oocytes were not different between control and heat-shocked oocytes, suggesting a partial beneficial effect of IGF1. There was no effect of IGF1 on microtubule organization. Heat shock also reduced the percentage of oocytes that reached the blastocyst stage, blastocyst cell number, and increased the percentage of TUNEL-positive blastomeres. However, there was no effect of 100 ng/mL IGF1 on oocyte development to the blastocyst stage and blastocyst quality. Therefore, 100 ng/mL IGF1 prevented some heat shock-induced cellular damage in bovine oocytes but had no effect on oocyte developmental competence. In contrast, a low IGF1 concentration (25 ng/mL) had a thermoprotective effect on oocyte developmental competence to the blastocyst stage. In conclusion, IGF1 prevented part of the damage induced by heat shock on oocyte function. This effect was modulated by IGF1 concentration.

The mechanism of oocyte activation influences the cell cycle-related genes expression during bovine preimplantation development.

The first cleavage divisions and preimplantation embryonic development are supported by mRNA and proteins synthesized and stored during oogenesis. Thus, mRNA molecules of maternal origin decrease and embryonic development becomes gradually dependent on expression of genetic information derived from the embryonic genome. However, it is still unclear what the role of the sperm cell is during this phase and whether the absence of the sperm cell during the artificial oocyte activation affects subsequent embryonic development. The objective of this study was to determine, in bovine embryos, changes in cell cycle-associated transcript levels (cyclin A, cyclin B, cyclin E, CDC2, CDK2, and CDK4) after oocyte activation in the presence or absence of the sperm cell. To evaluate that, in vitro-produced (IVP) and parthenogenetically activated (PA) embryos (2-4 cells (2-4C), 8-16 cells (8-16C) and blastocysts) were evaluated by real-time PCR. There was no difference in cleavage and blastocyst rates between IVP and PA groups. Transcript level was higher in oocytes than in IVP and PA embryos. Cleaved PA embryos showed higher expression of cyclin A, cyclin B, cyclin E, and CDK2 and lower expression of CDC2 when compared with that from the IVP group. At the time of activation, all transcripts were expressed less in PA than in IVP embryos, whereas at the blastocyst stage, almost all genes were expressed at a higher level in the PA group. These results suggest that in both groups there is an initial consumption of these transcripts in the early stages of embryonic development. Furthermore, 8-16C embryos seem to synthesize more cell cycle-related genes than 2-4C embryos. However, in PA embryos, activation of the cell cycle genes seems to occur after the 8- to 16-cell stage, suggesting a failure in the activation process.

Leptin promotes meiotic progression and developmental capacity of bovine oocytes via cumulus cell-independent and -dependent mechanisms.

Leptin has been shown to exert positive effects during the maturation of bovine oocytes, influencing blastocyst development, apoptosis, and the transcript levels of developmentally important genes. The present study was conducted to characterize further the mechanisms of leptin action on oocytes and the role of cumulus cells (CCs) in this context. In the first series of experiments, cumulus-oocyte complexes (COCs) were matured in serum-free medium that contained 0, 1 or 10 ng/ml leptin or in medium that was supplemented with 10% (v/v) estrus cow serum (ECS). Leptin concentrations of 1 and 10 ng/ml stimulated the meiotic progression of oocytes. Moreover, TUNEL staining demonstrated that these leptin doses reduced the proportion of apoptotic CCs. In the second series of experiments, COCs or denuded oocytes (DOs) were matured in the presence of 0 or 10 ng/ml leptin. The percentages of COCs and DOs with extruded polar bodies were increased by leptin. In contrast, positive effects of leptin on fertilization rates and blastocyst development were only observed after treatment of COCs but not of DOs. Leptin treatment of COCs consistently enhanced blastocyst development even after parthenogenetic activation of oocytes or after the removal of CCs before fertilization. The proportion of polyspermic oocytes was not affected by leptin treatment or oocyte denudation. In the third series of experiments, COCs were matured in the presence of 0, 1 or 10 ng/ml leptin. The transcript levels of specific genes were determined by reverse transcriptase-quantitative PCR (RT-qPCR) analysis of cumulus cells and single oocytes. Leptin treatment increased the levels of FAS, FASLG, and STAT3 transcripts in oocytes, but did not affect the LEPR, BAX, and BIRC4 mRNA concentrations. In cumulus cells, leptin treatment increased the mRNA levels for LEPR, STAT3, BAX, BIRC4, and FAS, but did not alter FASLG mRNA abundance. In conclusion, leptin differentially regulates gene expression in oocytes and cumulus cells. Moreover, leptin enhances both oocyte maturation and developmental capacity via cumulus cell-independent and -dependent mechanisms.

Maturation of bovine oocytes in the presence of leptin improves development and reduces apoptosis of in vitro-produced blastocysts.

The series of events associated with oocyte growth and maturation determines the oocyte's ability to undergo successful fertilization, cleavage and embryonic development. Among the molecules involved in these events, leptin has been identified as a modulator of oocyte function. Experiments were conducted to determine whether leptin treatment of oocytes during maturation affects their developmental capacity after fertilization and whether it has long-lasting effects on apoptosis and gene expression in the resulting blastocysts. Cumulus-oocyte complexes (COCs) were matured in serum-free medium containing 0 (control), 1, 10, or 100 ng/ml leptin or in medium supplemented with 10% (v/v) estrous cow serum (ECS). Addition of leptin during oocyte maturation had no effect on cleavage rate after fertilization. However, an increased proportion of oocytes that matured in the presence of 1 or 10 ng/ml leptin developed to blastocysts, which exhibited increased cell numbers. The proportion of apoptotic cells was reduced in blastocysts originating from leptin- or ECS-treated oocytes. Transcript levels of the genes encoding leptin receptor (LEPR), signal transducer and activator of transcription (STAT3), BCL2 associated X-protein (BAX), and baculoviral inhibitor of apoptosis protein repeat-containing 4 (BIRC4, also known as XIAP), were determined by reverse transcriptase-quantitative polymerase chain reaction analysis of expanded and hatched blastocysts. Depending on the dose used, leptin treatment of oocytes resulted in increased LEPR, STAT3, and BIRC4 mRNA levels and reduced BAX mRNA levels in blastocysts. In conclusion, leptin improved the ability of the oocyte to sustain embryonic development and had long-term effects on blastocyst apoptosis and transcript abundance of LEPR, STAT3, and apoptosis-associated genes.