Insulin-like growth factor-I promotes resistance of bovine preimplantation embryos to heat shock through actions independent of its anti-apoptotic actions requiring PI3K signaling

Livestock-Forest integrated system attenuates deleterious heat stress effects in bovine oocytes

Global warming poses significant challenges to the fertility of tropical dairy cattle. One promising approach to mitigate heat stress effects on reproductive function and reduce the carbon footprint is the use of integrated livestock-forest (ILF) systems. The aim of this study was to investigate the effects of two different systems, namely Full Sun (FS) and ILF, on maternal hyperthermia and oocyte quality of Holstein and Girolando heifers during the tropical summer season. The temperature-humidity index (THI) data revealed intense heat stress during the experiment. Both the system (P<0.01) and the breed (P<0.01) factors had a significant impact on vaginal temperature, being hyperthermia more pronounced in the FS system and in the Holstein breed. Over the five time points collected at a 33-day interval, we observed distinct patterns for ILF (P=0.65) and FS (P<0.001) systems, suggesting an adaptive response in animals kept in FS systems. Furthermore, oocyte quality assessment revealed an effect of the system for oocyte diameter (P<0.001) and levels of IGFBP2 (P<0.001), and caspase 3 levels showed a decrease in ILF compared to FS for both Holstein (P<0.001) and Girolando (P<0.001) breeds. Collectively, these parameters indicate that oocyte quality during the summer months was superior in animals maintained in the ILF system. In conclusion, the ILF system demonstrated promising results in attenuating maternal hyperthermia and mitigating its effects on oocyte quality. Additionally, our observations suggest that animals in the FS system may exhibit an adaptive response to heat stress.

Impact of Heat Stress on Oocyte Developmental Competence and Pre-Implantation Embryo Viability in Cattle

Rectal and vaginal temperatures are utilised in both in vivo and in vitro models to study the effects of heat stress on oocyte competence and embryo viability in cattle. However, uterine temperature increases by only 0.5 °C in heat-stressed cows, significantly lower than simulated increases in in vitro models. Temperature variations within oviducts and ovarian follicles during heat stress are poorly understood or unavailable, and evidence is lacking that oocytes and pre-implantation embryos experience mild (40 °C) or severe (41 °C) heat stress inside the ovarian follicle and the oviduct and uterus, respectively. Gathering detailed temperature data from the reproductive tract and follicles is crucial to accurately assess oocyte competence and embryo viability under realistic heat stress conditions. Potential harm from heat stress on oocytes and embryos may result from reduced nutrient availability (e.g., diminished blood flow to the reproductive tract) or other unidentified mechanisms affecting tissue function rather than direct thermal effects. Refining in vivo stress models in cattle is essential to accurately identify animals truly experiencing heat stress, rather than assuming heat stress exposure as done in most studies. This will improve model reliability and aid in the selection of heat-tolerant animals.

The Effect of Month and District on 100-Day In-Calf Rate in Year-Round Calving Dairy Herds

Monitoring 100-day in-calf rate (100DICR) is an integral part of the assessment of reproductive performance in year-round calving dairy herds. The objective of this study was to investigate the effect of month on 100DICR in year-round calving herds in New South Wales (NSW), Australia and determine whether a fluctuating 100DICR target is an appropriate alternative to a constant 100DICR target. The 100DICR is defined as the percentage of all current lactating cows over 100 days in milk (DIM) that conceive on or before 100 DIM. As dairy cows are typically dried off 7 months after conception, 100DICR was an approximate 7-month rolling average. Mean monthly 100DICRs were calculated with a generalised linear model for six NSW north coast herds located 15-140 km from the coast and four NSW south coast herds located less than 10 km from the coast, over a two-year period. The mean 100DICR was lowest in May at 28.62% (95%CI 28.31-28.93) and increased during winter and spring, peaking in December at 34.74% (95%CI 34.32-35.15). The observed trend was similar for north and south coast herds, although north coast herds experienced a greater change in 100DICR from the peak to a nadir of 27.58% (95%CI 27.18-27.98), a 7.15-point difference, compared to south coast herds with a nadir of 30.18% (95%CI 29.69-30.67), a 4.67-point difference between the peak and nadir. In conclusion, 100DICR is affected by month with the lowest 100DICRs observed in late autumn and the highest 100DICRs observed in late spring and early summer. Therefore, a fluctuating target 100DICR is an appropriate alternative to a constant target when assessing reproductive performance in year-round calving herds. While the district does not affect mean 100DICR per se, the district does affect the difference between peak and nadir 100DICR.

Insulin-like growth factor-1 (IGF-1) selectively modulates the metabolic and lipid profile of bovine embryos according to their kinetics of development

Supplementation of culture media with IGF-1 during in vitro culture of embryos has had controversial results over the years. In the present study, we show that differences previously observed in response to IGF addition might be related to intrinsic heterogeneity of the embryos. In other words, the effects exerted by IGF-1 are dependent on the characteristics of the embryos and their ability to modulate metabolism and overcome stressful conditions, such as the ones found in a non-optimized in vitro culture system. To test this hypothesis, in vitro produced bovine embryos with distinct morphokinetics (fast- and slow-cleavage) were submitted to treatment with IGF-1 and then evaluated for embryo production rates, total cell number, gene expression and lipid profile. Our results show that remarkable differences were found when fast and slow embryos treated with IGF-1 were compared. Fast embryos respond by upregulating genes related to mitochondrial function, stress response, and lipid metabolism, whereas slow embryos presented lower mitochondrial efficiency and lipid accumulation. We conclude that indeed the treatment with IGF-1 selectively affects embryonic metabolism according to early morphokinetics phenotypes, and this information is relevant for decision-making in the design of more appropriate in vitro culture systems.

Bioactive supplements influencing bovine in vitro embryo development

Ovum pickup and in vitro production (IVP) of bovine embryos are replacing traditional multiple ovulation embryo transfer (MOET) as the primary means for generating transferable embryos from genetically elite sires and dams. However, inefficiencies in the IVP process limit the opportunities to produce large numbers of transferable embryos. Also, the post-transfer competency of IVP embryos is inferior to embryos produced by artificial insemination or MOET. Numerous maternal, paternal, embryonic, and culture-related factors can have adverse effects on IVP success. This review will explore the various efforts made on describing how IVP embryo development and post-transfer competency may be improved by supplementing hormones, growth factors, cytokines, steroids and other bioactive factors found in the oviduct and uterus during early pregnancy. More than 40 of these factors, collectively termed as embryokines, are reviewed here. Several embryokines contain abilities to promote embryo development, including improving embryo survivability, improving blastomere cell numbers, and altering the distribution of blastomere cell types in blastocysts. A select few embryokines also can benefit pregnancy retention after IVP embryo transfer and improve neonatal calf health and performance, although very few embryokine-supplemented embryo transfer studies have been completed. Also, supplementing several embryokines at the same time holds promise for improving IVP embryo development and competency. However, more work is needed to explore the post-transfer consequences of adding these putative embryokines for any adverse outcomes, such as large offspring syndrome and poor postnatal health, and to specify the specific embryokine combinations that will best represent the ideal conditions found in the oviduct and uterus.

Baicalin enhances the thermotolerance of mouse blastocysts by activating the ERK1/2 signaling pathway and preventing mitochondrial dysfunction

Heat stress causes oxidative damage and induces excessive cell apoptosis and thus affects the development and/or even causes the death of preimplantation embryos. The effects of baicalin on the developmental competence of heat-stressed mouse embryos were investigated in this experiment. Two-cell embryos were cultured in the presence of baicalin and subjected to heat stress (42 °C for 1 h) at their blastocyst stage followed by continuous culture at 37 °C until examination. The results showed that heat stress (H group) increased reactive oxygen species (ROS) production, apoptosis and even embryo death, along with reductions in both mitochondrial activity and membrane potential (ΔΨm). Both heat stress (H group) and inhibition of the ERK1/2 signaling pathway (U group) led to significantly reduced expression levels of the genes c-fos, AP-1 and ERK2, and the phosphorylation of ERK1/2 and c-Fos, along with significantly increased c-Jun mRNA expression and phosphorylation levels. These negative effects of heat stress on the ERK1/2 signaling pathway were neutralized by baicalin treatment. To explore the signal transduction mechanism of baicalin in improving embryonic tolerance to heat stress, mitochondrial quality and apoptosis rate in the mouse blastocysts were also examined. Baicalin was found to up-regulate the expression of mtDNA and TFAM mRNA, increased mitochondria activity and ΔΨm, and improved the cellular mitochondria quality of mouse blastocysts undergoing heat stress. Moreover, baicalin decreased Bax transcript abundance in blastocyst, along with an increase in the blastocyst hatching rate, which were negatively affected by heat stress. Our findings suggest that baicalin improves the developmental capacity and quality of heat-stressed mouse embryos via a mechanism whereby mitochondrial quality is improved by activating the ERK1/2 signaling pathway and inducing anti-cellular apoptosis.

Human amniotic membrane stem cells' conditioned medium has better support for in-vitro production of bovine embryos than FBS

Apart from oocyte quality, the media used has a significant effect on the production and quality of blastocysts produced in vitro. This study was designed to evaluate the replacement of serum with human amniotic membrane stem cells' conditioned medium (hAMSCs-CM) during bovine embryo culture on the quantity and quality of produced blastocysts. The in-vitro-produced embryos on the third day of IVC were randomly divided into the following culture groups: SOFaa + 5% FBS (Control), SOFaa + 5% hAMSCs-CM (5% CM), SOFaa + 2.5% hAMSCs-CM + 2.5% FBS (2.5% CM) and SOFaa + hAMSC co-culture (co-culture). The blastocyst and hatching rates, blastocyst cells number (the number of trophectoderm, inner cell mass and total cells), and the expression of some developmentally important genes (OCT4, PLAC8 and COX2 genes) in the treated groups, especially in the 5% CM, compared to the control had improved (p < .05). No significant difference was observed between groups for viability and hatching rate in vitrified-warmed blastocysts. Due to the positive effect of hAMSCs' conditioned medium (hAMSCs-CM) on blastocyst production, as well as its ease of preparation and the need to avoid the transmission of microbial contamination to the culture medium, hAMSCs-CM can be used as a suitable alternative to FBS during 3 to 8 days of bovine embryo culture.

Atlas of receptor genes expressed by the bovine morula and corresponding ligand-related genes expressed by uterine endometrium

Regulation of the mammalian embryo involves cell‐signaling molecules produced by the maternal oviduct and endometrium. Here, datasets on the transcriptome of the gestational Days 5 and 6 bovine morula and Day 5 maternal endometrium were examined to identify receptor genes expressed by the morula and expression of the corresponding ligand‐related genes in the endometrium. A total of 175 receptor genes were identified in the morula, including 48 encoding for growth factors or WNT signaling molecules, 25 for cytokines and chemokines, 35 involved in juxtacrine and matricellular signaling and 25 encoding for receptors for small molecules. Some of the highly‐expressed pairs of endometrial ligand and embryo receptor genes included MDK and its receptors ITGB1, SDC4 and LRP2, WNT5A (RYK), VEGFA (ITGB1), GPI (AMFR), and the hedgehog proteins IHH and DHH (HHIP). The most highly expressed receptors for small molecules were GPRC5C (retinoic acid receptor), PGRMC1 (progesterone), and CHRNB2 (acetylcholine). There were also 84 genes encoding for cell signaling ligands expressed by the morula, with the most highly expressed being GPI, AIMP1, TIMP1, IK, and CCN2. The atlas of receptor and ligand genes should prove useful for understanding details of the communication between the embryo and mother that underlies optimal embryonic development.

Cytokines That Serve as Embryokines in Cattle

Simple Summary

This review will explore how some cytokines also influence early embryonic development. We term these types of molecules as embryokines. Understanding how cytokines serve as embryokines could offer new opportunities to improve embryo development and the overall health of the embryo so that pregnancies will be retained after embryo transfer and so that viable offspring are produced. At least two cytokines may offer these benefits to bovine embryos produced in vitro. Additional cytokines also are identified in this review that may contain beneficial activities on bovine embryos.

Abstract

The term “embryokine” has been used to denote molecules produced by the endometrium, oviduct, or by embryo itself that will influence embryo development. Several cytokines have been identified as embryokines in cattle and other mammals. This review will describe how these cytokines function as embryokines, with special emphasis being placed on their actions on in vitro produced (IVP) bovine embryos. Embryokines are being explored for their ability to overcome the poor development rates of IVP embryos and to limit post-transfer pregnancy retention efficiencies that exist in IVP embryos. This review will focus on describing two of the best-characterized cytokines, colony-stimulating factor 2 and interleukin 6, for their ability to modify bovine embryo quality and confirmation, promote normal fetal development, and generate healthy calves. Additional cytokines will also be discussed for their potential to serve as embryokines.

Early embryo losses, progesterone and pregnancy associated glycoproteins levels during summer heat stress in dairy cows

Objectives of this study were to characterize the effects of heat stress on pregnancy associated glycoproteins (PAG) and progesterone and its involvement in embryo survival. In trial 1, blood samples collected from days 29 to 36 post insemination were examined for the comparison of PAG concentrations between winter (n = 3721) and summer (n = 2388). In trial 2, embryo losses were assessed in winter (n = 144) and in summer (n = 133), in days 31 or 32 of pregnancy. Pregnancy diagnosis was carried out by ultrasonography on days 24 or 25, and it was repeated a week later; in the second occasion PAG concentration was also determined. In trial 3 the PAG and progesterone concentrations were assessed in days 33 to 36 in winter and summer. In trial 1 PAG levels did not differ between winter and summer, the conception rate and the proportion of uncertain pregnancies were higher in winter than summer. The likelihood of pregnancy was 10 to 15% higher in winter. In trial 2, the embryo death rate was higher in summer, but the PAG levels of cows that had embryo loss in summer were higher than those in winter. In both seasons, lower PAG levels were associated with higher risk of pregnancy loss, while embryo death was five times more likely to occur in summer than in winter and lower PAG concentrations were positively associated with higher risk of embryo loss. In trial 3, mean PAG levels were higher and of progesterone were lower during the summer than during the winter. We infer that despite the devastating effects of heat stress on cows' fertility, those early embryos that survive under continuous heat stress can form a well-functioning placenta; hence, the high embryo mortality rate observed during the summer months could be mainly attributed to luteal insufficiency.

Changes in Oviductal Cells and Small Extracellular Vesicles miRNAs in Pregnant Cows

Early embryonic development occurs in the oviduct, where an ideal microenvironment is provided by the epithelial cells and by the oviductal fluid produced by these cells. The oviductal fluid contains small extracellular vesicles (sEVs), which through their contents, including microRNAs (miRNAs), can ensure proper cell communication between the mother and the embryo. However, little is known about the modulation of miRNAs within oviductal epithelial cells (OECs) and sEVs from the oviductal fluid in pregnant cows. In this study, we evaluate the miRNAs profile in sEVs from the oviductal flushing (OF-sEVs) and OECs from pregnant cows compared to non-pregnant, at 120 h after ovulation induction. In OF-sEVs, eight miRNAs (bta-miR-126-5p, bta-miR-129, bta-miR-140, bta-miR-188, bta-miR-219, bta-miR-345-3p, bta-miR-4523, and bta-miR-760-3p) were up-regulated in pregnant and one miRNA (bta-miR-331-5p) was up-regulated in non-pregnant cows. In OECs, six miRNAs (bta-miR-133b, bta-miR-205, bta-miR-584, bta-miR-551a, bta-miR-1193, and bta-miR-1225-3p) were up-regulated in non-pregnant and none was up-regulated in pregnant cows. Our results suggest that embryonic maternal communication mediated by sEVs initiates in the oviduct, and the passage of gametes and the embryo presence modulate miRNAs contents of sEVs and OECs. Furthermore, we demonstrated the transcriptional levels modulation of selected genes in OECs in pregnant cows. Therefore, the embryonic-maternal crosstalk potentially begins during early embryonic development in the oviduct through the modulation of miRNAs in OECs and sEVs in pregnant cows.

Heat stress on cattle embryo: gene regulation and adaptation

Global warming has been affecting animal husbandry and farming production worldwide via changes in organisms and their habitats. In the tropics, these conditions are adverse for agriculture and animal production in some areas, due to high temperatures and relative humidity, affecting competitiveness related to economic activities. These environments have deteriorated livestock production, due to periods of drought, reduction in forage quality and heat stress, eliciting negative effects on reproduction, weight gain, and reduced meat and milk production. However, the use of animals adapted to tropics such as breeds derived from subspecies Bos primigenius indicus and native breeds from tropical countries or their crossings, is an alternative to improve production under high-temperature conditions. Therefore, physiological adaptation including gene expression induced by heat stress have been studied to understand the response of animals and to improve cross-breeding between cattle breeds to maintain high productivity in adverse weather conditions. Heat stress has been associated with lower reproductive performance in cows, due to the impact on blastocyst production, decreased implantation and increased embryonic death. Thus, for decades, in vitro fertilization and embryo transfer techniques have focused on studying the optimal conditions for production of high-quality embryos to transfer. The aim of this review is to discuss the effects of heat stress in bovine embryos, and their physiological and genetic modulation, focusing on the genes that are related with major adaptability to heat stress conditions and their relationship with different embryonic stages.

Heat stress on calves and heifers: a review

The current review is designed with aims to highlight the impact of heat stress (HS) on calves and heifers and to suggest methods for HS alleviation. HS occurs in animals when heat gain from environment and metabolism surpasses heat loss by radiation, convection, evaporation and conduction. Although calves and heifers are comparatively heat resistant due to less production of metabolic heat and more heat dissipation efficiency, they still suffer from HS to some degree. Dry matter intake and growth performance of calves and heifers are reduced during HS because of redistributing energy to heat regulation through a series of physiological and metabolic responses, such as elevated blood insulin and protein catabolism. Enhanced respiration rate and panting during HS accelerate the loss of CO2, resulting in altered blood acid-base chemistry and respiratory alkalosis. HS-induced alteration in rumen motility and microbiota affects the feed digestibility and rumen fermentation. Decreased luteinizing hormone, estradiol and gonadotrophins due to HS disturb the normal estrus cyclicity, depress follicular development, hence the drop in conception rate. Prenatal HS not only suppresses the embryonic development by the impaired placenta, which results in hypoxia and malnutrition, but also retards the growth, immunity and future milk production of newborn calves. Based on the above challenges, we attempted to describe the possible impacts of HS on growth, health, digestibility and reproduction of calves and heifers. Likewise, we also proposed three primary strategies for ameliorating HS consequences. Genetic development and reproductive measures, such as gene selection and embryo transfers, are more likely long-term approaches to enhance heat tolerance. While physical modification of the environment, such as shades and sprinkle systems, is the most common and easily implemented measure to alleviate HS. Additionally, nutritional management is another key approach which could help calves and heifers maintain homeostasis and prevent nutrient deficiencies because of HS.

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.

Regulation of present and future development by maternal regulatory signals acting on the embryo during the morula to blastocyst transition - insights from the cow

The preimplantation embryo has a remarkable ability to execute its developmental program using regulatory information inherent within itself. Nonetheless, the uterine environment is rich in cell signaling molecules termed embryokines that act on the embryo during the morula-to-blastocyst transition, promoting blastocyst formation and programming the embryo for subsequent developmental events. Programming can not only affect developmental processes important for continuance of development in utero but also affect characteristics of the offspring during postnatal life. Given the importance of embryokines for regulation of embryonic development, it is likely that some causes of infertility involve aberrant secretion of embryokines by the uterus. Embryokines found to regulate development of the bovine embryo include insulin-like growth factor 1, colony stimulating factor 2 (CSF2), and dickkopf WNT signaling pathway inhibitor 1. Embryo responses to CSF2 exhibit sexual dimorphism, suggesting that sex-specific programming of postnatal function is caused by maternal signals acting on the embryo during the preimplantation period that regulate male embryos differently than female embryos.

Post-transfer outcomes in cultured bovine embryos supplemented with epidermal growth factor, fibroblast growth factor 2, and insulin-like growth factor 1

This work examined the downstream fetal and placental outcomes of introducing a cocktail of uterine-derived growth factors during bovine embryo culture. Abattoir-derived bovine oocytes were matured and fertilized in vitro. On day 4 post-fertilization, ≥ 8-cell embryos were harvested, pooled and exposed to an embryokine mix, termed EFI, which contained recombinant human epidermal growth factor (10 ng/ml), bovine fibroblast growth factor-2 (10 ng/ml) and human insulin-like growth factor 1 (50 ng/ml) or to a carrier-only control treatment (CON). On day 7, individual, transfer-quality embryos were transferred to recipients. Timed ovulation was completed in mature, non-suckled commercial beef cows. Cows either were artificial inseminated (AI) or received an embryo (ET) on day 7 post-estrus (n = 23-31 cows/treatment over 4 replicate studies). The percentage of grade 1 and 2 morulae and blastocysts was greater (P < 0.05) for EFI-treated embryos than CON. The percentage of pregnant cows diagnosed by transrectal ultrasonography did not differ among the AI and ET groups on days 28, 42 and 56 post-estrus. There also were no differences in the ratio of male to female fetuses determined on day 60 post-estrus by transrectal ultrasonography. On day 21 post-estrus, the relative abundance of three interferon-stimulated gene (ISG) transcripts in peripheral leukocytes were not different based on AI/ET group or the sex of the conceptus. Circulating pregnancy-associated glycoprotein (PAG) concentrations differed (P < 0.05) among days. Also, a difference in PAG concentrations (P < 0.05) were detected between male and female pregnancies in the CON-ET group but not in the AI or EFI-ET groups. Crown-rump length was not affected by AI/ET group on day 42 but were less (P < 0.05) in the CON and EFI-ET groups than the AI group on day 56. These findings implicate EFI supplementation as a means for improving transferable embryo production in a bovine IVP system, but it is not clear if this treatment improves embryo competency after ET.

Influence of elevated temperature on bovine oviduct epithelial cells (BOECs)

The aim of this study was to evaluate the influence of elevated temperature on bovine oviduct epithelial cells (BOECs), based on the expression and localization of both heat shock protein 70 (HSP70), responsible for the cellular defence mechanism, and oviduct specific glycoprotein 1 (OVGP1) which is the most important embryotrophic protein. BOECs were cultured alone and co-cultured with cattle embryos at control (38.5°C) and elevated temperature (41°C) for 168 h. The elevated temperature had no effect on the viability of BOECs but exerted a negative effect on embryo development. The elevated temperature increased the expression of HSP70 and decreased the expression of OVGP1 at both mRNA and protein levels in BOECs cultured alone and those co-cultured with embryos. However, the presence of embryos limited the decrease in OVGP1 expression in BOECs at elevated temperature but did not alter the expression of HSP70. These results demonstrate for the first time the influence of elevated temperature on BOECs, consequently providing insights into the interactions between the embryo and the oviduct at elevated temperature.

Developmental and molecular responses of buffalo (Bubalus bubalis) cumulus–oocyte complex maturedin vitrounder heat shock conditions

To investigate the effects of physiologically relevant heat shock during oocyte maturation, buffalo cumulus–oocyte complexes (COCs) were cultured at 38.5°C (control) or were exposed to 39.5°C (T1) or 40.5°C (T2) for the first 6 h ofin vitromaturation (IVM), followed by 38.5°C through the next 18 h/IVM and early embryonic development up to the blastocyst stage. Gene expression analysis was performed on selected target genes (HSF-1,HSF-2,HSP-70,HSP-90,BAX,p53,SOD1,COX1,MAPK14) in denuded oocytes and their isolated cumulus cells resulting from control COCs as well as from COCs exposed to a temperature of 39.5°C (T1). The results indicated that heat shock significantly (P< 0.01) decreased the maturation rate in T1 and T2 cells compared with the control. Afterin vitrofertilization (IVF), cleavage rate was lower (P< 0.01) for oocytes exposed to heat stress, and the percentage of oocytes arrested at the 2- or 4-cell stage was higher (P< 0.01) than that of the control. The percentage of oocytes that developed to the 8-cell, 16-cell or blastocyst stage was lower (P< 0.01) in both T1 and T2 groups compared with the control group. mRNA expression levels for the studied genes were decreased (P< 0.05) in treated oocytes (T1) except forHSP-90andHSF-1, which were increased. In cumulus cells isolated from COCs (T1), the expression for the target genes was upregulated except forBAX, which was downregulated. The results of this study demonstrated that exposure of buffalo oocytes to elevated temperatures for 6 h severely compromised their developmental competence and gene expression.

Addition of insulin-like growth factor I to the maturation medium of bovine oocytes subjected to heat shock: effects on the production of reactive oxygen species, mitochondrial activity and oocyte competence

This study was performed to investigate the effects of insulin-like growth factor-I (IGF-I) addition to in vitro maturation (IVM) medium on apoptosis, mitochondrial membrane potential, ROS production, and developmental competence of bovine oocytes subjected to heat shock. Two temperatures (conventional: 24 h at 38.5°C, or heat shock: 12 h at 41°C followed by 12 h at 38.5°C) and 3 IGF-I concentrations (0, 25, and 100 ng/mL) were tested during IVM. The oocytes were then fertilized in vitro, and the presumptive zygotes were cultured until reaching the blastocyst stage. There was no interaction between temperature and IGF-I concentration for any variable evaluated (P > 0.05). The addition of IGF-I did not alter the proportion of nuclear maturation, TUNEL-positive oocytes and caspase-3 activity, or blastocyst proportion on Days 7 and 8 post-fertilization. Furthermore, the total number of cells and the number of cells in the inner cell mass (ICM) in the blastocyst were not altered (P > 0.05). However, IGF-I increased (P < 0.05) the mitochondrial membrane potential and the production of ROS in oocytes and decreased (P < 0.05) the proportion of apoptotic cells in the ICM in blastocysts. Heat shock increased (P < 0.05) the proportion of TUNEL-positive oocytes and ROS production and reduced (P < 0.05) the mitochondrial membrane potential. Moreover, heat shock increased (P < 0.05) the apoptosis proportion in the ICM cells. In conclusion, supplementing IVM medium with IGF-I may increase the mitochondrial membrane potential and ROS production in oocytes and decrease apoptosis in the ICM in blastocysts. Heat shock for 12 h compromised oocyte developmental competence and increased apoptosis within the ICM cells of the blastocysts.

Actions of activin A, connective tissue growth factor, hepatocyte growth factor and teratocarcinoma-derived growth factor 1 on the development of the bovine preimplantation embryo

The reproductive tract secretes bioactive molecules collectively known as embryokines that can regulate embryonic growth and development. In the present study we tested four growth factors expressed in the endometrium for their ability to modify the development of the bovine embryo to the blastocyst stage and alter the expression of genes found to be upregulated (bone morphogenetic protein 15 (BMP15) and keratin 8, type II (KRT8)) or downregulated (NADH dehydrogenase 1 (ND1) and S100 calcium binding protein A10 (S100A10)) in embryos competent to develop to term. Zygotes were treated at Day 5 with 0.01, 0.1 or 1.0 nM growth factor. The highest concentration of activin A increased the percentage of putative zygotes that developed to the blastocyst stage. Connective tissue growth factor (CTGF) increased the number of cells in the inner cell mass (ICM), decreased the trophectoderm : ICM ratio and increased blastocyst expression of KRT8 and ND1. The lowest concentration of hepatocyte growth factor (HGF) reduced the percentage of putative zygotes becoming blastocysts. Teratocarcinoma-derived growth factor 1 increased total cell number at 0.01 nM and expression of S100A10 at 1.0 nM, but otherwise had no effects. Results confirm the prodevelopmental actions of activin A and indicate that CTGF may also function as an embryokine by regulating the number of ICM cells in the blastocyst and altering gene expression. Low concentrations of HGF were inhibitory to development.

Stem Cell Conditioned Media Contains Important Growth Factors and Improves In Vitro Buffalo Embryo Production

The present study was designed to investigate the effect of MSCs-conditioned media (CM) on quality buffalo embryo production in vitro. MSCs were harvested from Wharton's jelly of 2-3 month old fetus and MSCs CM was collected. Immunocytochemistry and western blot assay revealed that MSCs secrete several important growth factors viz. FGF-2, IGF-1, LIF, TGF-β, and VEGF. Slaughterhouse derived culture grade cumulus oocyte complexes (COCs) were matured and fertilized in vitro. Presumptive zygotes were divided in four groups and cultured in vitro in respective media viz. group I (100% mSOF), Group II (100% Knockout Media DMEM+SR), Group III (50% CM + 50% mSOF), and group IV (100% CM). It was found that though the cleavage rate did not changed significantly (p < 0.05), but blastocyst rate was increased significantly (p < 0.05) in Group III and IV (24.24 ± 1.34 and 23.29 ± 1.25, respectively) compared to group I and II (16.04 ± 1.46 and 17.72 ± 0.94, respectively). Similarly, TCN was significantly (p < 0.05) higher in 50% CM and 100% CM replacement group (93.33 ± 1.91 and 92.13 ± 1.04, respectively) than the other two groups. It can be concluded from the study that MSCs secrete several important growth factors and MSCs-CM can be effectively used for enhancement of quality buffalo embryo production in vitro.

The embryonic stress response to in vitro culture: insight from genomic analysis

Recent genomic studies have shed light on the impact of in vitro culture (IVC) on embryonic homeostasis and the differential gene expression profiles associated with lower developmental competence. Consistently, the embryonic stress responses to IVC conditions correlate with transcriptomic changes in pathways related to energetic metabolism, extracellular matrix remodelling and inflammatory signalling. These changes appear to result from a developmental adaptation that enhances a Warburg-like effect known to occur naturally during blastulation. First discovered in cancer cells, the Warburg effect (increased glycolysis under aerobic conditions) is thought to result from mitochondrial dysfunction. In the case of IVC embryos, culture conditions may interfere with mitochondrial maturation and oxidative phosphorylation, forcing cells to rely on glycolysis in order to maintain energetic homeostasis. While beneficial in the short term, such adaptations may lead to epigenetic changes with potential long-term effects on implantation, foetal growth and post-natal health. We conclude that lessening the detrimental effects of IVC on mitochondrial activity would lead to significantly improved embryo quality.

Developmental competence and expression profile of genes in buffalo (Bubalus bubalis) oocytes and embryos collected under different environmental stress

The study examined the effects of different environmental stress on developmental competence and the relative abundance (RA) of various gene transcripts in oocytes and embryos of buffalo. Oocytes collected during cold period (CP) and hot period (HP) were matured, fertilized and cultured in vitro to blastocyst hatching stage. The mRNA expression patterns of genes implicated in developmental competence (OCT-4, IGF-2R and GDF-9), heat shock (HSP-70.1), oxidative stress (MnSOD), metabolism (GLUT-1), pro-apoptosis (BAX) and anti-apoptosis (BCL-2) were evaluated in immature and matured oocytes as well as in pre-implantation stage embryos. Oocytes reaching MII stage, cleavage rates, blastocyst yield and hatching rates increased (P < 0.05) during the CP. In MII oocytes and 2-cell embryos, the RA of OCT-4, IGF-2R, GDF-9, MnSOD and GLUT-1 decreased (P < 0.05) during the HP. In 4-cell embryos, the RA of OCT-4, IGF-2R and BCL-2 decreased (P < 0.05) in the HP, whereas GDF-9 increased (P < 0.05). In 8-to 16-cell embryos, the RA of OCT-4 and BCL-2 decreased (P < 0. 05) in the HP, whereas HSP-70.1 and BAX expression increased (P < 0.05). In morula and blastocyst, the RA of OCT-4, IGF-2R and MnSOD decreased (P < 0.05) during the HP, whereas HSP-70.1 was increased (P < 0.05). In conclusion, deleterious seasonal effects induced at the GV-stage carry-over to subsequent embryonic developmental stages and compromise oocyte developmental competence and quality of developed blastocysts.

Developmental block and programmed cell death in Bos indicus embryos: effects of protein supplementation source and developmental kinetics

The aims of this study were to determine if the protein source of the medium influences zebu embryo development and if developmental kinetics, developmental block and programmed cell death are related. The culture medium was supplemented with either fetal calf serum or bovine serum albumin. The embryos were classified as Fast (n = 1,235) or Slow (n = 485) based on the time required to reach the fourth cell cycle (48 h and 90 h post insemination - hpi -, respectively). The Slow group was further separated into two groups: those presenting exactly 4 cells at 48 hpi (Slow/4 cells) and those that reached the fourth cell cycle at 90 hpi (Slow). Blastocyst quality, DNA fragmentation, mitochondrial membrane potential and signs of apoptosis or necrosis were evaluated. The Slow group had higher incidence of developmental block than the Fast group. The embryos supplemented with fetal calf serum had lower quality. DNA fragmentation and mitochondrial membrane potential were absent in embryos at 48 hpi but present at 90 hpi. Early signs of apoptosis were more frequent in the Slow and Slow/4 cell groups than in the Fast group. We concluded that fetal calf serum reduces blastocyst development and quality, but the mechanism appears to be independent of DNA fragmentation. The apoptotic cells detected at 48 hpi reveal a possible mechanism of programmed cell death activation prior to genome activation. The apoptotic cells observed in the slow-developing embryos suggested a relationship between programmed cell death and embryonic developmental kinetics in zebu in vitro-produced embryos.

Genetic variation in resistance of the preimplantation bovine embryo to heat shock

Reproduction is among the physiological functions in mammals most susceptible to disruption by hyperthermia. Many of the effects of heat stress on function of the oocyte and embryo involve direct effects of elevated temperature (i.e. heat shock) on cellular function. Mammals limit the effects of heat shock by tightly regulating body temperature. This ability is genetically controlled: lines of domestic animals have been developed with superior ability to regulate body temperature during heat stress. Through experimentation in cattle, it is also evident that there is genetic variation in the resistance of cells to the deleterious effects of elevated temperature. Several breeds that were developed in hot climates, including Bos indicus (Brahman, Gir, Nelore and Sahiwal) and Bos taurus (Romosinuano and Senepol) are more resistant to the effects of elevated temperature on cellular function than breeds that evolved in cooler climates (Angus, Holstein and Jersey). Genetic differences are expressed in the preimplantation embryo by Day 4–5 of development (after embryonic genome activation). It is not clear whether genetic differences are expressed in cells in which transcription is repressed (oocytes >100 µm in diameter or embryos at stages before embryonic genome activation). The molecular basis for cellular thermotolerance has also not been established, although there is some suggestion for involvement of heat shock protein 90 and the insulin-like growth factor 1 system. Given the availability of genomic tools for genetic selection, identification of genes controlling cellular resistance to elevated temperature could be followed by progress in selection for those genes within the populations in which they exist. It could also be possible to introduce genes from thermotolerant breeds into thermally sensitive breeds. The ability to edit the genome makes it possible to design new genes that confer protection of cells from stresses like heat shock.

Developmental competence and expression pattern of bubaline (Bubalus bubalis) oocytes subjected to elevated temperatures during meiotic maturation in vitro

OBJECTIVE

To determine the direct effect of physiologically relevant high temperatures (40.5 and 41.5 °C) for two time periods (12 and 24 h) on bubaline oocytes during in vitro maturation.

METHOD

The control group oocytes were cultured at 38.5 °C for 24 h. The treatment 1 (T1) and 3 (T3) group oocytes were cultured at 40.5 and 41.5 °C respectively, for the first 12 h and at 38.5 °C for rest of the 12 h. However, treatment 2 (T2) and 4 (T4) group oocytes were cultured at 40.5 and 41.5 °C for complete 24 h.

RESULTS

Development of oocytes to blastocyst was severely compromised (p < 0.001) when matured at 40.5 and 41.5 °C for both exposure periods (12 h and 24 h). It was found that the cleavage rates, blastocyst yield and mean cell number decreased remarkably (p < 0.001) in the treatment groups compared to control. The relative mRNA expression of heat shock protein (Hsp 70.1, 70.2, 70.8, 60, 10 and HSF1), pro-apoptotic (caspases-3, -7, -8, Bid and Bax) and oxidative stress (iNOS) related genes was significantly higher (p < 0.05) in all the treatment groups compared to control. However, mRNA abundance of anti-apoptotic (Bcl-2, Mcl-1, Bcl-xl), glucose transport (Glut1, Glut3 and IGF1R), developmental competence (ZAR1 and BMP15) and oxidative stress (MnSOD) related genes was significantly decreased (p < 0.05) in the treatment groups compared to control.

CONCLUSION

The present study clearly establishes that physiologically relevant elevated temperatures during in vitro meiotic maturation reduce developmental competence of bubaline oocytes.

IGF-I slightly improves nuclear maturation and cleavage rate of bovine oocytes exposed to acute heat shock in vitro

An in vitro model of embryo production was used to examine the effects of insulin-like growth factor (IGF)-I on maturation and developmental competence of oocytes exposed to heat shock. Cumulus–oocyte complexes were matured at 38.5°C or exposed to acute heat shock (HS; 41.5°C), with or without 100 ng/ml IGF-I, for 22 h through in vitro maturation. The experimental groups were control (C), C + IGF-I, HS, and HS + IGF-I. Oocytes were fertilized at the end of maturation, and the proportion of cleaved embryos was recorded 44 h later. HS during maturation increased the proportion of TUNEL-positive oocytes (P < 0.05). HS did not have any effect on cortical granule translocation but impaired resumption of meiosis, expressed as a decreased proportion of oocytes with nuclei in metaphase I (P < 0.05) and metaphase II (MII; P < 0.05). HS decreased the proportion of oocytes that cleaved (P < 0.05), in particular those oocytes that further developed to 4-cell-stage embryos (P < 0.05). IGF-I alleviated, to some extent, the deleterious effects of HS on the oocytes as reflected by a reduced proportion of TUNEL-positive oocytes (P < 0.03). While not significant, IGF-I tended to increase the proportion of MII-stage oocytes (P < 0.08) and 4-cell-stage cleaved embryos (P < 0.06). Further examination is required to explore whether IGF-I also affects the developmental competence of oocytes exposed to HS.

A diet enriched in linoleic acid compromises the cryotolerance of embryos from superovulated beef heifers

Dietary rumen-protected fat rich in linoleic acid may affect the superovulatory response and embryo yield; however, its effects on in vivo embryo cryotolerance are unknown in zebu cattle. The present study evaluated the production and cryotolerance after freezing or vitrification of embryos from Nelore heifers supplemented with rumen-protected polyunsaturated fatty acids (PUFA). Forty heifers kept in pasture were randomly distributed into two groups according to the type of feed supplement (F, supplement with rumen-protected PUFA, predominantly linoleic; C, control fat-free supplement with additional corn). Supplements were formulated to be isocaloric and isonitrogenous. Each heifer underwent both treatments in a crossover design with 70 days between replicates. After 50 days feeding, heifers were superovulated. Embryos were evaluated morphologically and vitrified or frozen. After thawing or warming, embryo development was evaluated in vitro. There was no difference between the F and C groups (P > 0.10) in terms of embryo production. Regardless of the cryopreservation method used, Group C embryos had a greater hatching rate after 72 h in vitro culture than Group F embryos (44.3 ± 4.2% (n = 148) vs 30.9 ± 4.0% (n = 137), respectively; P = 0.04). Moreover, vitrified and frozen embryos had similar hatching rates (P > 0.10). In conclusion, dietary rumen-protected PUFA rich in linoleic acid did not improve embryo production and compromised the cryotolerance of conventionally frozen or vitrified embryos from Nelore heifers.

Discovery of single nucleotide polymorphisms in candidate genes associated with fertility and production traits in Holstein cattle

Background

Identification of single nucleotide polymorphisms (SNPs) for specific genes involved in reproduction might improve reliability of genomic estimates for these low-heritability traits. Semen from 550 Holstein bulls of high (≥ 1.7; n = 288) or low (≤ −2; n = 262) daughter pregnancy rate (DPR) was genotyped for 434 candidate SNPs using the Sequenom MassARRAY® system. Three types of SNPs were evaluated: SNPs previously reported to be associated with reproductive traits or physically close to genetic markers for reproduction, SNPs in genes that are well known to be involved in reproductive processes, and SNPs in genes that are differentially expressed between physiological conditions in a variety of tissues associated in reproductive function. Eleven reproduction and production traits were analyzed.

Results

A total of 40 SNPs were associated (P < 0.05) with DPR. Among these were genes involved in the endocrine system, cell signaling, immune function and inhibition of apoptosis. A total of 10 genes were regulated by estradiol. In addition, 22 SNPs were associated with heifer conception rate, 33 with cow conception rate, 36 with productive life, 34 with net merit, 23 with milk yield, 19 with fat yield, 13 with fat percent, 19 with protein yield, 22 with protein percent, and 13 with somatic cell score. The allele substitution effect for SNPs associated with heifer conception rate, cow conception rate, productive life and net merit were in the same direction as for DPR. Allele substitution effects for several SNPs associated with production traits were in the opposite direction as DPR. Nonetheless, there were 29 SNPs associated with DPR that were not negatively associated with production traits.

Conclusion

SNPs in a total of 40 genes associated with DPR were identified as well as SNPs for other traits. It might be feasible to include these SNPs into genomic tests of reproduction and other traits. The genes associated with DPR are likely to be important for understanding the physiology of reproduction. Given the large number of SNPs associated with DPR that were not negatively associated with production traits, it should be possible to select for DPR without compromising production.

Effect of physiologically relevant heat shock on development, apoptosis and expression of some genes in buffalo (Bubalus bubalis) embryos produced in vitro

For investigating the effects of physiologically relevant heat shock, buffalo oocytes/embryos were cultured at 38.5°C (control) or were exposed to 39.5°C (Group II) or 40.5°C (Group III) for 2 h once every day throughout in vitro maturation (IVM), fertilization (IVF) and culture (IVC). Percentage of oocytes that developed to 8-cell, 16-cell or blastocyst stage was lower (p < 0.05) and the number of apoptotic nuclei was higher (p < 0.05) for Group III > Group II > controls. At both 8-16-cell and blastocyst stages, relative mRNA abundance of stress-related genes HSP 70.1 and HSP 70.2 and pro-apoptotic genes CASPASE-3, BID and BAX was higher (p < 0.05) in Groups III and II than that in controls with the exception of stress-related gene HSF1. Expression level of anti-apoptotic genes BCL-XL and MCL-1 was also higher (p < 0.05) in Groups III and II than that in controls at both 8-16-cell and blastocyst stages. Among the genes related to embryonic development, at 8-16-cell stage, the expression level of GDF9 was higher (p < 0.05) in Group III than that in controls, whereas that of GLUT1, ZAR1 and BMP15 was not significantly different among the three groups. At the blastocyst stage, relative mRNA abundance of GLUT1 and GDF9 was higher (p < 0.05) in Group II than that in controls, whereas that of ZAR-1 and BMP15 was not affected. The results of this study demonstrate that exposure of buffalo oocytes and embryos to elevated temperatures for duration of time that is physiologically relevant severely compromises their developmental competence, increases apoptosis and affects stress-, apoptosis- and development-related genes.

Changes in the transcriptome of morula-stage bovine embryos caused by heat shock: relationship to developmental acquisition of thermotolerance

BACKGROUND

While initially sensitive to heat shock, the bovine embryo gains thermal resistance as it progresses through development so that physiological heat shock has little effect on development to the blastocyst stage by Day 5 after insemination. Here, experiments using 3' tag digital gene expression (3'DGE) and real-time PCR were conducted to determine changes in the transcriptome of morula-stage bovine embryos in response to heat shock (40 degrees C for 8 h) that could be associated with thermotolerance.

RESULTS

Using 3'DGE, expression of 173 genes were modified by heat shock, with 94 genes upregulated by heat shock and 79 genes downregulated by heat shock. A total of 38 differentially-regulated genes were associated with the ubiquitin protein, UBC. Heat shock increased expression of one heat shock protein gene, HSPB11, and one heat shock protein binding protein, HSPBP1, tended to increase expression of HSPA1A and HSPB1, but did not affect expression of 64 other genes encoding heat shock proteins, heat shock transcription factors or proteins interacting with heat shock proteins. Moreover, heat shock increased expression of five genes associated with oxidative stress (AKR7A2, CBR1, GGH, GSTA4, and MAP2K5), decreased expression of HIF3A, but did not affect expression of 42 other genes related to free radical metabolism. Heat shock also had little effect on genes involved in embryonic development. Effects of heat shock for 2, 4 and 8 h on selected heat shock protein and antioxidant genes were also evaluated by real-time PCR. Heat shock increased steady-state amounts of mRNA for HSPA1A (P<0.05) and tended to increase expression of HSP90AA1 (P<0.07) but had no effect on expression of SOD1 or CAT.

CONCLUSIONS

Changes in the transcriptome of the heat-shocked bovine morula indicate that the embryo is largely resistant to effects of heat shock. As a result, transcription of genes involved in thermal protection is muted and there is little disruption of gene networks involved in embryonic development. It is likely that the increased resistance of morula-stage embryos to heat shock as compared to embryos at earlier stages of development is due in part to developmental acquisition of mechanisms to prevent accumulation of denatured proteins and free radical damage.

Effects of oxygen tension and IGF-I on HIF-1α protein expression in mouse blastocysts

PURPOSE

Hypoxia inducible factors (HIFs) are key regulators of oxygen homeostasis in response to reduced oxygenation in somatic cells. In addition, HIF-1α protein can be also induced by insulin-like growth factor I (IGF-I) treatment in various cell lines under normoxic condition. However, the expression and function of HIF-1α in embryogenesis are still unclear. Therefore, the objectives of this study were to examine the expression of HIF-1α in mouse blastocysts cultured under hypoxic and normoxic conditions, and to determine whether oxygen tension and IGF-I influence embryonic development through stimulation of HIF-1α expression.

METHODS

Mouse embryos were cultured from the 1-cell to blastocyst stage under 5 % or 20 % O(2) in both the absence and presence of IGF-I.

RESULTS

The embryonic development rates to the blastocyst stage were not affected by oxygen tension or IGF-I treatment. HIF-1α protein was localized to the cytoplasm of blastocysts, and its levels were independent of oxygen concentration or IGF-I treatment. Blastocysts cultured under 5 % O(2) exhibited significantly higher total cell numbers (83.4 ± 18.1) and lower apoptotic index (3.7 ± 1.5) than those cultured under 20 % O(2) (67.4 ± 15.6) (6.9 ± 3.5) (P<0.05). IGF-I reduced the apoptotic index in both oxygen conditions, but a significant decrease was detected in the 20 % O(2) group.

CONCLUSIONS

HIF-1α may not be a major mediator that responds to change in oxygen tension within blastocysts, inconsistent with that of somatic cells. Supplementation of culture media with IGF-I has been shown to promote embryo development by an anti-apoptotic effect, instead of increasing HIF-1α protein expression.

Neurodevelopmental effects of insulin-like growth factor signaling

Insulin-like growth factor (IGF) signaling greatly impacts the development and growth of the central nervous system (CNS). IGF-I and IGF-II, two ligands of the IGF system, exert a wide variety of actions both during development and in adulthood, promoting the survival and proliferation of neural cells. The IGFs also influence the growth and maturation of neural cells, augmenting dendritic growth and spine formation, axon outgrowth, synaptogenesis, and myelination. Specific IGF actions, however, likely depend on cell type, developmental stage, and local microenvironmental milieu within the brain. Emerging research also indicates that alterations in IGF signaling likely contribute to the pathogenesis of some neurological disorders. This review summarizes experimental studies and shed light on the critical roles of IGF signaling, as well as its mechanisms, during CNS development.

Differential glycolytic and glycogenogenic transduction pathways in male and female bovine embryos produced in vitro

Previous studies have shown that developmental kinetic rates following IVF are lower in female than in male blastocysts and that this may be related to differences in glucose metabolism. In addition, an inhibition of phosphatidylinositol 3-kinase (PI3-K) inhibits glucose uptake in murine blastocysts. Therefore, the aim of this study was to identify and compare the expression of proteins involved in glucose metabolism (hexokinase-I, HK-I; phosphofructokinase-1, PFK-1; pyruvate kinase 1/2, PK1/2; glyceraldehyde-3-phosphate dehydrogenase, GAPDH; glucose transporter-1, GLUT-1; and glycogen synthase kinase-3, GSK-3) in male and female bovine blastocysts to determine whether PI3-K has a role in the regulation of the expression of these proteins. Hexokinase-I, PFK-1, PK1/2, GAPDH and GLUT-1 were present in bovine embryos. Protein expression of these proteins and GSK-3 was significantly higher in male compared with female blastocysts. Inhibition of PI3-K with LY294002 significantly decreased the expression of HK-I, PFK-1, GAPDH, GSK-3A/B and GLUT-1. Results showed that the expression of glycolytic proteins HK-I, PFK-1, GAPDH and PK1/2, and the transporters GLUT-1 and GSK-3 is regulated by PI3-K in bovine blastocysts. Moreover, the differential protein expression observed between male and female blastocysts might explain the faster developmental kinetics seen in males, as the expression of main proteins involved in glycolysis and glycogenogenesis was significantly higher in male than female bovine embryos and also could explain the sensitivity of male embryos to a high concentration of glucose, as a positive correlation between GLUT-1 expression and glucose uptake in embryos has been demonstrated.

Improving post-transfer survival of bovine embryos produced in vitro: actions of insulin-like growth factor-1, colony stimulating factor-2 and hyaluronan

Technologies for in vitro embryo production have the potential to enhance the efficiency of cattle production systems. However, utilization of in vitro-produced embryos for transfer remains limited throughout much of the world. Despite improvements over the past two decades, problems associated with the production of bovine embryos in vitro still exist which limit the widespread commercial application of this technology. In particular, bovine embryos produced in vitro have a reduced capacity to establish and maintain pregnancy as compared with their in vivo-derived counterparts. Embryo competence for survival following transfer is improved by in vivo culture in the sheep oviduct, thus indicating that standard embryo culture conditions are sub-optimal. Therefore, one strategy to improve post-transfer survival is to modify embryo culture media to more closely mimic the in vivo microenvironment. The maternal environment in which the bovine embryo develops in vivo contains various growth factors, cytokines, hormones, and other regulatory molecules. In addition to affecting bovine embryo development in vitro, recent research indicates that embryo competence for survival following transfer can also be improved when such molecules are added to embryo culture medium. Among the specific molecules that can increase post-transfer embryo survival are insulin-like growth factor-1 (IGF-1), colony stimulating factor-2 (CSF-2) and hyaluronan. This paper will review the effects IGF-1, CSF-2 and hyaluronan on post-culture embryo viability and discuss the potential mechanisms through which each of these molecules improves post-transfer survival.

Timing and dependence upon mitogen-activated protein kinase signaling for pro-developmental actions of insulin-like growth factor 1 on the preimplantation bovine embryo

Insulin like growth factor-1 (IGF1) increases the proportion of embryos that develop to the blastocyst stage. The objective of the present study was to determine whether the pro-developmental actions of IGF1 are exerted before or after Day 4 of development (i.e., on events occurring through the period of genomic activation versus events coincident with compaction and blastocoel formation) and whether mitogen-activated protein kinase (MAPK) signaling pathways mediate effects of IGF1. Treatment with IGF1 increased the proportion becoming blastocysts at concentrations of 10, 100 and 200 ng/mL, with 100 ng/mL being more effective than 10 or 200 ng/mL. At Day 8, the percent of oocytes that became blastocysts was 30, 34, 43, and 36%, respectively (SEM=2.6). As compared to controls (30.4%), IGF1 increased the percent of oocytes that were blastocysts at Day 8 when added from Days 4 to 8 (42%) or Days 0 to 8 post-insemination (40%) but there was no significant effect when IGF1 was added from Days 0 to 4 (37%; SEM=2.2). Actions of IGF1 to increase blastocyst development were reduced when embryos were co-treated with the MAPK inhibitor PD98059. The percentage of oocytes becoming a blastocyst at Day 8 was 21 versus 37% for 0 and 100 ng/mL in the absence of inhibitor and 24 versus 29% in the presence of inhibitor (IGF1×inhibitor interaction, P<0.05; pooled SEM=1.3). In conclusion, IGF1 promotes development to the blastocyst stage by regulating MAPK-dependent events at Day 4 or later of development.

Developmental changes in thermoprotective actions of insulin-like growth factor-1 on the preimplantation bovine embryo

Insulin-like growth factor 1 (IGF1) is an important endocrine signal for regulation of early embryonic development. It increases the proportion of preimplantation embryos becoming blastocysts, alters blastocyst gene expression, improves resistance of embryos to various stresses and can enhance survival of embryos after transfer to recipients. The present study had two objectives. The first was to determine whether the thermoprotective actions of IGF1 on the preimplantation bovine embryo was developmentally regulated, with the two-cell embryo being refractory to IGF1. The second was to determine the molecular basis for the improved competence of embryos treated with IGF1 to establish pregnancy after transfer to heat-stressed recipients. Treatment of embryos with 100 ng/ml IGF1 reduced the effects of heat shock on embryos ≥16 cells at day 5 after insemination but did not provide thermoprotection to two-cell embryos. Failure of IGF1 to alter embryo survival after heat shock was not associated with reduced expression of genes involved in IGF1 signaling (IGF1R, RAF1, PI3K, and MAPK) or immunoreactive IGF1R protein. Treatment with IGF1 had little effect on the transcriptome at the blastocyst stage of development, with a total of 102 differentially expressed genes identified. Among the differentially expressed genes were several involved in apoptosis, protection against free radicals and development. Changes in gene expression were consistent with IGF1 acting to induce an anti-apoptotic state and inhibit neurulation. In conclusion, thermoprotective actions of IGF1 are developmentally regulated. Failure of IGF1 to protect the two-cell embryo from heat shock could reflect the fact that these embryos are maximally sensitive to damage caused by heat shock or reflect the quiescence of the embryonic genome at this stage of development. Changes in gene expression at the blastocyst stage induced by IGF1 could contribute to the increased survival of IGF1-treated embryos when transferred during periods of heat stress.

Increased apoptosis in bovine blastocysts exposed to high levels of IGF1 is not associated with downregulation of the IGF1 receptor

The hypothesis that high concentrations of IGF1 can impair embryo development was investigated in a bovine in vitro model to reflect conditions in polycystic ovary syndrome (PCOS) patients. Embryos were either cultured in the absence or presence of a physiological (100 ng/ml) or supraphysiological (1000 ng/ml) IGF1 concentration. Cell allocation, apoptosis, transcript and protein expression of selected genes involved in apoptosis, glucose metabolism and the IGF system were analysed. Supraphysiological IGF1 concentration did not improve blastocyst formation over controls, but induced higher levels of apoptosis, decreased TP53 protein expression in the trophectoderm and increased the number of cells in the inner cell mass (ICM). The increase in ICM cells corresponded with an increase in IGF1 receptor (IGF1R) protein in the ICM. A small, but significant, percentage of blastocysts displayed a hypertrophic ICM, not observed in controls and virtually absent in embryos treated with physiological concentrations of IGF1. Physiological IGF1 concentrations increased total IGF1R protein expression and upregulated IGFBP3 transcripts leading to an increase in blastocyst formation with no effects on cell number or apoptosis. In conclusion, the results support the hypothesis of detrimental effects of supraphysiological IGF1 concentrations on early pregnancy. However, our results do not support the premise that increased apoptosis associated with high levels of IGF1 is mediated via downregulation of the IGF1R as previously found in preimplantation mouse embryos. This in vitro system with the bovine preimplantation embryo reflects critical features of fertility in PCOS patients and could thus serve as a useful model for in-depth mechanistic studies.

Developmental changes in expression of genes involved in regulation of apoptosis in the bovine preimplantation embryo

The early bovine preimplantation embryo is resistant to proapoptotic signals until around the 8- to 16-cell stage. We hypothesized that 2-cell embryos have higher amounts of antiapoptotic proteins and lower amounts of proapoptotic proteins when compared to embryos ≥16 cells. Steady-state concentrations of mRNA for the antiapoptotic genes BCL2 and HSPA1A were higher for MII oocytes, 2-cell embryos, and 2-cell embryos treated with alpha-amanitin as compared to ≥16-cell embryos. Steady-state concentrations of mRNA for the proapoptotic gene BAD increased in embryos ≥16 cells. There was no significant effect of stage of development on steady-state mRNA concentrations of BCL2L1, DFFA, or BAX. Using immunohistochemistry, it was found that BCL2 was present in greater relative concentrations for 2-cell embryos than for embryos ≥16 cells. These results were confirmed by Western blotting. Relative amounts of immunoreactive BAX detected by immunofluorescence were lower for 2-cell embryos than for embryos ≥16 cells. Using Western blotting, a high molecular weight (46 kDa) form of BAX was highest in ≥16-cell embryos, intermediate in 2-cell embryos, and lowest in MII oocytes. There were no effects of stage of development on relative amounts of immunoreactive BCL2L1, HSPA1A, or BAD, as determined by immunofluorescence. Treatment of embryos with alpha-amanitin from Day 0 to Day 5 or Day 4 to Day 5 after insemination reduced activation of group II caspases and terminal deoxynucleotidyl transferase dUTP nick end labeling after treatment with the proapoptotic signal C(2) ceramide at Day 5 after fertilization. Thus, transcription of BAX or other proteins is required for acquisition of the capacity for apoptosis. Results support the idea that changes in amounts of BCL2 family members are important for the inhibition of apoptosis in the 2-cell embryo and in the establishment of the capacity for apoptosis later in development.

Effects of gamete source and culture conditions on the competence of in vitro-produced embryos for post-transfer survival in cattle

One limitation to the use of in vitro-produced embryos in cattle production systems is the fact that pregnancy rates after transfer to recipients are typically lower than when embryos produced in vivo are transferred. Conceptually, the oocyte and spermatozoon from which the embryo is derived could affect competence for post-transfer survival. There are sire differences in embryonic survival after transfer, but there is little evidence that an embryo's ability to establish pregnancy is determined by sex sorting of spermatozoa by flow cytometry. The role of the source of the oocyte as a determinant of embryonic survival after transfer has not been examined carefully. Conditions for embryo culture after fertilisation can have an impact on the ability of the embryo to establish pregnancy following transfer. Among the specific molecules produced in the reproductive tract of the cow that have been shown to improve competence of in vitro-produced embryos for post-transfer survival are colony-stimulating factor 2, insulin-like growth factor-1 (for recipients exposed to heat stress) and hyaluronan (for less-advanced embryos). There is also a report that embryo competence for post-transfer survival can be improved by inclusion of a carbon-activated air filtration system in the incubator used to culture embryos. Progress in developing culture systems to improve embryonic competence for survival after transfer would be hastened by the development of in vitro assays that accurately predict the potential of an embryo to establish pregnancy after transfer. A group of 52 genes has been identified that are differentially expressed in embryos that developed to term v. embryos that did not establish pregnancy. Perhaps a gene microarray consisting of these genes, alone or in combination with other genes, could be used to screen embryos for competence to establish pregnancy.