Effects of either glucose or fructose and metabolic regulators on bovine embryo development and lipid accumulation in vitro

Effect of estradiol and IGF1 on glycogen synthesis in bovine uterine epithelial cells

In brief

Glucose is an important nutrient for the endometrium and embryo during pregnancy. This study shows that estradiol (E2)/IGF1 signaling stimulates glycogen synthesis in the uterine epithelium of cows, which could provide glucose when needed.

Abstract

Glycogen storage in the uterine epithelium peaks near estrus and is a potential source of glucose for the endometrium and embryos. However, the hormonal regulation of glycogen synthesis in the uterine epithelium is poorly understood. Our objective was to evaluate the effect of E2 and insulin-like growth factor 1 (IGF1) on glycogenesis in immortalized bovine uterine epithelial (BUTE) cells. Treatment of BUTE cells with E2 (0.1-10 nM) did not increase glycogen levels. However, treatment of BUTE cells with IGF1 (50 or 100 ng/mL) resulted in a >2-fold increase in glycogen. To determine if the uterine stroma produced IGF1 in response to E2, bovine uterine fibroblasts were treated with E2, which increased IGF1 levels. Immunohistochemistry showed higher levels of IGF1 in the stroma on day 1 than on day 11, which coincides with higher glycogen levels in the uterine epithelium. Western blots revealed that IGF1 treatment increased the levels of phospho-AKT, phospho-GSKβ, hexokinase 1, and glycogen synthase in BUTE cells. Metabolomic (GC-MS) analysis showed that IGF1 increased 3-phosphoglycerate and lactate, potentially indicative of increased flux through glycolysis. We also found higher levels of N-acetyl-glucosamine and protein glycosylation after IGF1 treatment, indicating increased hexosamine biosynthetic pathway activity. In conclusion, IGF1 is produced by uterine fibroblasts due to E2, and IGF1 increases glucose metabolism and glycogenesis in uterine epithelial cells. Glycogen stored in the uterine epithelium due to E2/IGF1 signaling at estrus could provide glucose to the endometrium or be secreted into the uterine lumen as a component of histotroph.

Sequential IVM by CNP preincubation and cooperating of PGE2 with AREG enhances developmental competence of SCNT reconstructs in goat

Developmental competence of in vitro matured cumulus oocyte complexes (COCs) in conventional IVM (C.IVM) is lower than in vivo maturated COCs and is related to unsynchronized nuclear and cytoplasmic maturation. To overcome this dearth, COCs can be exposed to granulosa secreted factors in a two-step system. Therefore, in the first experiment, 1000 nM of C-type natriuretic peptide for 8 h was determined (CAPA), as the best time and concentration to retain oocytes in germinal vesicle stage. This condition, also reduces lipid droplets and increases the expression of ATGL and PLIN2 involved in lipolysis and lipogenesis, respectively. In the second experiment, maturation was stimulated with prostaglandin E2 and amphiregulin for 18 h (CAPA-IVM), and their optimal concentrations based on blastocyst formation rates through in vitro fertilization (IVF) were determined as 1 and 600 nM, respectively. In the third experiment, the in vitro and in vivo developmental competency of SCNT embryos in CAPA-IVM group were determined. Despite similar blastocyst formation rates in IVF and SCNT between CAPA-IVM and C.IVM, the quality of blastocysts were quality was higher in CAPA-IVM, which reflected itself, as higher ICM/TE ratio and also expression of NANOG in SCNT blastocysts. Pregnancy rate, live births rate and SCNT efficiency were not significant between CAPA-IVM and C.IVM groups. Therefore, CAPA-IVM can improve the developmental competency of SCNT derived embryos.

Improved cryopreservation of in vitro produced bovine embryos using FGF2, LIF, and IGF1

In vitro embryo production systems are limited by their inability to consistently produce embryos with the competency to develop to the blastocyst stage, survive cryopreservation, and establish a pregnancy. Previous work identified a combination of three cytokines [fibroblast growth factor 2 (FGF2), leukemia inhibitory factor (LIF), and insulin-like growth factor 1 (IGF1)], called FLI, that we hypothesize improve preimplantation development of bovine embryos in vitro. To test this hypothesis, FLI was supplemented into oocyte maturation or embryo culture medium. Embryos were produced in vitro using abattoir-derived oocytes and fertilized with sperm from a single bull known to have high fertility. After an 18-20 h fertilization period, putative zygotes were cultured in synthetic oviductal fluid (SOF) for 8 days. The addition of FLI to the oocyte maturation medium increased (P < 0.05) the dissociation of transzonal projections at 12, 18, and 24 h of maturation, as well as, the proportion of oocytes that reached the metaphase II stage of meiosis. Additionally, lipid content was decreased (P < 0.05) in the blastocyst stage embryo. The addition of FLI during the culture period increased development to the blastocyst stage, cytoskeleton integrity, and survival following slow freezing, as well as, decreased post thaw cell apoptosis (P < 0.05). In conclusion, the supplementation of these cytokines in vitro has the potential to alleviate some of the challenges associated with the cryo-survival of in vitro produced bovine embryos through improving embryo development and embryo quality.

Effect of nicotinamide supplementation in in vitro fertilization medium on bovine embryo development

Increased oxidative stress is one of the main causes of poorly developed embryos in assisted reproductive technologies. Nicotinamide (NAM) has been shown to suppress reactive oxygen species (ROS) production through its potent antioxidative and anti-senescent effects. In the present study, we explored the effects of short-term NAM-treatment (3 and 5 h) during in vitro fertilization (IVF) on the development of bovine embryos. Treatment with 10 mM NAM for 3 h significantly increased the blastocyst formation but extending the treatment to 5 h did not enhance the benefits any further. Immunofluorescence analysis demonstrated that treatment with 10 mM NAM for 3 h decreased the expression of intracellular ROS, 8-oxo-7,8-dihydroguanine, caspase-3, and increased the expression of Sirt1, and incorporation of bromodeoxyuridine in one-cell stage embryos. Similarly, the level of H3K56ac significantly increased in the NAM-treated (3 and 5 h) one-cell stage embryos. Contrastingly, the treatment with 10 mM NAM for 5 h increased the caspase-9 level in blastocysts. Collectively, these findings suggest that NAM possesses antioxidant activity and supplementation of IVF medium with 10 mM NAM for 3 h improves the in vitro developmental competence of bovine embryos.

The Effect of L-Carnitine Additive During In Vitro Maturation on the Vitrification of Pig Oocytes

Cryopreservation of oocytes/embryos is an important technique for genetic resources; however, the success of vitrification in pig oocytes remained at a relatively lower level due to the high content of lipid droplets (LDs). Considering the positive effect of L-carnitine on the function of LDs, the present study was designed to investigate the effect of the addition of L-carnitine on the vitrification of porcine cumulus cells of complexes (cumulus/oocyte complexes [COCs]). First, COCs were randomly divided into two groups: one group of COCs were commonly in vitro maturation (IVM) for 42-46 hours (nonvitrification [NV]), while another group of COCs were IVM with 10 mM L-carnitine (NVL [nonvitrification with L-carnitine addition in IVM]). In addition, random parts of COCs with L-carnitine addition were vitrified (VL [vitrification with L-carnitine addition in IVM]), while vitrification was performed on COCs without L-carnitine used as control group (V). Results showed that the maturation rate of pig oocytes reduced significantly when the vitrification was performed at 16 hours during IVM (VL vs. NVL, 40.09 ± 2.85 vs. 90.76 ± 1.16; V vs. NV, 34.41 ± 2.55 vs. 89.71 ± 1.33, p < 0.01). With the addition of L-carnitine, intracellular LDs were decreased significantly (p < 0.01). However, no difference was observed on the efficiency of vitrification in pig oocytes (VL vs. V, 40.09 ± 2.85 vs. 34.41 ± 2.55, p > 0.05). In addition, not only the reactive oxygen species (ROS) level in pig oocytes with the L-carnitine addition group reduced significantly (p < 0.01), but also the expression of SOD1 gene was improved (p < 0.05). In conclusion, results demonstrated that although no difference could be observed on pig COC vitrification, the LDs and ROS level in pig oocytes could be modified by the addition of L-carnitine, which might be helpful for further development.

Nanoparticle technology improves in-vitro attachment of cattle (Bos taurus) trophectoderm cells

The bovine cell line, cow trophectoderm-1 (CT-1), provides an excellent in-vitro cell culture model to study early embryonic development. Obtaining consistent attachment and outgrowth, however, is difficult because enzymatic disassociation into single cells is detrimental; therefore, CT-1 cells must be passaged in clumps, which do not attach readily to the surface of the dish. We tested whether magnetic nanoparticles, NanoShuttle™-PL, could be used to improve cell attachment and subsequent proliferation of the cattle trophectoderm cell line without altering cellular metabolism or immunofluorescent detection of the lineage marker Caudal Type Homeobox 2 (CDX2). Confluency was achieved more consistently by using the NanoShuttle™-PL system to magnetically force attachment (75-100% of wells) as compared to the control (11%). Moreover, there were no alterations in characteristic morphology, nuclear-localized expression of the trophectoderm marker CDX2, or glycolytic metabolism. By enhancing attachment, magnetic nanoparticles improved culture efficiency and reproducibility in an anchorage-dependent cell line that otherwise was recalcitrant to efficient passaging.

L-carnitine supplementation in culture media improves the pregnancy rate of in vitro produced embryos with sexed semen from Bos taurus indicus cows

The in vitro embryo production industry in the actual world presents some difficulties related to low embryonic production rates, a problem that could be associated with in vitro culture conditions that differed from the in vivo (oviductal) conditions, mainly related to cytoplasmic lipid accumulation. L-carnitine is known as a modulator of β-oxidation in the developing embryo, as it has been demonstrated that it improves embryo quality without affecting the in vitro embryo production rate. The aim of the present work was to evaluate the effect of L-carnitine supplemented during the in vitro maturation and culture processes on the implantation rate of in vitro produced embryos. Supplementation with 3.8 mM of L-carnitine was used during in vitro maturation, and later, during late in vitro culture, it was added at 1.5 mM. A control group contained no L-carnitine supplementation. Bovine oocytes obtained by ultrasound-guided follicle aspiration from healthy Bos taurus indicus cows were matured, fertilized and cultured in vitro. Multiparous F1 (Bos taurus taurus × Bos taurus indicus) cows were used as recipients. Overall, 460 oocytes were processed in three independent replicates from in vitro maturation until day 8 of the in vitro culture. No significant difference was found between treatments of in vitro embryo production. However, pregnancy rate at days 45 and 72 was significantly higher in blastocysts derived from L-carnitine treatment (31.55 ± 9.78%) compared to the control group (18.68 ± 6.31%). In conclusion, addition of L-carnitine at 3.8 mM and 1.5 mM in the maturation, and culture medium after day 3 of in vitro production process, significantly improved pregnancy rate after embryo transfer.

Effect of delipidant agents during in vitro culture on the development, lipid content, gene expression and cryotolerance of bovine embryos

In vitro produced embryos are still sensitive to the freezing process which can be explained, in part, by the high-lipid accumulation that characterizes these embryos. Therefore, we aimed to evaluate the effect of delipidating agents, L-carnitine and the trans-10 cis-12 conjugated linoleic acid (CLA) isomer, on blastocyst development, lipid content, gene expression and cryotolerance when added to embryo culture media. Embryos were cultured in four different media: T1: control (n = 616), synthetic oviduct fluid (SOF) media with 5% foetal bovine serum (FBS); T2: L-carnitine (n = 648), SOF medium with 5% FBS and 0.6 mg/ml of L-carnitine; T3: CLA (n = 627), SOF medium with 5% FBS and 100 μM trans-10 cis-12 CLA; and T4: L-carnitine + CLA: (n = 597), SOF medium with 5% FBS plus 0.6 mg/ml L-carnitine and 100 μM trans-10 cis-12 CLA. Supplementation of culture medium with either or both delipidating agents reduced (p < .05) blastocyst rate on D7 (T1 = 49 ± 3.5; T2 = 39 ± 3.0; T3 = 42 ± 3.9 and T4 = 39 ± 3.9), but did not affected gene expression (p > .05). Although embryos cultured in the presence of L-carnitine contained fewer (p < .05) lipid droplets than the control embryos, they showed a lower re-expansion rate 24 hr post-thaw than those (p < .05). In conclusion, although L-carnitine reduced the amount of lipids in cultured embryos, the use of L-carnitine and CLA during in vitro culture was not able to improve the embryo production and the response to cryopreservation.

Polydatin and I-CBP112 protects early bovine embryo against nicotinamide-induced mitochondrial dysfunction

The mammalian Sirtuin family of seven enzymes, members of the NAD⁺-dependent histone deacetylase family that modify histones via direct deacetylation, is involved in the regulation of many antioxidant and oxidative stresses. In the present study, we explored the effects of nicotinamide (NAM)-induced oxidative stress on the in vitro development of bovine embryos, on the acetylation of histone H3 lysine 56 (H3K56ac) and on expression of apoptosis-related genes. Treatment with NAM (10, 20 or 40 mM for 24, 48 or 196 h) during IVC resulted in significantly decreased blastocyst formation (24 h: 38.8 vs. 33.1, 27.3 and 10.2%, with P > 0.05, P < 0.05 and P < 0.01, respectively; 48 h: 37.5 vs. 28.2, 13.4 and 0%, with P < 0.05 and P < 0.01, respectively; 196 h: 35.8 vs. 23.4, 0 and 0%, with P < 0.05, respectively). Treatment with NAM (20 and 40 mM for 24 h) resulted in increased intracellular reactive oxygen species (ROS) levels in 2-cell and blastocysts, and apoptotic cell numbers in blastocysts and decreased mitochondrial membrane potential (ΔΨ) in 2-cell embryos (P < 0.05). Polydatin (PD) and I-CBP112 rescued the 20 mM NAM-induced embryo developmental defects and reduced ROS levels and apoptotic cell numbers in blastocysts (P < 0.05). The gene expression of NF-κB, COX2 and p53 was significantly increased in the NAM-treated group. Immunofluorescence analysis confirmed that the protein levels of nuclear factor-kappa B (NF-κB) decreased significantly after PD and I-CBP112 treatment compared with the control (P < 0.05). High level of H3K56ac induced by NAM was decreased after PD and I-CBP112 treatment (P < 0.05). These findings suggest that NAM treatment induces high levels of H3K56 acetylation that may be involved in oxidative stress-induced bovine developmental defects, which can be tolerated by PD and I-CBP112 treatment.

Updating the Impact of Lipid Metabolism Modulation and Lipidomic Profiling on Oocyte Cryopreservation

Oocyte cryopreservation has drastically improved in recent years and is receiving widespread clinical use with increasing demand for fertility preservation and assisted reproduction treatments. However, there are still several points to be reviewed in terms of suppressing sub-lethal damages and improving overall safety, especially when trying to preserve oocytes at the germinal vesicle stage or oocytes matured in vitro. The lipid content of oocytes is highly associated with both their competence and cryotolerance. Differences in lipid content are observed not just between different species but also at different developmental stages and when the oocytes are kept under different conditions, including cryopreservation. Many efforts have been made to understand how physiological or in vitro alterations in the lipid profile of oocytes impacts cryotolerance and vice-versa; however, the dynamics of cytosolic and membrane lipid involvement in the cryopreservation process remains poorly clarified in the human female gamete. This review presents an updated overview of the current state of cryopreservation techniques and oocyte lipidomics and highlights possible ways to improve cryotolerance, focussing on lipid content modulation.

Phosphoric acid and phosphorylation levels are potential biomarkers indicating developmental competence of matured oocytes

We identified biomarkers for mice oocyte maturation in metaphase II in vivo and in situ using Raman spectroscopy.

Effects of fetal calf serum on cGMP pathway and oocyte lipid metabolism in vitro

Intracellular levels of cyclic nucleotides, such as cGMP, are involved in the regulation of adipocyte lipolysis. Cumulus-oocyte complexes (COCs) express enzymes that both synthesise (guanylate cyclase) and degrade (phosphodiesterase (PDE) 5A) cGMP. Because serum interferes with lipid metabolism, its effects on the cGMP pathway and lipid content in bovine COCs were examined. COCs were matured in medium containing fetal calf serum (FCS; 2% or 10%) or 0.4% bovine serum albumin (BSA; control). At both 2% and 10%, FCS decreased cGMP levels in COCs compared with BSA (0.64 and 1.04 vs 9.46 fmol per COC respectively; P<0.05) and decreased transcript levels of guanylate cyclase 1, soluble, beta 3 (GUCY1B3), whereas PDE5A levels were increased. FCS also affected the expression of genes related to lipolysis, increasing relative expression of perilipin 2 (PLIN2) and carnitine palmitoyltransferase 1B (CPT1B) in cumulus cells. Effects of FCS and cGMP on the lipid content of oocytes and embryos were evaluated by Nile red staining. COCs were matured with 10% FCS, FCS+10^-5 M sildenafil (SDF), a PDE5 inhibitor, or 0.4% BSA. The lipid content was increased in oocytes matured in FCS compared with BSA (fluorescence intensity 20.1 vs 17.61 respectively; P<0.05), whereas the lipid content in oocytes matured in FCS+SDF (fluorescence intensity 16.33) was similar to that in the BSA-treated group (P>0.05). In addition, lipid content was higher in embryos from oocytes matured with FCS than BSA (fluorescence intensity 31.12 vs 22.31 respectively; P<0.05), but was increased even further in the FCS+SDF-treated group (fluorescence intensity 40.35; P<0.05), possibly due to a compensatory mechanism during embryo culture without SDF for the reduction in lipid content during IVM. The present study provides, for the first time, evidence that the cGMP pathway may be involved in lipid metabolism in bovine COCs and that this pathway is affected by FCS.

The role of cGMP as a mediator of lipolysis in bovine oocytes and its effects on embryo development and cryopreservation

This study aimed to determine the influence of cyclic guanosine 3’5’-monophosphate (cGMP) and cGMP-dependent kinase (PKG) during in vitro maturation (IVM) on lipolysis-related parameters in bovine cumulus-oocyte complexes (COCs), and on embryo development and cryosurvival. COCs were matured with cGMP/PKG modulators and assessed for metaphase II rates (MII), cGMP levels, lipid content in oocytes (OO), transcript abundance for genes involved in lipolysis (ATGL) and lipid droplets (PLIN2) in cumulus cells (CC) and OO, and presence of phosphorylated (active) hormone sensitive lipase (HSL^ser563) in OO. Embryo development, lipid contents and survival to vitrification were also assessed. Phosphodiesterase 5 inhibition (PDE5; cGMP-hydrolyzing enzyme) with 10^-5M sildenafil (SDF) during 24 h IVM increased cGMP in COCs (56.9 vs 9.5 fMol/COC in untreated controls, p<0.05) and did not affect on maturation rate (84.3±6.4% MII). Fetal calf serum (FCS) in IVM medium decreased cGMP in COCs compared to bovine serum albumin (BSA) + SDF (19.6 vs 66.5 fMol/COC, respectively, p<0.05). FCS increased lipid content in OO (40.1 FI, p<0.05) compared to BSA (34.6 FI), while SDF decreased (29.8 and 29.6 FI, with BSA or FCS, respectively p<0.05). PKG inhibitor (KT5823) reversed this effect (38.9 FI, p<0.05). ATGL and PLIN2 transcripts were detected in CC and OO, but were affected by cGMP and PKG only in CC. HSL^ser563 was detected in OO matured with or without modulators. Reduced lipid content in embryos were observed only when SDF was added during IVM and IVC (27.6 FI) compared to its use in either or none of the culture periods (34.2 FI, p<0.05). Survival to vitrification was unaffected by SDF. In conclusion, cGMP and PKG are involved in lipolysis in OO and possibly in CC and embryos; serum negatively affects this pathway, contributing to lipid accumulation, and cGMP modulation may reduce lipid contents in oocytes and embryos, but without improving embryo cryotolerance.

Low serum concentration in bovine embryo culture enhances early blastocyst rates on Day-6 with quality traits in the expanded blastocyst stage similar to BSA-cultured embryos

In bovine, single in vitro embryo culture in protein-free medium from Day-6 to Day-7 leads to expanded blastocyst (XB) with improved pregnancy and birth rates after cryopreservation. Under these conditions, early blastocysts (EB) progress to the XB stage at higher rates than morulae (M). However, embryo production with BSA in culture prior to Day-6 leads to low EB rates. We investigated whether a very low FCS concentration (0.1%) in culture from Day-1 to Day-6 would improve EB rates and, subsequently, increase XB rates on Day-7 after single culture in protein-free medium. The quality of embryos produced was evaluated in terms of survival to cryopreservation, apoptosis percentage, lipid accumulation and transfer to recipients. On Day-6, EB rates from embryos cultured with FCS were higher than with BSA (P=0.022). On Day-7, XB rates were higher in embryos from Day-6 EB than from Day-6M, both with and without FCS (P<0.005). After vitrification/warming of Day-7 XB, 100% embryos survived at 24h in all treatments, and total cell number and apoptosis percentage were not affected by the presence of FCS or embryonic stage on Day-6. Cryopreserved and fresh embryos produced with FCS until Day-6, and then deprived of protein and cultured individually, led to pregnancies after ET. In conclusion, minute FCS concentration improves EB rates on Day-6 leading, after one-day single culture without protein, to more XBs. The quality of XB produced with FCS compares well with XB produced with BSA in terms of apoptosis, lipid accumulation and pregnancy.

Applying metabolomic analyses to the practice of embryology: physiology, development and assisted reproductive technology

The advent of metabolomics technology and its application to small samples has allowed us to non-invasively monitor the metabolic activity of embryos in a complex culture environment. The aim of this study was to apply metabolomics technology to the analysis of individual embryos from several species during in vitro development to gain an insight into the metabolomics pathways used by embryos and their relationship with embryo quality. Alanine is produced by both in vivo- and in vitro-derived human, murine, bovine and porcine embryos. Glutamine is also produced by the embryos of these four species, but only those produced in vitro. Across species, blastocysts significantly consumed amino acids from the culture medium, whereas glucose was not significantly taken up. There are significant differences in the metabolic profile of in vivo- compared with in vitro-produced embryos at the blastocyst stage. For example, in vitro-produced murine embryos consume arginine, asparagine, glutamate and proline, whereas in vivo-produced embryos do not. Human embryos produce more alanine, glutamate and glutamine, and consume less pyruvate, at the blastocyst compared with cleavage stages. Glucose was consumed by human blastocysts, but not at a high enough level to reach significance. Consumption of tyrosine by cleavage stage human embryos is indicative of blastocyst development, although tyrosine consumption is not predictive of blastocyst quality. Similarly, although in vivo-produced murine blastocysts consumed less aspartate, lactate, taurine and tyrosine than those produced in vitro, consumption of these four amino acids by in vitro-derived embryos with high octamer-binding transcription factor 4 (Oct4) expression, indicative of high quality, did not differ from those with low Oct4 expression. Further application of metabolomic technologies to studies of the consumption and/or production of metabolites from individual embryos in a complete culture medium could transform our understanding of embryo physiology and improve our ability to produce developmentally competent embryos in vitro.

Polydatin improves the developmental competence of bovine embryos in vitro via induction of sirtuin 1 (Sirt1)

The aim of the present study was to investigate the beneficial effect of polydatin (PD), the glycoside form of resveratrol, on embryo development in vitro. Oocytes were aspirated from ovaries of Korean Hanwoo cows and cultured until Day 8 in a humidified atmosphere of 5% CO2 in air at 38.5°C. Protein and gene expression levels were determined through confocal microscopy and reverse transcription–polymerase chain reaction respectively, whereas the number of total and apoptotic cells in Day 8 blastocysts was determined using Hoechst 33342 staining and terminal deoxyribonucleotidyl transferase-mediated dUTP–digoxigenin nick end-labelling. Of the different concentrations of PD (0.5, 1.0 and 2.0 µM) added to the IVM medium, only 1.0 µM PD significantly improved blastocyst development. Immunofluorescence analysis confirmed that protein levels of sirtuin 1 (Sirt1) increased significantly (P < 0.05) after PD treatment, whereas levels of reactive oxygen species (ROS) were significantly (P < 0.05) decreased, as evidenced by reductions in 8-oxoguanine immunoreactivity. Similarly, protein levels of nuclear factor (NF)-κB and cyclo-oxygenase (COX)-2  were significantly (P < 0.05) lower in the PD-treated group than in the control group. Treatment with 1.0 µM PD reduced gene expression of BCL2-associated X protein, inducible nitric oxide synthase, COX2 and Nfkb, but increased the expression of Sirt1, supporting the immunofluorescence data. PD possesses antioxidant activity and is useful for embryo development in vitro. We conclude that supplementation of IVM medium with PD improves embryo developmental competence via Sirt1.

Cell apoptosis and lipid content of in vitro-produced, vitrified bovine embryos treated with forskolin

The presence of fetal calf serum in culture medium influences embryo quality, causing a reduction in postcryopreservation survival. Forskolin has been used to induce lipolysis and increase cryotolerance, functioning as an activator of adenylate cyclase and elevating cAMP levels. In the present experiment, bovine zygotes were cultured in synthetic oviduct fluid with amino acid plus 2.5% fetal calf serum for 6 days, when forskolin was added in three concentrations: 2.5, 5, and 10 μM. Treatment with forskolin lasted for 24 hours. Blastocyst formation rate, quantification of lipid granules, total cell numbers, and apoptosis rate were evaluated. In a second assessment, embryos were vitrified, and warming, re-expansion rate, total cell numbers, and apoptosis rate were also evaluated. There was no difference due to forskolin in blastocyst formation or re-expansion rates after vitrification. However, lipid measurements were lower (control: 136.8 and F 2.5 μM: 128.5; P < 0.05), and number of cells per embryo higher (control: 140.1 and F 2.5 μM: 173.5; P < 0.05) than controls for 2.5 μM forskolin but not for higher forskolin concentrations. The number of intact cells per embryo was higher, and the rate of apoptosis was lower in fresh than in vitrified embryos (number of cells of warmed embryos, control: 104.1, F 2.5 μM: 101.3, F 5 μM: 115.4, F 10 μM: 95.1; apoptotic of fresh cells, control: 12.1%, F 2.5 μM: 16.7%, F 5 μM: 11.1%, F 10 μM: 14.2%; and apoptotic warmed embryos, control: 22.3%, F 2.5 μM: 37.3%, F 5 μM: 33.2%, F 10 μM: 30.3%; P < 0.05). It was concluded that forskolin is an effective lipolytic agent even at low concentrations, leading to formation of blastocysts with a comparatively larger number of cells.

Direct and Osmolarity-Dependent Effects of Glycine on Preimplantation Bovine Embryos

Concentrations of glycine (Gly) in embryo culture media are often lower (~0.1 mM) than those in oviductal or uterine fluids (≥1.2 mM). The objective of this study was to determine direct and osmolarity-dependent effects of physiological concentrations of Gly on blastocyst formation and hatching, cell allocation to the trophectoderm (TE) and inner cell mass (ICM), and metabolic activity of bovine embryos. In experiment 1, zygotes were cultured with 100 or 120 mM NaCl and 0 or 1 mM Gly for the first 72 h of culture. Blastocyst formation and hatching were improved (P<0.05) when embryos were cultured with 100 compared to 120 mM NaCl. Inclusion of 1 mM Gly improved (P<0.05) blastocyst formation compared to 0 mM Gly, but this effect was only significant (P<0.05) for embryos cultured with 120 mM NaCl, suggesting bovine embryos can utilize Gly as an osmolyte. In experiment 2, embryos were cultured with 0.1, 1.1, 2.1, or 4.1 mM Gly (100 mM NaCl) for the final 96 h of culture. Blastocyst development was not affected (P>0.05) by Gly, but hatching (0.1 mM Gly, 18.2%) was improved (P<0.05) when embryos were cultured with 1.1 (31.4%) or 2.1 (29.4%) mM Gly. Blastocyst, TE, and ICM cell numbers were not affected (P>0.05) by Gly in either experiment. Blastocysts produced alanine, glutamine, pyruvate, and urea and consumed aspartate, but this metabolic profile was not affected (P>0.05) by Gly. In conclusion, Gly (1.0 mM) improves the development of both early and late stage embryos, but beneficial effects are more pronounced for early embryos exposed to elevated osmolarity.

Fateful triad of reactive oxygen species, mitochondrial dysfunction and lipid accumulation is associated with expression outline of the AMP-activated protein kinase pathway in bovine blastocysts

Low cryotolerance is considered as the major drawback of in vitro-produced bovine embryos and is frequently associated with a triad encompassing increased cytoplasmic lipid accumulation, enhanced levels of reactive oxygen species (ROS) and mitochondrial dysfunction. The aim of the present study was to explore the role of the AMP-activated protein kinase (AMPK) pathway in the process resulting such phenotypes. Comparative analysis under different environmental conditions revealed downregulation of AMP-activated protein kinase cytalytic subunit 1alpha (AMPKA1), peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC1A) and carnitine palmitoyltransferase 1 (CPT1) genes and upregulation of acetyl-CoA carboxylase α (ACC). In contrast, the presence of fatty acids within the culture medium resulted in a distinct molecular profile in the embryo associated with enhanced levels of ROS, mitochondrial dysfunction and elevated lipid accumulation in bovine embryos. Because AMPKA1 regulates PGC1A, CPT1 and ACC, the results of the present study reveal that AMPK in active its form is the key enzyme promoting lipolysis. Because AMPK1 activity is, in turn, controlled by the AMP : ATP ratio, it is possible to speculate that excessive uptake of exogenous free fatty acids could increase cellular ATP levels as a result of the disturbed β-oxidation of these external fatty acids and could therefore bypass that molecular feedback mechanism. Subsequently, this condition would cause enhanced generation of ROS, which negatively affect mitochondrial activity. Both enhanced generation of ROS and low mitochondrial activity are suggested to enhance the accumulation of lipids in bovine embryos.

Preliminary trials of a specific gravity technique in the determination of early embryo growth potential†

STUDY QUESTION

Can a modified specific gravity technique be used to distinguish viable from nonviable embryos?

SUMMARY ANSWER

Preliminary data suggests a modified specific gravity technique can be used to determine embryo viability and potential for future development.

WHAT IS KNOWN ALREADY

Single embryo transfer (SET) is fast becoming the standard of practice. However, there is currently no reliable method to ensure development of the embryo transferred.

STUDY DESIGN, SIZE, DURATION

A preliminary, animal-based in vitro study of specific gravity as a predictor of embryo development using a mouse model.

PARTICIPANTS/MATERIALS, SETTING, METHODS

After a brief study to demonstrate embryo recovery, experiments were conducted to assess the ability of the specific gravity system (SGS) to distinguish between viable and nonviable embryos. In the first study, 1-cell mouse embryos were exposed to the SGS with or without previous exposure to an extreme heat source (60°C); measurements were repeated daily for 5 days. In the second experiment, larger pools of 1-cell embryos were either placed directly in culture or passed through the SGS and then placed in culture and monitored for 4 days.

MAIN RESULTS AND THE ROLE OF CHANCE

In the first experiment, viable embryos demonstrated a predictable pattern of descent time over the first 48 h of development (similar to previous experience with the SGS), while embryos that were heat killed demonstrated significantly altered drop patterns (P < 0.001); first descending faster. In the second experiment, average descent times were different for embryos that stalled early versus those that developed to blastocyst (P < 0.001). Interestingly, more embryos dropped through the SGS developed to blastocyst than the culture control (P < 0.01).

LIMITATIONS, REASONS FOR CAUTION

As this is a preliminary report of the SGS technology determining viability, a larger embryo population will be needed. Further, the current in vitro study will need to be followed by fecundity studies prior to application to a human population.

WIDER IMPLICATIONS OF THE FINDINGS

If proven, the SGS would provide a noninvasive means of assessing embryos prior to transfer after assisted reproductive technologies procedures, thereby improving fecundity and allowing more reliable SET.

STUDY FUNDING/COMPETING INTERESTS

The authors gratefully acknowledge the funding support of the U.S. Jersey Association, the Laura W. Bush Institute for Women's Health and a Howard Hughes Medical Institute grant through the Undergraduate Science Education Program to Texas Tech University. None of the authors have any conflict of interest regarding this work.

TRIAL REGISTRATION NUMBER

none.

Bovine embryo survival under oxidative-stress conditions is associated with activity of the NRF2-mediated oxidative-stress-response pathway

In present study, we sought to examine the ability of preimplantation bovine embryos to activate the NF-E2-related factor 2 (NRF2)-mediated oxidative-stress response under an oxidative stress environment. In vitro 2-, 4-, 8-, 16-cell-, and blastocyst-stage embryos were cultured under low (5%) or high (20%) oxygen levels. The expression of NRF2, KEAP1 (NRF2 inhibitor), antioxidants downstream of NRF2, and genes associated with embryo metabolism were analyzed between the embryo groups using real-time quantitative PCR. NRF2 and KEAP1 protein abundance, mitochondrial activity, and accumulation of reactive oxygen species (ROS) were also investigated in blastocysts of varying competence that were derived from high- or low-oxygen levels. The expression levels of NRF2 and its downstream antioxidant genes were higher in 8-cell, 16-cell, and blastocyst stages under high oxygen tension, whereas KEAP1 expression was down-regulated under the same conditions. Higher expression of NRF2 and lower ROS levels were detected in early (competent) blastocysts compared to their late (noncompetent) counterparts in both oxygen-tension groups. Similarly, higher levels of active nuclear NRF2 protein were detected in competent blastocysts compared to their noncompetent counterparts. Thus, the survival and developmental competence of embryos cultured under oxidative stress are associated with activity of the NRF2-mediated oxidative stress response pathway during bovine pre-implantation embryo development.

Differential expression of selected candidate genes in bovine embryos produced in vitro and cultured with chemicals modulating lipid metabolism

Lipid accumulated in embryos produced in vitro has been linked to reductions in both quality and postcryopreservation viability. Therefore, the objective of the present study was to investigate the influence of lipid-reducing chemicals on embryo development, quality, and postcryopreservation viability, in addition to expression profiles of selected lipid metabolism-regulating genes. Bovine cumulus-oocyte complexes were matured and fertilized in vitro; eight-cell stage embryos were cultured in IVC medium supplemented with phenazine ethosulfate (PES), L-carnitine (LC), PES + LC, or no supplementation (control). Culturing embryos in medium with LC increased (P < 0.05) blastocyst rate (38.8%) compared with the other groups (control = 28.1%, PES = 27.1%, PES + LC = 26.3%). Embryos cultured with supplements had greater total cell number and fewer apoptotic cells than the control. Cytoplasmic lipid content was reduced, whereas mitochondria density was increased in embryos treated with culture supplements; this was linked to altered expression profiles of selected genes regulating lipid metabolism. For example, transcript abundance of transmembrane lipid gene (SGPP1) was greater in LC- and PES-treated embryos, and they had increased postcryopreservation hatching ability (indicative of embryo cryotolerance). In conclusion, the two lipid metabolism regulators added to the culture media had improved embryo quality and cryotolerance, but embryo development rate and downstream lipid metabolism-regulating genes were more influenced with LC supplementation.

Lipid droplet analysis using in vitro bovine oocytes and embryos

The aim of this study was to quantify the content of lipid droplets in bovine oocytes and embryos from Bos indicus (Bi), Bos taurus (Bt) and Bos indicus × Bos taurus (Bi × Bt). Oocytes were aspirated post-mortem and subjected to in vitro maturation, in vitro fertilization and in vitro development; the medium employed at each stage (TCM-199, TALP, SOF) was supplemented with (i) serum replacement (SR), (ii) foetal calf serum (FCS) or (iii) oestrous cow serum (ECS). The structure and distribution of the lipid droplets were established using electron microscopy, but were quantified using an optical microscope on semi-fine toluidine blue-stained sections. The highest percentage of embryos corresponded to those produced with FCS and ECS, which differed from embryos generated with SR (p < 0.05). The highest percentage of morulae and the lowest percentage of blastocysts were obtained with the SR supplement (p < 0.05). The oocytes cultured in FCS demonstrated a higher number of lipid droplets compared to those cultured in SR and ECS (p < 0.05). Less accumulation of lipids was observed in embryos supplemented with SR. The lowest and highest numbers of lipid droplets in oocytes corresponded to the Bi and Bt strain, respectively. The lowest amount of lipid droplets in embryos was observed in Bi (p < 0.05). In conclusion, supplementation of the in vitro development culture medium (synthetic oviduct fluid) with a synthetic substitute serum produced similar results in terms of embryo development compared to those obtained with FCS, but a decreased degree of lipid droplet accumulation was observed in the in vitro-cultured embryos.

Oocyte cryopreservation: searching for novel improvement strategies

PURPOSE

To highlight emerging techniques aimed at improving oocyte cryopreservation.

METHODS

Review of available and relevant literature through Pubmed and Medline searches.

RESULTS

Oocyte cryopreservation is an increasingly common procedure utilized for assisted reproduction and may benefit several patient populations. Therefore, improving efficiency is paramount in realizing the tremendous promise of this approach. However, in addition to numerous studies looking to improve oocyte cryopreservation efficacy via examination of variables involved with protocol methodology, such as type/concentration of cryoprotectant (CPA), type of storage device, or cooling/warming rates, there are more novel approaches for improvement. These alternate approaches include utilizing different the stages of oocytes, examining alteration of basal media and buffer composition, optimizing CPA exchange protocols and device loading through use of automated technology, as well as examination/manipulation of oocyte cellular composition to improve cryotolerance. Finally, elucidating more accurate or insightful indicators of "success" is crucial for continued improvement of oocyte cryopreservation.

CONCLUSION

Oocyte cryopreservation has improved dramatically in recent years and is receiving widespread clinical use. Novel approaches to further improve success, as well as improved methods to assess this success will aid in continued improvement.

Phosphatidylcholine and sphingomyelin profiles vary in Bos taurus indicus and Bos taurus taurus in vitro- and in vivo-produced blastocysts

Lipid droplets, subspecies (Bos taurus indicus vs. Bos taurus taurus), and in vitro culture are known to influence cryopreservation of bovine embryos. Limited information is available regarding differences in membrane lipids in embryo, such as phosphatidylcholines (PC) and sphingomyelins (SM). The objective of the present study was to compare the profiles of several PC and SM species and relate this information to cytoplasmic lipid levels present in Nellore (B. taurus indicus) and Simmental (B. taurus taurus) blastocysts produced in vitro (IVP) or in vivo (ET). Simmental and IVP embryos had more cytoplasmic lipid content than Nellore and ET embryos (n = 30). Blastocysts were submitted to matrix-assisted laser desorption/ionization mass spectrometry. Differences in the PC profile were addressed by principal component analysis. The lipid species with PC (32:1) and PC (34:1) had higher ion abundances in Nellore embryos, whereas PC (34:2) was higher in Simmental embryos. IVP embryos had less abundant ions of PC (32:1), PC (34:2), and PC (36:5) compared to ET embryos. Moreover, ion abundance of PC (32:0) was higher in both Nellore and Simmental IVP embryos compared to ET embryos. Therefore, mass spectrometry profiles of PC and SM species significantly differ with regard to unsaturation level and carbon chain composition in bovine blastocysts due to subspecies and in vitro culture conditions. Because PC abundances of Nellore and Simmental embryos were distinct (34:1 vs. 34:2), as were those of IVP and ET embryos (32:0 vs. 36:5), they are potential markers of postcryopreservation embryonic survival.

Forskolin effect on the cryosurvival of in vitro-produced bovine embryos in the presence or absence of fetal calf serum

The objective of this study was to assess the viability and cryotolerance of zebu embryos produced in vitro with or without the addition of fetal calf serum (FCS) and forskolin (F). Embryos produced in vivo were used as a control. Presumptive zygotes were cultured in modified synthetic oviductal fluid supplemented with amino acids (SOFaa), bovine serum albumin (BSA) and with (2.5%) or without (0%) FCS. On day 6 of growth, the embryos from each group were divided into treatments with or without 10 μM F to induce embryonic lipolysis, comprising a total of four experimental groups: 2.5% FCS, 0% FCS, 2.5% + F and 0% + F. For vitrification, embryos were exposed to vitrification solution 1 (5 M EG (ethylene glycol)) for 3 min and then transferred to vitrification solution 2 (7 M EG, 0.5 M galactose solution and 18% (w/v) Ficoll 70) before being introduced to liquid nitrogen. The presence of FCS in the culture medium resulted in the production of embryos with a similar rate of damaged cells compared with in vivo-produced embryos. After vitrification, the 2.5% FCS group had a significantly higher rate of damaged cells when compared with the other groups (P < 0.05). The results of this experiment indicated that the omission of FCS and the addition of forskolin do not have deleterious effect on embryo production rates. In addition, embryos produced in the presence of FCS had greater sensitivity to cryopreservation, but this effect was reversed when forskolin was added to the medium, which improved embryo survival without affecting embryo development and quality after vitrification.

Crucial surviving aspects for vitrified in vitro-produced bovine embryos

The objective of the present study was to correlate some parameters (cleavage, blastocyst production, quality degree score, total cell number, fresh apoptosis and lipid content) with embryo survival after cryopreservation. A total of 1727 in vitro-produced bovine blastocysts were used to establish the parameters (mean ± standard error of the mean (SEM)) for cleavage (85.6 ± 0.8), blastocyst production (39.9 ± 1.4), quality degree score (1.6 ± 0.1), total cell number (140.1 ± 2.9), fresh apoptosis (20.8 ± 1.1) and lipid content (21.3 ± 0.8 droplets). On the same way 1316 blastocysts were vitrified for the determination of post-cryopreservation embryo survival (49.4 ± 1.9). Fresh apoptosis rate and total lipid droplets value were correlated (P < 0.05) with embryo survival after cryopreservation (r = 0.91 and r = 0.59; respectively). However, cleavage, blastocyst production, quality degree score and total cell number were not correlated (P > 0.05) with embryo cryotolerance (r = 0.23, r = 0.38, r = 0.22 and r = 0.28; respectively). Therefore, the increased lipid content was moderately correlated with apoptosis in vitrified blastocysts. On the other hand, increased apoptosis in fresh blastocysts was strongly correlated with apoptosis in vitrified blastocysts, which indicated that the apoptosis rate in fresh embryos was a better parameter than the lipid content to predict post-vitrification embryo survival.

Differential gene expression profile in bovine blastocysts resulting from hyperglycemia exposure during early cleavage stages

To understand the compromised survival of embryos derived from assisted reproductive techniques, transcriptome survey of early embryonic development has shown the impact of in vitro culture environment on gene expression in bovine or other living species. However, how the differentially expressed genes translate into developmentally compromised embryos is unresolved. We therefore aimed to characterize transcriptomic markers expressed by bovine blastocysts cultured in conditions that are known to impair embryo development. As increasing glucose concentrations has been shown to be stressful for early cleavage stages of mammalian embryos and to decrease subsequent blastocyst survival, in vitro-matured/fertilized bovine zygotes were cultured in control (0.2 mM) or high-glucose (5 mM) conditions until the 8- to 16-cell stage, and then transferred to control media until they reached the blastocyst stage. The concentration of 5 mM glucose was chosen as a stress treatment because there was a significant effect on blastocyst rate without the treatment's being lethal as with 10 mM. Microarray analysis revealed gene expression differences unrelated to embryo sex or hatching. Overrepresented processes among differentially expressed genes in treated blastocysts were extracellular matrix signalling, calcium signaling, and energy metabolism. On a pathophysiological level, higher glucose treatment impacts pathways associated with diabetes and tumorigenesis through genes controlling the Warburg effect, i.e., emphasis on use of anaerobic glycolysis rather than oxidative phosphorylation. These results allowed us to conclude that disruption of in vitro preattachment development is concomitant with gene expression modifications involved in metabolic control.

Inclusion of bovine lipoproteins and the vitamin E analogue, Trolox, during in vitro culture of bovine embryos changes both embryo and fetal development

This experiment investigated effects of lipoproteins and Trolox (vitamin E analogue) on bovine embryo and fetal development. The treatments were: in vitro culture (IVC) in synthetic oviducal fluid alone (SOF); with bovine lipoproteins (2% v/v; SOFLP); with Trolox (100 μM; SOFT); and with lipoproteins and Trolox (SOFLPT). In vitro culture with lipoproteins increased fatty acid content of blastocysts (P < 0.001) whereas inclusion of Trolox had no effect (P > 0.05). Whereas lipoproteins reduced zygote development to blastocysts (P = 0.03), Trolox facilitated increased development (P < 0.001) and counteracted the reduction observed with lipoproteins (interaction, P = 0.009). Lipoproteins also compromised (P < 0.001) but presence of Trolox (P > 0.05) had no effect on blastocyst morphological grade. Pregnancy rates resulting from synchronous transfer of IVP embryos were not affected by IVC treatment. At Day 70 of pregnancy, compared with SOF, fetal weight was lower in SOFLP but not SOFLPT (interaction, P < 0.001). Liver weight (g kg–1 fetal weight) was greater (P = 0.03) in treatments containing Trolox. Placentome numbers were greater in SOF and SOFLPT compared with SOFLP and SOFT (interaction, P = 0.002); superior embryo grades were also associated with increased numbers of placentomes (P = 0.024). In conclusion, the interactive effects of lipoprotein and Trolox inclusion on in vitro embryo development were also evident in fetal development at Day 70.

Effect of energy source during culture on in vitro embryo development, resistance to cryopreservation and sex ratio

The aim of this work was to evaluate whether minimizing the glucose concentration during culture or replacing the hexose with other energy substrates and/or embryotrophic compounds would affect the in vitro development, the resistance to cryopreservation and the sex ratio of bovine embryos. In vitro matured and fertilized oocytes were randomly assigned to 4 groups for in vitro culture, that differed in the energy substrates included: group A) 1.5 mM glucose, as in standard SOF; group B) 0.15 mM glucose; group C) 0.125 mM G3P, in the presence of 0.15 mM glucose and group D) 0.34 mM citrate, in combination with 2.77 mM myo-inositol. Blastocysts were evaluated on day 7, then vitrified by cryotop in 16.5% DMSO, 16.5% EG and 0.5 M sucrose and warmed in decreasing concentration of sucrose (0.25 to 0.15 M sucrose). The survival rates were assessed after 24 h in vitro culture. Finally, the blastocysts produced were sexed by PCR. An increased blastocyst rate was recorded in groups B, C and D, i.e., when glucose concentration was reduced, compared to group A (28.2, 41.0, 35.7 and 35.8, respectively in groups A, B, C and D; P < 0.01). However, the embryos cultured in group D showed the slowest developmental speed, indicated by the lowest percentage of advanced stage-embryos (expanded and hatched blastocysts) out of the total blastocysts (56.1, 45.8, 56.9 and 31.8 %, respectively in groups A, B, C and D; P < 0.01). Furthermore, survival rates after 24 h culture of vitrified-warmed blastocysts also decreased in group D (73.3, 73.1, 71.4 and 58.4%, respectively in groups A, B, C and D; P < 0.01). Interestingly, in group D a higher percentage of female embryos was obtained compared to group A, with intermediate values in groups B and C (45.6, 53.4, 50.0 and 61.5%, respectively in groups A, B, C and D; P < 0.05). In conclusion, it was demonstrated that the energy substrate during in vitro culture affects both the production and the viability of blastocysts. Furthermore, manipulating the metabolic profile of embryos during in vitro culture may have an impact on sex ratio.

Current progress in oocyte and embryo cryopreservation by slow freezing and vitrification

Preservation of female genetics is currently done primarily by means of oocyte and embryo cryopreservation. The field has seen much progress during its four-decade history, progress driven predominantly by research in humans, cows, and mice. Two basic cryopreservation techniques rule the field – controlled-rate freezing, the first to be developed, and vitrification, which, in recent years, has gained a foothold. While much progress has been achieved in human medicine, the cattle industry, and in laboratory animals, this is far from being the case for most other mammals and even less so for other vertebrates. The major strides and obstacles in human and other vertebrate oocyte and embryo cryopreservation will be reviewed here.

Cross-validation of techniques for measuring lipid content of bovine oocytes and blastocysts

The main objective was to test and validate a fluorescence approach to quantify lipid content of individual bovine oocytes and blastocysts. For Experiment 1, denuded oocytes were evaluated, as well as in vitro-produced blastocysts in a factorial design: cows versus feedlot heifers; three additives during Days 2.5-7.5 of culture (Control; 10% FCS; 0.3 μM phenazine ethosulfate (PES), an electron acceptor that oxidizes NADPH); and two blastocyst stages (early versus expanded). All blastocysts were graded subjectively for darkness (1 = clear … 4 = dark). In Experiment 2, denuded oocytes were used to measure lipid content in a factorial design of: cows versus heifers and four subjective darkness grades (1 = clear … 4 = dark). To quantify lipids, oocytes and 7.5 d blastocysts were fixed and then stained with 1 μg/mL Nile Red dye in mPBS overnight. A digital photograph of the equatorial part of the oocyte and embryo was taken at 200×, and fluorescence intensity (Arbitrary Fluorescence Units, AFU) was measured with Image Pro software. Reverse images of the same photographs were used to count numbers of cytoplasmic lipid droplets of various sizes (LC). The linear regression equation of LC with AFU in oocytes had an r(2) = 0.84, and for blastocysts r(2) = 0.91. The LC and AFU also had similar coefficients of variation from the ANOVA for blastocysts (38 vs 44%, respectively). Treatment differences were of similar magnitude with both procedures: lipid content in oocytes and blastocysts from heifers and cows was similar (P > 0.1); PES reduced lipid accumulation, and FCS increased it relative to the Control for AFU (18.6 vs 46.6 vs 36.9 units, respectively), and LC (1763 vs 4081 vs 3310, respectively; all, P < 0.01). Early blastocysts resulted in more lipid accumulation per unit area than expanded ones based on AFU (41.5 vs 26.6) and LC (3519 vs 2583; both P <0.01). There was a strong relationship (P < 0.01) between subjective oocyte and blastocyst darkness and lipid content. The less labor intensive fluorescence staining was a reliable technique for quantifying lipid droplets in oocytes and blastocysts.

Effect of timing of development on total cell number and expression profile of HSP-70.1 and GLUT-1 in buffalo (Bubalus bubalis) oocytes and preimplantation embryos produced in vitro

The present study was designed to compare the expression profile of two developmentally important genes (HSP-70.1 and GLUT-1) and TCN (total cell number) count in fast (group A) and slow (group B) cleaved buffalo embryos to access their in vitro developmental competence. Buffalo COCs (cumulus oocyte complexes) were collected from local abattoir ovaries and subjected to in vitro maturation in: TCM-199 supplemented with 10% FBS (fetal bovine serum), BSA (3 mg/ml), sodium pyruvate (0.25 mM) and 20 ng/ml EGF (epidermal growth factor) at 38.5 degrees C under 5% CO2. In vitro derived embryos were collected at 4-8, 8-16 cell, morula and blastocyst stages at specific time points for gene expression analysis and total cell count. A semiquantitative RT-PCR (reverse transcriptase-PCR) assay was used to determine the HSP-70.1 and GLUT-1 transcripts. Results showed that developmental competence and TCN count in fast (group A)-cleaving embryos was significantly (P<0.05) higher than in the slow group (group B). The gene transcript of HSP-70.1 and GLUT-1 was expressed in oocytes (immature and mature) and throughout the embryonic developmental stages in the fast group (group A), while in the slow (group B) cleaving embryos, the expression of HSP-70.1 was absent in all the embryonic developmental stages, and expression of GLUT-1 was absent after 8-16 cell stage. In conclusion, TCN count and expression profile of HSP-70.1 and GLUT-1 genes in buffalo embryos are different taking into account the cleavage rate. Quality of such embryos for research purposes, TCN and expression profiling of developmentally important genes should be employed to optimize the in vitro culture system to produce superior quality of embryos.

Single embryo and oocyte lipid fingerprinting by mass spectrometry

Methods used for lipid analysis in embryos and oocytes usually involve selective lipid extraction from a pool of many samples followed by chemical manipulation, separation and characterization of individual components by chromatographic techniques. Herein we report direct analysis by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) of single and intact embryos or oocytes from various species. Biological samples were simply moisturized with the matrix solution and characteristic lipid (represented by phosphatidylcholines, sphingomyelins and triacylglycerols) profiles were obtained via MALDI-MS. As representative examples, human, bovine, sheep and fish oocytes, as well as bovine and insect embryos were analyzed. MALDI-MS is shown to be capable of providing characteristic lipid profiles of gametes and embryos and also to respond to modifications due to developmental stages and in vitro culture conditions of bovine embryos. Investigation in developmental biology of the biological roles of structural and reserve lipids in embryos and oocytes should therefore benefit from these rapid MALDI-MS profiles from single and intact species.