Haploid androgenetic development of bovine embryos reveals imbalanced WNT signaling and impaired cell fate differentiation†.

Haploid embryos have contributed significantly to our understanding of the role of parental genomes in development and can be applied to important biotechnology for human and animal species. However, development to the blastocyst stage is severely hindered in bovine haploid androgenetic embryos (hAE). To further our understanding of such developmental arrest, we performed a comprehensive comparison of the transcriptomic profile of morula-stage embryos, which were validated by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) of transcripts associated with differentiation in haploid and biparental embryos. Among numerous disturbances, results showed that pluripotency pathways, especially the wingless-related integration site (WNT) signaling, were particularly unbalanced in hAE. Moreover, transcript levels of KLF4, NANOG, POU5F1, SOX2, CDX2, CTNNBL1, AXIN2, and GSK3B were noticeably altered in hAE, suggesting disturbance of pluripotency and canonical WNT pathways. To evaluate the role of WNT on hAE competence, we exposed early Day-5 morula stage embryos to the GSK3B inhibitor CHIR99021. Although no alterations were observed in pluripotency and WNT-related transcripts, exposure to CHIR99021 improved their ability to reach the blastocysts stage, confirming the importance of the WNT pathway in the developmental outcome of bovine hAE.

Characterization of histone lysine ß-hydroxybutyrylation in bovine tissues, cells, and cumulus-oocyte complexes.

Besides their canonical roles as energy sources, short-chain fatty acids act as metabolic regulators of gene expression through histone posttranslational modifications. Ketone body ß-hydroxybutyrate (BHB) causes a novel epigenetic modification, histone lysine ß-hydroxybutyrylation (Kbhb), which is associated with genes upregulated in starvation-responsive metabolic pathways. Dairy cows increase BHB in early lactation, and the effects of this increase on cellular epigenomes are unknown. We searched for and identified that Kbhb is present in bovine tissues in vivo and confirmed that this epigenetic mark is responsive to BHB in bovine and human fibroblasts cultured in vitro in a dose-dependent manner. Maturation of cumulus-oocyte complexes with high concentrations of BHB did not affect the competence to complete meiotic maturation or to develop until the blastocyst stage. BHB treatment strongly induced H3K9bhb in cumulus cells, but faintly in oocytes. RNA-seq analysis in cumulus cells indicated that BHB treatment altered the expression of 345 genes. The downregulated genes were mainly involved in glycolysis and ribosome assembly pathways, while the upregulated genes were involved in mitochondrial metabolism and oocyte development. The genes and pathways altered by BHB will provide entry points to carry out functional experiments aiming to mitigate metabolic disorders and improve fertility in cattle.

Small extracellular vesicles derived from in vivo- or in vitro-produced bovine blastocysts have different miRNAs profiles-Implications for embryo-maternal recognition.

In vivo- and in vitro-produced bovine embryos have different metabolic profiles and differences in gene transcription patterns. These embryos also have a distinct ability to establish and sustain early pregnancies. Small extracellular vesicles (sEVs) are secreted by embryos and carry bioactive molecules, such as miRNAs. We hypothesize that in vivo or in vitro-produced bovine hatched blastocysts on Day 9 and the sEVs secreted by them have different miRNA profiles. To address this hypothesis, embryos of both groups were placed in in vitro culture on Day 7. After 48 h, hatched embryos and hatched embryo-conditioned media (eCM) of both groups were collected. A total of 210 miRNAs were detected in embryos of both groups, of these 6 miRNAs were downregulated, while 7 miRNAs were upregulated in vitro group when compared to in vivo group. sEVs were isolated from eCM to determine miRNA profile. A total of 106 miRNAs were detected in both groups, including 14 miRNAs upregulated in sEVs from in vivo-eCM, and 2 miRNAs upregulated in sEVs from in vitro-eCM. These miRNAs express in embryos and sEVs secreted by them regulate early embryonic developmental and endometrial pathways, which can modify embryo-maternal communication during early pregnancy and consequently affect pregnancy establishment.

Mitofusin 1 is required for oocyte growth and communication with follicular somatic cells.

Mitochondrial function, largely regulated by the dynamics of this organelle, is inextricably linked to the oocyte health. In comparison with most somatic cells, mitochondria in oocytes are smaller and rounder in appearance, suggesting limited fusion. The functional implications of this distinct morphology, and how changes in the mitochondrial shape translate to mitochondrial function in oogenesis is little understood. We, therefore, asked whether the pro-fusion proteins mitofusins 1 (MFN1) and 2 (MFN2) are required for the oocyte development. Here we show that oocyte-specific deletion of Mfn1, but not Mfn2, prevents the oocyte growth and ovulation due to a block in folliculogenesis. We pinpoint the loss of oocyte growth and ovulation to impaired PI3K-Akt signaling and disrupted oocyte-somatic cell communication. In support, the double loss of Mfn1 and Mfn2 partially rescues the impaired PI3K-Akt signaling and defects in oocyte development secondary to the single loss of Mfn1. Together, this work demonstrates that the mitochondrial function influences the cellular signaling during the oocyte development, and highlights the importance of distinct, nonredundant roles of MFN1 and MFN2 in oogenesis.

Mice born to females with oocyte-specific deletion of mitofusin 2 have increased weight gain and impaired glucose homeostasis.

Offspring born to obese and diabetic mothers are prone to metabolic diseases, a phenotype that has been linked to mitochondrial dysfunction and endoplasmic reticulum (ER) stress in oocytes. In addition, metabolic diseases impact the architecture and function of mitochondria-ER contact sites (MERCs), changes which associate with mitofusin 2 (MFN2) repression in muscle, liver and hypothalamic neurons. MFN2 is a potent modulator of mitochondrial metabolism and insulin signaling, with a key role in mitochondrial dynamics and tethering with the ER. Here, we investigated whether offspring born to mice with MFN2-deficient oocytes are prone to obesity and diabetes. Deletion of Mfn2 in oocytes resulted in a profound transcriptomic change, with evidence of impaired mitochondrial and ER function. Moreover, offspring born to females with oocyte-specific deletion of Mfn2 presented increased weight gain and glucose intolerance. This abnormal phenotype was linked to decreased insulinemia and defective insulin signaling, but not mitochondrial and ER defects in offspring liver and skeletal muscle. In conclusion, this study suggests a link between disrupted mitochondrial/ER function in oocytes and increased risk of metabolic diseases in the progeny. Future studies should determine whether MERC architecture and function are altered in oocytes from obese females, which might contribute toward transgenerational transmission of metabolic diseases.

Cytokines in the grass, a lesson learnt: Measuring cytokines in plasma using multiple reaction monitoring mass spectrometry.

RATIONALE: Cytokines are cell regulatory molecules of high importance as indicators for homeostasis and pathology in many species. The current method to measure cytokines in body fluids is reagent dependent, requiring highly specific paired antibodies. METHODS: A liquid chromatography/multiple reaction monitoring mass spectrometry (LC/MRM-MS)-based approach was developed to simultaneously establish the limits of detection (LODs) and quantification (LOQs) for recombinant cytokines IL-1ß, IL-6, IFNγ and TNFα as pure standards and in bovine sera. All experimental LC/MRM-MS data are available at CSIRO Data Access Portal repository under identifier doi.org/10.25919/5de8a0232a862. RESULTS: The present method enabled LODs and LOQs as low as 1.05 and 1.12 fmol/µL in the experiment comprised of pure standards. Comparable results were obtained in the experiment where digested cytokines were mixed with pre-digested sera proteins. The intrinsic matrix effects were evident when intact cytokines were co-digested within undiluted and undigested sera decreasing the ability to detect and quantify cytokines by 10,000-fold compared with pure standards and pre-digested sera. CONCLUSIONS: The developed LC/MRM-MS method provided insights into the difficulties in detecting the target peptides when embedded in complex matrices. Nonetheless, the method may potentially be readily applied in biomarker-focused research interrogating fluids of lesser complexity such as synovial fluid, cerebrospinal fluid and tissue culture media.

In vitro maturation impacts cumulus-oocyte complex metabolism and stress in cattle.

The influence of in vitro maturation (IVM) in oocytes is still not totally understood. The aim of this study was to determine the influence of IVM on the metabolism and homeostasis of bovine cumulus-oocyte complexes. In the present study, we demonstrated that IVM leads to accumulation of neutral lipids associated with differential levels of the mono-, di- and triacylglycerols in both cumulus cells and oocytes. We observed that in vitro-matured oocytes exhibited decreased glutathione and reactive oxygen species levels and a lower ATP/ADP ratio when compared to in vivo-matured oocytes, with no significant differences in metabolism and stress-related mRNA or miRNA levels. Moreover, in addition to an increase in lipids in in vitro-matured cumulus cells, fatty acid synthesis and accumulation as well as glycolysis pathway genes were upregulated, whereas those affiliated with the ß-oxidation pathway were decreased. Our gene expression data in cumulus cells suggest the disruption of endoplasmic reticulum stress, apoptosis and cellular stress response pathways during IVM. Furthermore, a total of 19 miRNAs were significantly altered by the maturation process in cumulus cells. These results indicate some new negative influences of the in vitro system in cumulus-oocyte complexes, demonstrating the occurrence of functional disruption in lipid metabolism and stress pathways and showing evidences suggesting the occurrence of altered mitochondrial activity and energy metabolism during IVM, with a massive dysregulation of the corresponding transcripts in the surrounding cumulus cells.

Antioxidant responses and deregulation of epigenetic writers and erasers link oxidative stress and DNA methylation in bovine blastocysts.

Early mammalian embryos derived from in vitro fertilization are exposed to conditions distinct from the native oviduct-uterine environment, including atmospheric oxygen that promotes cellular oxidative stress and alters gene expression. High oxygen partial pressure during embryo development is associated with low pregnancy rates and increased embryonic apoptosis. We investigated how bovine embryos responded to high (20%) or low (5%) oxygen partial pressure during in vitro culture, evaluating levels of reactive oxygen species (ROS) as well as changes in the expression of oxidative stress- and epigenetic-related transcripts and miRNAs in blastocysts. Additionally, we determined the global DNA methylation levels in the resulting embryos. Our data indicated that bovine blastocysts produced in vitro under high oxygen partial pressure possessed elevated ROS abundance and exhibited increased expression of CAT, GLRX2, KEAP1, NFR2, PRDX1, PRDX3, SOD1, TXN, and TXNRD1, versus reduced levels of the oxidative stress-related bta-miR-210. These stressed embryos also presented altered expression of the epigenetic-associated transcripts DNMT3A, H2AFZ, H3F3B, HDAC2, MORF4L2, REST, and PAF1. In addition, we demonstrated that embryos cultured under high oxygen partial pressure have increased global DNA methylation, suggesting that DNA hypermethylation is mediated by the deregulation of epigenetic-related enzymes due to oxidative stress.

Nuclear transfer alters placental gene expression and associated histone modifications of the placental-specific imprinted gene pleckstrin homology-like domain, family A, member 2 (PHLDA2) in cattle.

Abnormal placental development is frequent in nuclear transfer (NT) pregnancies and is likely to be associated with altered epigenetic reprogramming. In the present study, fetal and placental measurements were taken on Day 60 of gestation in cows with pregnancies produced by AI, IVF and NT. Placentas were collected and subjected to histological evaluation, the expression of genes important in trophoblast differentiation and expression of the placental imprinted gene pleckstrin homology-like domain, family A, member 2 (PHLDA2), as well as chromatin immunoprecipitation (ChIP) for histone marks within the promoter of PHLDA2. Fewer binucleated cells were observed in NT cotyledons, followed by IVF and AI cotyledons (P<0.05). Expression of heart and neural crest derivatives expressed 1 (HAND1), placental lactogen (PL), pregnancy-associated glycoprotein 9 (PAG-9) and PHLDA2 was elevated in NT cotyledons compared with AI cotyledons. Expression of PHLDA2 was higher in IVF than AI samples (P<0.05). ChIP revealed an increase in the permissive mark dimethylation of lysine 4 on histone H3 (H3K4me2), surprisingly associated with the silent allele of PHLDA2, and a decrease in the inhibitory mark H3K9me2 in NT samples. Thus, genes critical for placental development were altered in NT placentas, including an imprinted gene. Allele-specific changes in the permissive histone mark in the PHLDA2 promoter indicate misregulation of imprinting in clones. Abnormal trophoblast differentiation could have resulted in lower numbers of binucleated cells following NT. These results suggest that the altered expression of imprinted genes associated with NT are also caused by changes in histone modifications.

In vitro maturation alters gene expression in bovine oocytes.

Gene expression profiling of in vivo- and in vitro-matured bovine oocytes can identify transcripts related to the developmental potential of oocytes. Nonetheless, the effects of in vitro culturing oocytes are yet to be fully understood. We tested the effects of in vitro maturation on the transcript profile of oocytes collected from Bos taurus indicus cows. We quantified the expression of 1488 genes in in vivo- and in vitro-matured oocytes. Of these, 51 genes were up-regulated, whereas 56 were down-regulated (≥2-fold) in in vivo-matured oocytes in comparison with in vitro-matured oocytes. Quantitative real-time polymerase chain reaction (PCR) of nine genes confirmed the microarray results of differential expression between in vivo- and in vitro-matured oocytes (EZR, EPN1, PSEN2, FST, IGFBP3, RBBP4, STAT3, FDPS and IRS1). We interrogated the results for enrichment of Gene Ontology categories and overlap with protein-protein interactions. The results revealed that the genes altered by in vitro maturation are mostly related to the regulation of oocyte metabolism. Additionally, analysis of protein-protein interactions uncovered two regulatory networks affected by the in vitro culture system. We propose that the differentially expressed genes are candidates for biomarkers of oocyte competence. In vitro oocyte maturation can affect the abundance of specific transcripts and are likely to deplete the developmental competence.

MAC-T cells as a tool to evaluate lentiviral vector construction targeting recombinant protein expression in milk.

Prior to generating transgenic animals for bioreactors, it is important to evaluate the vector constructed to avoid poor protein expression. Mammary epithelial cells cultured in vitro have been proposed as a model to reproduce the biology of the mammary gland. In the present work, three lentiviral vectors were constructed for the human growth hormone (GH), interleukin 2 (IL2), and granulocyte colony-stimulating factor 3 (CSF3) genes driven by the bovine ß-casein promoter. The lentiviruses were used to transduce mammary epithelial cells (MAC-T), and the transformed cells were cultured on polystyrene in culture medium with and without prolactin. The gene expression of transgenes was evaluated by PCR using cDNA, and recombinant protein expression was evaluated by Western-blotting using concentrated medium and cellular extracts. The gene expression, of the three introduced genes, was detected in both induced and non induced MAC-T cells. The human GH protein was detected in the concentrated medium, whereas CSF3 was detected in the cellular extract. Apparently, the cellular extract is more appropriate than the concentrated medium to detect recombinant protein, principally because concentrated medium has a high concentration of bovine serum albumin. The results suggest that MAC-T cells may be a good system to evaluate vector construction targeting recombinant protein expression in milk.

Genome-wide association analysis of feed intake and residual feed intake in Nellore cattle.

BACKGROUND: Feed intake plays an important economic role in beef cattle, and is related with feed efficiency, weight gain and carcass traits. However, the phenotypes collected for dry matter intake and feed efficiency are scarce when compared with other measures such as weight gain and carcass traits. The use of genomic information can improve the power of inference of studies on these measures, identifying genomic regions that affect these phenotypes. This work performed the genome-wide association study (GWAS) for dry matter intake (DMI) and residual feed intake (RFI) of 720 Nellore cattle (Bos taurus indicus). RESULTS: In general, no genomic region extremely associated with both phenotypic traits was observed, as expected for the variables that have their regulation controlled by many genes. Three SNPs surpassed the threshold for the Bonferroni multiple test for DMI and two SNPs for RFI. These markers are located on chromosomes 4, 8, 14 and 21 in regions near genes regulating appetite and ion transport and close to important QTL as previously reported to RFI and DMI, thus corroborating the literature that points these two processes as important in the physiological regulation of intake and feed efficiency. CONCLUSIONS: This study showed the first GWAS of DMI to identify genomic regions associated with feed intake and efficiency in Nellore cattle. Some genes and QTLs previously described for DMI and RFI, in other subspecies (Bos taurus taurus), that influences these phenotypes are confirmed in this study.

Human proinsulin production in the milk of transgenic cattle.

BACKGROUND: The worldwide growing demand for human insulin for treating diabetes could be supplied by transgenic animals producing insulin in their milk. METHODS AND RESULTS: Pseudo-lentivirus containing the bovine ß-casein promoter and human insulin sequences was used to produce modified adult fibroblasts, and the cells were used for nuclear transfer. Transgenic embryos were transferred to recipient cows, and one pregnancy was produced. Recombinant protein in milk was evaluated using western blotting and mass spectrometry. One transgenic cow was generated, and in milk analysis, two bands were observed in western blotting with a molecular mass corresponding to the proinsulin and insulin. The mass spectrometry analysis showed the presence of human insulin more than proinsulin in the milk, and it identified proteases in the transgenic milk that could convert proinsulin into insulin and insulin-degrading enzyme that could degrade the recombinant protein. CONCLUSION: The methodologies used for generating the transgenic cow allowed the detection of the production of recombinant protein in the milk at low relative expression compared to milk proteins, using mass spectrometry, which was efficient for detecting recombinant protein with low expression in milk. Milk proteases could act on protein processing converting recombinant protein to functional protein. On the other hand, some milk proteases could act in degrading the recombinant protein.

Soybean molasses increases subcutaneous fat deposition while reducing lipid oxidation in the meat of castrated lambs.

This study aimed to evaluate the effect of including soybean molasses (SM) on performance, blood parameters, carcass traits, meat quality, fatty acid, and muscle (longissimus thoracis) transcriptomic profiles of castrated lambs. Twenty Dorper × Santa Inês lambs (20.06 ±â€…0.76 kg body weight [BW]) were assigned to a randomized block design, stratified by BW, with the following treatments: CON: 0 g/kg of SM and SM20: 200 g/kg of SM on dry matter basis, allocated in individual pens. The diet consisted of 840 g/kg concentrate and 160 g/kg corn silage for 76 d, with the first 12 d as an adaptation period and the remaining 64 d on the finishing diet. The SM20 diet increased blood urea concentration (P = 0.03) while reduced glucose concentration (P = 0.04). Lambs fed SM showed higher subcutaneous fat deposition (P = 0.04) and higher subcutaneous adipocyte diameter (P < 0.01), in addition to reduced meat lipid oxidation (P < 0.01). SM reduced the quantity of branched-chain fatty acids in longissimus thoracis (P = 0.05) and increased the quantity of saturated fatty acids (P = 0.01). In the transcriptomic analysis, 294 genes were identified as differentially expressed, which belong to pathways such as oxidative phosphorylation, citric acid cycle, and monosaccharide metabolic process. In conclusion, diet with SM increased carcass fat deposition, reduced lipid oxidation, and changed the energy metabolism, supporting its use in ruminant nutrition.

This study investigated the effects of incorporating soybean molasses (SM) into the diet of castrated lambs on various aspects of their performance and meat quality. Twenty lambs were divided into two groups: one was fed a control diet without SM whereas the other was fed a similar diet but containing 20% of SM. The feeding trial lasted for 76 d. Results showed that the SM inclusion in the diet led to increased blood urea levels and decreased glucose concentrations. SM inclusion also resulted in lambs with higher levels of subcutaneous fat and larger adipocytes, while reducing meat lipid oxidation. Moreover, SM altered fatty acid composition in the meat, decreasing branched-chain fatty acids and increasing saturated fatty acids. In agreement with these findings, transcriptomic analysis revealed a significant change in the expression of genes related to energy metabolism in the muscle of lambs fed SM. In conclusion, incorporating SM in lamb's diet increased fat deposition, improved meat quality, and induced a transcriptomic change in the muscle energy metabolism, supporting its potential use in ruminant nutrition.

Development of bovine embryos derived from reproductive techniques.

Assisted reproduction techniques have improved agricultural breeding in the bovine. However, important development steps may differ from the situation in vivo and there is a high mortality rate during the first trimester of gestation. To better understand these events, we investigated the development of embryos and fetal membranes following fixed-time AI (FTAI), IVF and nuclear transfer (NT). The onset of yolk-sac development was not normal in cloned embryos. Later steps differed from conditions in vivo in all three groups; the yolk-sac was yellowish and juxtaposed with the amniotic membrane. Vascularisation of the chorioallantoic membrane was relatively late and low in NT gestations, but normal in the others. The overall development of the embryos was normal, as indicated by morphology and regression analysis of growth rate. However, NT conceptuses were significantly smaller, with the livers in some embryos occupying the abdominal cavity and others exhibiting heart abnormalities. In conclusion, the yolk-sac and the cardiovascular system seem to be vulnerable to morphogenetic alterations. Future studies will focus on gene expression and early vascularisation processes to investigate whether these changes may be responsible for the high incidence of intrauterine mortality, especially in clones.

Transmission of mitochondrial DNA diseases and ways to prevent them.

Recent reports of strong selection of mitochondrial DNA (mtDNA) during transmission in animal models of mtDNA disease, and of nuclear transfer in both animal models and humans, have important scientific implications. These are directly applicable to the genetic management of mtDNA disease. The risk that a mitochondrial disorder will be transmitted is difficult to estimate due to heteroplasmy-the existence of normal and mutant mtDNA in the same individual, tissue, or cell. In addition, the mtDNA bottleneck during oogenesis frequently results in dramatic and unpredictable inter-generational fluctuations in the proportions of mutant and wild-type mtDNA. Pre-implantation genetic diagnosis (PGD) for mtDNA disease enables embryos produced by in vitro fertilization (IVF) to be screened for mtDNA mutations. Embryos determined to be at low risk (i.e., those having low mutant mtDNA load) can be preferentially transferred to the uterus with the aim of initiating unaffected pregnancies. New evidence that some types of deleterious mtDNA mutations are eliminated within a few generations suggests that women undergoing PGD have a reasonable chance of generating embryos with a lower mutant load than their own. While nuclear transfer may become an alternative approach in future, there might be more difficulties, ethical as well as technical. This Review outlines the implications of recent advances for genetic management of these potentially devastating disorders.

Micro-vibration results in vitro-derived bovine blastocysts with greater cryotolerance, epigenetic abnormalities, and a massive transcriptional change.

Much effort has been employed to improve the quality of embryos obtained by in vitro production (IVP) given the relevance of this technology to current livestock systems. In this context, dynamic IVP systems have proved beneficial to the embryo once they mimic fluid flows and mechanical forces resulting from the movement of ciliated cells and muscle contraction in the reproductive tract. In the present study, we sought to confirm these initial findings as well as assess potential molecular consequences to the embryo by applying micro-vibration (45 Hz for 5 s once per 60 min) during both oocyte maturation and embryo culture in cattle. As a result, micro-vibration led to lower incidence of apoptosis in blastocysts following vitrification-thawing. Further analyses revealed epigenetic and transcriptional changes in blastocysts derived from the micro-vibration treatment, with a total of 502 differentially expressed genes. Enrichment analyses linked differentially expressed genes to 'Oxidative phosphorylation', 'Cytokine-cytokine receptor interaction', and 'Signaling pathways regulating pluripotency of stem cells'. Yet, a meta-analysis indicated that the transcriptional changes induced by micro-vibration were not toward that of in vivo-derived embryos. In conclusion, micro-vibration increases the cryoresistance of bovine embryos, but caution should be taken given the unclear consequences of epigenetic and transcriptional abnormalities induced by the treatment.

A new topology of ACBP from Moniliophthora perniciosa.

Acyl-CoA binding protein (ACBP) is a housekeeping protein and is an essential protein in human cell lines and in Trypanosoma brucei. The ACBP of Moniliophthora perniciosa is composed of 104 amino acids and is possibly a non-classic isoform exclusively from Basidiomycetes. The M. perniciosa acbp gene was cloned, and the protein was expressed and purified. Acyl-CoA ester binding was analyzed by isoelectric focusing, native gel electrophoresis and isothermal titration calorimetry. Our results suggest an increasing affinity of ACBP for longer acyl-CoA esters, such as myristoyl-CoA to arachidoyl-CoA, and best fit modeling indicates two binding sites. ACBP undergoes a shift from a monomeric to a dimeric state, as shown by dynamic light scattering, fluorescence anisotropy and native gel electrophoresis in the absence and presence of the ligand. The protein's structure was determined at 1.6 A resolution and revealed a new topology for ACBP, containing five alpha-helices instead of four. alpha-helices 1, 2, 3 and 4 adopted a bundled arrangement that is unique from the previously determined four-helix folds of ACBP, while alpha-helices 1, 2, 4 and 5 formed a classical four-helix bundle. A MES molecule was found in the CoA binding site, suggesting that the CoA site could be a target for small compound screening.

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.

Embryo mitochondrial DNA depletion is reversed during early embryogenesis in cattle.

The extensive replication of mitochondria during oogenesis and the wide variability in mitochondrial DNA (mtDNA) copy numbers present in fully grown oocytes indicate that mtDNA amount may play an important role during early embryogenesis. Using bovine oocytes derived from follicles of different sizes to study the influence of mtDNA content on development, we showed that oocytes obtained from small follicles, known to be less competent in developing into blastocysts, contain less mtDNA than those originating from larger follicles. However, because of the high variability in copy number, a more accurate approach was examined in which parthenogenetic one-cell embryos were biopsied to measure their mtDNA content and then cultured to assess development capacity. Contrasting with previous findings, mtDNA copy number in biopsies was not different between competent and incompetent embryos, indicating that mtDNA content is not related to early developmental competence. To further examine the importance of mtDNA on development, one-cell embryos were partially depleted of their mtDNA (64% +/- 4.1% less) by centrifugation followed by the removal of the mitochondrial-enriched cytoplasmic fraction. Surprisingly, depleted embryos developed normally into blastocysts, which contained mtDNA copy numbers similar to nonmanipulated controls. Development in depleted embryos was accompanied by an increase in the expression of genes (TFAM and NRF1) controlling mtDNA replication and transcription, indicating an intrinsic ability to restore the content of mtDNA at the blastocyst stage. Therefore, we concluded that competent bovine embryos are able to regulate their mtDNA content at the blastocyst stage regardless of the copy numbers accumulated during oogenesis.