Adipose Tissue Transcriptome Is Related to Pollutant Exposure in Polar Bear Mother-Cub Pairs from Svalbard, Norway.

Being at the food chain apex, polar bears (Ursus maritimus) are highly contaminated with persistent organic pollutants (POPs). Females transfer POPs to their offspring through gestation and lactation; therefore, young cubs present higher POPs concentrations than their mothers. Recent studies suggest that POPs affect the lipid metabolism in female polar bears; however, the mechanisms and impact on their offspring remain unknown. Here, we hypothesized that exposure to POPs differentially alters genome-wide gene transcription in the adipose tissue from mother polar bears and their cubs, highlighting molecular differences in response between adults and young. Adipose tissue biopsies were collected from 13 adult female polar bears and their twin cubs in Svalbard, Norway, in April 2011, 2012, and 2013. Total RNA extracted from biopsies was subjected to next-generation RNA sequencing. Plasma concentrations of summed polychlorinated biphenyls, organochlorine pesticides, and polybrominated diphenyl ethers in mothers ranged from 897 to 13620 ng/g wet weight and were associated with altered adipose tissue gene expression in both mothers and cubs. In mothers, 2502 and 2586 genes in total were positively and negatively, respectively, correlated to POP exposure, whereas in cubs, 2585 positively and 1690 negatively genes. Between mothers and cubs, 743 positively and negatively genes overlapped between mothers and cubs suggesting partially shared molecular responses to ΣPOPs. ΣPOP-associated genes were involved in numerous metabolic pathways in mothers and cubs, indicating that POP exposure alters the energy metabolism, which, in turn, may be linked to metabolic dysfunction.

Intragenic sequences in the trophectoderm harbour the greatest proportion of methylation errors in day 17 bovine conceptuses generated using assisted reproductive technologies.

BACKGROUND: Assisted reproductive technologies (ART) are widely used to treat fertility issues in humans and for the production of embryos in mammalian livestock. The use of these techniques, however, is not without consequence as they are often associated with inauspicious pre- and postnatal outcomes including premature birth, intrauterine growth restriction and increased incidence of epigenetic disorders in human and large offspring syndrome in cattle. Here, global DNA methylation profiles in the trophectoderm and embryonic discs of in vitro produced (IVP), superovulation-derived (SOV) and unstimulated, synchronised control day 17 bovine conceptuses (herein referred to as AI) were interrogated using the EmbryoGENE DNA Methylation Array (EDMA). Pyrosequencing was used to validate four loci identified as differentially methylated on the array and to assess the differentially methylated regions (DMRs) of six imprinted genes in these conceptuses. The impact of embryo-production induced DNA methylation aberrations was determined using Ingenuity Pathway Analysis, shedding light on the potential functional consequences of these differences. RESULTS: Of the total number of differentially methylated loci identified (3140) 77.3 and 22.7% were attributable to SOV and IVP, respectively. Differential methylation was most prominent at intragenic sequences within the trophectoderm of IVP and SOV-derived conceptuses, almost a third (30.8%) of the differentially methylated loci mapped to intragenic regions. Very few differentially methylated loci were detected in embryonic discs (ED); 0.16 and 4.9% of the differentially methylated loci were located in the ED of SOV-derived and IVP conceptuses, respectively. The overall effects of SOV and IVP on the direction of methylation changes were associated with increased methylation; 70.6% of the differentially methylated loci in SOV-derived conceptuses and 57.9% of the loci in IVP-derived conceptuses were more methylated compared to AI-conceptuses. Ontology analysis of probes associated with intragenic sequences suggests enrichment for terms associated with cancer, cell morphology and growth. CONCLUSION: By examining (1) the effects of superovulation and (2) the effects of an in vitro system (oocyte maturation, fertilisation and embryo culture) we have identified that the assisted reproduction process of superovulation alone has the largest impact on the DNA methylome of subsequent embryos.

Genome-wide DNA methylation patterns of bovine blastocysts derived from in vivo embryos subjected to in vitro culture before, during or after embryonic genome activation.

BACKGROUND: Aberrant DNA methylation patterns of genes required for development are common in in vitro produced embryos. In this regard, we previously identified altered DNA methylation patterns of in vivo developed blastocysts from embryos which spent different stages of development in vitro, indicating carryover effects of suboptimal culture conditions on epigenetic signatures of preimplantation embryos. However, epigenetic responses of in vivo originated embryos to suboptimal culture conditions are not fully understood. Therefore, here we investigated DNA methylation patterns of in vivo derived bovine embryos subjected to in vitro culture condition before, during or after major embryonic genome activation (EGA). For this, in vivo produced 2-, 8- and 16-cell stage embryos were cultured in vitro until the blastocyst stage and blastocysts were used for genome-wide DNA methylation analysis. RESULTS: The 2- and 8-cell flushed embryo groups showed lower blastocyst rates compared to the 16-cell flush group. This was further accompanied by increased numbers of differentially methylated genomic regions (DMRs) in blastocysts of the 2- and 8-cell flush groups compared to the complete in vivo control ones. Moreover, 1623 genomic loci including imprinted genes were hypermethylated in blastocyst of 2-, 8- and 16-cell flushed groups, indicating the presence of genomic regions which are sensitive to the in vitro culture at any stage of embryonic development. Furthermore, hypermethylated genomic loci outnumbered hypomethylated ones in blastocysts of 2- and 16-cell flushed embryo groups, but the opposite occurred in the 8-cell group. Moreover, DMRs which were unique to blastocysts of the 2-cell flushed group and inversely correlated with corresponding mRNA expression levels were involved in plasma membrane lactate transport, amino acid transport and phosphorus metabolic processes, whereas DMRs which were specific to the 8-cell group and inversely correlated with corresponding mRNA expression levels were involved in several biological processes including regulation of fatty acids and steroid biosynthesis processes. CONCLUSION: In vivo embryos subjected to in vitro culture before and during major embryonic genome activation (EGA) are prone to changes in DNA methylation marks and exposure of in vivo embryos to in vitro culture during the time of EGA increased hypomethylated genomic loci in blastocysts.

Cumulus Cell Transcripts Transit to the Bovine Oocyte in Preparation for Maturation.

So far, the characteristics of a good quality egg have been elusive, similar to the nature of the physiological, cellular, and molecular cues leading to its production both in vivo and in vitro. Current understanding highlights a strong and complex interdependence between the follicular cells and the gamete. Secreted factors induce cellular responses in the follicular cells, and direct exchange of small molecules from the cumulus cells to the oocyte through gap junctions controls meiotic arrest. Studying the interconnection between the cumulus cells and the oocyte, we previously demonstrated that the somatic cells also contribute transcripts to the gamete. Here, we show that these transcripts can be visualized moving down the transzonal projections (TZPs) to the oocyte, and that a time course analysis revealed progressive RNA accumulation in the TZPs, indicating that RNA transfer occurs before the initiation of meiosis resumption under a timetable fitting with the acquisition of developmental competence. A comparison of the identity of the nascent transcripts trafficking in the TZPs, with those in the oocyte increasing in abundance during maturation, and that are present on the oocyte's polyribosomes, revealed transcripts common to all three fractions, suggesting the use of transferred transcripts for translation. Furthermore, the removal of potential RNA trafficking by stripping the cumulus cells caused a significant reduction in maturation rates, indicating the need for the cumulus cell RNA transfer to the oocyte. These results offer a new perspective to the determinants of oocyte quality and female fertility, as well as provide insight that may eventually be used to improve in vitro maturation conditions.

Genetic influence on the reduction in bovine embryo lipid content by l-carnitine.

The decreased rate of pregnancy obtained in cattle using frozen in vitro embryos compared with in vivo embryos has been associated with over-accumulation of intracellular lipid, which causes cell damage during cryopreservation. It is believed that the higher lipid content of blastomeres of bovine embryos produced in vitro results in darker-coloured cytoplasm, which could be a consequence of impaired mitochondrial function. In this study, l-carnitine was used as a treatment to reduce embryonic lipid content by increasing metabolism in cultured bovine embryos. We have observed previously that in vivo embryos of different dairy breeds collected from cows housed and fed under the same conditions differed in lipid content and metabolism. As such, breed effects between Holstein and Jersey were also examined in terms of general appearance, lipid composition, mitochondrial activity and gene expression. Adding l-carnitine to the embryo culture medium reduced the lipid content in both breeds due to increased mitochondrial activity. The response to l-carnitine was weaker in Jersey than in Holstein embryos. Our results thus show that genetics influence the response of bovine embryos to stimulation of mitochondrial metabolism.

Breed-specific factors influence embryonic lipid composition: comparison between Jersey and Holstein.

Some embryos exhibit better survival potential to cryopreservation than others. The cause of such a phenotype is still unclear and may be due to cell damage during cryopreservation, resulting from overaccumulation and composition of lipids. In cattle embryos, in vitro culture conditions have been shown to impact the number of lipid droplets within blastomeres. Thus far, the impact of breed on embryonic lipid content has not been studied. In the present study were compared the colour, lipid droplet abundance, lipid composition, mitochondrial activity and gene expression of in vivo-collected Jersey breed embryos, which are known to display poor performance post-freezing, with those of in vivo Holstein embryos, which have good cryotolerance. Even when housed and fed under the same conditions, Jersey embryos were found to be darker and contain more lipid droplets than Holstein embryos, and this was correlated with lower mitochondrial activity. Differential expression of genes associated with lipid metabolism and differences in lipid composition were found. These results show genetic background can impact embryonic lipid metabolism and storage.

Impact of whole-genome amplification on the reliability of pre-transfer cattle embryo breeding value estimates.

BACKGROUND: Genome-wide profiling of single-nucleotide polymorphisms is receiving increasing attention as a method of pre-implantation genetic diagnosis in humans and of commercial genotyping of pre-transfer embryos in cattle. However, the very small quantity of genomic DNA in biopsy material from early embryos poses daunting technical challenges. A reliable whole-genome amplification (WGA) procedure would greatly facilitate the procedure. RESULTS: Several PCR-based and non-PCR based WGA technologies, namely multiple displacement amplification, quasi-random primed library synthesis followed by PCR, ligation-mediated PCR, and single-primer isothermal amplification were tested in combination with different DNA extractions protocols for various quantities of genomic DNA inputs. The efficiency of each method was evaluated by comparing the genotypes obtained from 15 cultured cells (representative of an embryonic biopsy) to unamplified reference gDNA. The gDNA input, gDNA extraction method and amplification technology were all found to be critical for successful genome-wide genotyping. The selected WGA platform was then tested on embryo biopsies (n = 226), comparing their results to that of biopsies collected after birth. Although WGA inevitably leads to a random loss of information and to the introduction of erroneous genotypes, following genomic imputation the resulting genetic index of both sources of DNA were highly correlated (r = 0.99, P<0.001). CONCLUSION: It is possible to generate high-quality DNA in sufficient quantities for successful genome-wide genotyping starting from an early embryo biopsy. However, imputation from parental and population genotypes is a requirement for completing and correcting genotypic data. Judicious selection of the WGA platform, careful handling of the samples and genomic imputation together, make it possible to perform extremely reliable genomic evaluations for pre-transfer embryos.

An integrated platform for bovine DNA methylome analysis suitable for small samples.

BACKGROUND: Oocytes and early embryos contain minute amounts of DNA, RNA and proteins, making the study of early mammalian development highly challenging. The study of the embryo epigenome, in particular the DNA methylome, has been made accessible thanks to the possibility of amplifying specific sequences according to their initial methylation status. This paper describes a novel platform dedicated to the genome-wide study of bovine DNA methylation, including a complete pipeline for data analysis and visualization. The platform allows processing and integrating of DNA methylome and transcriptome data from the same sample. Procedures were optimized for genome-wide analysis of 10 ng of DNA (10 bovine blastocysts). Bovine sperm and blastocysts were compared as a test of platform capability. RESULTS: The hypermethylation of bovine sperm DNA compared to the embryo genome was confirmed. Differentially methylated regions were distributed across various classes of bovine sperm genomic feature including primarily promoter, intronic and exonic regions, non-CpG-island regions (shore, shelf and open-sea) and CpG islands with low-to-intermediate CpG density. The blastocyst genome bore more methylation marks than sperm DNA only in CpG islands with high CpG density. Long-terminal-repeat retrotransposons (LTR), LINE and SINE were more methylated in sperm DNA, as were low-complexity repetitive elements in blastocysts. CONCLUSIONS: This is the first early embryo compatible genome-wide epigenetics platform for bovine. Such platforms should improve the study of the potential epigenetic risks of assisted reproductive technologies (ART), the establishment sequence of embryonic cell lines and potential deviations in both gene expression and DNA methylation capable of having long-term impact.

Sexual dimorphism in developmental programming of the bovine preimplantation embryo caused by colony-stimulating factor 2.

Physiology of the adult can be modified by alterations in prenatal development driven by the maternal environment. Developmental programming, which can be established before the embryo implants in the uterus, can affect females differently than males. The mechanism by which sex-specific developmental programming is established is not known. Here we present evidence that maternal regulatory signals change female embryos differently than male embryos. In particular, actions of the maternally derived cytokine CSF2 from Day 5 to Day 7 of development affected characteristics of the embryo at Day 15 differently for females than males. CSF2 decreased length and IFNT secretion of female embryos but increased length and IFNT secretion of male embryos. Analysis of a limited number of samples indicated that changes in the transcriptome and methylome caused by CSF2 also differed between female and males. Thus, sex-specific programming by the maternal environment could occur when changes in secretion of maternally derived regulatory molecules alter development of female embryos differently than male embryos.

Improvement of bovine in vitro embryo production by vitamin K2 supplementation.

Mitochondria play an important role during early development in mammalian embryos. It has been shown that properly controlled follicular preparation increases the likelihood of in-vitro-produced bovine embryos reaching the blastocyst stage and that competent embryos exhibit heightened expression of genes associated with mitochondrial function. We hypothesized that apparently incompetent embryos could be rescued by restoring mitochondrial function. It has been shown that vitamin K2 (a membrane-bound electron carrier similar to ubiquinone) can restore mitochondrial dysfunction in eukaryotic cells. The aim of this study was therefore to investigate the effects of vitamin K2 on bovine embryonic development in vitro. The vitamin was found most effective when added 72 h after fertilization. It produced a significant (P<0.05) increase in the percentage of blastocysts (+8.6%), more expanded blastocysts (+7.8%), and embryos of better morphological quality. It improved the mitochondrial activity significantly and had a measurable impact on gene expression. This is the first demonstration that current standard conditions of in vitro production of bovine embryos may be inadequate due to the lack of support for mitochondrial function and may be improved significantly by supplementing the culture medium with vitamin K2.

Exploring the function of long non-coding RNA in the development of bovine early embryos.

Now recognised as part of the cellular transcriptome, the function of long non-coding (lnc) RNA remains unclear. Previously, we found that some lncRNA molecules in bovine embryos are highly responsive to culture conditions. In view of a recent demonstration that lncRNA may play a role in regulating important functions, such as maintenance of pluripotency, modification of epigenetic marks and activation of transcription, we sought evidence of its involvement in embryogenesis. Among the numerous catalogued lncRNA molecules found in oocytes and early embryos of cattle, three candidates chosen for further characterisation were found unexpectedly in the cytoplasmic compartment rather than in the nucleus. Transcriptomic survey of subcellular fractions found these candidates also associated with polyribosomes and one of them spanning transzonal projections between cumulus cells and the oocyte. Knocking down this transcript in matured oocytes increased developmental rates, leading to larger blastocysts. Transcriptome and methylome analyses of these blastocysts showed concordant data for a subset of four genes, including at least one known to be important for blastocyst survival. Functional characterisation of the roles played by lncRNA in supporting early development remains elusive. Our results suggest that some lncRNAs play a role in translation control of target mRNA. This would be important for managing the maternal reserves within which is embedded the embryonic program, especially before embryonic genome activation.

Combined methylation mapping of 5mC and 5hmC during early embryonic stages in bovine.

BACKGROUND: It was recently established that changes in methylation during development are dynamic and involve both methylation and demethylation processes. Yet, which genomic sites are changing and what are the contributions of methylation (5mC) and hydroxymethylation (5hmC) to this epigenetic remodeling is still unknown. When studying early development, options for methylation profiling are limited by the unavailability of sufficient DNA material from these scarce samples and limitations are aggravated in non-model species due to the lack of technological platforms. We therefore sought to obtain a representation of differentially 5mC or 5hmC loci during bovine early embryo stages through the use of three complementary methods, based on selective methyl-sensitive restriction and enrichment by ligation-mediated PCR or on subtractive hybridization. Using these strategies, libraries of putative methylation and hydroxymethylated sites were generated from Day-7 and Day-12 bovine embryos. RESULTS: Over 1.2 million sequencing reads were analyzed, resulting in 151,501 contigs, of which 69,136 were uniquely positioned on the genome. A total of 101,461 putative methylated sites were identified. The output of the three methods differed in genomic coverage as well as in the nature of the identified sites. The classical MspI/HpaII combination of restriction enzymes targeted CpG islands whereas the other methods covered 5mC and 5hmC sites outside of these regions. Data analysis suggests a transition of these methylation marks between Day-7 and Day-12 embryos in specific classes of repeat-containing elements. CONCLUSIONS: Our combined strategy offers a genomic map of the distribution of cytosine methylation/hydroxymethylation during early bovine embryo development. These results support the hypothesis of a regulatory phase of hypomethylation in repeat sequences during early embryogenesis.

Comprehensive cross production system assessment of the impact of in vitro microenvironment on the expression of messengers and long non-coding RNAs in the bovine blastocyst.

In vitro production (IVP) of cattle embryos over the past two decades has revealed several negative impacts that have been attributed to the artificial microenvironment. Studies on embryos produced in vitro clearly point to aberrant gene expression levels. So far, the causal association between phenotype and measured gene expression has not led to substantial improvement of IVP systems. The aim of this study was to generate a unique dataset composed of microarray-derived relative transcript abundance values for blastocysts produced in ten in vitro systems differing primarily in culture medium formulation. Between-group comparisons determine the level of overall similarity among systems relative to in vivo reference embryos. The use of the dataset to contrast all in vitro treatments with the in vivo blastocysts pointed to a single common gene network. The 'boutique' array contained a panel of novel uncharacterized transcripts that were variably expressed depending on the medium in which the blastocysts were produced. These novel transcripts were differentially expressed in blastocysts even as carryover from conditions encountered 7 days earlier during oocyte maturation. All of the selected novel candidates thus expressed were from intergenic regions. The function of this long non-coding RNA remains unknown but clearly points to an additional level of complexity in early embryo development.

Combining resources to obtain a comprehensive survey of the bovine embryo transcriptome through deep sequencing and microarrays.

While most assisted reproductive technologies (ART) are considered routine for the reproduction of species of economical importance, such as the bovine, the impact of these manipulations on the developing embryo remains largely unknown. In an effort to obtain a comprehensive survey of the bovine embryo transcriptome and how it is modified by ART, resources were combined to design an embryo-specific microarray. Close to one million high-quality reads were produced from subtracted bovine embryo libraries using Roche 454 Titanium deep sequencing technology, which enabled the creation of an augmented bovine genome catalog. This catalog was enriched with bovine embryo transcripts, and included newly discovered indel type and 3'UTR variants. Using this augmented bovine genome catalog, the EmbryoGENE Bovine Microarray was designed and is composed of a total of 42,242 probes, including 21,139 known reference genes; 9,322 probes for novel transcribed regions (NTRs); 3,677 alternatively spliced exons; 3,353 3'-tiling probes; and 3,723 controls. A suite of bioinformatics tools was also developed to facilitate microrarray data analysis and database creation; it includes a quality control module, a Laboratory Information Management System (LIMS) and microarray analysis software. Results obtained during this study have already led to the identification of differentially expressed blastocyst targets, NTRs, splice variants of the indel type, and 3'UTR variants. We were able to confirm microarray results by real-time PCR, indicating that the EmbryoGENE bovine microarray has the power to detect physiologically relevant changes in gene expression.

Application of Carnobacterium maltaromaticum as a feed additive for weaned rabbits to improve meat microbial quality and safety.

This study addresses the improvement of meat microbial quality by enriching the diet of farm animals with a protective culture. Weaned Grimaud rabbits were divided into two experimental groups: a control and a diet supplemented with Micocin® (Carnobacterium maltaromaticum CB1; 8Log10CFU/kg of feed). Overall, meat quality was not affected substantially by the treatment. Total Aerobic Mesophilic (TAM), Escherichia coli and other coliforms, Enterobacteriaceae, Staphylococcus aureus, Pseudomonas spp., Listeria spp. and presumptive lactic acid bacteria counts were evaluated on whole thighs stored under aerobic (0, 3, 6, 8days) and anaerobic (0, 5, 10, 15, 20days) conditions at 4°C. The results demonstrated that the microflora on refrigerated thighs was modulated by the addition of Micocin® (P<0.05) and that the most effective reduction of Listeria monocytogenes growth was observed with ground meat stored under anaerobic conditions at 4°C with a 2 Log difference at the end of a 15-day storage (P=0.025).

Responses of bovine early embryos to S-adenosyl methionine supplementation in culture.

AIM: There is a growing concern about the potential adverse effects of high dose folic acid (FA) supplementation before and during pregnancy. FA metabolism generates S-adenosyl methionine (SAM) which is an important cofactor of epigenetic programming. We sought to assess the impact of a large dose of SAM on early embryo development. MATERIALS & METHODS: In vitro cultured bovine embryos were treated with SAM from the eight-cell stage to the blastocyst stage. In addition to the phenotype, the genome-wide epigenetic and transcription profiles were analyzed. RESULTS: Treatment significantly improved embryo hatching and caused a shift in sex ratio in favor of males. SAM caused genome-wide hypermethylation mainly in exonic regions and in CpG islands. Although differentially expressed genes were associated with response to nutrients and developmental processes, no correspondence was found with the differentially methylated regions, suggesting that cellular responses to SAM treatment during early embryo development may not require DNA methylation-driven changes. CONCLUSION: Since bovine embryos were not indifferent to SAM, effects of large-dose FA supplements on early embryonic development in humans cannot be ruled out.

The human decapping scavenger enzyme DcpS modulates microRNA turnover.

The decapping scavenger enzyme DcpS is known for its role in hydrolyzing the cap structure following mRNA degradation. Recently, we discovered a new function in miRNA degradation activation for the ortholog of DcpS in C. elegans. Here we show that human DcpS conserves its role in miRNA turnover. In human cells, DcpS is a nucleocytoplasmic shuttling protein that activates miRNA degradation independently of its scavenger decapping activity in the cytoplasmic compartment. We also demonstrate that this new function for DcpS requires the contribution of the 5'-3' exonuclease Xrn2. Our findings support a conserved role of DcpS as a modulator of miRNA turnover in animals.

Genome-Wide DNA Methylation Patterns of Bovine Blastocysts Developed In Vivo from Embryos Completed Different Stages of Development In Vitro.

Early embryonic loss and altered gene expression in in vitro produced blastocysts are believed to be partly caused by aberrant DNA methylation. However, specific embryonic stage which is sensitive to in vitro culture conditions to alter the DNA methylation profile of the resulting blastocysts remained unclear. Therefore, the aim of this study was to investigate the stage specific effect of in vitro culture environment on the DNA methylation response of the resulting blastocysts. For this, embryos cultured in vitro until zygote (ZY), 4-cell (4C) or 16-cell (16C) were transferred to recipients and the blastocysts were recovery at day 7 of the estrous cycle. Another embryo group was cultured in vitro until blastocyst stage (IVP). Genome-wide DNA methylation profiles of ZY, 4C, 16C and IVP blastocyst groups were then determined with reference to blastocysts developed completely under in vivo condition (VO) using EmbryoGENE DNA Methylation Array. To assess the contribution of methylation changes on gene expression patterns, the DNA methylation data was superimposed to the transcriptome profile data. The degree of DNA methylation dysregulation in the promoter and/or gene body regions of the resulting blastocysts was correlated with successive stages of development the embryos advanced under in vitro culture before transfer to the in vivo condition. Genomic enrichment analysis revealed that in 4C and 16C blastocyst groups, hypermethylated loci were outpacing the hypomethylated ones in intronic, exonic, promoter and proximal promoter regions, whereas the reverse was observed in ZY blastocyst group. However, in the IVP group, as much hypermethylated as hypomethylated probes were detected in gene body and promoter regions. In addition, gene ontology analysis indicated that differentially methylated regions were found to affected several biological functions including ATP binding in the ZY group, programmed cell death in the 4C, glycolysis in 16C and genetic imprinting and chromosome segregation in IVP blastocyst groups. Furthermore, 1.6, 3.4, 3.9 and 9.4% of the differentially methylated regions that were overlapped to the transcriptome profile data were negatively correlated with the gene expression patterns in ZY, 4C, 16C and IVP blastocyst groups, respectively. Therefore, this finding indicated that suboptimal culture condition during preimplantation embryo development induced changes in the DNA methylation landscape of the resulting blastocysts in a stage dependent manner and the altered DNA methylation pattern was only partly explained the observed aberrant gene expression patterns of the blastocysts.

The microRNA pathway controls germ cell proliferation and differentiation in C. elegans.

The discovery of the miRNA pathway revealed a new layer of molecular control of biological processes. To uncover new functions of this gene regulatory pathway, we undertook the characterization of the two miRNA-specific Argonaute proteins in Caenorhabditis elegans, ALG-1 and ALG-2. We first observed that the loss-of-function of alg-1 and alg-2 genes resulted in reduced progeny number. An extensive analysis of the germline of these mutants revealed a reduced mitotic region, indicating fewer proliferating germ cells. We also observed an early entry into meiosis in alg-1 and alg-2 mutant animals. We detected ALG-1 and ALG-2 protein expressions in the distal tip cell (DTC), a specialized cell located at the tip of both C. elegans gonadal arms that regulates mitosis-meiosis transition. Re-establishing the expression of alg-1 specifically in the DTC of mutant animals partially rescued the observed germline defects. Further analyses also support the implication of the miRNA pathway in gametogenesis. Interestingly, we observed that disruption of five miRNAs expressed in the DTC led to similar phenotypes. Finally, gene expression analysis of alg-1 mutant gonads suggests that the miRNA pathway is involved in the regulation of different pathways important for germline proliferation and differentiation. Collectively, our data indicate that the miRNA pathway plays a crucial role in the control of germ cell biogenesis in C. elegans.

Contribution of oocyte source and culture conditions to phenotypic and transcriptomic variation in commercially produced bovine blastocysts.

Bovine embryo production is practiced worldwide for commercial purposes. A major concern of embryo suppliers is the impact of in vitro production systems on embryo quality. In the present study, we compared Buffalo Rat Liver cell coculture with semidefined, medium-based culture, oocytes recovered postmortem with those obtained from live animals, and in vitro with in vivo embryo development. Gene expression levels in expanded blastocysts were measured using microarray and quantitative RT-PCR. The systems were similar in terms of blastocyst yield and rate of development, whereas embryo productivity was greater for immature oocytes collected in vivo. Although immature oocytes collected in vivo had greater developmental competence, they yielded blastocysts that were indistinguishable (in terms of level of gene expression) from embryos derived from immature oocytes recovered postmortem. Culture conditions had a significant impact on gene expression, particularly among genes involved in lipid metabolism. Numerous uncharacterized novel transcript regions were also influenced by in vitro treatments. In conclusion, ovum pick-up combined with in vitro culture in semidefined medium provided a high blastocyst yield, without the deleterious effects associated with coculture.