Unknown,Transcriptomics,Genomics,Proteomics

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Analysis of the gene expression pattern of bovine blastocysts at three stages of development

ABSTRACT: Blastocyst formation is a primordial event of pre-implantation development since it is required for pregnancy establishment and progression. The blastocyst plays a pivotal role because it is the stage at which the embryo is transferred and starts coordinated cross-talks with the mother. It is also the terminal step of pre-implantation developmentbefore transfer; it reflects all stresses the embryo may have faced during the process of in-vitro treatment. Achieving the formation of a morphologically healthy blastocyst following normal kinetics is a good sign but remains a poor indicator of embryo quality. Considering the limitation of the invasive methods for competence assessment, the analysis of blastocysts’ gene expression is a promising way to improve our understanding of blastocyst formation and to study the effects of different treatments on gene expression. Methods: Early, expanded and hatched blastocysts were collected for RNA extraction, amplification, and cDNA microarray hybridization. Gene candidates (IFNt, PLAC8, SSLP1, AKR1B1, HNRNPA2B1, ARGFX, NANOS, CCNB1) were selected and confirmed using Q-RT-PCR to validate the microarray data. Results: Our analysis show that hatched blastocysts are enriched in genes transcripts implicated in implantation, cell adhesion and extracellular matrix digestion. Early blastocysts expressed genes mainly involved in cell cycle control, transcription and translation. Q-RT-PCR validated most microarray results (87.5%). Some of the differentially expressed genes are interesting as potential markers of competence. Conclusions: Overall, our study provides new insights into the molecular regulation of blastocyst formation. In addition, it could help assess blastocyst staging and select better embryos based on the expression of quality markers. In the present study the Laval/Sirard_bovine_embryo_3K_V3.0 array was used to conduct a series of 18 hybridizations (for three Blastocysts stages (early, expended, hatched) with three biological replicates and dye swaps) in a loop design experiment.

ORGANISM(S): Bos taurus

SUBMITTER: Isabelle Dufort

PROVIDER: E-GEOD-25606 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Metabolic stress associated with negative energy balance in high producing dairy cattle and obesity in women is a risk factor for decreased fertility. Non-esterified fatty acids (NEFA) are involved in this pathogenesis as they jeopardize oocyte and embryo development. Growing evidence indicates that maternal metabolic disorders can disturb epigenetic programming, and more specifically DNA methylation, in the offspring. Final oocyte maturation and early embryo development coincide with specific methylation changes and both time periods are sensitive to adverse environments. Therefore, we investigated whether elevated NEFA concentrations affect the establishment and maintenance of DNA methylation patterns in oocytes and embryos and subsequently alter transcriptomic profiles and developmental competence of the resultant blastocysts. To do this, bovine oocytes and embryos were exposed to different NEFA concentrations in two separate experiments. In the first experiment, oocytes were matured in vitro for 24 hours in medium containing: 1) physiological (âBASALâ) concentrations of oleic (OA), palmitic (PA) and stearic (SA) or 2) elevated (pathophysiological or âHIGH COMBIâ) concentrations of OA, PA and SA. In the second experiment, zygotes were cultivated in vitro for 6.5 days under BASAL or HIGH COMBI conditions. The developmental competence was evaluated by assessing cleavage and blastocyst rate. Overall gene expression and DNA methylation of resultant blastocysts were analyzed using microarray techniques. Data regarding DNA methylation were re-evaluated by pyrosequencing. HIGH COMBI-exposed oocytes and embryos displayed a lower competence to develop into blastocysts compared to their BASAL-exposed counterparts (19.3 % compared to 23.2 % and 18.2 % compared to 25.3 %, respectively) (P < 0.05). HIGH COMBI-exposed oocytes and embryos resulted in blastocysts with altered DNA methylation profiles and transcriptomic fingerprints, compared to BASAL-exposed counterparts. Differences in gene expression and methylation were more pronounced after exposure during culture compared to maturation suggesting that zygotes are more susceptible to an adverse environment. Main gene networks affected were related to lipid and carbohydrate metabolism, cell death, immune response and metabolic disorders. This may offer clues regarding the high rate of embryonic loss and metabolic diseases during later stages of life observed in offspring from mothers displaying lipolytic disorders. Two experiments were set up to characterize the epigenomic profile of the resultant day 7.5 blastocysts. In the first (in vitro maturation or IVM) experiment, the effect of elevated NEFA exposure during oocyte maturation (24 h) on DNA methylation profiles was evaluated by exposing oocytes to the BASAL or HIGH COMBI conditions. In the second (in vitro culture or IVC) experiment, the effect of elevated NEFA exposure during embryo culture (6.5 days) on DNA methylation marks was evaluated by exposing embryos to the BASAL or HIGH COMBI conditions. A total of 1039 and 1412 oocytes were used in the IVM and IVC experiment, respectively, equally distributed between treatments in 4 replicates. Resultant day 7.5 blastocysts were snap frozen for subsequent DNA methylation analysis (80 blastocysts in each experiments, equally collected between treatments in 4 replicates).

Project description:Genes and signaling pathways involved in pluripotency have been studied extensively in mouse and human pre-implantation embryos and embryonic stem (ES) cells. The unsuccessful attempts to generate ES cell lines from other species including cattle suggests that other genes and pathways are involved in maintaining pluripotency in these species. To investigate which genes are involved in bovine pluripotency, expression profiles were generated from morula, blastocyst, trophectoderm and inner cell mass (ICM) samples using microarray analysis. As MAPK inhibition can increase the NANOG/GATA6 ratio in the inner cell mass, additionally blastocysts were cultured in the presence of a MAPK inhibitor and changes in gene expression in the inner cell mass were analyzed. Between morula and blastocyst 3,774 genes were differentially expressed and the largest differences were found in blastocyst up-regulated genes. Gene ontology (GO) analysis shows lipid metabolic process as the term most enriched with genes expressed at higher levels in blastocysts. Genes with higher expression levels in morulae were enriched in the RNA processing GO term. Of the 497 differentially expressed genes comparing ICM and TE the expression of NANOG, SOX2 and POU5F1 was indeed increased in the ICM confirming their evolutionary preserved role in pluripotency. Several genes implicated to be involved in differentiation or fate determination were also expressed at higher levels in the ICM. Genes expressed at higher levels in the ICM were enriched in the RNA splicing and regulation of gene expression GO term. Although NANOG expression was elevated upon MAPK inhibition, SOX2 and POU5F1 expression showed little increase. Expression of other genes in the MAPK pathway including DUSP4 and SPRY4, or influenced by MAPK inhibition such as IFNT, was affected. The data obtained from the microarray studies provide further insight in gene expression during bovine embryonic development. They show an expression profile in pluripotent cells that indicates a pluripotent but epiblast-like state. These data indicate that MAPK inhibition alone is not sufficient to maintain a pluripotent character in bovine cells. Microarrays used were bovine whole genome gene expression microarrays V2 (Agilent Technologies) representing 43,653 Bos taurus 60-mer oligos in a 4x44K layout. RNA samples from morula, blastocyst and dissected inner cell mass (ICM) and trophectoderm (TE) were compared in a common reference experiment design using 8 dual channel microarrays with each sample hybridized against an identical sample consisting of a pool of blastocysts total RNA. Within each group of two microarrays for each stage/tissue type, sample versus common reference hybridizations were performed in balanced dye-swap.

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Analysis of the gene expression pattern of bovine blastocysts at three stages of development

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