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: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. The effect of elevated NEFA exposure during embryo culture (6.5 days) on gene expression was evaluated by exposing embryos to the BASAL or HIGH COMBI conditions. A total of 1412 oocytes were used, equally distributed between treatments in 4 replicates. Resultant day 7.5 blastocysts were snap frozen for subsequent transcriptome analysis (80 blastocysts in each experiments, equally collected between treatments in 4 replicates).

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