Background Porcine embryos undergo rapid differentiation and expansion between Days 8 and 12 before attaching to the maternal uterine epithelial surface after Day 13. It is known that maternal recognition of pregnancy and successful implantation are driven by mutual interactions between the elongated conceptus and the maternal endometrium. While most of the genes involved in regulation of embryo development are located on autosomal chromosomes, gene expression on sex chromosomes is modulating development through sex-specific transcription. To gain more insights into the dynamic transcriptome of preimplantation embryos at the onset of elongation and into X-linked gene expression, RNA-seq analyses were performed for single female and male porcine embryos collected on Days 8, 10, and 12 of pregnancy. Results A high number of genes were differentially expressed across the developmental stages (2174 and 3275 for Days 8 vs 10, and 10 vs 12, respectively). The majority of differentially expressed genes (DEGs) were involved in embryo elongation, development, and embryo-maternal interaction. Interestingly, a number of DEGs was found with respect to embryo sex (137, 37, and 56 on Days 8, 10 and 12, respectively). At Day 8, most of these DEGs were X-linked (96). Strikingly, the number of DEGs encoded on the X chromosome dramatically decreased from Day 10 to Day 12. Conclusions The obtained results deepen the understanding about temporary transcriptomic changes in porcine embryos during the phase of conceptus elongation, meanwhile reveal dynamic compensation of X chromosome in the female and distinct transcriptional differences between female and male embryos. Electronic supplementary material The online version of this article (10.1186/s12864-019-6044-z) contains supplementary material, which is available to authorized users.

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BackgroundThe expression of microRNAs (miRNAs) is essential for the proper development of the mammalian embryo. A maternal exposure to endocrine disrupting chemicals during preimplantation bears the potential for transgenerational inheritance of disease through the epigenetic perturbation of the developing embryo. A comprehensive assembly of embryo-specific miRNAs and respective isoforms (isomiR) is lacking to date. We aimed at revealing the sex-specific miRNA expression profile of single porcine blastocysts developing in gilts orally exposed to exogenous estradiol-17 (E2). Therefore we analyzed the miRNA profile specifically focusing on isomiRs and potentially embryo-specific miRNAs.ResultsDeep sequencing of small RNA (small RNA-seq) result in the detection of miRNA sequences mapping to known and predicted porcine miRNAs as well as novel miRNAs highly conserved in human and cattle. A set of highly abundant miRNAs and a large number of rarely expressed miRNAs were identified by using a small RNA analysis pipeline, which was integrated into a novel Galaxy workflow specifically benefits incompletely annotated species. In particular, orthologue species information increased the total number of annotated miRNAs, while mapping to other non-coding RNAs avoided falsely annotated miRNAs. Neither the low nor the high dose of E2 treatment (10 and 1000 µ E2/kg body weight daily, respectively) affected the miRNA profile in blastocysts despite the distinct differential mRNA expression and DNA methylation found in previous studies. The high number of generated sequence reads enabled a comprehensive analysis of the isomiR repertoire showing various templated and non-templated modifications. Furthermore, potentially blastocyst-specific miRNAs were identified.ConclusionsIn pre-implantation embryos, numerous distinct isomiRs were discovered indicating a high complexity of miRNA expression. Neither the sex of the embryo nor a maternal E2 exposure affected the miRNA expression profile of developing porcine blastocysts. The adaptation to the continuous duration of the E2 treatment might explain the lack of an effect.Electronic supplementary materialThe online version of this article (10.1186/s12864-018-4954-9) contains supplementary material, which is available to authorized users.

Endocrine disrupting chemicals (EDC) interfere with the natural hormone balance and may induce epigenetic changes through exposure during sensitive periods of development. In this study, the effects of short-term estradiol-17β (E2) exposure on various tissues of pregnant sows (F0) and on day 10 blastocysts (F1) were assessed. Intergenerational effects were investigated in the liver of 1-year old female offspring (F1). During gestation, sows were orally exposed to two low doses and a high dose of E2 (0.05, 10, and 1000 µg/kg body weight/day). In F0, perturbed tissue specific mRNA expression of cell cycle regulation and tumour suppressor genes was found at low and high dose exposure, being most pronounced in the endometrium and corpus luteum. The liver showed the most significant DNA hypomethylation in three target genes; CDKN2D, PSAT1, and RASSF1. For CDKN2D and PSAT1, differential methylation in blastocysts was similar as observed in the F0 liver. Whereas blastocysts showed hypomethylation, the liver of 1-year old offspring showed subtle, but significant hypermethylation. We show that the level of effect of estrogenic EDC, with the periconceptual period as a sensitive time window, is at much lower concentration than currently presumed and propose epigenetics as a sensitive novel risk assessment parameter.

Porcine conceptuses synthesize estrogens between Day 11 and 12 as signal for maternal recognition of pregnancy. A preimplantational estrogen exposure to pregnant gilts has been associated with embryonic losses and changes in endometrial mRNA expression. MicroRNAs (miRNAs) play a key role in the mRNA regulation by modulating the expression. Effects of estrogens on endometrial miRNAs have not been investigated in this context so far. Thus, we studied the endometrial expression profile of miRNAs in the pig at gestational Day 10 after daily estradiol-17β (E2) application starting at fertilization using either 0, 0.05 (ADI-acceptable daily intake), 10 (NOEL-no-observed-effect level) and 1,000 (high dose) µg E2/kg body weight/day, respectively. In endometrial homogenates, E2 (p < 0.001) and total estrogen concentrations (p < 0.001) were significantly increased, namely 28- and 160-fold, respectively, in the high dose group as compared to the control. Additionally, total estrogens were sixfold elevated in the NOEL group. Interestingly, high-throughput sequencing of small non-coding RNA libraries did not indicate any differentially expressed miRNAs between the treatment groups and the control group. The expression of 12 potential E2 target miRNAs investigated by RT-qPCR were equally unaffected. Thus, preimplantational E2 exposure resulted in significantly higher endometrial estrogen concentrations, but did not perturb the expression profile of endometrial miRNAs.

Maternal exposure to estrogens can induce long-term adverse effects in the offspring. The epigenetic programming may start as early as the period of preimplantation development. We analyzed the effects of gestational estradiol-17 (E2) exposure on blastocysts with two distinct low doses, corresponding to the acceptable daily intake "ADI" and close to the no-observed-effect level "NOEL," and a high dose (0.05, 10 and 1000 g E2/kg body weight daily, respectively). The E2 doses were orally applied to sows from insemination until sampling at day 10 of pregnancy and compared to carrier-treated controls leading to a significant increase in E2 in plasma, bile and selected somatic tissues including the endometrium in the high dose group. Conjugated and unconjugated E2 metabolites were as well elevated in the NOEL group. Although RNA-sequencing revealed a dose-dependent effect of 14, 17 and 27 differentially expressed genes (DEG) in the endometrium, single embryos were much more affected with 982 DEG in female blastocysts of the high dose group, while none were present in the corresponding male embryos. Moreover, the NOEL treatment caused 62 and 3 DEG in female and male embryos, respectively. Thus, we detected a perturbed sex-specific gene expression profile leading to a leveling of the transcriptome profiles of female and male embryos. The preimplantation period therefore demonstrates a vulnerable time window for estrogen exposure, potentially constituting the cause for lasting consequences. The molecular fingerprint of low-dose estrogen exposure on developing embryos warrants a careful revisit of effect level thresholds.

Background The transcriptional changes around the time of embryonic genome activation in pre-implantation embryos indicate that this process is highly dynamic. In vitro produced porcine blastocysts are known to be less competent than in vivo developed blastocysts. To understand the conditions that compromise developmental competence of in vitro embryos, it is crucial to evaluate the transcriptional profile of porcine embryos during pre-implantation stages. In this study, we investigated the transcriptome dynamics in in vivo developed and in vitro produced 4-cell embryos, morulae and hatched blastocysts. Results In vivo developed and in vitro produced embryos displayed largely similar transcriptome profiles during development. Enriched canonical pathways from the 4-cell to the morula transition that were shared between in vivo developed and in vitro produced embryos included oxidative phosphorylation and EIF2 signaling. The shared canonical pathways from the morula to the hatched blastocyst transition were 14–3-3-mediated signaling, xenobiotic metabolism general signaling pathway, and NRF2-mediated oxidative stress response. The in vivo developed and in vitro produced hatched blastocysts further were compared to identify molecular signaling pathways indicative of lower developmental competence of in vitro produced hatched blastocysts. A higher metabolic rate and expression of the arginine transporter SLC7A1 were found in in vitro produced hatched blastocysts. Conclusions Our findings suggest that embryos with compromised developmental potential are arrested at an early stage of development, while embryos developing to the hatched blastocyst stage display largely similar transcriptome profiles, irrespective of the embryo source. The hatched blastocysts derived from the in vitro fertilization-pipeline showed an enrichment in molecular signaling pathways associated with lower developmental competence, compared to the in vivo developed embryos.