Genome-wide assessment of DNA methylation in mouse oocytes reveals effects associated with in vitro growth, superovulation, and sexual maturity

Abstract: Background: In vitro follicle culture (IFC), as applied in the mouse system, allows the growth and maturation of a large number of immature preantral follicles to become mature and competent oocytes. In the human oncofertility clinic, there is increasing interest in developing this technique as an alternative to ovarian cortical tissue transplantation and to preserve the fertility of prepubertal cancer patients. However, the effect of IFC and hormonal stimulation on DNA methylation in the oocyte is not fully known, and there is legitimate concern over epigenetic abnormalities that could be induced by procedures applied during assisted reproductive technology (ART). Results: In this study, we present the first genome-wide analysis of DNA methylation in MII oocytes obtained after natural ovulation, after IFC and after superovulation. We also performed a comparison between prepubertal and adult hormonally stimulated oocytes. Globally, the distinctive methylation landscape of oocytes, comprising alternating hyper- and hypomethylated domains, is preserved irrespective of the procedure. The conservation of methylation extends to the germline differential methylated regions (DMRs) of imprinted genes, necessary for their monoallelic expression in the embryo. However, we do detect specific, consistent, and coherent differences in DNA methylation in IFC oocytes, and between oocytes obtained after superovulation from prepubertal compared with sexually mature females. Several methylation differences span entire transcription units. Among these, we found alterations in Tcf4, Sox5, Zfp521, and other genes related to nervous system development. Conclusions: Our observations show that IFC is associated with altered methylation at specific set of loci. DNA methylation of superovulated prepubertal oocytes differs from that of superovulated adult oocytes, whereas oocytes from superovulated adult females differ very little from naturally ovulated oocytes. Importantly, we show that regions other than imprinted gDMRs are susceptible to methylation changes associated with superovulation, IFC, and/or sexual immaturity in mouse oocytes. Our results provide an important reference for the use of in vitro growth and maturation of oocytes, particularly from prepubertal females, in assisted reproductive treatments or fertility preservation

Correction to: Genome-wide assessment of DNA methylation in mouse oocytes reveals effects associated with in vitro growth, superovulation, and sexual maturity.

After publication of the original article [1], we were notified that

Correction to: Genome-wide assessment of DNA methylation in mouse oocytes reveals effects associated with in vitro growth, superovulation, and sexual maturity.

After publication of the original article [1], we were notified that

Effect of Embryo Vitrification on Rabbit Foetal Placenta Proteome during Pregnancy

Very limited information on the post-implantatory effects of vitrification has been published till now. We observed in a previous study that the vitrification procedure for the cryopreservation of embryos introduced transcriptomic and proteomic modifications in the rabbit foetal placenta at the middle of gestation. Now, we have conducted a proteomic study to determine whether protein alterations in the foetal placenta induced by the vitrification procedure remain during pregnancy. In this study, we used 2D-DIGE and mass spectrometry (MALDI-TOF-TOF and LC-MS/MS analysis) to identify the protein changes during middle and late stages of gestation (Day 14 and Day 24, respectively) in rabbit foetal placenta. We identified 11 differentially expressed proteins at Day 14 and 13 proteins at Day 24. Data are available via ProteomeXchange with identifiers PXD001840 and PXD001836. In addition, we demonstrate the presence of three proteins, serum albumin, isocitrate dehydrogenase 1 [NADP+], and phosphoglycerate mutase 1, which were altered during pregnancy. We demonstrate the existence of changes in foetal placental protein during pregnancy induced by the vitrification procedure, which brings into question whether vitrification effects observed during foetal development could lead to physiological and metabolic disorders in adulthood. This effect, taken together with other effects reported in the literature, suggests that embryo cryopreservation is not neutral.This work was supported by the Generalitat Valenciana research program (Prometeo 2014/036) and the Spanish Research Projects (CICYT AGL2011-29831-C03-01). M. D. Saenz-de-Juano was supported by a research grant from Generalitat Valenciana (Programa VALI+d, ACIF/2011/254). Nofima AS provided support in the form of salaries for author KH, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the Author Contributions section.Saenz De Juano Ribes, MDLD.; Vicente Antón, JS.; Hollung, K.; Marco Jiménez, F. (2015). Effect of Embryo Vitrification on Rabbit Foetal Placenta Proteome during Pregnancy. PLoS ONE. 10(4):e0125157-e0125157. https://doi.org/10.1371/journal.pone.0125157Se0125157e012515710

List of identified altered proteins at Day 24 of gestation.

<p>Mol. Mass: Molecular Mass; pI: Isoelectric point; Seq. Cov.: sequence coverage.</p><p>List of identified altered proteins at Day 24 of gestation.</p

List of identified altered proteins at Day 14 of gestation.

<p>Mol. Mass: Molecular Mass; pI: Isoelectric point; Seq. Cov.: sequence coverage.</p><p>List of identified altered proteins at Day 14 of gestation.</p

Protein interaction network of altered proteins at Day 24.

<p>In the network generated by STRING v.9.1, each node represents a protein and each edge represents an interaction, coloured by evidence type (see STRING website for colour legend).</p

Representation of 2D-DIGE gel at Day 24.

<p>Proteins picked for identification are outlined with an arrow and the tagged numbers correspond to the same ones indicated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0125157#pone.0125157.t003" target="_blank">Table 3</a>.</p

Representation of 2D-DIGE gel at Day 14.

<p>Proteins picked for identification are outlined with an arrow and the tagged numbers correspond to the same ones indicated in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0125157#pone.0125157.t002" target="_blank">Table 2</a>.</p

Protein interaction network of altered proteins at Day 14.

<p>In the network generated by STRING v.9.1, each node represents a protein and each edge represents an interaction, coloured by evidence type (see STRING website for colour legend). The original graphic output was modified including circles to group the proteins according to their regulation. A green line means upregulation and a red line downregulation.</p