Processes of conceptus implantation and placentation vary among mammalian species. However, differences in physiological and biochemical processes were once thought not to differ so much, particularly as to the kinds of genes expressed. In fact, recent progress has identified that in addition to the hormones, cytokines, proteases and cell adhesion molecules classically characterized, epithelial-mesenchymal transition (EMT), epigenetic regulation and the expression of endogenous retroviruses (ERV) are all required for the progression of conceptus implantation to placentation. Thus, continued research into EMT, epigenetic regulation and the expression of ERVs will aid in enhancing understanding of their impact on reproductive physiology in humans and domestic animals.

Epigenetic regulation of gene expression plays critical roles in differentiation of cells and organs. In mammalian placentation, it is clearly shown that genomic imprinting which is primarily controlled by DNA methylation is essential for placentation. Addition to DNA methylation, histone modifications and non-coding RNAs are also involved in placentation. Recently, it has been shown that epigenetic mutations could cause medical complications during pregnancy such as FGR (Fetal Growth Restriction) and PIH (Pregnancy Induced Hypertension). Developmental epigenetics would contribute to establish new concepts of diseases and provide new treatments in future.

The two LTR retrotransposon-derived genes PEG10 and PEG11/RTL1 play essential roles in placental formation and its maintenance in the current mammalian developmental system. The former is a therian-specific and the latter is a eutherian-specific gene, suggesting that once they had been acquired in common ancestors of the therian and eutherian mammals, respectively, they have underwent positive selection during the course of mammalian evolution due to developmental advantages they conferred. Thus, their exaptation had a profound impact on the evolution of mammalian viviparity as well as the emergence of the therians and eutherians, the infraclass and subclass of mammals, respectively. How the exaptation of PEG10 and PEG11/RTL1 come to take place in the mammalian lineage? We propose that the exaptaion mechanism comprises two subsequent steps. The first follows the pattern of nearly neutral theory of molecular evolution, where the retrotransposons were neutralized by DNA methylation and genetic drift fixed them in the population. At the next step, Darwinian evolution propagated these genes into all the therian and eutherian population by natural selection. In the course of these processes, the placenta, a mammalian-specific extraembyonic tissue, may have been of special importance as a sort of “natural laboratory” for mammalian evolution.

Sirtuins, a family of NAD -dependent protein deacetylases, regulate important physiological events including aging and cell metabolism, mainly by protecting cells/tissues from oxidative damage. Ovarian aging decreases the quality of oocytes through induction of mitochondrial dysfunction and increases in DNA strand breaks by accumulation of reactive oxygen species. However, involvement of sirtuins in regulating oocyte quality with aging has not been determined. Here, we found the expression of sirtuin genes (Sirt1–7) in mouse ovaries and isolated oocytes and cumulus cells in a cell-specific manner. Based on real-time RT-PCR, all seven sirtuin genes were detected in the ovary with Sirt2 transcript levels showing the highest abundance. Oocyte expressed high levels of Sirt6, whereas the expressions of Sirt1, Sirt2, Sirt4, and Sirt6 were high in cumulus cells. When comparing samples from young and aged mice, oocyte levels of Sirt1–7 mRNA were not different. However, Sirt2 and Sirt6 transcript levels were decreased in cumulus cells of aged mice. Our findings suggest a possible association of Sirt2 and Sirt6 transcript levels in cumulus cells with impaired oocyte quality in aged mice. Further understanding the roles of these sirtuins in cumulus cell and oocyte could provide a better strategy to minimize aging-related decline in oocyte quality.

The aim of this retrospective study was to investigate the relationship between the oxygen consumption rate of blastocysts before freezing and their viability after warming with respect to their re-expansion and blastomere loss after warming. A total of 41 blastocysts from 29 in vitro fertilization (IVF) treatment cycles, that were not scheduled for cryopreservation for the next cycle, were examined. Good quality blastocysts were defined those having as less than 20% of blastomere loss, and rapid re-expanded blastocysts were defined those having as more than 50% blastocoel re-expansion during post-warming culture of 2 h. We evaluated the oxygen consumption rates before freezing and after warming as well as their relationship with the morphological features of good-quality and rapid re-expanded blastocysts during the post-warming culture. Good-quality blastocysts had a significantly higher oxygen consumption rate after warming than damaged blastocysts; furthermore, rapid re-expanded blastocysts had a significantly higher oxygen consumption rate before freezing than slow or no re-expansion blastocysts. These observations suggest that measurements of the oxygen consumption rate of individual blastocysts before freezing provides important information regarding viability after warming from the viewpoint of blastocoel re-expansion.

The objective of the present study was to investigate the in vitro developmental competence of porcine in vitro matured (IVM) oocytes vitrified after removal of cytoplasmic lipid droplets (delipation). After vitrification and warming, the delipated porcine IVM oocytes were inseminated and subsequently cultured in vitro. The rate of development to the blastocyst stage of delipated, vitrified oocytes (5.9%) was significantly lower than that of control oocytes (untreated oocytes) (26.2%). We also examined the influence of delipation of porcine IVM oocytes on development to the blastocyst stage following in vitro fertilization (IVF). Delipated porcine IVM oocytes (not vitrified) were inseminated and subsequently cultured in vitro. The rates of development to the blastocyst stage were similar for delipated and undelipated oocytes (21.1% and 26.2%, respectively). The results of the present study showed that delipated, vitrified porcine IVM oocytes can develop to the blastocyst stage following IVF, though blastocyst formation rate was low, and that delipation of porcine IVM oocytes did not negatively affect their development to blastocyst stage.

Global transcriptome studies have provided important information advancing our understanding of nuclear reprogramming in somatic cell nuclear transfer (SCNT) embryos. The expression of the Eif1a gene is down-regulated in mouse Sertoli cell nuclear transfer (SeCNT) embryos during the preimplantation stages, however its protein expression level remains unclear. Here we observed the protein expression level of EIF1A by immunofluorescence and western blot analysis during the preimplantation stages in mouse SeCNT embryos. The results reveal that EIF1A protein is constantly expressed in germinal-vesicle and metaphase II oocytes and preimplantation stage embryos. Importantly, the localization and expression level of EIF1A were similar in control in vitro fertilized embryos and SeCNT embryos. Thus, since maternally derived EIF1A persisted throughout preimplantation development, repression of Eif1a is not likely to be involved in the developmental potency of mouse SeCNT embryos.