Abstract
Polycystic ovary syndrome (PCOS) is the most common endocrine disorder in women of childbearing age and is the main cause of anovulatory infertility. To increase the number of oocytes obtained, controlled ovarian stimulation (COS) has become a routine choice for in vitro fertilization-embryo transfer (IVF-ET), which is one of the common assisted reproductive technologies for PCOS patients. However, for these patients, there is a high risk of ovarian hyperstimulation syndrome (OHSS). Obtaining in vitro maturation (IVM) of immature oocytes, and then in vitro fertilization and embryo transfer of mature oocytes provides a possible way for people to solve the above problems. Since the IVM technology will expose oocytes to in vitro conditions for a longer period of time, theoretically increasing the risk of the oocytes being affected by the culture environment, further research and explorations are needed for study in gene programming, epigenetics, etc. Therefore, to explore the impact of IVM operation on embryonic development is of great significance for further clarifying assisted reproductive safety and improving IVM operation conditions. Here we focused on DNA methylation reprogramming process which was essential for embryonic development. We tested the DNA methylation of sperm, IVM oocytes and IVM generated early stage embryos including pronucleus, 4cell, 8cell, morula, inner cell mass, trophoectoderm (TE) as well as six-week embryos by Nimble Gen Human DNA Methylation 3x729K CpG Island Plus RefSeq Promoter Array and compared the data with our published genome-wide DNA methylomes of human gametes and early embryos generated from in vivo maturation oocytes. We showed that IVM embryos show abnormal DNA methylation reprogramming pattern. By analyzing the abnormally reprogrammed promoters, we further found that IVM may affect the functions of demethylation related genes. Oocytes from IVM manipulation were tested with higher DNA methylation levels, and their abnormal methylated promoters mainly enriched in immune and metabolism pathways. Furthermore, we investigated the DNA methylation of TE, which was directly related with implantation process and revealed the abnormal methylated promoters were related with metabolism pathway too. Our data support that IVM may influence the DNA methylome of oocytes, which in turn affects the methylome of their embryos. However, due to the limited number of samples and the inability of the chip to cover all CpG sites, the results of this study require further research and validation.
DNA methylation in porcine preimplantation embryos developed in vivo and produced by in vitro fertilization, parthenogenetic activation and somatic cell nuclear transfer
