Hypomethylation and Genetic Instability in Monosomy Blastocysts May Contribute to Decreased Implantation Potential

Abstract

DNA methylation is a key epigenetic mechanism responsible for gene regulation, chromatin remodeling, and genome stability, playing a fundamental role during embryonic development. The aim of this study was to determine if these epigenetic marks are associated with chromosomal aneuploidy in human blastocysts. Surplus, cryopreserved blastocysts that were donated to research with IRB consent were chosen with varying chromosomal aneuploidies and respective implantation potential: monosomies and trisomies 7, 11, 15, 21, and 22. DNA methylation analysis was performed using the Illumina Infinium HumanMethylation450 BeadChip (~485,000 CpG sites). The methylation profiles of these human blastocysts were found to be similar across all samples, independent of chromosome constitution; however, more detailed examination identified significant hypomethylation in the chromosome involved in the monosomy. Real-time PCR was also performed to determine if downstream messenger RNA (mRNA) was affected for genes on the monosomy chromosome. Gene dysregulation was observed for monosomy blastocysts within significant regions of hypo-methylation (AVEN, CYFIP1, FAM189A1, MYO9A, ADM2, PACSIN2, PARVB, and PIWIL3) (P < 0.05). Additional analysis was performed to examine the gene expression profiles of associated methylation regulators including: DNA methyltransferases (DNMT1, DNMT3A, DNMT3B, DNMT3L), chromatin modifying regulators (CSNK1E, KDM1, PRKCA), and a post-translational modifier (PRMT5). Decreased RNA transcription was confirmed for each DNMT, and the regulators that impact DNMT activity, for only monosomy blastocysts (P < 0.05). In summary, monosomy blastocysts displayed hypomethylation for the chromosome involved in the error, as well as transcription alterations of associated developmental genes. Together, these modifications may be contributing to genetic instability and therefore be responsible for the limited implantation potential observed for full monosomy blastocysts.

Aberrations in sperm DNA methylation patterns of males suffering from reduced fecundity

“…The results of this study obtained from validation phase showed a significant decrease in the methylation level in the case compared to the control groups in all CpGs, which related to TYRO3, CGβ, and FAM189A1 gene‐related amplicon. Each one of this CpGs was located in gene bodies and CpG islands, and these genes were found to be related to spermatogenesis and male fertility (Berger et al., ; Chen et al., ; McCallie et al., ; Parrott, Sriram, Liu, & Mathews, ). In general, our results are in agreement with the results of previous studies that have shown a variation at sperm DNA methylation in subfertile males compared to normal males (El Hajj et al., ; Kläver et al., ; Montjean et al., ) and in addition to other studies that report males suffering from reduced fecundity have low levels of sperm DNA methylation compared to their counterparts of proven fertility (Aoki, Emery, & Carrell, ; Boissonnas et al., ; Ferfouri et al., ; Laqqan, Solomayer, & Hammadeh, ).…”

“…These proteins are expressed on the surface of B cells which are important for antibody response. With pregnancy being a pro‐inflammatory state, proper expression of these proteins would be required for successful implantation to occur (McCallie et al., ). The alteration in the level of methylation may lead to changes in the activity and function of the gene especially CGB and TYRO3, which affects the spermatogenesis process and semen parameters, and this is consistent with the hypothesis that observed that the variations in methylation status are the possible reason for the abnormality in semen parameters of subfertile males and change in the gene expression (Miller‐Lindholm, LaBenz, Ramey, Bedows, & Ruddon, ; Lu & Lemke, ; Uusküla et al., ; van der Gun et al., ).…”

Oocyte and Embryo Manipulation and Epigenetics

“…McCallie et al sequenced the global methylation patterns of 316 cryopreserved aneuploid blastocysts, which were compared with control euploid blastocysts utilizing the Infinium Human-Methylation 450K BeadChip. 73 Significant hypomethylation of regulatory genes coding for DNA methyltransferases, chromatin modifying regulators, and posttranslational modifiers were observed in monosomic but not trisomic or euploid embryos. Given the diminutive reproductive potential of monosomic embryos, such findings highlight a potential epigenetic contribution to aneuploidy.…”

Aneuploidy and DNA Methylation as Mirrored Features of Early Human Embryo Development

“…In an earlier study, no differences were found in the DNA methylation profile of blastocysts with trisomy from euploid blastocysts, but in cases of monosomies, individual chromosomes with monosomy were hypermethylated. A decrease in DNA methylation has been recorded in several genes that are necessary for implantation and normal embryo development [79]. Moreover, along with a decrease in the level of gene methylation on chromosomes with monosomy, there was also a decrease in the transcription level of DNA methyltransferase genes.…”