Maintenance of Mest imprinted methylation in blastocyst-stage mouse embryos is less stable than other imprinted loci following superovulation or embryo culture

Abstract

Assisted reproductive technologies are fertility treatments used by subfertile couples to conceive their biological child. Although generally considered safe, these pregnancies have been linked to genomic imprinting disorders, including Beckwith–Wiedemann and Silver–Russell Syndromes. Silver–Russell Syndrome is a growth disorder characterized by pre- and post-natal growth retardation. The Mest imprinted domain is one candidate region on chromosome 7 implicated in Silver–Russell Syndrome. We have previously shown that maintenance of imprinted methylation was disrupted by superovulation or embryo culture during pre-implantation mouse development. For superovulation, this disruption did not originate in oogenesis as a methylation acquisition defect. However, in comparison to other genes, Mest exhibits late methylation acquisition kinetics, possibly making Mest more vulnerable to perturbation by environmental insult. In this study, we present a comprehensive evaluation of the effects of superovulation and in vitro culture on genomic imprinting at the Mest gene. Superovulation resulted in disruption of imprinted methylation at the maternal Mest allele in blastocysts with an equal frequency of embryos having methylation errors following low or high hormone treatment. This disruption was not due to a failure of imprinted methylation acquisition at Mest in oocytes. For cultured embryos, both the Fast and Slow culture groups experienced a significant loss of maternal Mest methylation compared to in vivo-derived controls. This loss of methylation was independent of development rates in culture. These results indicate that Mest is more susceptible to imprinted methylation maintenance errors compared to other imprinted genes.

Assisted reproductive technologies are associated with limited epigenetic variation at birth that largely resolves by adulthood

“…This implies an effect of the ovarian stimulation or subfertility itself, rather than any of the additional embryo culturing processes associated with IVF. A similar direct effects of ovarian stimulation on offspring epigenetic profile have been reported for maternally imprinted regions 63,64 . and for LINE1 methylation, which was decreased in association with high-dose hormone treatment 65 .…”

The effects of superovulation and reproductive aging on the epigenome of the oocyte and embryo

“…Gain‐of‐methylation on paternally methylated H19 was observed in human MI (Sato et al, ) oocytes as well as in murine MI and MII oocytes (Sato et al, ) and blastocysts (Market‐Velker et al, ). Nevertheless, other studies reported no change in levels of DMR methylation of Igf2r , Peg1 , Peg3 , Plagl1 , Snrpn , H19 , and KvDmr1 in murine MII oocytes (Anckaert, Adriaenssens, Romero, Dremier, & Smitz, ; Denomme, Zhang, & Mann, ; Sato et al, ; Velker et al, ), or of Snrpn and H19 in Day‐9.5 mouse embryos (Fortier, Lopes, Darricarrere, Martel, & Trasler, ); furthermore, no change in allelic expression of H19 , Igf2 , Snrpn , and Kcnq1ot1 was observed in Day 9.5 mouse embryos (Fortier et al, ).…”

“…In humans, hormonal hyperstimulation was observed to alter maternally inherited imprinted DNA methylation in oocytes at the GV ( PEG1, KVDMR1 ) (Khoueiry et al, ; Sato, Otsu, Negishi, Utsunomiya, & Arima, ; Sutcliffe et al, ) and metaphase I (MI) stages (Khoueiry et al, ; Sato et al, ). Similarly, results in mice revealed a loss of DNA methylation on the maternal allele of multiple imprinted differentially methylated regions (DMRs) in morulae ( Snrpn ) (El Hajj et al, ), blastocysts ( Mest [also known as Peg1 ] , Peg3, Snrpn ) (Market‐Velker, Zhang, Magri, Bonvissuto, & Mann, ; Velker, Denomme, Krafty, & Mann, ), and postnatal brain tissue of juvenile offspring ( Peg3 ) (de Waal et al, )). Gain‐of‐methylation on paternally methylated H19 was observed in human MI (Sato et al, ) oocytes as well as in murine MI and MII oocytes (Sato et al, ) and blastocysts (Market‐Velker et al, ).…”

“…Alternatively, differences in DNA methylation and allelic expression may have been missed in genes whose expression is not solely dependent on DNA methylation, requiring other epigenetic marks such as histone modification (Weaver et al, ). Furthermore, epigenetic changes seen in the embryo but not the oocyte could indicate disruption of maintenance rather than acquisition of DNA methylation (Velker et al, ). Future investigation should focus on determining the full effects of hormone introduction on gain or loss of DNA methylation at these regions.…”

Harvesting of Mouse Embryos at 0.5 Dpc as a Tool to Reduce Animal Use: Data from C57BL/6J, B6*129 and FVB/NJ Strains

“…It has also been associated with alterations in essential proteins involved in regulation and translation of maternally stored mRNA with short poly A tail, such as poly(A)-binding protein (Epab) and poly(A)-binding protein cytoplasmic 1 (Pabpc1) [16] [19]. Important genes can be dysregulated due to superovulation, such as the Mest gene or the Grb10 [20] [21] and regulatory proteins can also be changed by this procedure like STAT3, leptin, transforming growth factor β-2 among others [22].…”