Germline-specific epigenetic reprogramming of primary epimutations in mice produced by assisted reproductive technology

Assistive reproductive technologies (ART) including intra-cytoplasmic sperm injection (ICSI) are now commonly used in human and other animals. However, epigenetic defects have been in individuals produced by ART. Interestingly, in animal studies, epigenetic defects observed in individuals produced by ART are typically not transmitted to progeny produced by natural reproduction. This suggests that these defects are corrected by germline-specific epigenetic reprogramming, but this has not previously been directly demonstrated experimentally. To investigate this further, we examined three imprinted genes, H19 , Snrpn and Peg3 to assess the occurrence of epimutations in mice produce by intracytoplasmic sperm injection (ICSI—a form of ART), and the subsequent correction of these epimutations in the germ line. We examined allele-specific DNA methylation profiles in differentially methylated regions (DMRs) of these genes, as well as allele-specific expression of these genes in somatic cells and germ cells. We found that - primary epimutations and correlated abnormal expression were present in many of the samples obtained from mice generated by ICSI, but not in any of the naturally conceived mice. We further observed that following natural mating of the ICSI mice, these epimutations were not transmitted to offspring. Subsequent analysis of germ cells from the ICSI mice revealed that the epimutations were corrected by germline-specific reprogramming. Additional analyses of epigenetic profiles of imprinted genes in ICSI mice at 6 days postpartum (dpp), as well as in mice produced from oocytes that had undergone endocrine stimulation followed by natural insemination implicate endocrine stimulation (superovulation) as one causative agent leading to primary epimutations in ART mice.