Blastomere biopsy influences epigenetic reprogramming during early embryo development, which impacts neural development and function in resulting mice

Abstract

Blastomere biopsy is used in preimplantation genetic diagnosis; however, the long-term implications on the offspring are poorly characterized. We previously reported a high risk of memory defects in adult biopsied mice. Here, we assessed nervous function of aged biopsied mice and further investigated the mechanism of neural impairment after biopsy. We found that aged biopsied mice had poorer spatial learning ability, increased neuron degeneration, and altered expression of proteins involved in neural degeneration or dysfunction in the brain compared to aged control mice. Furthermore, the MeDIP assay indicated a genome-wide low methylation in the brains of adult biopsied mice when compared to the controls, and most of the genes containing differentially methylated loci in promoter regions were associated with neural disorders. When we further compared the genomic DNA methylation profiles of 7.5-days postconception (dpc) embryos between the biopsy and control group, we found the whole genome low methylation in the biopsied group, suggesting that blastomere biopsy was an obstacle to de novo methylation during early embryo development. Further analysis on mRNA profiles of 4.5-dpc embryos indicated that reduced expression of de novo methylation genes in biopsied embryos may impact de novo methylation. In conclusion, we demonstrate an abnormal neural development and function in mice generated after blastomere biopsy. The impaired epigenetic reprogramming during early embryo development may be the latent mechanism contributing to the impairment of the nervous system in the biopsied mice, which results in a hypomethylation status in their brains.

Embryo biopsy and development: the known and the unknown

“…These studies showed deregulated expression of genes involved in DNA methylation, chromatin remodeling, cell cycle and differentiation, oxidative stress, metabolism (Wu et al 2014) and of three imprinted genes UBE3A, SNRPN and PEG1 (S Sampino, F Zacchini, GE Ptak, unpublished observation) in 4.5 dpc blastocysts. Epigenetic analysis of 7.5 dpc embryos, following BB, revealed a reduced global methylation profile vs that of control embryos.…”

“…cell proliferation and differentiation) or the onset of developmentally related diseases (i.e. cardiovascular disease and infertility) (Wu et al 2014).…”

“…Though the majority of studies did not show an increased incidence of pregnancy complications following embryo biopsy, some reported that BB is associated with reduced implantation rates, increased risks of low birth weight or preterm birth (Banerjee et al 2008, Thomaidis et al 2012, Cimadomo et al 2016 and, in early childhood, with impaired cognitive and/or motor development (Banerjee et al 2008, Middelburg et al 2011, Thomaidis et al 2012, Cimadomo et al 2016, while no indication on TB pregnancy/babies are available. Research on mouse model has shown that BB is not only associated with increased pregnancy loss and reduced/delayed fetal development, but also with impaired placental functions and epigenetic defects in both fetuses and placentae (Sugawara et al 2012, Yang et al 2012, Sato et al 2014, Wu et al 2014, Yao et al 2016. Regarding TB, research on mouse model is very limited so far.…”

“…body weight, blood parameters or gross morphology of major internal organs) (BB: Cui et al 1993Cui et al , 1994TB: Gentry & Critser 1995). However, in the last decade, different research groups have described increased body weight/size and impaired behavior in BB mice and have suggested reduced fertility in adult females (Yu et al 2009, Zeng et al 2013, Sampino et al 2014, Wu et al 2014). …”

Noninvasive chromosome screening of human embryos by genome sequencing of embryo culture medium for in vitro fertilization

“…(i) PGS requires invasive embryo biopsy, which has been shown to decrease embryo quality after cleavage-stage biopsy (17); (ii) longterm biosafety of embryo biopsy in humans has not been evaluated, whereas animal studies have shown negative influences on neural and adrenal development (18)(19)(20); (iii) it involves technical expertise, requiring special training and experienced embryologists to perform the biopsy, which significantly increase the overall costs of clinical PGS cycles. Therefore, a noninvasive and easy-to-perform screening tool would greatly facilitate the widespread performing of chromosome screening before embryo implantation, thereby improving success rates.…”