Aberrant nucleosome organization in mouse SCNT embryos revealed by ULI-MNase-seq.

Somatic cell nuclear transfer (SCNT) can reprogram terminally differentiated somatic cells into totipotent embryos, but with multiple defects. The nucleosome positioning, as an important epigenetic regulator for gene expression, is largely unexplored during SCNT embryonic development. Here, we mapped genome-wide nucleosome profiles in mouse SCNT embryos using ultra-low-input MNase-seq (ULI-MNase-seq). We found that the nucleosome-depleted regions (NDRs) around promoters underwent dramatic reestablishment, which is consistent with the cell cycle. Dynamics of nucleosome position in SCNT embryos were delayed compared to fertilized embryos. Subsequently, we found that the aberrant gene expression levels in inner cell mass (ICM) were positively correlated with promoter NDRs in donor cells, which indicated that the memory of nucleosome occupancy in donor cells was a potential barrier for SCNT-mediated reprogramming. We further confirmed that the histone acetylation level of donor cells was associated with the memory of promoter NDRs. Our study provides insight into nucleosome reconfiguration during SCNT preimplantation embryonic development.