Dynamic Reprogramming of Histone Acetylation and Methylation in the First Cell Cycle of Cloned Mouse Embryos1

Abstract

Epigenetic reprogramming is thought to play an important role in the development of cloned embryos reconstructed by somatic cell nuclear transfer (SCNT). In the present study, dynamic reprogramming of histone acetylation and methylation modifications was investigated in the first cell cycle of cloned embryos. Our results demonstrated that part of somatic inherited lysine acetylation on core histones (H3K9, H3K14, H4K16) could be quickly deacetylated following SCNT, and reacetylation occurred following activation treatment. However, acetylation marks of the other lysine residues on core histones (H4K8, H4K12) persisted in the genome of cloned embryos with only mild deacetylation occurring in the process of SCNT and activation treatment. The somatic cloned embryos established histone acetylation modifications resembling those in normal embryos produced by intracytoplasmic sperm injection through these two different programs. Moreover, treatment of cloned embryos with a histone deacetylase inhibitor, Trichostatin A (TSA), improved the histone acetylation in a manner similar to that in normal embryos, and the improved histone acetylation in cloned embryos treated with TSA might contribute to improved development of TSA-treated clones. In contrast to the asymmetric histone H3K9 tri-and dimethylation present in the parental genomes of fertilized embryos, the triand dimethylations of H3K9 were gradually demethylated in the cloned embryos, and this histone H3K9 demethylation may be crucial for gene activation of cloned embryos. Together, our results indicate that dynamic reprogramming of histone acetylation and methylation modifications in cloned embryos is developmentally regulated. developmental biology, early development, embryo, epigenetic reprogramming, fertilization, histone acetylation, histone methylation, somatic cell nuclear transfer, TSA

Effect of the enucleation procedure on the reprogramming potential and developmental capacity of mouse cloned embryos treated with valproic acid

“…In ME or AE cytoplasts, a rapid and almost complete H3K14 deacetylation occurred in the somatic nucleus during the first 3 h after injection, followed by an equally rapid and complete re-acetylation after activation. A similar H3K14 acetylation dynamics has been described by others for cloned embryos produced from ME cytoplasts and treated with TSA (Wang et al 2007). In contrast, in IE cytoplasts, the deacetylation of H3K14 Values with different superscripts within the same column differ significantly (P!0.05).…”

“…In this sense, the lower deacetylation activity in the IE cytoplasts could represent an advantage of the IE protocol with regard to ME or AE methods concerning nuclear reprogramming. But, on the other hand, studies indicate that a complete deacetylation of the lysine residues of core histones before the beginning of the re-acetylation, as occurred in our ME and AE cytoplasts, may be necessary for the correct regulation of gene expression and the establishment of totipotency in the cloned embryos (Wang et al 2007). Histone deacetylation would allow the silencing of the somatic gene expression program before the initiation of the embryonic pattern of gene expression is induced by histone re-acetylation.…”

“…In addition, as nuclear reprogramming in cloned embryos is thought to occur at an epigenetic level and as one of the epigenetic pathways related to chromatin structure is the global level of histone acetylation (Yang et al 2007), the acetylation dynamics in core histones after NT can also be used as a good marker of the extent of nuclear reprogramming (Wang et al 2007). In particular, acetylation of H3K14 plays an important role in mediating nucleosome remodeling, facilitating the access of the transcriptional machinery to nucleosomal DNA (MacDonald & Howe 2009), and its acetylation/ deacetylation dynamics has been analyzed in several studies involving SCNT embryos prepared by ME (Rybouchkin et al 2006, Wang et al 2007). …”

Somatic cell reprogrammed by oocyte: process and barricade

“…As discussed above, the genes silence in somatic nucleus facilitates the reprogramming of somatic cell. At the same time, MFs can associate with somatic chromatin in the interphase of each cell cycle and exert their effect on the epigenetic modifications of somatic genome; for example, DNA demethylation, the change in histone acetylation and methylation, chromatin remodeling and X chromosome reactivation (Kang et al 2001;Chen et al 2004;Nolen et al 2005;Wang et al 2007;Bui et al 2010). Although epigenetic modifications are usually abnormal in cloned embryos, nevertheless, MFs can reprogram them into an imperfect totipotent state.…”

“…Abnormal histone modifications were also observed in cloned embryo, including acetylation (such as low level of acetylation at H3K9, H3K14, and H4K16; acetylation does not change dynamically at H4K8 and H4K12) and methylation (such as low levels of methylation at H3K4 and H3K27; high levels of methylation at H3K9 and 4 × H3K9) (Santos et al 2003;Wang et al 2007;Shao et al 2008;Zhang et al 2009). In fact, different types of epigenetic modifications can interact with each other (as shown in Figure 2); the abnormality in one type of epigenetic modification must result in the abnormality in other types of epigenetic modifications.…”