Abstract
The low full-term developmental efficiency of porcine somatic cell nuclear transfer (SCNT) embryos is mainly attributed to imperfect epigenetic reprogramming in the early embryos. However, dynamic expression patterns of histone methylation involved in epigenetic reprogramming progression during porcine SCNT embryo early development remain to be unknown. In this study, we characterized and compared the expression patterns of multiple histone methylation markers including transcriptionally repressive (H3K9me2, H3K9me3, H3K27me2, H3K27me3, H4K20me2 and H4K20me3) and active modifications (H3K4me2, H3K4me3, H3K36me2, H3K36me3, H3K79me2 and H3K79me3) in SCNT early embryos from different developmental stages with that from in vitro fertilization (IVF) counterparts. We found that the expression level of H3K9me2, H3K9me3 and H4K20me3 of SCNT embryos from 1-cell to 4-cell stages was significantly higher than that in the IVF embryos. We also detected a symmetric distribution pattern of H3K9me2 between inner cell mass (ICM) and trophectoderm (TE) in SCNT blastocysts. The expression level of H3K9me2 in both lineages from SCNT expanded blastocyst onwards was significantly higher than that in IVF counterparts. The expression level of H4K20me2 was significantly lower in SCNT embryos from morula to blastocyst stage compared with IVF embryos. However, no aberrant dynamic reprogramming of H3K27me2/3 occurred during early developmental stages of SCNT embryos. The expression of H3K4me3 was higher in SCNT embryos at 4-cell stage than that of IVF embryos. H3K4me2 expression in SCNT embryos from 8-cell stage to blastocyst stage was lower than that in the IVF embryos. Dynamic patterns of other active histone methylation markers were similar between SCNT and IVF embryos. Taken together, histone methylation exhibited developmentally stage-specific abnormal expression patterns in porcine SCNT early embryos.
Highlights
Somatic cell nuclear transfer (SCNT) is a reproductive biotechnology, which can reprogram highly differentiated somatic cells into totipotent embryos and further develop into individual animals
Given the general lack of evidences on histone methylation reprogramming during early development of porcine SCNT embryos, we investigated dynamic reprogramming of histone methylation modifications, such as di- and tri-methylation of H3 and H4 lysine residues, which probably affect the development of SCNT embryos
We examined epigenetic dynamics and distribution patterns of histone methylation in the process of early development of porcine in vitro fertilization (IVF) and SCNT embryos
Summary
Somatic cell nuclear transfer (SCNT) is a reproductive biotechnology, which can reprogram highly differentiated somatic cells into totipotent embryos and further develop into individual animals. Abnormal DNA methylation reprogramming in somatic cell cloned animals or embryos was reported in mouse[3], cattle[4,5,6,7], pig[8, 9], rabbit[10] and sheep[11], but reprogramming mechanisms of histone modifications during the early development process of SCNT embryos are still poorly understood[12, 13]. Recent studies found that abnormal reprogramming of histone methylation in early developmental procession of SCNT embryo, such as abnormal reprogramming of H3K9me3 [18] and H3K27me3 [19] in mouse, H3K9me3 [6] in bovine, H3K9me in sheep [20], and H3K36me3 [13] and H3K4me3 [12] in pig cloned embryos
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