Inheritable Histone H4 Acetylation of Somatic Chromatins in Cloned Embryos

Abstract

A viable cloned animal indicates that epigenetic status of the differentiated cell nucleus is reprogrammed to an embryonic totipotent state. However, molecular events regarding epigenetic reprogramming of the somatic chromatin are poorly understood. Here we provide new insight that somatic chromatins are refractory to reprogramming of histone acetylation during early development. A low level of acetylated histone H4-lysine 5 (AcH4K5) of the somatic chromatin was sustained at the pronuclear stage. Unlike in vitro fertilized (IVF) embryos, the AcH4K5 level remarkably reduced at the 8-cell stage in cloned bovine embryos. The AcH4K5 status of somatic chromatins transmitted to cloned and even recloned embryos. Differences of AcH4K5 signal intensity were more distinguishable in the metaphase chromosomes between IVF and cloned embryos. Two imprinted genes, Ndn and Xist, were aberrantly expressed in cloned embryos as compared with IVF embryos, which is partly associated with the AcH4K5 signal intensity. Our findings suggest that abnormal epigenetic reprogramming in cloned embryos may be because of a memory mechanism, the epigenetic status itself of somatic chromatins.To obtain developmental competence of cloned embryos to term, the differentiated cell nucleus should be subject to epigenetic reprogramming processes including chromatin remodeling and DNA methylation during preimplantation development. In the somatic cell nuclear transfer, many clinical anomalies such as high abortion rates, increased body weight, and early death after birth have been reported (1-4). These developmental failures could be because of aberrant reprogramming in the reciprocal interactions between donor nuclei and enucleated oocyte cytoplasm (5). In this context, it has been demonstrated that reprogramming of DNA methylation (6 -9), expression of imprinted and nonimprinted genes (10 -13), X-chromosome inactivation (14, 15), and telomerase activity (16) are incomplete in cloned embryos during early development as compared with normal embryos. Especially, abnormal epigenetic reprogramming may lead to faulty or differential gene expression, thereby resulting in developmental defects of cloned embryos.An intrinsic difference in the early embryonic development between fertilization and somatic cell cloning may arise from distinct chromatin architectures between spermatozoa and somatic cells. In fact, activation and remodeling in a reconstructed oocyte with a somatic cell nucleus might obviously differ from the processes of normal fertilization. In mammals, maternal and paternal genomes should reprogram to reach a totipotent state for normal development. During fertilization, the sperm genome remodels in the oocyte cytoplasm after replacement of its protamines with oocyte histones. In the somatic cell nuclear transfer, however, remodeling of somatic chromatins may be entirely discriminated because of a paucity of sperm factors and incomplete microenvironment within the enucleated oocyte cytoplasm. Differences of chromatin remodeling can be also becau...

Rabbit somatic cell cloning: effects of donor cell type, histone acetylation status and chimeric embryo complementation

“…Epigenetic reprogramming occurs abnormally in a large proportion of cloned embryos (Dean et al 2001, Kang et al 2003, Santos et al 2003, Hiendleder et al 2004, Wee et al 2006 and is apparently species-specific (Dean et al 2001, Beaujean et al 2004a, 2004b, Shi et al 2004 and largely dependent on the type of donor cells (Santos et al 2003). Epigenetic marks, which characterize specific DNA and chromatin modifications, are the main players in nuclear reprogramming and can be used to assess this process and predict SCNT efficiency.…”

Supplementation of fetal bovine serum alters histone modification H3R26me2 during preimplantation development of in vitro produced bovine embryos

“…Histone modification is one such epigenetic mechanism that is critical to embryo development of several species such as mice (Corry et al 2009), cattle (Santos et al 2003, Enright et al 2005, Wee et al 2006, Maalouf et al 2008, Ross et al 2008, pig (Park et al 2009, Gao et al 2010, sheep (Hou et al 2008) and human (Zhang et al 2012). In mice, Sarmento et al (2004), describes two types of histone patterns during preimplantation development, a consistent, stable mark during development and a dynamic, reversible mark.…”

“…In cattle, where much research has focused on the altered reprogramming of histones in embryos produced by somatic cell nuclear transfer, (Santos et al 2003, Morgan et al 2005, Wee et al 2006) fewer studies have examined the histone modifications throughout preimplantation stages (Maalouf et al 2008, Ross et al 2008 or the effects of culture conditions. Specific epigenetic patterns within each embryonic stage allow for proper development and successful pregnancy to ensue (Palini et al 2011).…”

Timing and Uniformity of Embryonic Gene Activation Affect Subsequent Pre-implantation Development of Cloned Bovine Embryos

“…Semiquantitative RT-PCR analysis has s h o w n t h a t t h e e x p r e s s i o n l e v e l s o f developmentally important genes, such as DNMT and Mash2, increase in bovine pre-implantation embryos [11]. The relative expression levels of Xist and Ndn, the imprinted genes correlated with EGA, were significantly higher in in vitro fertilized bovine embryos at the 8-cell stage than in NT embryos [10]. These findings may indicate that the increase in the gene transcripts reflects the developmental ability of the embryos.…”

“…Even if the offspring survive, they often have increased birth weights, which is referred to as "large offspring syndrome" [5][6][7]. Recently, it has been reported that aberration o f ep i g e ne t i c m o d i f i c a t i o n s s u c h a s D N A methylation and histone acetylation occur in bovine NT embryos [8][9][10]. Additionally, abnormal levels of expression of some developmentally important genes have also been observed at the blastocyst stage in bovine NT embryos [11,12].…”