Abstract. Phosphorylation of histone H3 at Ser10 (H3S10P) has been linked to a variety of cellular processes, such as chromosome condensation and gene activation/silencing. Remarkably, in mammalian somatic cells, H3S10P initiates in the pericentromeric heterochromatin during the late G2 phase, and phosphorylation spreads throughout the chromosomes arms in prophase, being maintained until the onset of anaphase when it gets dephosphorylated. Considerable studies have been carried out about H3S10P in different organisms; however, there is little information about this histone modification in mammalian embryos. We hypothesized that this epigenetic modification could also be a marker of pericentromeric heterochromatin in preimplantation embryos. We therefore followed the H3S10P distribution pattern in the G1/S and G2 phases through the entire preimplantation development in in vivo mouse embryos. We paid special attention to its localization relative to another pericentromeric heterochromatin marker, HP1β and performed immunoFISH using specific pericentromeric heterochromatin probes. Our results indicate that H3S10P presents a remarkable distribution pattern in preimplantation mouse embryos until the 4-cell stage and is a better marker of pericentromeric heterochromatin than HP1β. After the 8-cell stage, H3S10P kinetic is more similar to the somatic one, initiating during G2 in chromocenters and disappearing upon telophase. Based on these findings, we believe that H3S10P is a good marker of pericentromeric heterochromatin, especially in the late 1-and 2-cell stages as it labels both parental genomes and that it can be used to further investigate epigenetic regulation and heterochromatin mechanisms in early preimplantation embryos. Key words: Aurora, Embryo, Heterochromatin, Histone, Phosphorylation (J. Reprod. Dev. 58: [467][468][469][470][471][472][473][474][475] 2012) N owadays, it is known that the way in which the chromatin is positioned in the nucleus inside the cell can direct all the nuclear and chromatin functions essential for the cell cycle and development [1][2][3].It is believed that chromatin organization and nuclear architecture are governed by epigenetic mechanisms that are not random. Therefore, the chromatin and nucleus are controlled by these epigenetic modifications to achieve such a spatial organization and structure leading to the creation of functional nuclear compartments during cell cycle progression and development [4,5].Epigenetic modifications have been the focus of intense investigation. This includes DNA methylation and posttranslational histone modifications such as methylation, acetylation, phosphorylation, ubiquitination and ADP ribosylation. It is through these processes that chromatin and nuclear organization can be modulated to change gene expression. Many epigenetic modifications have been studied in different organisms, and it is believed that some of them are conserved in a variety of metazoan, fungi, plants and protozoa [6].It is known that the same histone modification can ha...
Somatic cell nuclear transfer (SCNT) is the injection of a donor nucleus into an enucleated egg. Despite the use of this technology for many years in research, it is still quite inefficient. One of the causes for this is thought to be incorrect or incomplete genome reprogramming. Embryos produced by nuclear transfer (cloned embryos) very often present abnormal epigenetic signatures and irregular chromatin reorganization. Of these two issues, the issue of chromatin rearrangements within the nuclei after transfer is the least studied. It is known that cloned embryos often present pericentromeric heterochromatin clumps very similar to the chromocenters structures present in the donor nuclei. Therefore, it is believed that the somatic nuclear configuration of donor nuclei, especially that of the chromocenters, is not completely lost after nuclear transfer, in other words, not well reprogrammed. To further investigate pericentromeric heterochromatin reorganization after nuclear transfer, we decided to study its rearrangements in cumulus-derived clones using several related epigenetic markers such as H3S10P, H3K9me3, and the double marker H3K9me3S10P. We observed that two of these markers, H3S10P and H3K9me3S10P, are the ones found on the part of the pericentromeric heterochromatin that is remodeled correctly, resembling exactly the embryonic heterochromatin configuration of naturally fertilized embryos. Conversely, H3K9me3 and heterochromatin protein 1 beta (HP1β)-associated protein were also detected in the perinuclear clumps of heterochromatin, making obvious the maintenance of the somatic epigenetic signature within these nuclear regions. Our results demonstrate that H3S10P and H3K9me3S10P could be good candidates for evaluating heterochromatin reorganization following nuclear reprogramming.
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