Regulation of chromatin and chromosome morphology by histone H3 modifications in pig oocytes

Abstract

Oocyte growth, maturation, and activation are complex processes that include transcription, heterochromatin formation, chromosome condensation and decondensation, two consecutive chromosome separations, and genomic imprinting. The objective of this study was to investigate changes in histone H3 modifications in relation to chromatin/chromosome morphology in pig oocytes during their growth, maturation, and activation. During the growth phase, histone H3 was acetylated at lysines 9, 14, and 18 (K9, K14, and K18), and became methylated at K9 when the follicles developed to the antral stage (oocyte diameter, 90 mm). When the fully grown oocytes (diameter, 120 mm) started their maturation, histone H3 became phosphorylated at serine 28 (S28) and then at S10, and deacetylated at K9, K14, and K18 as the chromosomes condensed. After the electroactivation of mature oocytes, histone H3 was reacetylated and dephosphorylated concomitant with the decondensation of the chromosomes. Histone H3 kinase activity increased over a similar time course to that of the phosphorylation of histone H3-S28 during oocyte maturation, and this activity decreased as histone H3-S10 and H3-S28 began to be dephosphorylated after the activation of the mature oocytes. These results suggest that the chromatin morphology of pig oocytes is regulated by the acetylation/deacetylation and the phosphorylation/dephosphorylation of histone H3, and the phosphorylation of histone H3 is the key event in meiotic chromosome condensation in oocytes. The inhibition of histone deacetylase with trichostatin A (TSA) inhibited the deacetylation and phosphorylation of histone H3, and chromosome condensation. Therefore, the deacetylation of histone H3 is thought to be required for its phosphorylation in meiosis. Although histone H3 acetylation and phosphorylation were reversible, the histone methylation that was established during the oocyte growth phase was stable throughout the course of oocyte maturation and activation.

Fully-mature antral mouse oocytes are transcriptionally silent but their heterochromatin maintains a transcriptional permissive histone acetylation profile

“…Our data on mouse antral oocytes are in agreement with those described before in pig [2] and show that once established during oocyte growth [10], this epigenetic signature is maintained, although its pattern of localisation changes during the stages of the NSN-to-SN transition: From a diffused distribution in NSN oocytes to the association with constitutive heterochromatin and then to the nucleolar surface region in SN oocytes.…”

Histone modifications during mammalian oocyte maturation: Dynamics, regulation and functions

“…27,33 Low expression of phosphorylated H3/Ser10 and 28 were detected in GV oocytes. Following gradual dephosphorylation from GV to L-GV stage, a transient phosphorylation of H3/Ser10 at the periphery of condensed chromatin was reestablished at early GVBD stage (E-GVBD), and then the dramatically increased signals covered whole chromosomes from Pre-MI to MII.…”

“…1). [25][26][27] First, the acetylation levels of six lysine residues mentioned above were uniformly decreased at the late GV (L-GV) stage, indicating that histone deacetylation may be required for the orderly progression through GV to GVBD. Second, H4/K5 and H4/K16 were completely deacetylated in MI oocytes, and after transient reacetylation in anaphase I (AI), they were dramatically deacetylated again at MII chromosomes.…”

Chromosome remodeling and differentiation of tetraploid embryos during preimplantation development

“…3; 2-6 hr). Recently Bui et al reported that the phosphorylation/dephosphorylation of histone H3 is the key event in chromosome condensation and decondensation in oocytes (Bui et al, 2007). For analyzing chromosome condensation and decondensation, we used histone phosphorylation at serine 10 (p-H3-S10).…”