156 DIFFERENTIAL REORGANIZATION OF HISTONE ACETYLATION THROUGH ATP-DEPENDENT REMODELING FACTOR DURING PRONUCLEAR FORMATION IN PORCINE ZYGOTIC CHROMATINS

Abstract

ATP-dependent remodeling complexes and histone acetyltransferase/deacetylase complexes in chromatin modification can be characterized by the use of energy from ATP hydrolysis or covalent modification. But they have similar functions during the transcriptional process. After fertilization, histone acetylation in paternal and maternal chromatin is reprogrammed to obtain transcriptional activity during chromatin remodeling such as decondensation. However, these mechanisms in zygotic chromatin are poorly understood. In the present study, the reorganization process of histone H4 acetylation after fertilization was investigated through co-localization in the nucleus of ATP-dependent remodeling factors and histone acetyltransferases during parental chromatin decondensation. The molecules were monitored by immunofluorescence analysis with specific antibodies directed against AcH4K5, HAT1, P300, Tip60, Brg-1, and Mi-2. Fluorescence signals of Brg-1 and Mi-2 in porcine embryonic fibroblasts and HeLa cells co-localized with chromatin during interphase and M phase, although the Mi-2 signal existed around chromosomes at metaphase. However, Brg-1 and Mi-2 in porcine oocytes did not interact with chromosomes during meiosis, despite their existence in the oocyte cytoplasm. At 6 h after fertilization, signals of Brg-1 and Mi-2 were observed in most parental chromatin and remained until syngamy of the pronuclear stage. In histone acetylation and chromatin remodeling, acetylation of H4K5 was generated from sperm chromatin at 4 h after fertilization and preceded the appearance of Brg-1. Additionally, HAT1 showed stronger intensities compared with P300 and Tip60, correlating with acetylated-H4K5, and also appeared earlier than Brg-1. In contrast to that in sperm chromatin, Brg-1 in maternal chromatin anteceded HAT1. Consequently, paternal chromatin remodeling was completed after histone acetylation, but maternal chromatin remodeling was preceded by histone acetylation. Our findings indicate that paternal and maternal chromatin undergo differential remodeling and reprogramming during pronuclear formation, suggesting that gene expression in the chromatin of each parent may be regulated separately.