134 INCOMPLETE HISTONE ACETYLATION OF SOMATIC CHROMATIN IN BOVINE OOCYTES
G. Wee A , S.-H. Kim A , K.P. Kim A , S. Yeo A , D.-B. Koo A , S.J. Moon B , K.-K. Lee A and Y.-M. Han AA Laboratory of Development and Differentiation, Korea Research Institute of Bioscience and Biotechnology, Daejeon, Korea email: ymhan@kribb.re.kr;
B Department of Animal Science, Chonnam National University, Gwangju, Korea.
Reproduction, Fertility and Development 16(2) 189-190 https://doi.org/10.1071/RDv16n1Ab134
Submitted: 1 August 2003 Accepted: 1 October 2003 Published: 2 January 2004
Abstract
Histone acetylation as an important regulatory mechanism of chromatin structure preceeding zygotic gene expression in early embryo development. After fertilization, transcriptional activation of the embryo begins during the S/G2 phase of the first cell cycle. However, the precise mechanism underlying activation of zygotic transcription remains to be understood, especially in bovine nuclear transfer (NT) embryos. It is known that acetylation of histone H4 lysine 5 (H4K5) represents hyperacetylation state, which is correlated with gene expression. In this study, the acetylation of H4K5 was observed during pronuclear formation by using immunofluorescence analysis with anti-AcH4K5. Our data were analyzed by the general linear models (GLM) procedure of the SAS. In IVF embryos, acetylation of H4K5 occurred on the paternal chromatin at 8 h after fertilization but did not occur on the maternal chromatin until 10 h after fertilization. Reconstructed oocytes with deactylated somatic cell nuclei began to show signs of acetylation on chromatin at 3 h after fusion. When acetylation intensity was calculated using an image analyzer, IVF embryos presented a higher acetylation signal than NT embryos (P < 0.05). To induce hyperacetylation in NT embryos, somatic cells were exposed to trichostatin A (TSA, 1 μM for 60 h), a specific inhibitor of histone deacetylase (HDAC), prior to NT. Acetylated signals of H4K5 increased significantly in TSA-treated cells as compared with non-treated cells (P < 0.05). The reconstructed embryos with TSA-treated cells showed a higher fluorescence intensity than the oocytes with non-treated cells (P < 0.05), but weak signals compared to IVF embryos. Thus, the results demonstrated low histone acetylation level of somatic cell nuclei after NT during the zygotic progress. Our findings suggest that developmental failures of NT embryos may be due to incomplete chromatin remodeling of somatic cell nuclei during early embryonic development.
