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Department of Reproduction and Development,4 Kunming Institute of Zoology & Kunming Primate Research Center, the Chinese Academy of Sciences, Kunming, Yunnan 650223, China
Graduate University of Chinese Academy of Sciences,5 Beijing 100049, China
INRA,6 UMR 1198; ENVA; CNRS, FRE 2857, Biologie du Développement et Reproduction, Jouy en Josas, F-78350, France
The State Key Laboratory of Reproductive Biology,7 Institute of Zoology, the Chinese Academy of Sciences, Beijing 100860, China
ABSTRACT
Until now, no primate animals have been successfully cloned to birth with somatic cell nuclear transfer (SCNT) procedures, and little is known about the molecular events that occurred in the reconstructed embryos during preimplantation development. In many SCNT cases, epigenetic reprogramming of the donor nuclei after transfer into enucleated oocytes was hypothesized to be crucial to the reestablishment of embryonic totipotency. In the present study, we focused on two major epigenetic marks, DNA methylation and histone H3 lysine 9 (H3K9) acetylation, which we examined by indirect immunofluorescence and confocal laser scanning microscopy. During preimplantation development, 67% of two-cell- and 50% of eight-cell-cloned embryos showed higher DNA methylation levels than their in vitro fertilization (IVF) counterparts, which undergo gradual demethylation until the early morula stage. Moreover, whereas an asymmetric distribution of DNA methylation was established in an IVF blastocysts with a lower methylation level in the inner cell mass (ICM) than in the trophectoderm, in most cloned blastocysts, ICM cells maintained a high degree of methylation. Finally, two donor cell lines (S11 and S104) that showed a higher level of H3K9 acetylation supported more blastocyst formation after nuclear transfer than the other cell line (S103), with a relatively low level of acetylation staining. In conclusion, we propose that abnormal DNA methylation patterns contribute to the poor quality of cloned preimplantation embryos and may be one of the obstacles to successful cloning in primates.
DNA methylation, donor cells, early development, embryo, embryonic development, epigenetic reprogramming, histone acetylation, in vitro fertilization, rhesus monkey, somatic cell nuclear transfer
1Supported by Major Projects of Knowledge Innovation Program from the Chinese Academy of Sciences (KSCX1-05), National Natural Science Foundation of China (30370166), Joint Scholar Plan for the Development of Western China, National Basic Research Program of China (973 program, 2004CCA01300), and the PRA (Programme de Recherches Avancées FrancoChinois).
Correspondence: 2 FAX: 86 871 513 9413; e-mail: wji{at}mail.kiz.ac.cn
Correspondence: 3 FAX: 86 10 626 50042; e-mail: qzhou{at}ioz.ac.cn
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