title: Limited demethylation leaves mosaic-type methylation states in cloned bovine pre-implantation embryos.
abstract: Cloning by nuclear transfer (NT) has been riddled with difficulties: most clones die before birth and survivors frequently display growth abnormalities. The cross-species similarity in abnormalities observed in cloned fetuses/animals leads us to suspect the fidelity of epigenetic reprogramming of the donor genome. Here, we found that single-copy sequences, unlike satellite sequences, are demethylated in pre-implantation NT embryos. The differential demethylation pattern between genomic sequences was confirmed by analyzing single blastocysts. It suggests selective demethylation of other developmentally important genes in NT embryos. We also observed a reverse relationship between methylation levels and inner cell mass versus trophectoderm (ICM/TE) ratios, which was found to be a result of another type of differential demethylation occurring in NT blastocysts where unequal methylation was maintained between ICM and TE regions. TE-localized methylation aberrancy suggests a widespread gene dysregulation in an extra-embryonic region, thereby resulting in placental dysfunction familiar to cloned fetuses/animals. These differential demethylations among genomic sequences and between differently allocated cells produce varied overall, but specified, methylation patterns, demonstrating that epigenetic reprogramming occurs in a limited fashion in NT embryos.
authors.affiliation: Animal Developmental Biotechnology Laboratory, Korea Research Institute of Bioscience and Biotechnology, PO Box 115, Yusong, Taejon 305-600, South Korea.
authors.forename: Yong-Kook
authors.initials: YK
authors.lastname: Kang
authors.forename: Jung Sun
authors.initials: JS
authors.lastname: Park
authors.forename: Deog-Bon
authors.initials: DB
authors.lastname: Koo
authors.forename: Young-Hee
authors.initials: YH
authors.lastname: Choi
authors.forename: Sun-Uk
authors.initials: SU
authors.lastname: Kim
authors.forename: Kyung-Kwang
authors.initials: KK
authors.lastname: Lee
authors.forename: Yong-Mahn
authors.initials: YM
authors.lastname: Han
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000378:metabolism*; D002417:Cattle / Q000196:embryology*; D002418:Cattle Diseases / Q000196:embryology / Q000235:genetics; D019070:Cell Lineage; D002467:Cell Nucleus; D019976:Cloning, Organism / Q000662:veterinary*; D000013:Congenital Abnormalities / Q000196:embryology / Q000235:genetics / Q000662:veterinary; D018899:CpG Islands; D019175:DNA Methylation; D004276:DNA, Satellite / Q000235:genetics; D004475:Ectoderm / Q000166:cytology; D005307:Fertilization in Vitro; D018507:Gene Expression Regulation, Developmental; D018390:Gene Targeting; D007633:Keratins / Q000235:genetics; D007782:Lactoglobulins / Q000235:genetics; D008845:Microinjections; D009030:Mosaicism; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D011401:Promoter Regions, Genetic / Q000235:genetics; D014327:Trophoblasts / Q000166:cytology
chemical_list: D004276:DNA, Satellite; D007782:Lactoglobulins; D007633:Keratins