title: rRNA genes are not fully activated in mouse somatic cell nuclear transfer embryos.
abstract: The well known and most important function of nucleoli is ribosome biogenesis. However, the nucleolus showed delayed development and malfunction in somatic cell nuclear transfer (NT) embryos. Previous studies indicated that nearly half rRNA genes (rDNA) in somatic cells were inactive and not transcribed. We compared the rDNA methylation level, active nucleolar organizer region (NORs) numbers, nucleolar proteins (upstream binding factor (UBF), nucleophosmin (B23)) distribution, and nucleolar-related gene expression in three different donor cells and NT embryos. The results showed embryonic stem cells (ESCs) had the most active NORs and lowest rDNA methylation level (7.66 and 6.76%), whereas mouse embryonic fibroblasts (MEFs) were the opposite (4.70 and 22.57%). After the donor cells were injected into enucleated MII oocytes, cumulus cells and MEFs nuclei lost B23 and UBF signals in 20 min, whereas in ESC-NT embryos, B23 and UBF signals could still be detected at 60 min post-NT. The embryos derived from ESCs, cumulus cells, and MEFs showed the same trend in active NORs numbers (7.19 versus 6.68 versus 5.77, p < 0.05) and rDNA methylation levels (6.36 versus 9.67% versus 15.52%) at the 4-cell stage as that in donor cells. However, the MEF-NT embryos displayed low rRNA synthesis/processing potential at morula stage and had an obvious decrease in blastocyst developmental rate. The results presented clear evidences that the rDNA reprogramming efficiency in NT embryos was determined by the rDNA activity in donor cells from which they derived.
authors.affiliation: Department of Histology and Embryology, Harbin Medical University, Harbin 150081, China.
authors.forename: Zhong
authors.initials: Z
authors.lastname: Zheng
authors.forename: Jia-Lin
authors.initials: JL
authors.lastname: Jia
authors.forename: Gerelchimeg
authors.initials: G
authors.lastname: Bou
authors.forename: Li-Li
authors.initials: LL
authors.lastname: Hu
authors.forename: Zhen-Dong
authors.initials: ZD
authors.lastname: Wang
authors.forename: Xing-Hui
authors.initials: XH
authors.lastname: Shen
authors.forename: Zhi-Yan
authors.initials: ZY
authors.lastname: Shan
authors.forename: Jing-Ling
authors.initials: JL
authors.lastname: Shen
authors.forename: Zhong-Hua
authors.initials: ZH
authors.lastname: Liu
authors.forename: Lei
authors.initials: L
authors.lastname: Lei
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000378:metabolism*; D002466:Cell Nucleolus / Q000378:metabolism*; D019175:DNA Methylation; D004275:DNA, Ribosomal / Q000378:metabolism*; D005260:Female; D020459:Genes, rRNA; D008297:Male; D051379:Mice; D009687:Nuclear Proteins / Q000378:metabolism; D053652:Nuclear Transfer Techniques; D000090243:Nucleophosmin; D012323:RNA Processing, Post-Transcriptional; D013997:Time Factors
chemical_list: D004275:DNA, Ribosomal; C000715570:Npm1 protein, mouse; D009687:Nuclear Proteins; D000090243:Nucleophosmin