title: Quantitative monitoring of pluripotency gene activation after somatic cloning in cattle.
abstract: The development of somatic cell nuclear transfer (SCNT) embryos critically depends on appropriate reprogramming and expression of pluripotency genes, such as Pou5f1/POU5F1 (previously known as Oct4/OCT4). To study POU5F1 transcription activation in living bovine SCNT embryos without interference by maternal POU5F1 mRNA, we generated chromosomally normal fetal fibroblast donor cells stably carrying a mouse Pou5f1 promoter-driven enhanced green fluorescent protein (EGFP) reporter gene at a single integration site without detectable EGFP expression. Morphologic and quantitative analyses of whole-mount SCNT embryos by confocal microscopy revealed robust initial activation of the Pou5f1 reporter gene during the fourth cell cycle. In Day 6 SCNT embryos EGFP expression levels were markedly higher than in Day 4 embryos but varied substantially between individual embryos, even at comparable cell numbers. Embryos with low EGFP levels had far more morphologically abnormal cell nuclei than those with high EGFP levels. Our data strongly suggest that bovine SCNT embryos consistently start activation of the POU5F1 promoter during the fourth cell cycle, whereas later in development the expression level substantially differs between individual embryos, which may be associated with developmental potential. In fibroblasts from phenotypically normal SCNT fetuses recovered on Day 34, the Pou5f1 reporter promoter was silent but was activated by a second round of SCNT. The restoration of pluripotency can be directly observed in living cells or SCNT embryos from such Pou5f1-EGFP transgenic fetuses, providing an attractive model for systematic investigation of epigenetic reprogramming in large mammals.
authors.affiliation: Institute of Molecular Animal Breeding and Biotechnology, Ludwig-Maximilians University, Feodor-Lynen-Strasse 22, D-81377 Munich, Germany.
authors.forename: Annegret
authors.initials: A
authors.lastname: Wuensch
authors.forename: Felix A
authors.initials: FA
authors.lastname: Habermann
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kurosaka
authors.forename: Regina
authors.initials: R
authors.lastname: Klose
authors.forename: Valeri
authors.initials: V
authors.lastname: Zakhartchenko
authors.forename: Horst-Dieter
authors.initials: HD
authors.lastname: Reichenbach
authors.forename: Fred
authors.initials: F
authors.lastname: Sinowatz
authors.forename: K John
authors.initials: KJ
authors.lastname: McLaughlin
authors.forename: Eckhard
authors.initials: E
authors.lastname: Wolf
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D002417:Cattle; D002478:Cells, Cultured; D019976:Cloning, Organism / Q000379:methods*; D046149:Embryo Culture Techniques; D004622:Embryo, Mammalian / Q000378:metabolism; D047108:Embryonic Development / Q000235:genetics*; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins; D008954:Models, Biological; D053652:Nuclear Transfer Techniques; D050814:Octamer Transcription Factor-3 / Q000235:genetics* / Q000378:metabolism; D039904:Pluripotent Stem Cells / Q000378:metabolism*; D015533:Transcriptional Activation; D014162:Transfection
chemical_list: D050814:Octamer Transcription Factor-3; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins