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1.
Article in English | MEDLINE | ID: mdl-21047900

ABSTRACT

The differentiated state of somatic cells is highly stable, but it can be experimentally reversed. The resulting cells can then be redirected into many different pathways. Nuclear reprogramming has been achieved by nuclear transfer to eggs, cell fusion, and overexpression of transcription factors. The mechanisms of nuclear reprogramming are not understood, but some insight into them is provided by comparing the efficiencies of different reprogramming strategies. Here, we compare these efficiencies by describing the frequency and rapidity with which reprogramming is induced and by the proportion of cells and level of expression in which reprogramming is achieved. We comment on the mechanisms that lead to successful somatic-cell reprogramming and on those that resist in helping to maintain the differentiated state of somatic cells.


Subject(s)
Cellular Reprogramming/genetics , Animals , Cell Differentiation/genetics , Cell Fusion , Cell Lineage , Humans , Induced Pluripotent Stem Cells/metabolism , Meiotic Prophase I , Nuclear Transfer Techniques , Ovum/metabolism , Transcription Factors/metabolism
2.
Methods ; 51(1): 56-65, 2010 May.
Article in English | MEDLINE | ID: mdl-20123126

ABSTRACT

Full-grown Xenopus oocytes in first meiotic prophase contain an immensely enlarged nucleus, the Germinal Vesicle (GV), that can be injected with several hundred somatic cell nuclei. When the nuclei of mammalian somatic cells or cultured cell lines are injected into a GV, a wide range of genes that are not transcribed in the donor cells, including pluripotency genes, start to be transcriptionally activated, and synthesize primary transcripts continuously for several days. Because of the large size and abundance of Xenopus laevis oocytes, this experimental system offers an opportunity to understand the mechanisms by which somatic cell nuclei can be reprogrammed to transcribe genes characteristic of oocytes and early embryos. The use of mammalian nuclei ensures that there is no background of endogenous maternal transcripts of the kind that are induced. The induced gene transcription takes place in the absence of cell division or DNA synthesis and does not require protein synthesis. Here we summarize new as well as established results that characterize this experimental system. In particular, we describe optimal conditions for transplanting somatic nuclei to oocytes and for the efficient activation of transcription by transplanted nuclei. We make a quantitative determination of transcript numbers for pluripotency and housekeeping genes, comparing cultured somatic cell nuclei with those of embryonic stem cells. Surprisingly we find that the transcriptional activation of somatic nuclei differs substantially from one donor cell-type to another and in respect of different pluripotency genes. We also determine the efficiency of an injected mRNA translation into protein.


Subject(s)
Blastodisc/metabolism , Cell Nucleus/metabolism , Cytological Techniques , Oocytes/cytology , Oocytes/metabolism , Transcription, Genetic , Xenopus laevis/metabolism , Animals , DNA/metabolism , Mice , Models, Biological , Polymerase Chain Reaction , RNA, Messenger/metabolism , Temperature , Transcriptional Activation
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