Dynamic instability of genomic methylation patterns in pluripotent stem cells
Steen KT Ooi17, Daniel Wolf2, Odelya Hartung3, Suneet Agarwal43, George Q Daley6435, Stephen P Goff2 and Timothy H Bestor1*
*Corresponding author: Timothy H Bestor thb12@columbia.edu
1 Department of Genetics and Development, Columbia University, New York, USA
2 HHMI and Department of Biochemistry and Molecular Biophysics, College of Physicians and Surgeons of Columbia University, New York, USA
3 Stem Cell Program, Children's Hospital Boston, Boston, MA 02115, USA
4Stem Cell Transplantation Program, Division of Pediatric Hematology/Oncology, Manton Center for Orphan Disease Research, Howard Hughes Medical Institute, Children's Hospital Boston and Dana Farber Cancer Institute; Harvard Stem Cell Institute, Boston, MA 02115, USA
5 Division of Hematology, Brigham and Women's Hospital, Boston, MA 02115, USA
6 Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
7 UCL Cancer Institute, Paul O'Gorman Building, University College London, London, WC1E 6BT, UK
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Epigenetics & Chromatin 2010, 3:17 doi:10.1186/1756-8935-3-17
Received: 15 June 2010
Accepted: 24 September 2010
Published: 24 September 2010
© 2010 Ooi et al; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Background
Genomic methylation patterns are established during gametogenesis, and perpetuated in somatic cells by faithful maintenance methylation. There have been previous indications that genomic methylation patterns may be less stable in embryonic stem (ES) cells than in differentiated somatic cells, but it is not known whether different mechanisms of de novo and maintenance methylation operate in pluripotent stem cells compared with differentiating somatic cells.
Results
In this paper, we show that ablation of the DNA methyltransferase regulator DNMT3L (DNA methyltransferase 3-like) in mouse ES cells renders them essentially incapable of de novomethylation of newly integrated retroviral DNA. We also show that ES cells lacking DNMT3L lose DNA methylation over time in culture, suggesting that DNA methylation in ES cells is the result of dynamic loss and gain of DNA methylation. We found that wild-type female ES cells lose DNA methylation at a much faster rate than do male ES cells; this defect could not be attributed to sex-specific differences in expression of DNMT3L or of any DNA methyltransferase. We also found that human ES and induced pluripotent stem cell lines showed marked but variable loss of methylation that could not be attributed to sex chromosome constitution or time in culture.
Conclusions
These data indicate that DNA methylation in pluripotent stem cells is much more dynamic and error-prone than is maintenance methylation in differentiated cells. DNA methylation requires DNMT3L in stem cells, but DNMT3L is not expressed in differentiating somatic cells. Error-prone maintenance methylation will introduce unpredictable phenotypic variation into clonal populations of pluripotent stem cells, and this variation is likely to be much more pronounced in cultured female cells. This epigenetic variability has obvious negative implications for the clinical applications of stem cells.
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NOTA DESTE BLOGGER:
Para os ardorosos proponentes das pesquisas científicas com células-tronco embrionárias, como a Mayana Zatz, o destaque desta pesquisa:
"This epigenetic variability has obvious negative implications for the clinical applications of stem cells. "
[Esta variabilidade epigenética tem implicações negativas óbvias para as aplicações clínicas de células-tronco.]
Alô Senado Federal, que tal rever o cheque em branco assinado por esta casa em favor de uma nota promissória científica sem nenhuma perspectiva, até aqui, de resgate, concedido às pesquisas com células-tronco embrionárias? Simplesmente por razões seculares e científicas...
