Epigenetic barrier against the propagation of fluctuating gene expression in embryonic stem cells

The expression of pluripotency genes fluctuates in a population of embryonic stem (ES) cells and the fluctuations in the expression of some pluripotency genes correlate. However, no correlation in the fluctuation of Pou5f1, Zfp42, and Nanog expression was observed in ES cells. Correlation between Pou5f1 and Zfp42 fluctuations was demonstrated in ES cells containing a knockout in the NuRD component Mbd3. ES cells containing a triple knockout in the DNA methyltransferases Dnmt1, Dnmt3a, and Dnmt3b showed correlation between the fluctuation of Pou5f1, Zfp42, and Nanog gene expression. We suggest that an epigenetic barrier is key to preventing the propagation of fluctuating pluripotency gene expression in ES cells.

Impaired respiratory function in MELAS-induced pluripotent stem cells with high heteroplasmy levels

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We modeled the mitochondrial disease MELAS by generating patient-specific iPS cells.

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MELAS-iPS cells show a wide variety of heteroplasmy levels.

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MELAS-iPS cells with high heteroplasmy levels showed impaired complex I activity.

Mitochondrial diseases are heterogeneous disorders, caused by mitochondrial dysfunction. Mitochondria are not regulated solely by nuclear genomic DNA but by mitochondrial DNA. It is difficult to develop effective therapies for mitochondrial disease because of the lack of mitochondrial disease models. Mitochondrial myopathy, encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) is one of the major mitochondrial diseases. The aim of this study was to generate MELAS-specific induced pluripotent stem cells (iPSCs) and to demonstrate that MELAS-iPSCs can be models for mitochondrial disease. We successfully established iPSCs from the primary MELAS-fibroblasts carrying 77.7% of m.3243A>G heteroplasmy. MELAS-iPSC lines ranged from 3.6% to 99.4% of m.3243A>G heteroplasmy levels. The enzymatic activities of mitochondrial respiratory complexes indicated that MELAS-iPSC-derived fibroblasts with high heteroplasmy levels showed a deficiency of complex I activity but MELAS-iPSC-derived fibroblasts with low heteroplasmy levels showed normal complex I activity. Our data indicate that MELAS-iPSCs can be models for MELAS but we should carefully select MELAS-iPSCs with appropriate heteroplasmy levels and respiratory functions for mitochondrial disease modeling.