The role of chromatin modifications in the efficiency of reprogramming

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The molecular mechanisms involved in reprogramming of a differentiated mammalian cell to an embryonic like pluripotent cell are poorly defined. In the first funding period we established a transposon based induced reprogramming assay using Neural Stem (NS) cells and analysed the role of histone methyltransferases and histone demethylases. Conditional mutagenesis of the methyltransferase Mll1 in NS cells resulted in a 8-fold increase of induced pluripotent stem cell (iPS) colonies. In contrast a reduction in the number of iPS colonies was observed after conditional inactivation of Mll2. We also obtained more iPS colonies after tetracycline-regulated overexpression of the histone demethylases Jmjd1a (H3K9me2) and Utx (H3K27me3). In the second funding period we aim at identifying the targets of the above-mentioned histone methyltransferases and demethylases in NS cells as a first step for unravelling the molecular mechanisms of reprogramming. Furthermore we will continue our efforts for generating conditional mutagenesis and inducible expression/RNAi systems for the other existing demethylases and extend the analysis using in addition to induced reprogramming assays, ES-cell fusion and nuclear transfer assays.