The generation of genome-wide data derived from methylated DNA immunoprecipitation followed by sequencing (MeDIP-seq) has become a major tool for epigenetic studies in health and disease. The computational analysis of such data, however, still falls short on accuracy, sensitivity, and speed. We propose a time-efficient statistical method that is able to cope with the inherent complexity of MeDIP-seq data with similar performance compared with existing methods. In order to demonstrate the computational approach, we have analyzed alterations in DNA methylation during the differentiation of human embryonic stem cells (hESCs) to definitive endoderm. We show improved correlation of normalized MeDIP-seq data in comparison to available whole-genome bisulfite sequencing data, and investigated the effect of differential methylation on gene expression. Furthermore, we analyzed the interplay between DNA methylation, histone modifications, and transcription factor binding and show that in contrast to de novo methylation, demethylation is mainly associated with regions of low CpG densities.[Supplemental material is available at http://www.genome.org. The MeDIP-seq data from this study have been submitted to NCBI Sequence Read Archive (http://www.ncbi.nlm.nih.gov/Traces/sra/sra.cgi) under accession no. SRA012665. The bead array gene expression data from this study have been submitted to the NCBI Gene Expression Omnibus (http:// www.ncbi.nlm.nih.gov/geo) under accession no. GSE21715. The MEDIPS software package, manual, data, and example data are available online at http://medips.molgen.mpg. et al. 2005), which can be detected either by tiling arrays (MeDIPChip) or by next-generation sequencing (MeDIP-seq). Methylation profiles obtained by the MeDIP approach are not base pair-specific but reflect methylation levels on a resolution restricted by the size of the sonicated DNA fragments after amplification and size selection. In contrast, bisulfite sequencing detects cytosine methylation on a base-pair level. Although whole-genome single-base resolution maps have been generated (Lister et al. 2008(Lister et al. , 2009, such techniques cannot yet be cost-effectively applied to screen large sets of sequences or samples. Reduced representation bisulfite sequencing (RRBS) was introduced in order to address this issue by selecting only some regions of the genome for sequencing. Here, reduced representation is achieved by the size-fractionation of DNA fragments after restriction enzyme digestion (Meissner et al. 2008;Laird 2010). In contrast to bisulfite sequencing, MeDIP-seq-derived methylation data are of far lower resolution, and therefore, it remains difficult to discriminate between CpG and non-CpG methylation when single-end short reads are considered. However, MeDIP-seq covers nearly as many CpGs per sample genome as does the more expensive whole-genome shotgun bisulfite sequencing (WGSBS) approach (Laird 2010). An advantage of the MeDIP approach is the generation of unbiased, cost-effective, and fullgenome methylation levels w...

In general, human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs) 1 can be cultured under variable conditions.However, it is not easy to establish an effective system for culturing these cells. Since the culture conditions can influence gene expression that confers pluripotency in hESCs and hiPSCs, the optimization and standardization of the culture method is crucial.The establishment of hESC lines was first described by using MEFs as feeder cells and fetal bovine serum (FBS)-containing culture medium 2 . Next, FBS was replaced with knockout serum replacement (KSR) and FGF2, which enhances proliferation of hESCs 3 . Finally, feeder-free culture systems enable culturing cells on Matrigel-coated plates in KSR-containing conditioned medium (medium conditioned by MEFs) 4 . Subsequently, hESCs culture conditions have moved towards feeder-free culture in chemically defined conditions [5][6][7] . Moreover, to avoid the potential contamination by pathogens and animal proteins culture methods using xeno-free components have been established

Somatic cells can be reprogrammed to induced pluripotent stem cells by over-expression of OCT4, SOX2, KLF4 and c-MYC (OSKM). With the aim of unveiling the early mechanisms underlying the induction of pluripotency, we have analyzed transcriptional profiles at 24, 48 and 72 hours post-transduction of OSKM into human foreskin fibroblasts. Experiments confirmed that upon viral transduction, the immediate response is innate immunity, which induces free radical generation, oxidative DNA damage, p53 activation, senescence, and apoptosis, ultimately leading to a reduction in the reprogramming efficiency. Conversely, nucleofection of OSKM plasmids does not elicit the same cellular stress, suggesting viral response as an early reprogramming roadblock. Additional initiation events include the activation of surface markers associated with pluripotency and the suppression of epithelial-to-mesenchymal transition. Furthermore, reconstruction of an OSKM interaction network highlights intermediate path nodes as candidates for improvement intervention. Overall, the results suggest three strategies to improve reprogramming efficiency employing: 1) anti-inflammatory modulation of innate immune response, 2) pre-selection of cells expressing pluripotency-associated surface antigens, 3) activation of specific interaction paths that amplify the pluripotency signal.