miR-6539 is a novel mediator of somatic cell reprogramming that represses the translation of Dnmt3b

An Insight into DNA-free Reprogramming Approaches to Generate Integration-free Induced Pluripotent Stem Cells for Prospective Biomedical Applications

More than a decade ago, a pioneering study reported generation of induced Pluripotent Stem Cells (iPSCs) by ectopic expression of a cocktail of reprogramming factors in fibroblasts. This study has revolutionized stem cell research and has garnered immense interest from the scientific community globally. iPSCs hold tremendous potential for understanding human developmental biology, disease modeling, drug screening and discovery, and personalized cell-based therapeutic applications. The seminal study identified Oct4, Sox2, Klf4 and c-Myc as a potent combination of genes to induce reprogramming. Subsequently, various reprogramming factors were identified by numerous groups. Most of these studies have used integrating viral vectors to overexpress reprogramming factors in somatic cells to derive iPSCs. However, these techniques restrict the clinical applicability of these cells as they may alter the genome due to random viral integration resulting in insertional mutagenesis and tumorigenicity. To circumvent this issue, alternative integration-free reprogramming approaches are continuously developed that eliminate the risk of genomic modifications and improve the prospects of iPSCs from lab to clinic. These methods establish that integration of transgenes into the genome is not essential to induce pluripotency in somatic cells. This review provides a comprehensive overview of the most promising DNA-free reprogramming techniques that have the potential to derive integration-free iPSCs without genomic manipulation, such as sendai virus, recombinant proteins, microRNAs, synthetic messenger RNA and small molecules. The understanding of these approaches shall pave a way for the generation of clinical-grade iPSCs. Subsequently, these iPSCs can be differentiated into desired cell type(s) for various biomedical applications.

The complex interplay between DNA methylation and miRNAs in gene expression regulation

The short, non-coding RNAs, also called microRNAs (miRNAs) can bind complementary sequences on cellular mRNAs. The consequence of this binding is generally the degradation of mRNA and the inhibition of its translation. For this reason, miRNAs are included among the epigenetic factors acting as a modulator of gene expression. How miRNAs expression is, in turn, regulated is still the object of active investigation, but DNA methylation, another epigenetic modification, seems to play a central role in this sense. The "one-carbon" metabolism is responsible for the metabolic regulation of trans-methylation reactions and, therefore, DNA methylation. For this reason, to investigate the possible correlations between alterations of the one-carbon metabolism and differential DNA methylation sounds interesting. Moreover, recent evidence indicates that, vice-versa, miRNAs are associated with DNA methylation modulation, in a mutual cross-talk. The present review will discuss the interplay between miRNAs and DNA methylation and its fall-out on gene expression regulation.