SummaryIn the last decade, there has been an explosion in both the number of and knowledge about miRNAs associated with both type 1 and type 2 diabetes. Even though we are presently in the initial stages of understanding how this novel class of posttranscriptional regulators are involved in diabetes, recent studies have demonstrated that miRNAs are important regulators of the islet transcriptome, controlling apoptosis, differentiation and proliferation, as well as regulating unique islet and beta-cell functions and pathways such as insulin expression, processing and secretion. Furthermore, a large number of miRNAs have been linked to diabetogenic processes induced by elevated levels of glucose, free fatty acids and inflammatory cytokines. Thus, miRNAs are novel therapeutic targets with the potential of protecting the beta-cell, and there is proof of principle that miRNA antagonists, so-called antagomirs, are effective in vivo for other disorders. miRNAs are exported out of cells in exosomes, raising the intriguing possibility of cell-to-cell communication between distant tissues via miRNAs and that miRNAs can be used as biomarkers of beta-cell function, mass and survival. The purpose of this review is to provide a status on how miRNAs control beta-cell function and viability in health and disease. Copyright © 2015 John Wiley & Sons, Ltd. Keywords miRNA; diabetes; apoptosis; islets; insulin; beta-cells Non-coding RNAs -an introductionA central dogma in molecular biology states that DNA is converted to messenger RNAs (mRNA) that carry the genetic information to ribosomes where the mRNAs are translated to polypeptides. This dogma has been moderated by the realization that large amounts of genomic regions harbour non-coding RNA (ncRNA), as well as the discovery of new classes of short and long ncRNAs with different regulatory roles in the cell. The involvement of ncRNAs in many regulatory systems in the cell and their diversity of functions have led to an increased focus on their role in cell development and differentiation, physiology and the pathophysiology of diseases such as diabetes [1][2][3].The provision of novel high-throughput, low-cost technologies to sequence millions of RNA reads has revolutionized the discovery of novel classes of RNA species, and RNA molecules with important regulatory functions have been identified, such as microRNA (miRNA), circular RNA, endogenous small-interfering RNA, Piwi interacting RNA, small nucleolar RNA, vault RNA, small nuclear RNA and several classes of long ncRNA [4][5][6] (Figure 1), many of which are emerging as interesting subjects in diabetes research [2,7].

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