Outstanding questions in the chromatin field bear on how large heterochromatin domains are formed in space and time. Positive feedback, where histone-modifying enzymes are attracted to chromosomal regions displaying the modification they catalyse, is believed to drive the formation of these domains; however, few quantitative studies are available to assess this hypothesis. Here we quantified the de novo establishment of a naturally occurring ∼20-kb heterochromatin domain in fission yeast through single-cell analyses, measuring the kinetics of heterochromatin nucleation in a region targeted by RNAi and its subsequent expansion. We found that nucleation of heterochromatin is stochastic and can take from one to ten cell generations. Further silencing of the full region takes another one to ten generations. Quantitative modelling of the observed kinetics emphasizes the importance of local feedback, where a nucleosome-bound enzyme modifies adjacent nucleosomes, combined with a feedback where recruited enzymes can act at a distance.

Summary The glycome undergoes characteristic changes during histogenesis and organogenesis, but our understanding of the importance of select glycan structures for tissue formation and homeostasis is incomplete. Here, we present a human organotypic platform that allows genetic dissection of cellular glycosylation capacities and systematic interrogation of the roles of distinct glycan types in tissue formation. We used CRISPR-Cas9 gene targeting to generate a library of 3D organotypic skin tissues that selectively differ in their capacity to produce glycan structures on the main types of N- and O-linked glycoproteins and glycolipids. This tissue library revealed distinct changes in skin formation associated with a loss of features for all tested glycoconjugates. The organotypic skin model provides phenotypic cues for the distinct functions of glycoconjugates and serves as a unique resource for further genetic dissection and identification of the specific structural features involved. The strategy is also applicable to other organotypic tissue models.

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].

Post‐translational modifications (PTMs) greatly expand the function and potential for regulation of protein activity, and O‐glycosylation is among the most abundant and diverse PTMs. Initiation of O‐GalNAc glycosylation is regulated by 20 distinct GalNAc‐transferases (GalNAc‐Ts), and deficiencies in individual GalNAc‐Ts are associated with human disease, causing subtle but distinct phenotypes in model organisms. Here, we generate a set of isogenic keratinocyte cell lines lacking either of the three dominant and differentially expressed GalNAc‐Ts. Through the ability of keratinocytes to form epithelia, we investigate the phenotypic consequences of the loss of individual GalNAc‐Ts. Moreover, we probe the cellular responses through global transcriptomic, differential glycoproteomic, and differential phosphoproteomic analyses. We demonstrate that loss of individual GalNAc‐T isoforms causes distinct epithelial phenotypes through their effect on specific biological pathways; GalNAc‐T1 targets are associated with components of the endomembrane system, GalNAc‐T2 targets with cell–ECM adhesion, and GalNAc‐T3 targets with epithelial differentiation. Thus, GalNAc‐T isoforms serve specific roles during human epithelial tissue formation.

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Cutaneous T-cell lymphoma (CTCL) is a devastating lymphoid malignancy characterised by accumulation of malignant T cells in the dermis and epidermis. Skin lesions cause serious symptoms hampering the quality of life and are entry sites for bacterial infection - a major cause of morbidity and mortality in advanced disease. What drives the pathological processes that compromise the skin barrier remains unknown. Here, we report on increased transepidermal water loss and compromised expression of skin barrier proteins filaggrin and filaggrin-2 in areas adjacent to TOX positive T cells in CTCL skin lesions. Malignant T cells secrete mediators (including cytokines such as IL-13, IL-22 and Oncostatin M) that activate STAT3 signalling and downregulate filaggrin and filaggrin-2 expression in human keratinocytes and reconstructed human epithelium. Consequently, repression of filaggrins could be counteracted by a cocktail of antibodies targeting these cytokines/receptors, by siRNA-mediated knockdown of JAK1/STAT3, and by JAK1 inhibitors. Notably, we show that treatment with a clinically approved JAK inhibitor, Tofacitinib, increases filaggrin expression in lesional skin from mycosis fungoides patients. Taken together, these findings indicate that malignant T cells secrete cytokines, which induce skin barrier defects through a JAK1/STAT3 dependent mechanism. As clinical grade JAK inhibitors largely abrogate the negative effect of malignant T cells on skin barrier proteins, our findings suggest that such inhibitors provide novel treatment options for CTCL patients with advanced disease and a compromised skin barrier.

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