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Psoriasis is a frequent and often severe inflammatory skin disease, characterized by altered epidermal homeostasis. Since we found previously that Akt/mTOR signaling is hyperactivated in psoriatic skin, we aimed at elucidating the role of aberrant mTORC1 signaling in this disease. We found that under healthy conditions mTOR signaling was shut off when keratinocytes switch from proliferation to terminal differentiation. Inflammatory cytokines (IL-1β, IL-17A, TNF-α) induced aberrant mTOR activity which led to enhanced proliferation and reduced expression of differentiation markers. Conversely, regular differentiation could be restored if mTORC1 signaling was blocked. In mice, activation of mTOR through the agonist MHY1485 also led to aberrant epidermal organization and involucrin distribution. In summary, these results not only identify mTORC1 as an important signal integrator pivotal for the cells fate to either proliferate or differentiate, but emphasize the role of inflammation-dependent mTOR activation as a psoriatic pathomechanism.

The insulin-producing β cells of pancreatic islets are coupled by connexin36 (Cx36) channels. To investigate what controls the expression of this connexin, we have investigated its pattern during mouse pancreas development, and the influence of three transcription factors that are critical for β-cell development and differentiation. We show that (1) the Cx36 gene (Gjd2) is activated early in pancreas development and is markedly induced at the time of the surge of the transcription factors that determine β-cell differentiation; (2) the cognate protein is detected about a week later and is selectively expressed by β cells throughout the prenatal development of mouse pancreas; (3) a 2-kbp fragment of the Gjd2 promoter, which contains three E boxes for the binding of the bHLH factor Beta2/NeuroD1, ensures the expression of Cx36 by β cells; and (4) Beta2/NeuroD1 binds to these E boxes and, in the presence of the E47 ubiquitous cofactor, transactivates the Gjd2 promoter. The data identify Cx36 as a novel early marker of β cells and as a target of Beta2/NeuroD1, which is essential for β-cell development and differentiation.

Type I diabetes (T1D) patients rely on cumbersome chronic injections of insulin, making the development of alternate durable treatments a priority. The ability of the pancreas to generate new β-cells has been described in experimental diabetes models and, importantly, in infants with T1D. Here we discuss recent advances in identifying the origin of new β-cells after pancreatic injury, with and without inflammation, revealing a surprising degree of cell plasticity in the mature pancreas. In particular, the inducible selective near-total destruction of β-cells in healthy adult mice uncovers the intrinsic capacity of differentiated pancreatic cells to spontaneously reprogram to produce insulin. This opens new therapeutic possibilities because it implies that β-cells can differentiate endogenously, in depleted adults, from heterologous origins.

Brown adipose tissue (BAT) uses the chemical energy of lipids and glucose to produce heat, a function that can be induced by cold exposure or diet. A key regulator of BAT is the gene encoding PR domain containing 16 (Prdm16), whose expression can drive differentiation of myogenic and white fat precursors to brown adipocytes. Here we show that after cold exposure, the muscle-enriched miRNA-133 is markedly downregulated in BAT and subcutaneous white adipose tissue (SAT) as a result of decreased expression of its transcriptional regulator Mef2. miR-133 directly targets and negatively regulates PRDM16, and inhibition of miR-133 or Mef2 promotes differentiation of precursors from BAT and SAT to mature brown adipocytes, thereby leading to increased mitochondrial activity. Forced expression of miR-133 in brown adipogenic conditions prevents the differentiation to brown adipocytes in both BAT and SAT precursors. Our results point to Mef2 and miR-133 as central upstream regulators of Prdm16 and hence of brown adipogenesis in response to cold exposure in BAT and SAT.

The establishment of rat embryonic stem cells constitutes a precious tool since rat has been extensively used in biomedical research, in particular for the generation of human neurodisease animal models. Up to now only a few studies have described the isolation of rat embryonic stem-like cells. One out of 9 isolated rat embryonic stem-like cell lines (B1-RESC) obtained from a 4.5-day post-coitum blastocyst were extensively characterized and kept in culture for up to 80 passages on feeders with LIF. The stable growth of these cells and the expression of pluripotent markers were confirmed up to a high number of passages in culture, also in the absence of feeders and LIF. B1-RESC expresses the three germ layers markers both in vitro, within differentiating embryoid bodies, and in vivo through teratoma formation. Collectively, the B1-RESC line with a stable near-diploid karyotype can be used as a highly sensitive tool for testing anti-proliferative molecules.

Summary In mammals, DNA is methylated at CpG sites, which play pivotal roles in gene silencing and chromatin organization. Furthermore, DNA methylation undergoes dynamic changes during development, differentiation, and in pathological processes. The conventional methods represent snapshots; therefore, the dynamics of this marker within living organisms remains unclear. To track this dynamics, we made a knockin mouse that expresses a red fluorescent protein (RFP)-fused methyl-CpG-binding domain (MBD) protein from the ROSA26 locus ubiquitously; we named it MethylRO (methylation probe in ROSA26 locus). Using this mouse, we performed RFP-mediated methylated DNA immunoprecipitation sequencing (MeDIP-seq), whole-body section analysis, and live-cell imaging. We discovered that mobility and pattern of heterochromatin as well as DNA methylation signal intensity inside the nuclei can be markers for cellular differentiation status. Thus, the MethylRO mouse represents a powerful bioresource and technique for DNA methylation dynamics studies in developmental biology, stem cell biology, as well as in disease states., Graphical Abstract, Highlights • Changes in DNA methylation are tracked in living mice • Heterochromatin structure changes dynamically during development and differentiation • Heterochromatin of preimplantation embryonic cells is highly dynamic than ESCs • Heterochromatin pattern in nucleus can be a marker for cell differentiation states, DNA methylation undergoes dynamic changes during development, differentiation, and in pathological processes. To track these dynamics, DNA methylation reporter mouse was generated and named MethylRO (methylation probe in ROSA26 locus). Using this mouse, Yamagata and colleagues discovered that mobility and pattern of heterochromatin as well as DNA methylation signal intensity inside the nuclei can be markers for cellular differentiation status.