Polycomb-mediated gene regulation in human brain development and neurodevelopmental disorders.

The neocortex is considered the seat of higher cognitive function in humans. It develops from a sheet of neural progenitor cells, most of which eventually give rise to neurons. This process of cell fate determination is controlled by precise temporal and spatial gene expression patterns that in turn are affected by epigenetic mechanisms including Polycomb group (PcG) regulation. PcG proteins assemble in multiprotein complexes and catalyze repressive posttranslational histone modifications. Their association with neurodevelopmental disease and various types of cancer of the central nervous system, as well as observations in mouse models, has implicated these epigenetic modifiers in controlling various stages of cortex development. The precise mechanisms conveying PcG-associated transcriptional repression remain incompletely understood and are an active field of research. PcG activity appears to be highly context-specific, raising the question of species-specific differences in the regulation of neural stem and progenitor regulation. In this review, we will discuss our growing understanding of how PcG regulation affects human cortex development, based on studies in murine model systems, but focusing mostly on findings obtained from examining impaired PcG activity in the context of human neurodevelopmental disorders and cancer. Furthermore, we will highlight relevant experimental approaches for functional investigations of PcG regulation in human cortex development.

The effect of four lanthanides onto a rat kidney cell line (NRK-52E) is dependent on the composition of the cell culture medium.

Lanthanide (Ln) exposure poses a serious health risk to animals and humans. In this study, we investigated the effect of 10-9-10-3 M La, Ce, Eu, and Yb exposure onto the viability of rat renal NRK-52E cells in dependence on Ln concentration, exposure time, and composition of the cell culture medium. Especially, the influence of fetal bovine serum (FBS) and citrate onto Ln cytotoxicity, solubility, and speciation was investigated. For this, in vitro cell viability studies using the XTT assay and fluorescence microscopic investigations were combined with solubility and speciation studies using TRLFS and ICP-MS, respectively. The theoretical Ln speciation was predicted using thermodynamic modeling. All Ln exhibit a concentration- and time-dependent effect on NRK-52E cells. FBS is the key parameter influencing both Ln solubility and cytotoxicity. We demonstrate that FBS is able to bind Ln3+ ions, thus, promoting solubility and reducing cytotoxicity after Ln exposure for 24 and 48 h. In contrast, citrate addition to the cell culture medium has no significant effect on Ln solubility and speciation nor cytotoxicity after Ln exposure for 24 and 48 h. However, a striking increase of cell viability is observable after Ln exposure for 8 h. Out of the four Ln elements under investigation, Ce is the most effective. Results from TRLFS and solubility measurements correlate well to those from in vitro cell culture experiments. In contrast, results from thermodynamic modeling do not correlate to TRLFS results, hence, demonstrating that big gaps in the database render this method, currently, inapplicable for the prediction of Ln speciation in cell culture media. Finally, this study demonstrates the importance and the synergistic effects of combining chemical and spectroscopic methods with cell culture techniques and biological methods.

Aldh1b1 expression defines progenitor cells in the adult pancreas and is required for Kras-induced pancreatic cancer.

The presence of progenitor or stem cells in the adult pancreas and their potential involvement in homeostasis and cancer development remain unresolved issues. Here, we show that mouse centroacinar cells can be identified and isolated by virtue of the mitochondrial enzyme Aldh1b1 that they uniquely express. These cells are necessary and sufficient for the formation of self-renewing adult pancreatic organoids in an Aldh1b1-dependent manner. Aldh1b1-expressing centroacinar cells are largely quiescent, self-renew, and, as shown by genetic lineage tracing, contribute to all 3 pancreatic lineages in the adult organ under homeostatic conditions. Single-cell RNA sequencing analysis of these cells identified a progenitor cell population, established its molecular signature, and determined distinct differentiation pathways to early progenitors. A distinct feature of these progenitor cells is the preferential expression of small GTPases, including Kras, suggesting that they might be susceptible to Kras-driven oncogenic transformation. This finding and the overexpression of Aldh1b1 in human and mouse pancreatic cancers, driven by activated Kras, prompted us to examine the involvement of Aldh1b1 in oncogenesis. We demonstrated genetically that ablation of Aldh1b1 completely abrogates tumor development in a mouse model of KrasG12D-induced pancreatic cancer.