Establishment of cell polarity—or symmetry breaking—relies on local accumulation of polarity regulators. Although simple positive feedback is sufficient to drive symmetry breaking, it is highly sensitive to stochastic fluctuations typical for living cells. Here, by integrating mathematical modelling with quantitative experimental validations, we show that in the yeast Saccharomyces cerevisiae a combination of actin- and guanine nucleotide dissociation inhibitor-dependent recycling of the central polarity regulator Cdc42 is needed to establish robust cell polarity at a single site during yeast budding. The guanine nucleotide dissociation inhibitor pathway consistently generates a single-polarization site, but requires Cdc42 to cycle rapidly between its active and inactive form, and is therefore sensitive to perturbations of the GTPase cycle. Conversely, actin-mediated recycling of Cdc42 induces robust symmetry breaking but cannot restrict polarization to a single site. Our results demonstrate how cells optimize symmetry breaking through coupling between multiple feedback loops.

SignificanceThis study provides a mechanistic explanation for the differentiation of trophoblasts from human pluripotent stem cells, a process relying on BMP morphogens. We found that a network of the transcription factors GATA2, GATA3, TFAP2A, and TFAP2C regulates early trophoblast progenitor specification by activating placental genes and inhibiting the pluripotency gene OCT4, thus acting to couple trophoblast specification with exit from pluripotency. To demonstrate the relevance of our findings in vivo, we show that down-regulating GATA3 in primate embryos prevents trophectoderm specification. In addition, we present a genome-wide analysis of active and inactive chromatin during trophoblast progenitor specification. These results provide a basis to guide investigations of human trophectoderm development.

Prenatal stress exposure is associated with risk for psychiatric disorders later in life. This may be mediated in part via enhanced exposure to glucocorticoids (GCs), which are known to impact neurogenesis. We aimed to identify molecular mediators of these effects, focusing on long-lasting epigenetic changes. In a human hippocampal progenitor cell (HPC) line, we assessed the short- and long-term effects of GC exposure during neurogenesis on messenger RNA (mRNA) expression and DNA methylation (DNAm) profiles. GC exposure induced changes in DNAm at 27,812 CpG dinucleotides and in the expression of 3,857 transcripts (false discovery rate [FDR] ≤ 0.1 and absolute fold change [FC] expression ≥ 1.15). HPC expression and GC-affected DNAm profiles were enriched for changes observed during human fetal brain development. Differentially methylated sites (DMSs) with GC exposure clustered into 4 trajectories over HPC differentiation, with transient as well as long-lasting DNAm changes. Lasting DMSs mapped to distinct functional pathways and were selectively enriched for poised and bivalent enhancer marks. Lasting DMSs had little correlation with lasting expression changes but were associated with a significantly enhanced transcriptional response to a second acute GC challenge. A significant subset of lasting DMSs was also responsive to an acute GC challenge in peripheral blood. These tissue-overlapping DMSs were used to compute a polyepigenetic score that predicted exposure to conditions associated with altered prenatal GCs in newborn’s cord blood DNA. Overall, our data suggest that early exposure to GCs can change the set point of future transcriptional responses to stress by inducing lasting DNAm changes. Such altered set points may relate to differential vulnerability to stress exposure later in life.

Epigenetic processes, including DNA methylation (DNAm), are among the mechanisms allowing integration of genetic and environmental factors to shape cellular function. While many studies have investigated either environmental or genetic contributions to DNAm, few have assessed their integrated effects. Here we examine the relative contributions of prenatal environmental factors and genotype on DNA methylation in neonatal blood at variably methylated regions (VMRs) in 4 independent cohorts (overall n = 2365). We use Akaike’s information criterion to test which factors best explain variability of methylation in the cohort-specific VMRs: several prenatal environmental factors (E), genotypes in cis (G), or their additive (G + E) or interaction (GxE) effects. Genetic and environmental factors in combination best explain DNAm at the majority of VMRs. The CpGs best explained by either G, G + E or GxE are functionally distinct. The enrichment of genetic variants from GxE models in GWAS for complex disorders supports their importance for disease risk.

Background Key pathogenic events of psoriasis and atopic eczema (AE) are misguided immune reactions of the skin. IL‐17C is an epithelial‐derived cytokine, whose impact on skin inflammation is unclear. Objective We sought to characterize the role of IL‐17C in human ISD. Methods IL‐17C gene and protein expression was assessed by immunohistochemistry and transcriptome analysis. Primary human keratinocytes were stimulated and expression of cytokines chemokines was determined by qRT‐PCR and luminex assay. Neutrophil migration towards supernatant of stimulated keratinocytes was assessed. IL‐17C was depleted using a new IL‐17C‐specific antibody (MOR106) in murine models of psoriasis (IL‐23 injection model) and AE (MC903 model) as well as in human skin biopsies of psoriasis and AE. Effects on cell influx (mouse models) and gene expression (human explant cultures) were determined. Results Expression of IL‐17C mRNA and protein was elevated in various ISD. We demonstrate that IL‐17C potentiates the expression of innate cytokines, antimicrobial peptides (IL‐36G, S100A7 and HBD2) and chemokines (CXCL8, CXCL10, CCL5 and VEGF) and the autocrine induction of IL‐17C in keratinocytes. Cell‐free supernatant of keratinocytes stimulated with IL‐17C was strongly chemotactic for neutrophils, thus demonstrating a critical role for IL‐17C in immune cell recruitment. IL‐17C depletion significantly reduced cell numbers of T cells, neutrophils and eosinophils in murine models of psoriasis and AE and led to a significant downregulation of inflammatory mediators in human skin biopsies of psoriasis and AE ex vivo. Conclusion IL‐17C amplifies epithelial inflammation in Th2 and Th17 dominated skin inflammation and represents a promising target for the treatment of ISD.