In both randomly moving Dictyostelium and mammalian cells, phosphatidylinositol (3,4,5)-trisphosphate and F-actin are known to propagate as waves at the membrane and act to push out the protruding edge. To date, however, the relationship between the wave geometry and the patterns of amoeboid shape change remains elusive. Here, by using phase map analysis, we show that morphology dynamics of randomly moving Dictyostelium discoideum cells can be characterized by the number, topology, and position of spatial phase singularities, i.e., points that represent organizing centers of rotating waves. A single isolated singularity near the cellular edge induced a rotational protrusion, whereas a pair of singularities supported a symmetric extension. These singularities appeared by strong phase resetting due to de novo nucleation at the back of preexisting waves. Analysis of a theoretical model indicated excitability of the system that is governed by positive feedback from phosphatidylinositol (3,4,5)-trisphosphate to PI3-kinase activation, and we showed experimentally that this requires F-actin. Furthermore, by incorporating membrane deformation into the model, we demonstrated that geometries of competing waves explain most of the observed semiperiodic changes in amoeboid morphology.reaction-diffusion | oscillations | excitable media | self-organization | PTEN

Extensive molecular analyses of ependymal tumors have revealed that supratentorial and posterior fossa ependymomas have distinct molecular profiles and are likely to be different diseases. The presence of C11orf95-RELA fusion genes in a subset of supratentorial ependymomas (ST-EPN) indicated the existence of molecular subgroups. However, the pathogenesis of RELA fusion-negative ependymomas remains elusive. To investigate the molecular pathogenesis of these tumors and validate the molecular classification of ependymal tumors, we conducted thorough molecular analyses of 113 locally diagnosed ependymal tumors from 107 patients in the Japan Pediatric Molecular Neuro-Oncology Group. All tumors were histopathologically reviewed and 12 tumors were re-classified as non-ependymomas. A combination of RT-PCR, FISH, and RNA sequencing identified RELA fusion in 19 of 29 histologically verified ST-EPN cases, whereas another case was diagnosed as ependymoma RELA fusion-positive via the methylation classifier (68.9%). Among the 9 RELA fusion-negative ST-EPN cases, either the YAP1 fusion, BCOR tandem duplication, EP300-BCORL1 fusion, or FOXO1-STK24 fusion was detected in single cases. Methylation classification did not identify a consistent molecular class within this group. Genome-wide methylation profiling successfully sub-classified posterior fossa ependymoma (PF-EPN) into PF-EPN-A (PFA) and PF-EPN-B (PFB). A multivariate analysis using Cox regression confirmed that PFA was the sole molecular marker which was independently associated with patient survival. A clinically applicable pyrosequencing assay was developed to determine the PFB subgroup with 100% specificity using the methylation status of 3 genes, CRIP1, DRD4 and LBX2. Our results emphasized the significance of molecular classification in the diagnosis of ependymomas. RELA fusion-negative ST-EPN appear to be a heterogeneous group of tumors that do not fall into any of the existing molecular subgroups and are unlikely to form a single category.Electronic supplementary materialThe online version of this article (10.1186/s40478-018-0630-1) contains supplementary material, which is available to authorized users.

Cell-cell signaling is subject to variability in the extracellular volume, cell number, and dilution that potentially increase uncertainty in the absolute concentrations of the extracellular signaling molecules. To direct cell aggregation, the social amoebae Dictyostelium discoideum collectively give rise to oscillations and waves of cyclic adenosine 3′,5′-monophosphate (cAMP) under a wide range of cell density. To date, the systems-level mechanism underlying the robustness is unclear. By using quantitative live-cell imaging, here we show that the magnitude of the cAMP relay response of individual cells is determined by fold change in the extracellular cAMP concentrations. The range of cell density and exogenous cAMP concentrations that support oscillations at the population level agrees well with conditions that support a large fold-change-dependent response at the singlecell level. Mathematical analysis suggests that invariance of the oscillations to density transformation is a natural outcome of combining secrete-and-sense systems with a fold-change detection mechanism.fold-change detection | oscillations | collective behavior | Dictyostelium | robustness C ell-cell signaling lies at the basis of development and maintenance of multicellular forms of life. Extracellular signals are often subject to greater fluctuations in the size of extracellular space and the number of cells (Fig. 1A), not to mention nonspecific binding to other molecules, degradation, and dilution. These factors introduce an uncertainty to the detectable number of extracellular ligand molecules, thus posing a threat to the fidelity of cell-cell communication. One of the means by which cells could cope with such uncertainties is to base their behavioral decisions on temporal changes in the extracellular signals. Persistent stimuli are often ignored while their changes in time elicit transient responses-a property collectively called adaptation (1-3). Recent studies have highlighted cellular response whose magnitude appears to be dictated by the fold change in the input stimuli-a property referred to as "fold-change detection" (FCD) (4, 5). In bacterial chemotaxis, cells respond adaptively to a fold change in chemoattractant concentration (6) so that their search patterns depend only on the spatial profiles of the chemoattractant irrespective of its absolute level. Fold-change dependence is also implied in eukaryotic chemotactic response (7, 8) as well as cell fate control and gene regulation in Xenopus embryo (9), Drosophila imaginal disk (10), and mammalian cells (11). These studies have shed light on the role of FCD for a simple unidirectional signal transduction from an extracellular ligand-receptor interaction (input) to a cellular response (output). However, cell-cell signaling and multicellular systems as a whole often use secretion and sensing of the same molecules (12), whereby the output is fed back to the responding cell itself in addition to the neighboring cells, thus forming a complex bidirectional signal transduction system. Th...

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