Intermediate geodesic growth in virtually nilpotent groups

We give a criterion on pairs $(G,S)$ - where $G$ is a virtually $s$-step nilpotent group and $S$ is a finite generating set - saying whether the geodesic growth is exponential or strictly sub-exponential. Whenever $s=1,2$, this goes further and we prove the geodesic growth is either exponential or polynomial. For $s\ge 3$ however, intermediate growth is possible. We provide an example of virtually $3$-step nilpotent group for which $\gamma_{\mathrm{geod}}(n) \asymp \exp\!\big(n^{3/5}\cdot \log(n)\big)$. This is the first known example of group with intermediate geodesic growth. Along the way, we prove results on the geometry of virtually nilpotent groups, including asymptotics with error terms for their volume growth.Comment: 24 pages, 11 figures. Comments welcome

Rational cross-sections, bounded generation and orders on groups

We provide new examples of groups without rational cross-sections (also called regular normal forms), using connections with bounded generation and rational orders on groups. Specifically, our examples are extensions of infinite torsion groups, groups of Grigorchuk type, wreath products similar to $C_2\wr(C_2\wr \mathbb Z)$ and $\mathbb Z\wr F_2$, a group of permutations of $\mathbb Z$, and a finitely presented HNN extension of the first Grigorchuk group. This last group is the first example of finitely presented group with solvable word problem and without rational cross-sections. It is also not autostackable, and has no left-regular complete rewriting system.Comment: Comments are welcome! 38 pages, 23 figure

FRET-Based Enzyme Activity Reporter: Practical Hints for Kinases as Indicators of Virulence

Modulation of protein kinases activity is often requested for pathogenicity or virulence. This chapter provides several hints for one who might be interested in using FRET-based kinase activity reporters. The archetypes of these reporters, which are now within the arsenal of biosensors, were devoted to the detection and characterization of the activity of the cAMP-Protein kinase A pathway. Based on the principle of this biosensor, other FRET-based kinase activity reporters emerged. Here, the choice of the kinase to be monitored, the artifacts that might be met, and the flexibility and amenability of the FRET-based kinase activity reporters both for high-throughput analysis and dissection of protein kinase functions are discussed

Mythologie cellulaire

Rapport de collaboration Art-ScienceLe projet « Mythologie cellulaire » confère une dimension imaginaire à des éléments microscopiques en s’appuyant sur des faits scientifiques. C’est une invitation à rêver la science, à laisser l’imagination envahir le domaine du scientifique. La cellule fascine les imaginaires des artistes et des scientifiques. Le développement des technologies d’observation à l’échelle cellulaire permet de produire des corpus de matériaux avec des caractéristiques esthétiques

Novel reporter for faithful monitoring of ERK2 dynamics in living cells and model organisms

Uncoupling of ERK1/2 phosphorylation from subcellular localization is essential towards the understanding of molecular mechanisms that control ERK1/2-mediated cell-fate decision. ERK1/2 non-catalytic functions and discoveries of new specific anchors responsible of the subcellular compartmentalization of ERK1/2 signaling pathway have been proposed as regulation mechanisms for which dynamic monitoring of ERK1/2 localization is necessary. However, studying the spatiotemporal features of ERK2, for instance, in different cellular processes in living cells and tissues requires a tool that can faithfully report on its subcellular distribution. We developed a novel molecular tool, ERK2-LOC, based on the T2A-mediated coexpression of strictly equimolar levels of eGFP-ERK2 and MEK1, to faithfully visualize ERK2 localization patterns. MEK1 and eGFP-ERK2 were expressed reliably and functionally both in vitro and in single living cells. We then assessed the subcellular distribution and mobility of ERK2-LOC using fluorescence microscopy in non-stimulated conditions and after activation/inhibition of the MAPK/ERK1/2 signaling pathway. Finally, we used our coexpression system in Xenopus laevis embryos during the early stages of development. This is the first report on MEK1/ERK2 T2A-mediated coexpression in living embryos, and we show that there is a strong correlation between the spatiotemporal subcellular distribution of ERK2-LOC and the phosphorylation patterns of ERK1/2. Our approach can be used to study the spatiotemporal localization of ERK2 and its dynamics in a variety of processes in living cells and embryonic tissues

Validation en consultation spécialisée d’un autotest identifiant les patients allergiques aux acariens de la poussière de maison

L’augmentation de la prévalence des allergies durant les dernières décennies et les nombreuses répercussions négatives d’une prise en charge tardive, nous poussent à trouver des moyens diagnostiques plus efficients. L’allergie aux acariens de la poussière de maison représente plus de 75 % des allergies respiratoires pédiatriques. L’objectif de cette étude est de valider en consultation spécialisée le nouvel autotest de la marque ExAller afin d’identifier les sujets allergiques aux acariens de la poussière de maison et de mettre en place une prise en charge adéquate. Une étude prospective non interventionnelle a été réalisée en 2020 sur une population belge de 40 patients âgés de 3 ans et 2 mois à 18 ans et 10 mois. En amont, nous avons expliqué le principe de l’autotest et obtenu le consentement éclairé des parents. Chaque patient a bénéficié d’une anamnèse pour évaluer la probabilité d’allergie aux acariens. Les patients ont également bénéficié de tests allergiques cutanés selon la méthode de prick test, d’une biologie avec immunoglobulines E spécifiques aux acariens de la poussière de maison et l’autotest. La comparaison a été faite entre les résultats de l’autotest, les tests allergiques cutanés et les dosages des immunoglobulines E spécifiques de Dermatophagoides pteronyssinus et farinae. Les résultats donnent une sensibilité de 93,3 % et une spécificité de 100 %. Ils permettent de valider in vivo le nouvel autotest ExAller et de le mettre à disposition des sujets potentiellement allergiques aux acariens de la poussière de maison

Optimization of ERK Activity Biosensors for both Ratiometric and Lifetime FRET Measurements

Among biosensors, genetically-encoded FRET-based biosensors are widely used to localize and measure enzymatic activities. Kinases activities are of particular interest as their spatiotemporal regulation has become crucial for the deep understanding of cell fate decisions. This is especially the case for ERK, whose activity is a key node in signal transduction pathways and can direct the cell into various processes. There is a constant need for better tools to analyze kinases in vivo, and to detect even the slightest variations of their activities. Here we report the optimization of the previous ERK activity reporters, EKAR and EKAREV. Those tools are constituted by two fluorophores adapted for FRET experiments, which are flanking a specific substrate of ERK, and a domain able to recognize and bind this substrate when phosphorylated. The latter phosphorylation allows a conformational change of the biosensor and thus a FRET signal. We improved those biosensors with modifications of: (i) fluorophores and (ii) linkers between substrate and binding domain, resulting in new versions that exhibit broader dynamic ranges upon EGF stimulation when FRET experiments are carried out by fluorescence lifetime and ratiometric measurements. Herein, we characterize those new biosensors and discuss their observed differences that depend on their fluorescence properties

The spatio-temporal dynamics of PKA activity profile during mitosis and its correlation to chromosome segregation

International audienceThe cyclic adenosine monophosphate dependent kinase protein (PKA) controls a variety of cellular processes including cell cycle regulation. Here, we took advantages of genetically encoded FRET-based biosensors, using an AKAR-derived biosensor to characterize PKA activity during mitosis in living HeLa cells using a single-cell approach. We measured PKA activity changes during mitosis. HeLa cells exhibit a substantial increase during mitosis, which ends with telophase. An AKAREV T>A inactive form of the biosensor and H89 inhibitor were used to ascertain for the specificity of the PKA activity measured. On a spatial point of view, high levels of activity near to chromosomal plate during metaphase and anaphase were detected. By using the PKA inhibitor H89, we assessed the role of PKA in the maintenance of a proper division phenotype. While this treatment in our hands did not impaired cell cycle progression in a drastic manner, inhibition of PKA leads to a dramatic increase in chromososme misalignement on the spindle during metaphase that could result in aneuploidies. Our study emphasizes the insights that can be gained with genetically encoded FRET-based biosensors, which enable to overcome the shortcomings of classical methologies and unveil in vivo PKA spatiotemporal profiles in HeLa cells

From FRET Imaging to Practical Methodology for Kinase Activity Sensing in Living Cells

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