Summary To successfully colonize their host, pathogens produce effectors that can interfere with host cellular processes. Here we investigated the function of CRN 13 candidate effectors produced by plant pathogenic oomycetes and detected in the genome of the amphibian pathogenic chytrid fungus Batrachochytrium dendrobatidis (Bd CRN 13). When expressed in Nicotiana , Ae CRN 13, from the legume root pathogen Aphanomyces euteiches , increases the susceptibility of the leaves to the oomycete Phytophthora capsici . When transiently expressed in amphibians or plant cells, Ae CRN 13 and Bd CRN 13 localize to the cell nuclei, triggering aberrant cell development and eventually causing cell death. Using Förster resonance energy transfer experiments in plant cells, we showed that both CRN 13s interact with nuclear DNA and trigger plant DNA damage response ( DDR ). Mutating key amino acid residues in a predicted HNH ‐like endonuclease motif abolished the interaction of Ae CRN 13 with DNA , the induction of DDR and the enhancement of Nicotiana susceptibility to P. capsici . Finally, H2 AX phosphorylation, a marker of DNA damage, and enhanced expression of genes involved in the DDR were observed in A. euteiches ‐infected Medicago truncatula roots. These results show that CRN 13 from plant and animal eukaryotic pathogens promotes host susceptibility by targeting nuclear DNA and inducing DDR .
> La reconnaissance du peptide antigenique par son recepteur (TCR) entraine une augmentation de la concentration de Ca2+ dans le cytosol ([Ca2+]i), necessaire a la differenciation et aux fonctions effectrices des lymphocytes (L)T. La stimulation via le TCR permet le recrutement de molecules adaptatrices et le couplage a des enzymes, dont la phospholipase Cγ, qui produit de l’inositol 1,4,5 tri-phosphate (IP3) et du diacylglycerol. L’IP3 en se fixant a ses recepteurs du reticulum endoplasmique libere les stocks de Ca2+ dans le cytosol (Figure 1). L’entree de Ca2+ a partir du milieu extracellulaire reconstitue ces stocks et maintient une signalisation soutenue. Les canaux calciques responsables sont definis comme des SOC (store-operated Ca2+ channels) mais leur identite moleculaire n’est pas completement elucidee. Un des principaux facteurs de transcription active par la voie calcique est NFAT (nuclear factor of activated T cells). La calcineurine, une phosphatase regulee par le Ca2+ dephosphoryle NFAT, ce qui permet sa localisation nucleaire et l’expression des genes cibles.
Quiescence is a reversible cell-cycle arrest which allows cancer stem-like cells to evade killing following therapies. Here, we show that proliferating glioblastoma stem-like cells (GSLCs) can be induced and maintained in a quiescent state by lowering the extracellular pH. Through RNAseq analysis we identified Ca2+ signalling genes differentially expressed between proliferating and quiescent GSLCs. Using the bioluminescent Ca2+ reporter EGFP-aequorin we observed that the changes in Ca2+ homeostasis occurring during the switch from proliferation to quiescence are controlled through store-operated channels (SOC) since inhibition of SOC drives proliferating GSLCs to quiescence. We showed that this switch is characterized by an increased capacity of GSLCs' mitochondria to capture Ca2+ and by a dramatic and reversible change of mitochondrial morphology from a tubular to a donut shape. Our data suggest that the remodelling of the Ca2+ homeostasis and the reshaping of mitochondria might favours quiescent GSLCs' survival and their aggressiveness in glioblastoma.
In vertebrates, neural induction occurs during gastrulation when ectodermal cells choose between two fates, neural and epidermal. In Xenopus, neural induction has been regarded as a default pathway as it occurs, in dorsal ectoderm, when ventralizing signals (mainly Bone Morphogenesis Proteins, BMPs, potent epidermal inducers) are inhibited by dorsalizing signals, including factors such as noggin, chordin, and follistatin. However, our previous studies demonstrated that an instructive signal triggered by the activation of L-type voltage-sensitive calcium channels, resulting in a transient increase in intracellular free calcium, appears to be a necessary and sufficient requirement to induce the competent ectoderm toward the neural pathway. Here we further explore the relationship between the Ca2+ transient signals observed and the expression of early neural genes. We have performed a subtractive approach to identify the genes which are transcribed early after the calcium signal and involved in neural determination. We have analyzed a candidate gene (xMLP) which encodes a MARCKS-like protein, a substrate for PKC. We show that this gene is activated by a calcium transient signals and induced by noggin overexpression. xMLP is expressed at the right time in presumptive neural territories. The putative role of xMLP in the process of neural induction is discussed.
The molecular mechanism of neural induction is still unknown and the identity of the natural inducer remains elusive. It has been suggested that both the protein kinase C and cAMP signal transduction pathways may be involved in mediating its action. Here we provide evidence that Ca2+ is implicated in the process of transduction of the neuralizing signal. We find that an increase in intracellular Ca2+ concentration [Ca2+]i occurs during neural induction provoked in vitro by the lectin Con A in Pleurodeles waltl embryo. We demonstrate that specific L-type Ca2+ channel agonists also trigger neural induction. Conversely, noninducing lectins do not raise [Ca2+]i. Ryanodine and caffeine trigger neural induction. An increase in [Ca2+]i was also observed after treatment with the phorbol 12-myristate 13-acetate, which has been reported to be inductive. The [Ca2+]i increase triggered by phorbol ester and Con A was abolished by staurosporine and by L-type Ca2+ channel antagonists. Our findings demonstrate that the [Ca2+]i increase occurs via L-type Ca2+ channels. We suggest an amplification of this increase by a Ca(2+)-induced Ca2+ release mechanism which involves intracellular ryanodine-sensitive stores. We propose that Ca(2+)-dependent processes controlled by protein kinase C are implicated in the regulation of gene expression in response to neural induction.
