PLoS Genet

To generate highly specific and adapted immune responses, B cells diversify their antibody repertoire through mechanisms involving the generation of programmed DNA damage. Somatic hypermutation (SHM) and class switch recombination (CSR) are initiated by the recruitment of activation-induced cytidine deaminase (AID) to immunoglobulin loci and by the subsequent generation of DNA lesions, which are differentially processed to mutations during SHM or to double-stranded DNA break intermediates during CSR. The latter activate the DNA damage response and mobilize multiple DNA repair factors, including Parp1 and Parp2, to promote DNA repair and long-range recombination. We examined the contribution of Parp3 in CSR and SHM. We find that deficiency in Parp3 results in enhanced CSR, while SHM remains unaffected. Mechanistically, this is due to increased occupancy of AID at the donor (Smu) switch region. We also find evidence of increased levels of DNA damage at switch region junctions and a bias towards alternative end joining in the absence of Parp3. We propose that Parp3 plays a CSR-specific role by controlling AID levels at switch regions during CSR

Statistical redundancy of instantaneous phases: theory and application to the seismic ambient wavefield

In order to detect possible signal redundancies in the ambient seismic wavefield, we develop a new method based on pairwise comparisons among a set of synchronous time-series. This approach is based on instantaneous phase coherence statistics. The first and second moments of the pairwise phase coherence distribution are used to characterize the phase randomness. For perfect phase randomness, the theoretical values of the mean and variance are equal to 0 and 1 2/À, respectively. As a consequence, any deviation from these values indicates the presence of a redundant phase in the raw continuous signal. A previously detected micro seismic source in the Gulf of Guinea is used to illustrate one of the possible ways of handling phase coherence statistics. The proposed approach allows us to properly localize this persistent source, and to quantify its contribution to the overall seismic ambient wavefield. The strength of the phase coherence statistics relies in its ability to quantify the redundancy of a given phase among a set of time-series with various useful applications in seismic noise-based studies (tomography and/or source characterization)

Introducing the Statistical Redundancy of Instantaneous Phases of the Seismic Signal to Isolate Persistent Sources

We introduce a new method based on pairwise comparisons among a set of synchronous time-series to detect signal redundancies in the seismic ambient wavefield. This approach is based on instantaneous phase coherence statistics, assuming the ergodicity property of a random signal. Both theory and synthetic experiments show that, for perfect phase randomness, the theoretical values of the mean and variance are equal to 0 and 1 2=, respectively. Any departure from these values signs the presence of a redundant phase in the raw continuous signal. The previously detected 26 s period microseismic source is used to illustrate one of the possible ways of handling phase coherence statistics. The dataset is composed of continuous vertical component during the month of August 2004, recorded at four stations. Each 31 day length seismogram is split into 372 2 h time windows to be cross-correlated among all possible station pairs. We observe that, for all station pairs, the mean overall coherence value is close to zero for most time lags, except for specific time windows. Using a constant group velocity, each mean overall coherence value is converted into a geographical location and points out a redundant source signal located in the Gulf of Guinea, as previously found in the literature. This result demonstrates that this approach enables to point out persistent sources, and to quantify their contribution to the overall seismic ambient wavefield. Further improvements to better constrain the strength of the repetitivenessPeer Reviewe

3-D crustal VS model of western France and the surrounding regions using Monte-Carlo inversion of seismic noise cross-correlation dispersion diagrams

International audienc

Modulation of Host Defence Systems

Arbuscular mycorrhizal (AM) fungi extensively invade host root tissues. This raises the question of how host plants contend with them; they must exert some kind of control over fungal proliferation since it is confined to a specific root tissue, the parenchymal cortex. Defence processes, which are triggered as a general plant response to microbial invasion, are modulated during root-fungus interactions in arbuscular mycorrhizas. This chapter presents an up-dated review of data on plant defence elicitation in these symbiotic systems and discusses possible mechanisms whereby defence reactions are maintained at a low level, as well as their implication in the phenomenon of bioprotection by AM fungi against soil-borne pathogens