Parp1 facilitates alternative NHEJ, whereas Parp2 suppresses IgH/c-myc translocations during immunoglobulin class switch recombination

Immunoglobulin class switch recombination (CSR) is initiated by DNA breaks triggered by activation-induced cytidine deaminase (AID). These breaks activate DNA damage response proteins to promote appropriate repair and long-range recombination. Aberrant processing of these breaks, however, results in decreased CSR and/or increased frequency of illegitimate recombination between the immunoglobulin heavy chain locus and oncogenes like c-myc. Here, we have examined the contribution of the DNA damage sensors Parp1 and Parp2 in the resolution of AID-induced DNA breaks during CSR. We find that although Parp enzymatic activity is induced in an AID-dependent manner during CSR, neither Parp1 nor Parp2 are required for CSR. We find however, that Parp1 favors repair of switch regions through a microhomology-mediated pathway and that Parp2 actively suppresses IgH/c-myc translocations. Thus, we define Parp1 as facilitating alternative end-joining and Parp2 as a novel translocation suppressor during CSR

Décisions réglementaires prises pour des raisons de sécurité des médicaments

LYON1-BU Santé (693882101) / SudocSudocFranceF

Rheological behaviour of colloidal dispersions of hydrophobic particles stabilised in water by amphiphilic polyelectrolytes.

International audienc

Coupling between polymer adsorption and colloidal particle aggregation

International audienc

Tissue-Specific Gain of RTK Signalling Uncovers Selective Cell Vulnerability during Embryogenesis

International audienceThe successive events that cells experience throughout development shape their intrinsic capacity to respond and integrate RTK inputs. Cellular responses to RTKs rely on different mechanisms of regulation that establish proper levels of RTK activation, define duration of RTK action, and exert quantitative/qualitative signalling outcomes. The extent to which cells are competent to deal with fluctuations in RTK signalling is incompletely understood. Here, we employ a genetic system to enhance RTK signalling in a tissue-specific manner. The chosen RTK is the hepatocyte growth factor (HGF) receptor Met, an appropriate model due to its pleiotropic requirement in distinct developmental events. Ubiquitously enhanced Met in Cre/loxP-based Rosa26 stopMet knock-in context (Del-R26 Met) reveals that most tissues are capable of buffering enhanced Met-RTK signalling thus avoiding perturbation of developmental programs. Nevertheless, this ubiquitous increase of Met does compromise selected programs such as myoblast migration. Using cell-type specific Cre drivers, we genetically showed that altered myoblast migration results from ectopic Met expression in limb mesenchyme rather than in migrating myoblasts themselves. qRT-PCR analyses show that ectopic Met in limbs causes molecular changes such as downregulation in the expression levels of Notum and Syndecan4, two known regulators of morphogen gradients. Molecular and functional studies revealed that ectopic Met expression in limb mesen-chyme does not alter HGF expression patterns and levels, but impairs HGF bioavailability. Together, our findings show that myoblasts, in which Met is endogenously expressed, are capable of buffering increased RTK levels, and identify mesenchymal cells as a cell type vulnerable to ectopic Met-RTK signalling. These results illustrate that embryonic cells are sensitive to alterations in the spatial distribution of RTK action, yet resilient to fluctuations in signalling levels of an RTK when occurring in its endogenous domain of activity

New TBT based conducting polymers functionalized with redox-active tetrazines

International audienceWe describe the synthesis of two new polymerizable monomers, and the subsequent polymers functionalized by tetrazine pendant groups, along with their electrochemical behaviour and fluorescence properties. In all cases a very stable conducting polymer is obtained, featuring both the redox activity of the main chain in oxidation and of the tetrazine functional group upon reduction. One of the polymers in addition exhibits an electrofluorochromic behaviour

Ubiquitously excess wild-type Met in developing embryos results into hyperflexed forelimbs.

<p>(A) Top: <i>Del-R26</i>^<i>Met</i> and control P0 mice showing hyperflexed limbs in mutants. Bottom: anti-myosin heavy chain II IHC using MF20 antibodies on forelimb transversal sections of P0 <i>Del-R26</i>^<i>Met</i> and control mice at the level of the forearm showing almost absence of extensor (asterisk) and a great reduction of flexor (arrowhead) muscle mass in mutants. (B, C) Whole mount ISH with <i>MyoD</i> probe of E12.5 embryos (B) and β-galactosidase staining of E11.5 embryos (C) showing that developing appendicular muscles are reduced in <i>Del-R26</i>^<i>Met</i> embryos (limbs are outlined in panels). The arrowhead in bottom panel B indicates developing ventral limb muscles (flexor). Scale: 500μm.</p

Enhanced Met expression levels in <i>Del-R26</i>^<i>Met</i> myoblasts does not perturb activation of downstream signalling effectors.

<p>Limb transverse sections of E10.5 control and <i>Del-R26</i>^<i>Met</i> embryos showing the distribution of phospho-Met (on Tyr_1234–1235), phospho-Akt, phospho-ERKs (red) and of Pax3 protein (green) in myoblasts. Note ectopic phospho-Met in limb mesenchyme (arrowheads) and in non-migrating myoblasts (arrows) in <i>Del-R26</i>^<i>Met</i> mutants. Asterisks indicate non-specific staining in blood cells. Scale: 100μm.</p

Myoblast migration is impaired in <i>Del-R26</i>^<i>Met</i> mutants.

<p>(A, B) Whole mount ISH of E10.5 embryos with <i>Lbx1</i> (A) and <i>Pax3</i> (B) probes showing drastic reduction of migrating myoblasts towards the developing tongue (arrowhead), fore and hind limbs. Bottom panel reports an enlargement at forelimb levels. (C, D) Quantification analyses of <i>Lbx1</i> (C) and <i>Pax3</i> (D) positive domains in forelimbs. Left panels: each plot represents the average signal distribution along the white line in forelimbs. Right panels: quantifications and statistical analyses of the sum of signal intensity based on intensity plots in left panels. Numbers of samples for <i>Lbx1</i>: control, n = 13; <i>Del-R26</i>^<i>Met</i>, n = 4; for <i>Pax3</i>: control, n = 11; <i>Del-R26</i>^<i>Met</i>, n = 8. The sum of <i>Pax3</i> signal intensity was calculated between point A and B: A indicating a fixed position between the somites and the limb whereas B being placed at a fixed distance from A. Note almost lack of signal in <i>Del-R26</i>^<i>Met</i> mutants. Scale: 500μm. Mann-Whitney and Student-<i>t</i> test.</p