A Myc-regulated transcriptional network controls B-cell fate in response to BCR triggering

BACKGROUND: The B cell antigen receptor (BCR) is a signaling complex that mediates the differentiation of stage-specific cell fate decisions in B lymphocytes. While several studies have shown differences in signal transduction components as being key to contrasting phenotypic outcomes, little is known about the differential BCR-triggered gene transcription downstream of the signaling cascades. RESULTS: Here we define the transcriptional changes that underlie BCR-induced apoptosis and proliferation of immature and mature B cells, respectively. Comparative genome-wide expression profiling identified 24 genes that discriminated between the early responses of the two cell types to BCR stimulation. Using mice with a conditional Myc-deletion, we validated the microarray data by demonstrating that Myc is critical to promoting BCR-triggered B-cell proliferation. We further investigated the Myc-dependent molecular mechanisms and found that Myc promotes a BCR-dependent clonal expansion of mature B cells by inducing proliferation and inhibiting differentiation. CONCLUSION: This work provides the first comprehensive analysis of the early transcriptional events that lead to either deletion or clonal expansion of B cells upon antigen recognition, and demonstrates that Myc functions as the hub of a transcriptional network that control B-cell fate in the periphery

Merkel Cells as Putative Regulatory Cells in Skin Disorders: An In Vitro Study

Merkel cells (MCs) are involved in mechanoreception, but several lines of evidence suggest that they may also participate in skin disorders through the release of neuropeptides and hormones. In addition, MC hyperplasias have been reported in inflammatory skin diseases. However, neither proliferation nor reactions to the epidermal environment have been demonstrated. We established a culture model enriched in swine MCs to analyze their proliferative capability and to discover MC survival factors and modulators of MC neuroendocrine properties. In culture, MCs reacted to bFGF by extending outgrowths. Conversely, neurotrophins failed to induce cell spreading, suggesting that they do not act as a growth factor for MCs. For the first time, we provide evidence of proliferation in culture through Ki-67 immunoreactivity. We also found that MCs reacted to histamine or activation of the proton gated/osmoreceptor TRPV4 by releasing vasoactive intestinal peptide (VIP). Since VIP is involved in many pathophysiological processes, its release suggests a putative regulatory role for MCs in skin disorders. Moreover, in contrast to mechanotransduction, neuropeptide exocytosis was Ca2+-independent, as inhibition of Ca2+ channels or culture in the absence of Ca2+ failed to decrease the amount of VIP released. We conclude that neuropeptide release and neurotransmitter exocytosis may be two distinct pathways that are differentially regulated

Filtres optiques à couplage de modes polarisés

We describe the operating principles of optical filters using energie transfert between coupled orthogonally polarised electromagnetic waves. This phenomenon was previously demonstrated in Wurtzite type materials and is also shown to occur in piezo-birefringent zinc-blende crystals. This gives some evidence that the coupling does exist in many materials and manifests at the wavelength were the cancelation of the birefringence allows phase matching. This extends the spectral range of the applications from the UV, ∼ 1 000 Å, to the near infra-red. Some experimental results have exhibited band-pass and cut-band features at fixed or continuously tunable frequencies. In Wurtzite type materials, CdS, CdSxSe 1-x and Zn1-xCd xS, the natural birefringence is strongly dispersive near the isotropic point and the selectivity is very high : Δλ ∼ 5 Å at 77 K and 300 K, while the rejection ratio is in the order of 103. The effective transmission in the band pass region can be as large as 80 % at 77 K but it reduces to 20 % at room temperature due to residual absorption near the fundamental edge. With materials of the zinc-blende symmetry, such as ZnTe, the main difference is that the magnitude of the piezo-birefringence is weak and this increases the band-with Δλ to ∼ 100 Å. However, in this case, the bandwith can be varied between roughly 20 Å to 150 Å by adjusting the magnitude of the applied stress. Finally we investigate the potential of the application of a CdS cut-band filter, with a rejection ratio as large as 75 db, in Raman spectroscopy.Nous décrivons le principe de fonctionnement de filtres optiques fonctionnant par transfert d'énergie entre deux modes électromagnétiques couplés polarisés à angle droit. Nous montrons que ce phénomène existe non seulement dans des matériaux à structure Wurtzite mais aussi dans des matériaux à structure zinc-blende. Ceci démontre que le couplage n'est pas spécifique à une classe cristalline et étend le domaine potentiel d'applications de l'ultra-violet, ∼ 1 000 Å, au proche infrarouge. Les matériaux à structure Wurtzite et à forte dispersion de biréfringence tels CdS, CdSxSe1- x et Zn1-xCdxS donnent des structures passe-bande ou coupe-bande extrêmement sélectives, Δλ ∼ 5 à 10 Å avec des taux de réjection hors-bande de l'ordre de 103. La fréquence d'accord est soit fixe soit continuement accordable depuis 4 300 Å jusqu'à 7 100 Å. Le facteur de transmission en bande passante atteint 80 % à 77 K mais est réduit à 20 % à 300 K par l'absorption résiduelle au voisinage du seuil d'absorption fondamentale. Dans les matériaux à structure zinc-blende, tel ZnTe, l'amplitude de la biréfringence induite par compression est faible ce qui donne une largeur de bande de l'ordre de 100 Å. Cette largeur de bande peut toutefois être modifiée entre quelque 20 et 150 Å en ajustant la valeur de la contrainte. A titre d'illustration nous terminons cet article par l'examen des performances limites d'une structure coupe-bande à CdS, dont le taux de réjection atteint 75 db, susceptible d'être utilisée dans une application du type spectroscopie Raman

FGF2 signalling is critical for DNA repair in human epidermal stem cells

The sensitivity of stem cells to DNA damaging agents is a matter of debate. For mouse somatic stem cells, both radiosensitive and radioresistant stem cells have been described. By contrast, the response of human stem cells to ionizing radiation has been poorly studied. We evaluated in the present work the radiosensitivity of the epithelial stem cells from human interfollicular epidermis. We used flow cytometry and antibodies against cell surface markers (a6 integrin and CD71) to isolate keratinocyte stem cells and progenitors from human foreskin. Using a short-term cell survival assay (XTT at 72 h) and a long-term cell survival assay (CFE at 2 weeks), we demonstrated that keratinocyte progenitors were radiosensitive whereas the stem cells were more radioresistant (1). Using microarrays, we found that radiation exposure induced specifically several cytokines and growth factors genes in the stem cells, and notably the FGF2 pathway. Furthermore, DNA repair genes were found overexpressed in the stem cells. We thus postulated that the stem cells might have a more efficient DNA repair than the progenitors and might acquire an activated stress signalling response compared to the progenitors. We first studied the DNA repair of double strand breaks with the ?H2AX foci assay to evaluate the repair of DNA double strand breaks. After irradiation, the number of foci per cell decreased much more rapidly in the stem cells, suggesting a faster repair of DNA breaks. Moreover, using new bioarrays that measure DNA repair enzyme activities, we found that several repair enzymes were more active in the stem cells. Thereafter, to address the relationship between FGF2 and DNA repair, we inhibited this pathway at the level of the FGF2 receptor. Blocking FGF2 signalling inhibited the rapid decrease of ?H2AX foci in stem cells, suggesting a direct role of FGF2 in DNA repair. These results show that keratinocyte stem cells are a radioresistant cell population with a high DNA repair capacity. Moreover, we demonstrate that the FGF2 pathway plays a direct and specific role in DNA repair in epidermis stem cells. As stem cells are a long-term reservoir, these processes may be important for epidermis renewal and for carcinoma formation. (1) Rachidi W, Radiother Oncol, 2007, 83, 26

INTERACTION OF CD4 WITH HLA CLASS-II ANTIGENS AND HIV GP120

We have developed a cellular adhesion assay in which B lymphocytes expressing HLA class II antigens form rosettes with COS cells expressing high levels of cell surface CD4 upon transient transfection with a CDM8-CD4 plasmid construct. The assay is specific, quantitative, and overcomes the difficulties encountered with a previously described system using an SV40 viral vector. Rosette formation was inhibited by a series of CD4- and HLA-DR-specific antibodies, as well as by human immunodeficiency virus (HIV) gp 120, and a synthetic peptide derived from part of its binding site for CD4 (amino acid residues 414-434), but not by a variety of other effectors, including several soluble CD4 derivatives. The comparison of this pattern of inhibition with those observed in other systems further emphasizes the great similarity, but incomplete identity, in the CD4 binding sites for HLA class II antigens and HIV gp120, and supports a model in which CD4 is considered as an allosteric servomodulator of T-cell adhesion and function which probably is induced to interact with HLA class II antigens when associated with the Tcr/CD3 complex

Genetic and Phenotypic Modifications of Hematopoietic Stem Cells in Response to Ionizing Radiation Exposure

Hematopoietic stem cells (HSC) constitute a rare population within the bone marrow (BM) which actively maintains continuous production of all mature blood cell-lineages throughout life. They are finely regulated to respond rapidly and specifically to modifications of the number of circulating cells or to environmental modifications such as radiation exposure. Although a marked sensibility to radiation exposure of these cells has been reported, little is known about the underlying mechanisms. To understand at the molecular level the cell-dependent IR response, phenotypical and transcriptional changes occurring in stem cells were monitored following exposure to total body irradiation at 2Gy, 3Gy, 6Gy, in a kinetic study from 1 hour up to 60 days. Different stem cell populations were isolated using combinations of surface molecules such as Lin-/low Sca+ C-Kit+ (LSK) with or without CD150+ and CD135+. Our results show that cells with this phenotype were completely eradicated 48h after radiation exposure. Microarray analysis showed that as early as 1 hour after radiation exposure stem cells elicit a specific damage response mostly triggered by the modulation of apoptotic genes. Many genes identified were never described before as playing a role in the IR response. Moreover, QT clustering of expression profiles and subsequent promoter analysis of co-clustered genes reveal several novel P53 co-regulated genes. The induction of these genes after radiation exposure was impaired in mutant mice deficient for P53. Two months after 3 Gy or 6 Gy TBI, the BM cellularity was back to normal but the percentage of LSK cells was reduced and the proportion of LSK subsets expressing CD150 and/or CD135 was modified in a dose-dependant manner. Moreover, HSC presented a major defect in their long-term reconstitution potential that aroused from a blockage in their differentiation potential. This blockage can be partially abrogated by the administration of thrombopoietin. Novel actors in this signalling pathway were identified and will be presented. These results demonstrate that irradiation, on the one hand, kill a vast majority of cycling cells in the BM by the early onset of genetic network of apoptotic genes, and on the other hand affect quiescent HSC in a cell-autonomous but reversible manner. Altogether our approach help producing a more complete knowledge of the molecular mechanisms of the stem cell radiation response by unraveling molecular networks and finding novel and specific molecules involved in this process. This information might facilitate the derivation of clinically useful targets for patient benefit