Thèse de doctorat : Automatique : Evry-Val d'Essonne : 2008. / Titre provenant de l'écran-titre.

No description available.

No description available.

RTEL1 (Regulator of telomere length1) DNA helicase has been demonstrated to be vital for the maintenance of telomere length and genomic stability. However, its biological role during development is unknown. Our recent finding that RTEL1 is selectively expressed in several types of adult stem cells, suggests that RTEL1 could play an essential role in the maintenance of these cells. Depending on the function of RTEL1 in the maintenance of genomic stability, we hypothesize that RTEL1 could be required for protecting adult stem cells from genomic instability, whose dysfunction may not only impair tissue homeostasis/regeneration, but also could transform these cells to form tumors. In this study, we have used mouse intestinal stem/progenitor cells model to address this hypothesis. With a transgenic lineage tracing assay, we demonstrated that RTEL1-expressing cells in intestinal crypts can self renew and differentiate to the progeny cells required for intestinal homeostasis. Using a conditional knockout approach, we also showed that loss of RTEL1 function could induce genomic instability in intestinal stem/progenitor cells, which significantly affected the survival of intestinal stem cells and intestinal regeneration. Finally, in this study, we also observed intestinal hyperplasia in our RTEL1 conditional knockout mice, indicating that loss of RTEL1 function may initiate intestinal tumorigenesis. All of these findings strongly support that RTEL1 could be one the key molecules necessary for the maintenance of intestinal stem/progenitor cells and this function could be important for preventing intestinal tumorigenesis.

No description available.

No description available.

No description available.

This study investigated enteric nervous system (ENS) involvement in intestinal secretion induced by cyclic GMP-dependent secretagogues. The investigation was based upon the study of transepithelial ion transport in rat small and large intestine and in guinea pig caecum using voltage-clamped in vitro preparations mounted in Ussing chambers. ENS participation was established from the use of neural blocking agents (tetrodotoxin (TTX), bicuculline and capsaicin). The relative contribution of the myenteric plexus was assessed by selectively stripping tissues of the longitudinal muscle layer. All tissues, both unstripped and stripped, responded to <I>Escherichia coli </I>STa enterotoxin, guanylin and the nitric oxide (NO) donor sodium nitroprusside (SNP) with a dose-dependent increase in inward short circuit current (I_SC). Regarding STa/guanylin, TTX inhibited this I_SCin unstripped rat distal colon, ileum and guinea pig caecum, demonstrating that the ENS plays an important role in these tissues. In rat distal colon, TTX induced an abolition of the STa/guanylin response in both preparations, indicating submucous plexus involvement. In rat proximal colon there was no discernible TTX-sensitive component observed. The ileum displayed partial control from both the myenteric and submucous plexuses, whereas the caecum exhibited partial control from the myenteric plexus alone. Bicuculline inhibited STa action to a significant degree in the caecum while capsaicin inhibited secretion in the proximal colon. In rat small intestine, the SNP-induced I_SC was inhibited by TTX in both unstripped and stripped tissues. In contrast, inhibitory pathways were shown to exist in distal colon exposed to SNP, TTX revealing an enhancement of SNP-induced secretion in the stripped preparation. Thus, although there is clear involvement of the ENS in the actions of STa/guanylin and SNP, it is not possible to make a general statement regarding its contribution throughout the length of the alimentary canal due to the extent of inter segmental and inter species variations.

Melphalan (the synthetic product of nitrogen mustard and L-phenylalanine) is an alkylating agent and is the drug of choice in the treatment of multiple myeloma. The bioavailability of melphalan is variable but factors affecting its absorption and the mechanism(s) by which the drug crosses the intestinal epithelium are not known. A sensitive assay for melphalan in plasma (down to a concentration of 2ng.ml^-1) has been developed. The method, involving solid phase extraction and derivatisation with o-phthalaldehyde followed by reversed-phase high-performance liquid chromatography, was applied to the study of melphalan pharmacokinetics in multiple myeloma patients. Bioavailability ranged from 0.16 to 1.37 in nine fasting patients and peak plasma concentrations of melphalan ranged from 8.0 to 170 ng.ml^-1 and occurred 0.5 to 2.0 hours after an oral dose of 10mg. When melphalan was taken with food (three patients) a mean reduction of 40% in bioavailability was observed. Significant correlations (P< 0.05) were observed between bioavailability and melphalan plasma concentrations in single samples drawn at 0.5, 1.0 and 2.0 hours. There was no significant correlation between renal function and melphalan absorption, distribution or elimination. A second peak was observed in the distribution phase of six of the eleven plasma concentration-time curves when melphalan was administered intravenously. The secondary peak may be attributed to either melphalan redistribution or enterohepatic circulation. An <i>in vitro</i> method (modified Ussing technique) was developed to investigate melphalan transport across rat and human small intestine. There was no evidence for the Na⁺-coupled (active) transport of melphalan in these tissues. The rate of melphalan transfer was non-saturable and values of apparent mass transfer coefficients were comparable with the diffusional contribution to the intestinal transport of amino acids The results indicate that passive diffusion is the major process responsible for the transfer of melphalan across intestinal epithelium.

Quantitative and qualitative analyses of the serum antibody responses of NIH, C57BL/10, BALB/c, DBA/2 and CFLP mice infected with Trichuris muris have been made using ELISA and immunoprecipitation techniques. No correlation was found between specific serum antibody titres measured using T. muris E/S products and the time of onset of expulsion in the different mouse strains examined. However, there were some differences in the antigen recognition profiles of some sera as determined by immunoprecipitation analyses. In all the strains of mice examined significant increases in detectable specific serum antibody to the parasite E/S products occurred around day 15 to 20 postinfection and continued to rise, as measured up to at least day 40 and even up to day 65. Cortisone acetate treatment during larval development, in infected CFLP mice, in order to establish heavy adult worm burdens, did not reduce specific antibody titres to T. muris E/S products. In responding and tolerant DBA/2 mice there was no marked difference in either the kinetics of specific serum antibody production during primary and secondary infections, or in the antigen specificities of secondary infection sera. The "defect" in mechanism in the tolerant DBA/2 mice, which allows primary infections of T. muris to develop to patency, was shown to be permanent as secondary infections with the parasite could also establish in these animals. An investigation was made of the phenomenon of tolerance in the DBA/2 model- system and in the cortisone treated CBA mice. The capacity of MLNC from different groups of animals to produce IL-2 in vitro upon mitogen stimulation was investigated, on the basis that IL-2 deficit during antigen presentation may result in immune tolerance. Although no differences were found in the responding and tolerant DBA/2 cell-Vpopulations, there was an apparently synergistic interaction between cortisone administration and T. muris infection which dramatically reduced the IL-2 producing capacity of the MLNC. However, IL-2 cannot yet be ruled out as a factor in the inherent tolerance of a proportion of the DBA/2 population as IL-2 receptor expression by the 2 groups of cells assayed was not examined. Basic analyses of the antigens of T. muris were performed. The major protein of adult male homogenate (AMA) was also the major protein of the excretory/secretory (E/S) products and the surface antigen preparations. In addition several common E/S and surface antigens were shown to have proteolytic enzyme activities against gelatin and/or casein. The relationship between T. muris and Trichinella spiralis was examined in greater detail, and the m. wts. of the cross-reacting antigens were determined. Evidence suggested that the stichosomes of these worms may be the source of these antigens. Both Trichuris muris adults and Trichinella spiralis infective larvae each had common major E/S and surface antigens, indeed, both were shown to have surface proteases. These studies were extended to examine the possibility of cross-reactivity between Trichuris muris and T. trichiura; mouse infection sera and human infection sera respectively were able to cross-react with heterologous antigen preparations. The demonstration that anti-Trichinella spiralis 48 kD and 50/55 kD stichocyte antigen MoAbs also reacted with Trichuris trichiura adult homogenate in ELISA supports the suggestion that common stichocyte antigens may exist amongst the trichuroid nematodes Trichuris muris, Trichuris trichiura and Trichinella spiralis. Monoclonal antibodies were produced against the E/S products of Trichuris muris, which were characterized in terms of isotype and antigen specificities. Initial experiments indicated that one of the IgA MoAbs recognizing 34,22,20 and 18 kD E/S proteins may be effective in the passive transfer of immunity.