Clostridium perfringens is a Gram-positive bacterium that secretes a biofilm matrix material. The goal of these experiments was to identify pilin mutants that are needed for secretion of the biofilm matrix and develop a functional model for a type II secretion system (T2SS) in C. perfringens. Protein tagging, western blot, and slot blot experiments were done to quantify protein secretion. After performing experiments using a CPE0515-FLAG construct, it was concluded from immunoblot densitometry data that, except for the pilA1 deletion mutant, none of the 18 tested pilin mutants had a statistically significant difference from the wild type (WT) with regard to protein secretion. From slot blot densitometry assays, it was concluded that the pilA1 and CPE2280 mutants showed statistically significant lower values than the WT but the pilA2 and CPE1841 mutants had values that were higher than the wild type. Testing the construct containing only CPE0514 and CPE0515-FLAG showed that CPE0516 and CPE0517 are not needed for secretion of the protein CPE0515. HA-tagged CPE0516 qualitative immunoblots showed that, unlike CPE0515, oligomerization of CPE0516 is not occurring, and that this protein likely forms a heat stable dimer. Overall, the data did not allow us to construct a T2SS model, since there were not enough proteins revealed to be involved to create a complete Type II secretion system. / Master of Science / The methods by which C. perfringens can persist and survive in environmental conditions is something that would be useful to learn more about. One of the methods that many bacteria use to survive is by creating a biofilm matrix material, which provides protection for the bacteria from environmental stresses. In this study, the goal was to determine which specific proteins are needed for the secretion of the biofilm matrix material. Using molecular biology techniques, the proteins thought to be involved in biofilm formation quantified. The results showed that while two proteins ultimately appeared to be needed for secretion, there were not enough proteins involved to create a complete model for a functional secretion system in C. perfringens.

No description available.

There is an ongoing worldwide obesity epidemic. As a consequence, prevalence of obesity- related diseases and conditions are rapidly increasing. One of these related conditions is type 2 diabetes (T2D), which alone caused 1.5 million deaths in 2012. Thus, it is of upmost importance to develop a more complete understanding of these interrelated diseases. At the heart of all these diseases lies the adipose tissue. This tissue is a major endocrine organ, and one of the key secreted cytokines is adiponectin. Adiponectin interplays with the complex insulin signaling network, and adiponectin levels are inversely related with increased adiposity. The presence of these complex dependencies argues for the usage of mathematical modelling. In the work of Brännmark et al, a model of short-term adiponectin release has been validated. However, this model did not include adrenergic signaling, which is the canonical pathway for in situ regulation of adiponectin secretion. To fill this gap, herein, a mechanistic model describing adrenaline-induced short-term adiponectin exocytosis in white adipocytes has been constructed. The newly constructed model is capable of describing experimental data depicting adiponectin release due to adrenergic stimulation as well as data for different mediator combinations. By implementing adrenergic receptor components, the transition to a more physiological model has been initiated. By finding the smallest possible model capable of describing data, one can argue that the model depicts, to some degree, the fundamental mechanisms for short-term adiponectin secretion. Thus, this work has contributed to solidifying the framework of the mechanisms behind short-term adiponectin secretion from white adipocytes. The result of the model work upholds the role of adrenergic signaling as a central regulatory mechanism for adiponectin release. The constructed model could be used as a fundament for creating a model describing adiponectin release under diabetic conditions.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第22495号 / 農博第2399号 / 新制||農||1076(附属図書館) / 学位論文||R2||N5275(農学部図書室) / 京都大学大学院農学研究科応用生命科学専攻 / (主査)教授 栗原 達夫, 教授 小川 順, 教授 木岡 紀幸 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

Les bactéries du genre Shigella sont responsables de la shigellose, une maladie diarrhéique invasive du colon. L’entrée et la dissémination de Shigella à travers l’épithélium colique sont médiées par un système de sécrétion de type III (SST3) codé par un plasmide de virulence. Au sein de ce plasmide se trouve une région de 30-kb comportant les gènes impliqués dans l’entrée de la bactérie dans les cellules hôtes. Ces gènes sont regroupés en deux loci :le locus ipa-ipg qui code pour les protéines sécrétées et leurs chaperons ainsi que le locus mxi-spa codant pour les composants de l’appareil de sécrétion de type III (AST3), constitué d’un bulbe cytoplasmique, d’un corps basal transmembranaire et d’une aiguille se projetant au niveau extracellulaire. Ce système permet la sécrétion ordonnée et hiérarchique de différentes classes de protéines et la translocation de certaines d’entre elles (appelées effecteurs) dans le cytoplasme de la cellule hôte où elles interfèrent avec les voies de signalisation cellulaires. Avant le contact avec la cellule hôte, l’AST3 est inactif et verrouillé par les protéines IpaB et IpaD formant le complexe d’extrémité.<p>Chez Shigella, le gatekeeper MxiC séquestre les effecteurs au niveau du cytoplasme bactérien avant la transmission par l’aiguille du signal d’activation de la sécrétion mais les composants intermédiaires liant l’aiguille à MxiC restaient inconnus. Au cours de ce travail, nous avons montré que MxiC forme un complexe avec la sous-unité de la tige interne, MxiI, afin de bloquer l’entrée du canal de sécrétion et que cette interaction est conservée chez Yersinia et Salmonella. Nous démontrons que, suite au contact cellulaire, la dissociation de ce complexe facilite le switch de sécrétion des translocateurs aux effecteurs. Nos résultats révèlent également que MxiC est capable de s’associer au chaperon IpgC afin de réguler la sécrétion des translocateurs. De plus, nous avons identifié les domaines de MxiC engagés dans la régulation du SST3 et rapporté un nouveau rôle de MxiC dans l’échappement aux macrophage impliquant une possible inhibition de la voie apoptotique classique afin de promouvoir une pyroptose. Chez Shigella, IpaD gouverne la composition du complexe d’extrémité et est impliqué dans la régulation de la sécrétion. Nous avons développé une étude phénotypique de ses régions coiled-coil et centrale et montré que la composition du complexe d’extrémité permet de définir à la fois l’état d’inductibilité de l’AST3 et la sécrétion des effecteurs tardifs. Par ailleurs, notre étude fonctionnelle des domaines de MxiC et IpaD suggère que les capacités de Shigella à échapper au macrophage et à insérer un pore de translocation ne sont pas strictement couplées. <p>La dernière partie de ce travail s’est focalisée sur la caractérisation de la protéine Spa13 de Shigella. Nous avons découvert que le défaut de sécrétion du mutant spa13 est dû à l’instabilité de la sous-unité MxiH de l’aiguille et que Spa13 n’est pas sécrété par le SST3. Nos résultats indiquent également un rôle de Spa13 dans l’escorte de chaperons et l’activation de l’appareil d’exportation afin de promouvoir la sécrétion des substrats./Shigella is the causative agent of shigellosis, also known as bacillary dysentery, an invasive disease of the human colonic epithelium. During infection, Shigella uses a type III secretion system (T3SS) to penetrate enterocytes and to disseminate into the colonic epithelium, leading to destruction of the mucosal lining and shigellosis symptoms. Most of the virulence factors of Shigella are encoded by a large plasmid harboring a 30-kb region that is sufficient to promote bacterial entry into host cells. This entry region is organized in two loci, one corresponding to the the ipa-ipg genes encoding the secreted proteins and their cognate chaperones while the other encodes Mxi-Spa proteins that form the type III secretion apparatus (T3SA), consisting of a cytoplasmic bulb, a basal body spanning the bacterial envelope and a hollow needle. The T3SS allows the ordered and hierarchical secretion of effectors by inserting a translocation pore in the host cell membrane through which effector proteins are injected into the cytosol. Before host cell contact, the T3SA is inactive and plugged by the tip complex proteins IpaB and IpaD. <p>In Shigella, the gatekeeper MxiC is known to sequester effectors within the cytoplasm prior to receiving the activation signal from the needle but the molecules involved in linking the needle and MxiC are unknown. We demonstrated that MxiC and the predicted inner-rod component MxiI form a complex plugging the T3SA entry gate and showed that this interaction is conserved in Yersinia and Salmonella. Dissociation of this complex seems to facilitate the switch in secretion from translocators to effectors upon host cell contact. Our results also revealed that MxiC binds to the chaperone IpgC to regulate translocators secretion. Moreover, we identified the domains of MxiC involved in the T3S regulation and reported a new role in macrophage escape by potential inhibition of the classical apoptosis to promote pro-inflammatory pyroptosis. <p>In Shigella, IpaD rules the composition of the tip complex and is involved in secretion control and translocon insertion. We therefore undertook a phenotypic analysis of its coiled-coil and central regions and showed that the composition of the tip complex defines both the T3SA inducibility state and late effectors secretion. Besides, our functional study on MxiC and IpaD domains suggests that Shigella abilities to escape macrophage vacuole and to insert the translocation pore are uncoupled.<p>The last part of this work is related to the characterization of the Spa13 protein of Shigella. We found that the secretion defect of the spa13 mutant is due to the instability of the needle component MxiH and that Spa13 is not a secreted substrat. Our results also support a dual role of Spa13 as a chaperone escort and as an export gate-activator switch to promote substrates secretion. / Doctorat en Sciences biomédicales et pharmaceutiques / info:eu-repo/semantics/nonPublished

Thesis (MScMedSc (Biomedical Sciences. Medical Biochemistry))--University of Stellenbosch, 2010. / Bibliography / ENGLISH ABSTRACT: The genome of the pathogen Mycobacterium tuberculosis contains five copies of the ESAT-6 (ESX) gene cluster region, which encodes for a novel type VII secretion system. These gene cluster regions, which are directly involved in pathogenicity and phagosomal escape, contain genes encoding exported T-cell antigens ESAT-6 and CFP-10. The mechanism of action of the ESX secretion system however, remains largely unknown. This study focused on ESX gene cluster region 4 (ESX-4), which has been shown to be the most ancestral region and is also present in other species of Mycobacteria and even in other high G+C Gram-positive bacteria, such as Corynebacterium diptheriae and Streptomyces coelicolor. This project aimed to investigate the protein-protein interactions of ESX-4 of M. tuberculosis in the model organism Mycobacterium smegmatis by means of Mycobacterial Protein Fragment Complementation (M-PFC). M-PFC is a two-hybrid technique which employs two cloning vectors, pUAB300 (conferring resistance to hygromycin B) and pUAB400 (conferring resistance to kanamycin). Genes of interest are cloned into these vectors and co-transformed into the model organism M. smegmatis after which it is expressed as fusion proteins. Interaction of the proteins allows selective growth on a medium containing the antibiotic trimethoprim. Various interactions were identified throughout this region, including selfinteractions as well as the expected interaction between the ESAT-6 and CFP-10 protein family members esxT and esxU. Since this region is ancestral, ESX-4 provides the basic model of the mechanism of secretion of the type VII secretion system. Many similarities were apparent when the interactions identified for ESX-4 were compared to the interactions previously identified in ESX-3. Interactions identified by means of M-PFC provide a basis for the further study of the structure of this secretion system, and should be confirmed by means of other techniques, such as co-immunoprecipitation. Despite the ability of M-PFC to identify protein-protein interactions in a mycobacterial system, and thus overcoming some of the limitations of the classical yeast two-hybrid model, it must still be regarded as a fishing experiment for potential interactions. A further aim of the project was to construct a knock-out of ESX-4 in the model organism M. smegmatis, which contains three ESX regions, namely ESX-1, -3 and -4. Homologous recombination proved to be an effective technique for the construction of the knock-out, also indicating that ESX-4 is not essential for in vitro growth of M. smegmatis. The knock-out strain showed no morphological differences to the wild type strain of M. smegmatis. The knock-out strain will in future be compared to the wild type strain in various functional studies in order to determine the function of the ancestral ESX region. / AFRIKAANSE OPSOMMING: Die genoom van die patogeen Mycobacterium tuberculosis bavat vyf kopieë van die ESAT-6 geen groep gebiede wat kodeer vir ‘n unieke tipe VII sekresie sisteem. Die geen groep gebiede, wat direk betrokke is by patogenisiteit en fagosomale ontsnapping, bevat gene wat kodeer vir die gesekreteerde T-sel antigene ESAT-6 en CFP-10. Die meganisme van die ESX sekresie sisteem is egter steeds tot ‘n groot mate onbekend. Hierdie studie het gefokus op die ESX geen groep gebied 4 (ESX-4), wat voorheen bepaal is om die vroegste kopie van die gebied te wees en wat ook in ander species van Mikobakterieë en hoë G+C Gram-positiewe bakterieë, soos Corynebacterium diptheriae en Streptomyces coelicolor, voorkom. Hierdie projek was daarop gemik om die proteïen-proteïen interaksies van ESX-4 van M. tuberculosis in die model organisme Mycobacterium smegmatis te ondersoek deur middel van Mikobakteriële Proteïen Fragment Komplementasie (M-PFK). M-PFK is ‘n twee-hibried tegniek wat van twee kloningsvektore, naamlik pUAB300 (wat weerstand teen hygromycin B bied) en pUAB400 (wat weerstand teen kanamycin bied) gebruik maak. Gene van belang word in die vektore ingekloneer en in die model organisme, M. smegmatis geko-transformeer, waarna dit as fusieproteïene uitgedruk word. Indien ‘n interaksie tussen die proteïene plaasvind, sal selektiewe groei op ‘n medium wat die antibiotikum trimethoprim bevat, waargeneem word. Verskeie interaksies is in hierdie gebied geïdentifiseer, insluitende self-interaksies, sowel as die verwagte interaksie tussen die ESAT-6 en CFP-10 proteïen familielede esxT en esxU. Aangesien hierdie gebied die vroegste kopie is, bied ESX-4 die basiese model vir die meganisme van sekresie van die tipe VII sekresie sisteem. Wanneer interaksies wat vir ESX-4 geïdentifiseer is met die wat voorheen vir ESX-3 geïdentifiseer is vergelyk word is daar heelwat ooreenkomste. Interaksies wat deur middel van M-PFK geïdentifiseer is, verskaf ‘n basis vir die vêrdere studie van interaksies van hierdie gebied, en sal bevestig moet word deur gebruik te maak van aanvullende tegnieke, soos ko-immunopresipitasie. Ten spyte van die vermoë van M-PFK om proteïen-proteïen interaksies in ‘n mikobakteriële sisteem, wat dus sommige van die beperkings van die klassieke gis twee-hibriedmodel oorkom, te bestudeer, behoort dit steeds as ‘n voorlopige metode van identifikasie beskou te word. ‘n Vêrdere doel van die projek was om ‘n uitslaanmutant van ESX-4 in die model organisme M. smegmatis, wat drie van die ESX gebiede, naamlik ESX-1, -3 en -4 bevat, te skep. Homoloë rekombinasie is bewys om ‘n effektiewe tegniek te wees vir die skep van ‘n uitslaanmuntant en het daarop gedui dat ESX-4 nie essensieel is vir die in vitro groei van M. smegmatis nie. Die uitslaanstam het ook geen morfologiese verskille getoon teenoor die oorspronklike stam nie. Die uitslaanmutant sal in die toekoms gebruik word in ‘n verskeidenheid funksionele studies waar dit vergelyk sal word met die oorspronklike stam, ten einde die funksie van die vroegste ESX-gebied te bepaal. / Medical Research Council of South Africa / National Research Foundation of South Africa / Ernst and Ethel Eriksen Trust

Les bactéries à Gram négatif sont entourées par une enveloppe cellulaire qui, contrairement aux bactéries à Gram positif, possèdent une organisation membranaire complexe composée d’une membrane interne appelée généralement membrane cytoplasmique, un espace périplasmique contenant une matrice de peptidoglycane et une membrane externe asymétrique constituée d’une monocouche de phospholipides surmontée d’une assise de lipopolysaccharide (LPS). Afin de franchir cette barrière, les bactéries à Gram négatif ont développé différentes voies de sécrétions spécifiques dédiées à l’export des protéines (effecteurs) du milieu intracellulaire vers le milieu extracellulaire. Jusqu'à présent, six systèmes de sécrétion ont été identifiés chez ces bactéries. Chez Pseudomonas aeruginosa, une bactérie pathogène opportuniste, le système de sécrétion de type II appelé aussi sécréton Xcp constitue l’un des facteurs principales de sa virulence. Le sécréton Xcp est un complexe macromoléculaire formé par 12 protéines, nommées XcpAO et XcpPC-XcpZM. Ce complexe macromoléculaire est organisé en trois sous-complexes : i) une plateforme d’assemblage ancrée dans la membrane interne formé par les protéines XcpRESFYLZM ii) un pore de sécrétion localisé dans la membrane externe formé par l’oligomérisation d’une protéine appelé la sécrétine XcpQD. Le pore de sécrétion est connecté à la plateforme de la membrane interne par une protéine appelée XcpPC iii) un pseudopilus périplasmique sous forme de fibre hélicoïdale qui est formé par la multimérisation d’une protéine appelée la pseudopiline majeure XcpTG. D’autres protéines appelées les pseudopilines mineures XcpUH-VI-WJ-XK intègrent le pseudopilus. La première partie du travail effectué au cours de cette thèse a eu pour but d’étudier et de comprendre par des approches structurales, biochimiques et biophysiques le mécanisme d’assemblage des pseudopilines en pseudopilus. La deuxième partie de ce travail a porté sur l’étude des réseaux d’interactions entre les substrats sécrétés et les composants de la machinerie Xcp. Durant cette thèse, nous avons ainsi i) identifier grâce à l’étude des interactions protéine-protéine l’existence d’un complexe quaternaire entre les pseudopilines mineures XcpUH-VI-WJ-XK localisées au sommet du pseudopilus ii) déterminer les structures de la pseudopiline majeure XcpTG par RMN et de la pseudopiline mineure XcpWJ par cristallographie aux rayons X iii) déterminer les différents éléments du sécréton qui interagissent avec les exoprotéines du sécréton. Ce réseau d’interaction nous a permis de proposer un modèle de fonctionnement du sécréton qui élucide le cheminement des exoprotéines dans le sécréton afin qu’elles soient exportées vers le milieu extracellulaire. / Gram-negative bacteria are characterized by a complex organization of their cell envelope composed by the inner membrane (IM) called cytoplasmic membrane, the periplasmic space containing a peptidoglycan layer and the outer membrane (OM) covered by the lipopolysaccharide matrix. Gram-negative bacteria have evolved several specialized machines called secretion systems to export their effectors from the intracellular medium to the extracellular milieu or to the host cells. Up to now, at least six secretion systems have been identified. In the opportunistic pathogen Pseudomonas aeruginosa, the type II secretion system called the Xcp secreton is the major pathway for the release of virulence factors. The Xcp secreton is a macromolecular complex composed by 12 proteins called XcpAO, XcpPC-XcpZM. This machinery is organized in 3 sub-complexes: i) the assembly platform localized in the IM implicating XcpRESFYLZM proteins ii) the OM pore composed by the oligomerization of the secretin XcpQD. The connection between the assembly platform and the secretin is performed by XcpPC anchored in the IM iii) a periplasmic pseudopilus consisting of the multimerization of the so-called major pseudopilin XcpTG. The pseudopilus is a helicoidally filament spanning the periplasmic area and pushing the substrate into the secretin pore. Four other proteins, the minor pseudopilins XcpUH-VI-WJ-XK, were found in the pseudopilus. In the present work we first focused on the study of the pseudopilus components by biochemical, biophysical and structural strategies to understand their assembly. Secondly, we investigate the protein interactome between periplasmic secreton component and secreted substrates. Thus, we revealed the presence of a quaternary complex composed by XcpUH-VI-WJ-XK located at the tip of the pseudopilus. To understand at atomic scale the regulation of the pseudopilus, we determined the structure of two components of the pseudopilus XcpTG by NMR and XcpWJ by X-ray crystallography. Using systematic protein-protein interaction studies between secreton components and purified exoproteins of Pseudomonas aeruginosa, we identified 5 proteins of the secreton able to interact with exoproteins. This interaction network allowed us to propose a model for the secretion process including the sequential steps followed by exoproteins inside the secreton to leave the cell envelop.

The Type Three Secretion Systems (T3SSs) of Gram-negative bacteria, including Shigella, Salmonella, and Enteropathogenic/Enterohaemorrhagic Escherichia coli (EPEC/EHEC), pass virulence factors directly into the host to mediate invasion. Prior to secretion down the narrow T3SS channel, effector proteins associate with chaperone proteins. The binding enables the T3SS to keep effectors soluble and partially unfolded for secretion. In the first part of this thesis, the association of one promiscuous chaperone, Spa15 of Shigella flexneri, with three of its cognate effectors has been studied. In addition to the role this plays in secretion, the binding of one particular substrate leads to Spa15 being involved in the regulation of the T3SS. The oligomerisation and impact of substrate binding upon Spa15 has been determined by crystallography and EPR. Once secreted, T3SS effectors subvert the host cytoskeleton for the benefit of the bacteria. Soluble homologues of Spa15 effectors from EHEC and Salmonella have been purified, and their interactions with host GTPases which lead to stress fibre phenotypes observed. The Twin Arginine Translocation (Tat) pathway provides a contrasting view of bacterial secretion. Instead of preventing folding in the cytoplasm, it is a criterion of transport that the protein be folded. One of the reasons for internal folding is the necessity to insert cofactors which could not be incorporated externally. In the second part of this thesis, a protein which exemplifies this necessity is studied. This is PhoD, the model protein for Tat export from Bacillus subtilis. PhoD is an alkaline phosphodiesterase expressed to scavenge phosphate in times of phosphate deficiency. The structure of PhoD has been solved, and the protein is shown to be able to cleave a component of its own cell wall. It uses an unusual catalytic site more reminiscent of the eukaryotic purple acid phosphatases than of other currently known alkaline phosphatases. Furthermore this site appears to require metal binding before export from the bacterial cytoplasm.

Ko Nga Ling. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 98-131). / Abstracts in English and Chinese. / Abstract (in English) --- p.ii / Abstract (in Chinese) --- p.v / Acknowledgements --- p.vii / Table of Contents --- p.ix / List of Figures --- p.xiv / List of Tables --- p.xvii / Symbols and Abbreviations --- p.xviii / Scientific Names --- p.xxi / Chapter Chapter 1 --- General Introduction / Chapter 1.1 --- Gonadotropins --- p.1 / Chapter 1.1.1 --- Structure --- p.1 / Chapter 1.1.2 --- Function --- p.3 / Chapter 1.1.3 --- Regulation --- p.5 / Chapter 1.1.3.1 --- Hypothalamic regulators (GnRH) --- p.5 / Chapter 1.1.3.2 --- Endocrine regulators from gonads (steroids) --- p.7 / Chapter 1.1.3.3 --- Paracrine regulators (activin) --- p.9 / Chapter 1.1.4 --- Promoter analysis --- p.9 / Chapter 1.2 --- Activin Family of Growth Factors --- p.12 / Chapter 1.2.1 --- Activin --- p.12 / Chapter 1.2.1.1 --- Structure --- p.12 / Chapter 1.2.1.2 --- Function --- p.13 / Chapter 1.2.1.3 --- Signaling --- p.15 / Chapter 1.2.2 --- Follistatin --- p.16 / Chapter 1.2.2.1 --- Structure --- p.16 / Chapter 1.2.2.2 --- Function --- p.17 / Chapter 1.3 --- Objectives --- p.18 / Chapter Chapter 2 --- Establishment and Characterization of Stable LβT2 Cell Lines Containing and Expressing SEAP Driven by the Goldfish FSHβ Promoter / Chapter 2.1 --- Introduction --- p.29 / Chapter 2.2 --- Materials and Methods --- p.31 / Chapter 2.2.1 --- Construction of expression plasmid --- p.31 / Chapter 2.2.2 --- Cell culture --- p.32 / Chapter 2.2.3 --- Cotransfection of LβT2 cells --- p.32 / Chapter 2.2.4 --- G418 selection of transfected LpT2 cells --- p.33 / Chapter 2.2.5 --- SEAP reporter gene assay --- p.33 / Chapter 2.2.6 --- Cloning of pSEAP/gfFSHβ promoter and pBK- CMV-transfected LβT2 cells by limited dilution --- p.34 / Chapter 2.2.7 --- Extraction of genomic DNA --- p.34 / Chapter 2.2.8 --- Isolation of total RNA --- p.35 / Chapter 2.2.9 --- Reverse transcription-polymerase chain reaction (RT-PCR) --- p.35 / Chapter 2.3 --- Results --- p.36 / Chapter 2.3.1 --- Optimization of G418 concentration for selection --- p.36 / Chapter 2.3.2 --- Expression of SEAP reporter gene by pSEAP/gfFSHβ promoter and pBK-CMV-transfected LβT2 cells --- p.37 / Chapter 2.3.3 --- Establishment of LβT2 cell lines that contain a functional gfFSHp promoter --- p.37 / Chapter 2.3.4 --- Characterization of LβT2#23 that contains a functional gfFSHβ promoter --- p.38 / Chapter 2.4 --- Discussion --- p.39 / Chapter Chapter 3 --- Hormonal Regulation of Goldfish Follicle-Stimulating Hormone β (FSHβ) Promoter Activity in LpT2#23 Cells / Chapter 3.1 --- Introduction --- p.52 / Chapter 3.2 --- Materials and Methods --- p.54 / Chapter 3.2.1 --- Cell culture --- p.55 / Chapter 3.2.2 --- Drug treatment --- p.56 / Chapter 3.2.3 --- SEAP reporter gene assay --- p.56 / Chapter 3.2.4 --- Isolation of total RNA --- p.57 / Chapter 3.2.5 --- Reverse transcription-polymerase chain reaction (RT-PCR) --- p.57 / Chapter 3.2.6 --- Data analysis --- p.58 / Chapter 3.3 --- Results --- p.59 / Chapter 3.3.1 --- Effects of goldfish activin on FSHβ promoter --- p.59 / Chapter 3.3.2 --- Blockade of activin effects by follistatin --- p.59 / Chapter 3.3.3 --- Effects of different hormones and steroids on FSHβ promoter --- p.60 / Chapter 3.4 --- Discussion --- p.61 / Chapter Chapter 4 --- Promoter Analysis for the Activin Responsive Element (ARE) in the Goldfish Follicle-Stimulating Hormone β (FSHβ) Gene / Chapter 4.1 --- Introduction --- p.71 / Chapter 4.2 --- Materials and Methods --- p.74 / Chapter 4.2.1 --- Generation of SEAP reporter plasmids containing the gfFSHβ promoter of different lengths --- p.74 / Chapter 4.2.2 --- PCR screening and restriction analysis --- p.75 / Chapter 4.2.3 --- Midiprep --- p.76 / Chapter 4.2.4 --- Cell culture --- p.77 / Chapter 4.2.5 --- Transfection of the pSEAP/gfFSHβ promoter constructs into LβT2 cells --- p.77 / Chapter 4.2.6 --- Activin treatment --- p.77 / Chapter 4.2.7 --- SEAP assay --- p.78 / Chapter 4.3 --- Results --- p.78 / Chapter 4.3.1 --- Subcloning of the gfFSHβ promoter of decreasing length into SEAP reporter vector --- p.78 / Chapter 4.3.2 --- Activin stimulation of the pSEAP/gfFSHβ promoter constucts in LβT2 cells --- p.79 / Chapter 4.4 --- Discussion --- p.80 / Chapter Chapter 5 --- General Discussion / Chapter 5.1 --- Overview --- p.92 / Chapter 5.2 --- Contribution of the present research --- p.95 / Chapter 5.2.1 --- Establishment of stable LβT2 cell lines containing and expressing SEAP driven by gfFSHβ promoter --- p.95 / Chapter 5.2.2 --- Hormonal regulation of the gfFSHβ promoterin LβT2#23 cells --- p.95 / Chapter 5.2.3 --- Identification of the activin responsive element (ARE) on the gfFSHβ promoter --- p.96 / Chapter 5.3 --- Future research direction --- p.96 / References --- p.98

Afin de caractériser les mécanismes moléculaires sous-jacents au processus d’adhésion des bactéries commensales, nous avons utilisé Streptococcus salivarius comme modèle. Streptococcus salivarius est une bactérie pionière dans la colonisation des surfaces orales chez le nouveau né, et devient par la suite un composant majoritaire du microbiote oral de l'adulte avec un rôle écologique majeur. Nous avons développé une méthode pour identifier, par des tests de criblage phénotypique, les gènes impliqués dans l’adhésion de S. salivarius aux surfaces bactériennes ou de l’hôte. Notre approche a permis d’identifier un ensemble de gènes codant pour des protéines de surfaces, des glycosyltransférases, des transporteurs qui sont impliqués dans les phénomènes d’auto-agréation et / ou de co-agrégation avec d’autres espèces et / ou l’adhésion aux protéines de l’hôte.En particulier, nous avons montré que le système SecA2Y2, qui comprend des gènes codant pour des protéines dédiées à la glycosylation et l'export de protéines de surface riche en sérine (SRRPs), participe aux processus d’agrégation, de formation de biofilms, à l'adhésion in vitro aux protéines de l’hôte et in vivo à la colonisation du tractus digestif de souris. Alors que toutes les bactéries contenant un système similaire possèdent un substrat unique au système, une SRRP, le locus génétique secA2Y2 comprend trois SRRPs qui présentent des rôles complémentaires dans les phénotypes précédement cités. SrpB est spécifiquement impliquée dans la liaison aux cellules epitheliales, tandis que SrpC participe à l’adhésion aux protéines de la matrice extracellulaire et le mucus. De manière atypique, nous avons démontré que le processus de maturation des SRRPs est supporté par glycosyltransférases extra-cluster. Cette étude est le premier rapport indiquant la présence dans une bactérie de trois SRRPs, qui présentent des rôles complémentaires dans l'interaction bactéries-hôte. Bien que le système SecA2Y2 soit principalement associé à la virulence des bactéries pathogènes, il semble être clairement impliqué dans les caractères de commensalité de S. salivarius, tels que la colonisation de ses niches écologiques orales et intestinales. Ce travail offre de nouvelles perspectives sur les mécanismes de colonisation des bactéries commensales. / To characterize molecular mechanisms underlying adhesion of commensal bacteria, we used Streptococcus salivarius (SSAL) as a model. SSAL is among the most important pioneer colonizers of neonatal oral mucosal surfaces, and later becomes a predominant component of the human adult oral microbiota with pre-eminent ecological role. We developed a method to identified, through phenotypic screening assays, genes involved in SSAL adhesion to host or bacterial surfaces. In particular, we showed that the SecA2Y2 system, which comprises genes devoted to glycosylation and export of surface Serine Rich Repeat Proteins (SRRPs), participates to bacterial aggregation, biofilm formation, in vitro adhesion and colonization of mice. While all bacteria containing a similar system possess only one SRRP, the SSAL secA2Y2 locus comprises three SRRPs with complementary role in line with the previous phenotypes. Interestingly, SrpB is specifically involved in the binding to epithelial cells, while SrpC to the extracellular matrix and mucus proteins. We showed that these interactions require glycosylation of both bacterial SRPs and host surfaces. Surprisingly, we demonstrated that this essential process is shared by glycosyltransferases located in other genomic regions. This work is the first report showing the presence in a bacterium of three SRPs, which display complementary roles in bacterial-host interaction. While the SecA2Y2 system is mostly associated to virulence in pathogenic bacteria, it appears to be involved in the expression of commensal traits in SSAL, such as its colonization and its resilience to oral and intestinal niches. This work may offer new insights into the mechanisms of niche establishment (host, microbial communities) of commensal bacteria.