<p>Across the tree of life, novel genes are thought to be a source of much of the unique behaviors and adaptions between the different taxa. This is especially true in the social insects where novel genes are proposed to contribute to novel social behaviors. In the honey bee (Apis mellifera L.), a group of novel genes called the major royal jelly proteins (MRJPs) are proposed to be important to the expression of novel social behaviors, particularly those related to nursing versus foraging tasks. Unfortunately, identifying the functional role of novel genes is often not possible due to a lack of functional genomic tools in non-model species such as the honey bee. Here I have developed a novel ectopic expression system in Drosophila melanogaster and used it to elucidate how the MRJPs contribute to behavioral and transcriptional changes in the insect brain. I found that the MRJPs regulated the expression of hundreds of genes in Drosophila, and these overlap with genes regulated differentially between nursing and foraging honey bees. Furthermore, I found that MRJP expression impairs or negatively regulated phototaxis. My results demonstrate the MRJPs play a role in behavioral plasticity and highlight that the MRJPs may have a much larger role in the nurse-forager transition than previously thought.</p>

Candida albicans, une levure pathogène de l’humain, cause des infections envahissantes chez les individus immunodéprimés. C. albicans peut changer sa morphologie entre les formes levures et filamenteuses, un déterminant de virulence considérable qui est influencé par plusieurs facteurs environnementaux comme le pH, le sérum, les nutriments, et le farnesol, une molécule de la détection du quorum. Le génome de C. albicans a été séquencé et à date, plusieurs gènes codant des régulateurs de transcription (RT) restent incaracterisés. Basé sur des criblages à grande-échelle, il a été possible d’attribuer des phénotypes à certains des RT incaractérisés, cependant, leurs cibles traduisant ces phénotypes restent inconnues. Le but de cette thèse était d’étudier les fonctions biologiques de RT sélectionnés et d’établir des réseaux transcriptionnels chez C. albicans. J’ai utilisé des approches génétiques et génomiques afin d’identifier et de caractériser le regulon de ces RT, ce qui a permis de déterminer leur fonctions biologiques. Notre groupe avait identifié Fcr1p, un RT dont la délétion augmente la filamentation et la tolérance à plusieurs antifongiques. Cependant, le mécanisme sous-jacent reste inconnu. Dans le Chapitre 2, j’ai identifié le régulon d’Fcr1p et j’ai trouvé qu’il régule ses cibles de façon complexe étant en même temps un activateur et un répresseur d’expression de gènes. J’ai démontré que Fcr1p agit comme répresseur direct des gènes de l’assimilation et du métabolisme de l’azote. L’expression de plusieurs de ces cibles était dépendante d’Fcr1p en conditions d’épuisement d’azote. J’ai montrés que Fcr1p agit aussi comme répresseur indirect de gènes hyphe-spécifiques ainsi qu’un activateur indirect de transport et de métabolisme du carbone et de gènes levure-spécifiques. De plus, la suréxpression d’Fcr1p abolit la filamentation sur le milieu Spider, confirmant que c’est un répresseur de filamentation. Dans le Chapitre 3, j’ai décris un crible génétique basé sur un principe de co-culture pour identifier des mutants de RT défectueux en production de farnesol. Conséquemment, les RT Ada2p, Cas5p, Fgr15p, Cas1p, et Rlm1p, impliqués dans le maintien de la paroi cellulaire, ont été identifiés. La quantification du farnesol intracellulaire de ces mutants a confirmé que le défaut observé peut être attribué à un défaut de la biosynthèse de farnesol plutôt qu’à un défaut de sécrétion de celui-ci. Pour comprendre le mécanisme responsable de ce défaut, nous avons commencé par caractériser le régulon de Cas5p par des analyses de profilages d’expression et de localisation. J’ai montré que Cas5p se lie à des gènes impliqués dans le catabolisme des hydrocarbures et la production d’énergie. Cas5p induit aussi des gènes impliqués dans le catabolisme des hydrocarbures et des lipides et réprime des gènes impliqués dans le métabolisme primaire, montrant que Cas5p régule plusieurs voies métaboliques, notamment celle du carbone. En plus des fonctions d’Ada2p et Rlm1p dans la liaison et/ou la régulation de gènes du catabolisme des hydrocarbures, nos résultats appuient avec la proposition que le farnesol constitue une traduction du métabolisme du carbone cellulaire. Dans l’ensemble, ces résultats ont aidé à élucider le rôle d’Fcr1p ainsi que 5 autres RT dans la régulation de voies métaboliques fondamentales influençant le dimorphisme, un attribut crucial de la virulence chez C. albicans. / Candida albicans, an important human fungal pathogen, causes life-threatening invasive infections in immuno-compromised individuals. It switches between yeast and filamentous forms. This dimorphism is a considerable virulence attribute and one that is influenced by many environmental factors, such as pH, serum, nutrients and farnesol, a quorum sensing molecule. The genome of C. albicans has been sequenced and to date, many of the genes encoding transcriptional regulators (TRs) remain uncharacterized. Based on large-scale screens, it was possible to assign phenotypes to some of the uncharacterized TRs, however the targets of these TRs that mediate these phenotypes remain to be identified. The aim of this thesis work was to understand the normal biological function of selected TRs and construct transcriptional networks in C. albicans. I used genetic and genomic approaches to identify and characterize the regulon of these TRs, which helped to define their biological functions. Our group has previously identified Fcr1p, a zinc cluster TR whose deletion increases cell tolerance to multiple drugs and enhances filamentation. However, the mechanism by which it mediates these phenotypes is still unknown. In Chapter 2, I identified the regulon of Fcr1p and found that it regulates its targets in a complex manner since it can act both as an activator and as a repressor of gene expression. I have shown that Fcr1p acts as a direct negative regulator of genes involved in nitrogen source assimilation and metabolism. The Fcr1p-dependent expression of a number of its targets also occurs under nitrogen starvation conditions. Results also showed that Fcr1p is an indirect negative regulator of hyphal-specific genes, and an indirect positive regulator of carbon source transport and metabolism, as well as yeast-specific genes. Furthermore, Fcr1p overexpression abrogates filamentation on Spider medium confirming that it is a negative regulator of filamentation. In Chapter 3, I describe a genetic screen based on a co-culture assay with A. nidulans to identify TR mutants defective in farnesol production. Our results identified Ada2p, Cas5p, Fgr15p, Cas1p, and Rlm1p, five TRs involved in cell wall integrity. Intracellular farnesol quantification in these mutants confirmed that the observed defect in farnesol production could be attributed to impairment in farnesol biosynthesis rather than export of this molecule. To get an insight into the molecular mechanism responsible for this defect, we started by identifying the regulon of Cas5p using expression and location profiling. Results showed that Cas5p binds genes involved in carbohydrate catabolism and energy production. Cas5p also upregulates genes involved in carbohydrate and lipid catabolism and downregulates genes involved in primary metabolism, indicating that Cas5p is involved in the regulation of many pathways, with a clear involvement in carbon metabolism. Coupled to the known function of Ada2p and Rlm1p in binding and/or regulating genes involved in carbohydrate catabolism, our results support the proposition that farnesol is a metabolic read-out of the cell carbon metabolic activity. Taken together, these results helped elucidate the role of Fcr1p as well as five other TRs in the regulation of central metabolic pathways that influence morphological switching, a crucial attribute of C.albicans virulence.

ABSTRACT The xyloglucan endo-transglycosylase/hydrolase (XTH) genes are found in all vascular and some nonvascular plants. The XTH genes encode proteins which comprise a subfamily of glycoside hydrolase (GH) family 16 in the Carbohydrate-Active enZYmes (CAZY) classification. The XTH gene products are believed to play intrinsic role in cell wall modification during growth and development throughout the lifetime of the plant. In the present investigation, biochemical and reverse genetic approaches were used to better understand the functions of individual members of the XTH gene family of two important plants: the model organism Arabidopsis thaliana and the grain crop barley (Hordeum vulgare). A phylogenetic tree of the xyloglucan-active enzymes of GH16 has previously been constructed, where enzymes with similar activities have been shown to cluster together. Several members of phylogenetic Group I/II and III-B, predicted to exhibit xyloglucan endo-transglycosylase activity (EC 2.4.1.207) and members of Group III-A, predicted to exhibit xyloglucan endo-hydrolase activity (EC 3.2.1.151), were included to analyze the functional diversity of XTH gene products. A heterologous expression system using the yeast Pichia pastoris was found to be effective for recombinant protein production with a success rate of ca. 50%. XTH gene products were obtained in soluble and active forms for subsequent biochemical characterization. In order to be able to screen larger numbers of protein producing clones, a fast and easy method is required to identify clones expressing active protein in high enough amounts. Thus, a miniaturized XET/XEH assay for high-throughput analysis was developed, which was able to identify activities with good precision and with a reduced time and materials consumption and a reduced work load. Enzyme kinetic analysis indicated that the XET or XEH activity of all XTH gene products characterized in the present study corresponded to predictions based on the previously revised phylogenetic clustering. To gain insight into the biological function of the predominant XEHs AtXTH31 and AtXTH32, which are highly expressed in rapidly developing tissues, a reverse genetic approach was employed using T-DNA insertion lines of the A. thaliana Columbia ecotype. Genotypic and phenotypic characterization, together with in situ assays of XET and XEH activities, in single- and double-knock-out mutants indicated that these Group III-A enzymes are active in expanding tissues of the A. thaliana roots and hypocotyl.  Although suppression of in muro XEH activity was clearly observed in the double-knock-out, no significant growth phenotype was observed, with the exception that radicle emergence appeared to be faster than in the wild type plants. Keywords: Arabidopis thaliana, Hordeum vulgare, plant cell wall, xyloglucan, glycoside hydrolase family 16, xyloglucan endo-transglycosylase/hydrolase gene family, xyloglucan endo-transglycosylase, xyloglucan endo-hydrolase, heterologous protein expression, Pichia pastoris, T-DNA insertion, in situ XET/XEH assay, high-throughput screening / QC 20110114

Indiana University-Purdue University Indianapolis (IUPUI) / Alcoholism inheritance rates have been estimated as high as 60% in a human population. Many significant features of alcohol dependence have been replicated in rodent animal models of alcoholism, however not in totality. These animal models include inbred preferring (iP) and nonpreferring (iNP) rat types. Congenic rats have been engineered from the iP and iNP strains whereby a P congenic rat has in its genome a well-chosen chromosomal portion taken from an NP rat (P.NP) and, reciprocally, an NP congenic rat has acquired the analogous DNA from a P rat (NP.P). In this case, a quantitative trait locus (QTL) from chromosome 4 is the donor genetic material for the congenic rats. It is of great interest to further study this chromosome 4 QTL because it has been found to control a significant portion of ethanol consumption behavior in iP and iNP rats. This study aimed to behaviorally profile the iP, iNP and reciprocal congenic rats. As a result of the behavioral profiling of these genetically related groups, some conclusions could be made regarding which behaviors appear to be controlled by the chromosome 4 donor DNA.This study primarily utilized the Multivariate Concentric Square Field apparatus (MCSF) to characterize behavioral profiles for the inbred and congenic rats. The Open field (OF) and Elevated plus maze (EPM) supported this effort. The MCSF is valuable in that it allows for the animals to interact within an environment that has ethological value. The 12 different zones that make up the field are characterized by some functional quality in terms of type and duration of behavior performed, etc. The behavioral data is aggregated and finally represented in terms of five functional categories, the elements of the behavioral profile: general activity, exploratory activity, risk assessment, risk taking, and shelter seeking. The study hypotheses were shaped by prior research suggesting that iPs should display lower general activity and risk taking strategy than iNPs in the MCSF. Inbred Ps should be more active in the OF and spend more time in the center of the EPM. Generally, it is expected that the iP QTL confer behavioral phenotypes to the iNP strain that deviate toward a "P" behavioral phenotype and reciprocally, the iNP QTL confer behavioral phenotypes to the iP strain that deviate toward an "NP" behavioral phenotype. The results showed that iP rats performed more risk assessment and risk taking behavior and less shelter seeking and anxiety-like behavior than iNP rats. It followed that P.NP congenic rats significantly downgraded their risk assessment and risk taking behavior when compared to iP rats. This decrease can be attributed to the chromosome 4 QTL donated from the iNP breed. All together this study concludes that risk assessment and risk taking behavior in the iP rats is controlled by the same DNA region that, in part, determines voluntary intake of ethanol consumption. Further fine mapping of the QTL region should help in discovering if the same DNA sequences that influence ethanol intake also significantly influence risk behavior.