The inherent design freedom of protein engineering and recombinant protein production enables specific tailoring of protein structure, function, and properties. Two areas of research where protein engineering has allowed for many advances in biomedical materials include the design of novel protein scaffolds for molecular recognition, as well as the use of recombinant proteins for production of next generation biomaterials. The main focus of my dissertation was to develop new biomedical materials using protein engineering. Chapters three and four discuss the engineering of repeat proteins as bio-recognition modules for biomedical sensing and imaging. Chapter three provides an overview of the most recent advances in engineering of repeat proteins in the aforementioned field. Chapter four discusses my contribution to this field. We have designed a de novo repeat protein scaffold based on the consensus sequence of the leucine rich repeat (LRR) domain of the NOD family of cytoplasmic innate immune system receptors. Innate immunity receptors have been described as pattern recognition receptors in that they recognize "global features" of a family of pathogens versus one specific antigen. In mammals, two main protein families of such receptors are: extracellular Toll-like receptors (TLRs) and cytoplasmic Nucletide-binding domain- and Leucine-rich Repeat-containing proteins (NLRs). NLRs are defined by their tripartite domain architecture that contains a C-terminal LRR (Leucine Rich Repeat) domain, the nucleotide-binding oligomerization (NACHT) domain, and the N-terminal effector domain. It is proposed that pathogen sensing in NLRs occurs through ligand binding by the LRR domain. Thus, we hypothesized that LRRs would be suitable for the design of alternative binding scaffolds for use in molecular recognition. The NOD protein family plays a very important role in innate immunity, and consequently serves as a promising scaffold for design of novel recognition motifs. However, engineering of de novo proteins based on the NOD family LRR domain has proven challenging due to problems arising from protein solubility and stability. Consensus sequence design is a protein design tool used to create novel proteins that capture sequence-structure relationships and interactions present in nature in order to create a stable protein scaffold. We implement a consensus sequence design approach to develop proteins based on the LRR domain of NLRs. Using a multiple sequence alignment we analyzed all individual LRRs found in mammalian NLRs. This design resulted in a consensus sequence protein containing two internal repeats and separate N- and C- capping repeats named CLRR2. Using biophysical characterization methods of size exclusion chromatography, circular dichroism, and fluorescence, CLRR2 was found to be a stable, monomeric, and cysteine free scaffold. Additionally, CLRR2, without any affinity maturation, displayed micromolar binding affinity for muramyl dipeptide (MDP), a bacterial cell wall fragment. To our knowledge, this is the first report of direct interaction of a NOD LRR with a physiologically relevant ligand. Furthermore, CLRR2 demonstrated selective recognition to the biologically active stereoisomer of MDP. Results of this study indicate that LRRs are indeed a useful scaffold for development of specific and selective proteins for molecular recognition, creating much potential for future engineering of alternative protein scaffolds for biomedical applications. My second research interest focused on the development of proteins for novel biomaterials. In the past two decades, keratin biomaterials have shown impressive results as scaffolds for tissue engineering, wound healing, and nerve regeneration. In addition to its intrinsic biocompatibility, keratin interacts with specific cell receptors eliciting beneficial biochemical cues, as well as participates in important regulatory functions such as cell migration and proliferation and protein signalling. The aforementioned properties along with keratins' inherent capacity for self-assembly poise it as a promising scaffold for regenerative medicine and tissue engineering applications. However, due to the extraction process used to obtain natural keratin proteins from natural sources, protein damage and formation of by-products that alter network self-assembly and bioactivity often occur as a result of the extensive processing conditions required. Furthermore, natural keratins require exogenous chemistry in order to modify their properties, which greatly limits sequence tunability. Recombinant keratin proteins have the potential to overcome the limitations associated with the use of natural keratins while also maintaining their desired structural and chemical characteristics. Thus, we have used recombinant DNA technology for the production of human hair keratins, keratin 31 (K31) and keratin 81 (K81). The production of recombinant human hair keratins resulted in isolated proteins of the correct sequence and molecular weight determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis and mass spectrometry. Proteins with no unwanted sequence truncations, deletions, or mutations indicate recombinant DNA technology can be used to reliably generate full length keratin proteins. This allows for consistent starting materials with no observable impurities or undesired by-products, which combats a major challenge associated with natural keratins. Additionally, recombinant keratins must maintain the intrinsic propensity for self-assembly found in natural keratins. To test the propensity for self-assembly, we implemented size exclusion chromatography (SEC), dynamic light scattering (DLS), and transmission electron microscopy (TEM) to characterize K31, K81, and an equimolar mixture of K31 and K81. The results of the recombinant protein characterization reveal novel homo-polymerization of K31 and K81, not previously reported, and formation of characteristic keratin fibers for the K31 and K81 mixture. Therefore, recombinant K31 and K81 retain the intrinsic biological activity (i.e. self-assembly) of natural keratin proteins. We have also conducted a comparative study of recombinant and extracted heteropolymer K31/K81. Through solution characterization and TEM analysis it was found that use of the recombinant heteropolymer allows for increased purity of starting material while also maintaining self-assembly properties necessary for functional use in biomaterials design. However, under the processing condition implemented, extracted keratins demonstrated increased efficiency of assembly. Through each study we conclude that recombinant keratin proteins provide a promising solution to overcome the challenges associated with natural protein materials and present an exceptional design platform for generation of new biomaterials for regenerative medicine and tissue engineering. / Ph. D.

<p>Für das Verständnis der Strukturbildung bei Proteinen ist es wichtig, allgemein geltende Prinzipien der Stabilität und Faltung zu verstehen. Bisher wurde viel Arbeit in die Erörterung von Gesetzmäßigkeiten zu den Faltungseigenschaften von globulären Proteinen investiert. Die große Proteinklasse der solenoiden Proteine, zu denen z. B. Leucine-Rich Repeat- (LRR-) oder Ankyrin-Proteine gehören, wurde dahingegen noch wenig untersucht. Die Proteine dieser Klasse sind durch einen stapelförmigen Aufbau von sich wiederholenden typischen Sequenzeinheiten gekennzeichnet, was in der Ausbildung einer elongierten Tertiärstruktur resultiert. In der vorliegenden Arbeit sollte versucht werden, die Stabilität und Faltung eines LRR-Proteins mittels verschiedener biophysikalischer Methoden zu charakterisieren. Als Untersuchungsobjekt diente die für die Infektion ausreichende zentrale LRR-Domäne des Invasionsproteins Internalin B (InlB₂₄₁) des Bakteriums <i>Listeria monocytogenes</i>. Des weiteren sollten die Integrität und die Stabilitäts- und Faltungseigenschaften der sogenannten Internalin-Domäne (InlB₃₂₁) untersucht werden. Hierbei handelt es sich um die bei allen Mitgliedern der Internalinfamilie vorkommende Domäne, welche aus einer direkten Fusion des C-terminalen Endes der LRR-Domäne mit einer Immunglobulin (Ig)-ähnlichen Domäne besteht.</p> <p>Von beiden Konstrukten konnte eine vollständige thermodynamische Charakterisierung, mit Hilfe von chemisch- bzw. thermisch-induzierten Faltungs- und Entfaltungsübergängen durchgeführt werden. Sowohl InlB₂₄₁ als auch InlB₃₂₁ zeigen einen reversiblen und kooperativen Verlauf der chemisch-induzierten Gleichgewichtsübergänge, was die Anwendung eines Zweizustandsmodells zur Beschreibung der Daten erlaubte. Die zusätzliche Ig-ähnliche Domäne im InlB₃₂₁ resultierte im Vergleich zum InlB₂₄₁ in einer Erhöhung der freien Enthalpie der Entfaltung (8.8 kcal/mol im Vergleich zu 4.7 kcal/mol). Diese Stabilitätszunahme äußerte sich sowohl in einer Verschiebung des Übergangsmittelpunktes zu höheren Guanidiniumchlorid-Konzentrationen als auch in einer Erhöhung der Kooperativität des Gleichgewichtsübergangs (9.7 kcal/mol/M im Vergleich zu 7.1 kcal/mol/M). Diese Beobachtungen zeigen dass die einzelnen Sequenzeinheiten der LRR-Domäne nicht unabhängig voneinander falten und dass die Ig-ähnliche Domäne, obwohl sie nicht direkt mit dem Wirtszellrezeptor während der Invasion interagiert, eine kritische Rolle für die <i style='mso-bidi-font-style:normal'>in&nbsp;vivo</i> Stabilität des Internalin B spielt. Des weiteren spiegelt die Kooperativität des Übergangs die Integrität der Internalin-Domäne wieder und deutet darauf hin, dass bei beiden Proteinen keine Intermediate vorliegen.</p> <p>Kinetische Messungen über Tryptophanfluoreszenz und Fern-UV<span style='color:red'> </span>Circulardichroismus deuteten auf die Existenz eines relativ stabilen Intermediates auf dem Faltungsweg der LRR-Domäne hin. Faltungskinetiken aus einem in pH&nbsp;2 denaturierten Zustand zeigten ein reversibles Verhalten und verliefen über ein Intermediat. Eine Erhöhung der Salzkonzentration des sauer-denaturierten Proteins führte zu einer Kompaktierung der entfalteten Struktur und resultierte im Übergang zu einem alternativ gefalteten Zustand. Bei der Internalin-Domäne deuteten kinetische Messungen des Fluoreszenz- und Fern-UV Circulardichroismus-Signals während der Entfaltung möglicherweise auf die Präsenz von zwei Prozessen hin. Der erste langsame Entfaltungsprozess kurz nach dem Übergangsmittelpunkt zeigte eine starke Abhängigkeit von der Temperatur, während der zweite schnellere Prozess der Entfaltung stärker von der Guanidiniumchlorid-Konzentration abhing. Renaturierungskinetiken zeigten das Auftreten von mindestens einem Faltungsintermediat. Kinetische Daten aus Doppelsprungexperimenten lieferten für die Erklärung der langsamen Faltungsphase zunächst keinen Hinweis auf dass Vorliegen einer Prolinisomerisierungsreaktion. Die vollständige Amplitude während der Renaturierung konnte nicht detektiert werden, weswegen von einer zweiten schnellen Phase im Submillisekundenbereich ausgegangen werden kann.</p> <p>Die Ergebnisse der Faltungskinetiken zeigen, dass die InlB-Konstrukte als Modelle für die Untersuchung der Faltung von Solenoidproteinen verwendet werden können.<span lang=EN-GB style='mso-ansi-language: EN-GB'><o:p></o:p></span></p> / <p class=MsoBodyText><span lang=EN-GB style='mso-ansi-language:EN-GB'>To understand the processes of protein structure formation, it is necessary to investigate protein stability and protein folding kinetics. The focus of many folding studies has been directed at small, globular proteins. The larger class of solenoid proteins, including leucine-rich repeat (LRR) and ankyrin proteins, has not been extensively investigated. These proteins contain tandem repeat motifs, and their tertiary structure consists of a regular linear array of modules that stack to form non-globular elongated or supercoiled structures. In the present work, the folding and stability of the central LRR domain of the invasion protein internalin B (InlB₂₄₁) from the bacterium <i>Listeria monocytogenes</i> was characterized using different biophysical techniques. In addition, the integrity, stability and folding behavior of the so-called internalin-domain (InlB₃₂₁) was investigated. In this single domain, which is found in all members of the internalin-family, an immunoglobulin (Ig)-like domain is directly fused to the C-terminal end of the LRR domain.<span style='color:red'><o:p></o:p></span></span></p> <p class=MsoBodyText><span lang=EN-GB style='mso-ansi-language:EN-GB'>A complete thermodynamic characterization of the stability of both constructs was performed, using chemical- and temperature-induced folding and unfolding transitions. The reversible and cooperative equilibrium transition of InlB₂₄₁ and InlB₃₂₁ allowed the use of a two-state model for the description of the data points. The additional Ig-like domain present in InlB₃₂₁ resulted in an increase of the unfolding free energy (8.8 kcal/mol compared to 4.7 kcal/mol). This resulted both, from a shift of the transition midpoint to higher denaturant concentration, and from an increase in the <i>m</i>-value, the denaturant dependence of the unfolding free energy (9.7 kcal/mol/M compared to 7.1 kcal/mol/M). These observations suggest that the unravelling of the individual structural repeats in the LRR region is a cooperative process and that the tight fusion with the Ig-like domain leads to a dramatically increased stability <i>in vivo</i> without interfering with the functionality of the protein. In addition, the cooperativity of the equilibrium transition reflects the integrity of the internalin-domain, and suggests that both InlB fragments unfold without significantly populated equilibrium intermediates.<o:p></o:p></span></p> <p class=MsoBodyText><span lang=EN-GB style='mso-ansi-language:EN-GB'>Kinetic measurements with tryptophan fluorescence and far-UV circular dichroism are indicative for the existence of a relative stable intermediate on the folding pathway of the LRR domain. Refolding kinetics from an acid-denatured state showed a reversible behavior and passes off an intermediate. An increase in the salt concentration of the acid-denatured protein results in a transition of the unfolded structure to a compact and alternatively folded state. Unfolding kinetics of the internalin-domain measured by fluorescence and far-UV circular dichroism are indicative for the possible presence of two processes. The first slow unfolding process after the transition midpoint showed a strong dependence on temperature, whereas the second and faster unfolding process showed a stronger dependence on the denaturant concentration. Renaturation kinetics indicated the existence of at least one folding intermediate. Preliminary double-mixing experiments revealed no evidence for a rate-limiting proline isomerization reaction. It was not possible to detect the complete amplitude of the renaturation reaction, suggesting existence of a second faster phase occuring in the submillisecond range.<o:p></o:p></span></p> <p class=MsoBodyText><span lang=EN-GB style='mso-ansi-language:EN-GB'>The results on folding kinetics prove the InlB constructs to be suitable models for the investigation of solenoid protein folding by techniques of high structural resolution.<o:p></o:p></span></p>

Pannexin 1 (Panx1) is a metabolite channel enriched in the brain and known to localize to the cell surface, where it is involved in a variety of neuronal processes including cell proliferation and differentiation. The mechanisms through which Panx1 is trafficked or stabilized at the surface, however, are not fully understood. The proximal Panx1 C-terminus (Panx1CT), upstream of a caspase-cleavage site has been demonstrated to be required for Panx1 cell-surface expression. We discovered a previously unreported putative leucine-rich repeat (LRR) motif within the proximal Panx1CT. I investigated the involvement of this putative LRR motif on Panx1 localization and oligomerization. Deletion of the putative LRR motif or uniquely the highly conserved segment of the putative LRR motif resulted in a significant loss of Panx1 cell surface expression. Finally, ectopic expression of Panx1-EGFP in HEK293T cells increased cell proliferation, which was not recapitulated by a Panx1 deletion mutant lacking the putative LRR motif. Overall the findings presented in this thesis provide new insights into the molecular determinants of Panx1 trafficking and oligomerization. / Graduate / 2020-02-14

Gliomas are the most common primary brain tumours, and their capacity to invade surrounding normal brain prevents complete removal of the tumour. Malignant glioma has still a poor prognosis. However, with the rapid development of molecular biology our understanding about glioma has increased dramatically. Among known growth factors, EGF and its receptor are frequently amplified and over expressed in malignant glioma. Therefore, it is of interest to find approaches to hamper the activity of EGF/EGFR. The aim of this thesis was to identify and characterize human analogues to a recently identified gene in Drosophilia, kekkon-1, which negatively regulates the activity of Drosophilia EGF receptor. In the first part, we set up a quantitative real-time RT-PCR assay, which showed good linearity, reproducibility and uniformity. We analyzed the expression of the most commonly used reference genes, and showed that 18S was the most reliable endogenous reference gene in this study. In the second part, we cloned, identified, and sequenced a gene family, which we named leucine-rich repeats and immunoglobulin–like domains family (LRIG). The LRIG gene family had three vertebrate paralogs and one homolog in ascidiacea. The proteins encoded by human LRIG genes shared an overall structure with a signal peptide, 15 tandems leucine-rich repeats with N- and C- terminal flanking regions followed by 3 immunoglobulin-like domains, a transmembrane domain, and a cytoplasmic tail. Northern blot showed the mRNA sizes to be 5.5 kb for LRIG1, 4.8 kb for LRIG2, and 5.1 kb for LRIG3. LRIG1-3 mRNAs were detected in all human and mouse tissues analyzed, however, at various levels. FISH and BLAST analysis showed that LRIG1 was located at 3p14, LRIG2 at 1q13, and LRIG3 at 12q13. LRIG1 was shown to be down-regulated in several cancer cell lines and proposed to be a tumour suppressor gene. In the third part, we analysed the expression of LRIG gene family in human astrocytic tumours. LRIG1-3 mRNAs were detected in all human glioma cell lines, in primary tumour tissues and control-matched normal brain tissues, at various levels. Subcellular localizations of LRIG1-GFP fusion proteins were visualized in nuclear, perinuclear, and cytoplasmic compartment. According to the predicted protein sequences, short peptides were synthesized and used to raise antibodies in rabbits. The antibodies were used for immunohistochemical analysis of LRIG1-3 in 404 human astrocytic tumours in a tissue micro array. The pattern of immunoreactivity of LRIG1-3 was heterogeneous with staining in nuclear, perinuclear and cytoplasmic compartment of positive tumour cells. Perinuclear staining of LRIG1-3 displayed a significant inverse correlation with WHO grade and especially positive LRIG3 perinuclear and cytoplasmic staining correlated with a low proliferation index. The LRIGs correlated with survival, and LRIG3 perinuclear staining was in addition to tumour grade an independent prognostic factor. The results suggest that LRIGs may play a role in normal tissue, and may be of importance in the pathogenesis and prognosis of tumours. The exact function of LRIG1-3 remains to be established.

Relaxin and insulin-like peptide-3 (INSL3) are closely related reproductive hormones that are derived from a common ancestor. Relaxin was initially named for its ability to relax the pubic symphysis in pregnant guinea pigs at parturition. Since then relaxin has been found to be involved in many physiological processes based on its ability to stimulate the breakdown and remodeling of collagen fibers. INSL3 is also known as Leydig insulin-like hormone and the relaxin-like factor, and is produced by the Leydig cells in the testis, the thecal and luteal cells of the ovary, the thyroid, placenta and mammary gland. INSL3 induces transabdominal testicular descent by stimulating the development of the gubernacular ligament, which subsequently swells and contracts to pull the fetal testes towards the inguinal wall. In adults however, evidence suggests that INSL3 is involved in reproductive function, acting to promote the survival of male and female germ cells.

Parkinson's Disease (PD) is a late-onset neurodegenerative disease characterized by progressive motor dysfunction caused by a loss of dopaminergic neurons for which there is no known cure. Among the most common genetic causes of PD are mutations in the leucine-rich repeat kinase 2 gene (LRRK2), encoding a multi-domain protein with kinase activity. The LRRK2 G2019S mutation causes hyperactivity of the kinase domain and is the most frequent LRRK2 mutation in patients with familial PD, though its role in PD pathology remains unclear. Preliminary data from the lab of our collaborator, Dr. David Park, demonstrated through a genetic screen in Drosophila melanogaster that the deletion of rbp9 encoding an RNA-binding protein prevented pathology induced by PD-relevant mutations in the LRRK2 kinase domain. The neuronal homolog of RBP9 in humans is HuD, a member of the Hu family of RNA-binding proteins that regulates the expression of many transcripts involved in neuronal development, plasticity, and survival. In addition, HuD has been shown to modify the age-at-onset or risk of developing PD. Here, we studied the effect of LRRK2 on the post-transcriptional regulation of mRNAs bound by HuD in the context of PD. Our findings showed that HuD is a substrate for LRRK2 phosphorylation in vitro, and that LRRK2 G2019S hyperphosphorylates HuD. We demonstrated that LRRK2 kinase activity is required for the binding of several transcripts by HuD that encode PD-relevant proteins such as α-synuclein and neuronal survival factor BDNF. Our findings in human neuroblastoma cells indicated that LRRK2 regulates the protein levels of HuD mRNA targets α-synuclein and BDNF in a mechanism that can by modified by HuD. Finally, we showed that the combination of HuD knockout with LRRK2 G2019S expression in mice rescues aberrant expression of HuD targets in mice with only the LRRK2 G2019S mutation or the knockout of HuD alone. Together, our findings demonstrate that LRRK2 affects the post-transcriptional regulation of HuD-bound mRNAs, and suggest the use of HuD as a potential therapeutic target in patients with PD caused by the LRRK2 G2019S mutation.

Indiana University-Purdue University Indianapolis (IUPUI) / Mutations in the gene encoding for leucine rich repeats kinase 2 (LRRK2) are commonly found in Parkinson’s disease. Recently, we found that the disease-associated point mutations at residue R1441 in the G domain (ROC) of LRRK2 resulted in perturbation of its GTPase activity. In this study, we compare the biochemical and biophysical properties of the ROC domain of LRRK2 carrying the PD-associated mutations at residue R1441 with those of the wild-type. We found that the disease-associated mutations (R1441C/G/H) showed marked quaternary structure compared to wild-type, in that the latter existed in solution in both monomeric and dimeric conformations dynamically regulated by GDP/GTP binding state, while we detected only monomeric conformation for three disease-associated mutants. To understand the structural basis for this plasticity and the activity reduction in the mutants, we solved a 1.6 Å crystal structure of the wild type ROC that shows a stable dimeric conformation in which the switch motifs and inter-switch regions mediate extensive interactions at the dimer interface. Residue R1441, where PD-associated mutations occur, forms exquisite interactions at the interface, thus suggesting a critical role of this residue in maintaining a dynamic dimer-monomer interconversion and conformational flexibility of the switch motifs. Consistently, substituting R1441 for other arbitrary mutations (R1441K/S/T) lead to similar perturbation of GTPase activity and dimerization defects as observed in the disease-associated mutants. Locking the ROC domain in either dimeric or monomeric conformations by engineered disulfide bond alters the binding affinity to GTP (but not GDP) and significantly reduce GTPase activity, thus suggesting that the dynamic dimer-monomer interconversion and conformational plasticity are essential for ROC function as a molecular switch modulating the kinase activity of LRRK2.

Soybean mosaic virus (SMV), has been the cause of numerous and often devastating disease epidemics, causing reduction in both the quality and quantity of soybeans worldwide. Two important genes for resistance to SMV are Rsv1 and Rsv4. Alleles at the Rsv1 locus have been shown to control resistance to all but the most virulent strain of SMV. This locus has been mapped previously to the soybean F linkage group. Rsv4 is an SMV resistance locus independent of Rsv1 and confers resistance to all strains of SMV. This locus has not been mapped previously. The purpose of this study is to investigate the two genomic regions that contain these vitally important resistance genes. A population of 281 F2 individuals that had previously been genotyped for reaction to SMV was evaluated in a mapping study which combined bulk segregant analysis with Amplified Fragment Length Polymorphism (AFLP). A Rsv4-linked marker, R4-1, was identified that mapped to soybean linkage group D1b using a reference mapping population. More than 40 markers were mapped in the Rsv4 segregating population including eleven markers surrounding Rsv4. This will provide the necessary framework for the fine mapping of this important genetic locus. Previous work has located Rsv1 to a genomic region containing several important resistance genes including Rps3, Rpg1, and Rpv. An RFLP probe, NBS5, whose sequence closely resembles that of several cloned plant disease resistance genes has been mapped to this chromosomal region. The efficacy of using this sequence to identify potential disease resistance genes was assessed by screening a cDNA library to uncover a candidate disease resistance gene which corresponds to this NBS5 sequence. Two related sequence classes were identified that correspond to NBS5. Interestingly, one class corresponds to a full length gene closely resembling other previously cloned disease resistance genes offering evidence that this NBS5-derived clone is a candidate disease resistance gene. A new marker technique was developed by combining the speed and efficiency of AFLP with DNA sequence information from cloned disease resistance genes. Using this strategy, three new markers tightly linked to Rsv1 were identified. One of these markers, which maps 0.6 cM away from Rsv1, has motifs consistent with other cloned disease resistance genes, providing evidence that this approach is an efficient method for targeting genomic regions where disease resistance genes are located. / Ph. D.

Les racines ont deux grands rôles. Le premier est le prélèvement de l’eau et des éléments nutritifs et le second est l’ancrage dans le sol. Identifier les gènes responsables de la mise en place des tissus et de l'architecture du système racinaire est donc essentiel pour pouvoir améliorer les variétés de riz soumises à des stress abiotiques de plus en plus fréquents et nombreux du fait du changement climatique. Au cours de cette thèse, j'ai réalisé une analyse fonctionnelle du gène DEFECTIVE IN OUTER CELL LAYER SPECIFICATION (DOCS1) qui appartient à la famille des récepteurs kinases à répétitions riches en leucine (LRR-RLK). Ces protéines sont composées de deux domaines principaux: un domaine extra-cytoplasmique composé de répétitions LRR et un domaine kinase intra-cytoplasmique. Un mutant de ce gène, nommé c68, possède une mutation non-sens dans le domaine kinase. Les plantes mutantes c68 présentent plusieurs phénotypes: une sensibilité accrue à l'aluminium, une réduction du nombre et de la taille des poils absorbants dans les racines, et des couches d’exoderme/épiderme d’identité mêlée. Le premier chapitre de la thèse porte sur l’étude conjointe de lignées knock-out CRISPRs du gène DOCS1 et de c68. Nos résultats ont montré que les mutants c68 et CRISPRs présentaient les mêmes phénotypes : sensibilité à l’aluminium, défauts des poils absorbants et tissus externes d’identité mixte. Ces résultats suggéraient que chez le mutant c68, soit la protéine DOCS1 n'était pas fonctionnelle, soit elle n'était pas traduite. Nos analyses phénotypiques ont aussi révélé que tous les mutants présentaient des défauts de réponse à la gravité à différents stades de développement. A 3 jours, un retard de réponse à la gravité était observé pendant la première heure après gravistimulation. Les plantules mutantes présentaient aussi des défauts de localisation d’un transporteur d’auxine. A 40 jours, nous avons observé que l'angle du cône racinaire des plantes mutantes était plus ouvert que celui des plantes sauvages. Deux gènes liés à l’auxine et plusieurs QTLs ont déjà été identifiés comme participant à ce phénotype chez le riz. Dans la suite de notre étude, nous avons donc cherché à identifier de nouveaux QTLs et gènes impliqués dans ce phénotype morphologique par étude d'association pan-génomique dans deux panels Indica et Japonica. Toutes les accessions de l'écotype bulu d'Indonésie et trois japonicas tempérés d'Asie du Sud présentaient un angle du cône racinaire très ouvert. En utilisant un modèle mixte associé à une technique de ré-échantillonnage, 55 QTLs ont été détectés. L'analyse des gènes sous-jacents ou voisin (+/- 50kb) a identifié 539 gènes, dont 6 LRR-RLK, 5 gènes liés à l’auxine et 5 gènes avec une fonction validée dans le développement ou l'architecture racinaire. Une approche complémentaire par cartographie génétique classique est proposée pour identifier les gènes en cause dans la ou les mutations à angle du cône racinaire très ouvert. Des perspectives de poursuite du travail effectué sont aussi présentées afin de déterminer si le phénotype affectant l'angle du cône racinaire induit par les mutations du gène DOCS1 ou des nouveaux gènes identifiés est lié à des perturbations des flux d’auxine. / Roots have two major roles. The first one is to uptake water and nutrients and the second one is to anchor plants into the ground. Identifying the genes responsible for the establishment of tissues and architecture of the root system is essential to improve rice varieties subject to increasingly frequent and numerous abiotic stresses due to climate change. During my PhD, I undertook a functional analysis of the DEFECTIVE IN OUTER CELL LAYER SPECIFICATION (DOCS1) gene which belongs to the Leucine-Rich Repeat Receptor-Like Kinase (LRR-RLK) family. These proteins are composed of two main domains: an extra-cytoplasmic domain containing LRR repeats and a cytoplasmic kinase domain. A mutant of this gene, named c68, carries a nonsense mutation in the kinase domain. The c68 mutant plants show several phenotypes: increased sensitivity to aluminum, reduced number and size of root hairs, and layers of external tissues with exodermis/epidermis mixed identity. The first chapter of the thesis focuses on the joint study of knockout CRISPRs lines of the DOCS1 gene and c68. Our results showed that the c68 and CRISPRs mutants displayed the same phenotypes: sensitivity to aluminum, defects in root hairs and mixed identity of external tissues. These results suggested that in the c68 mutant, either the DOCS1 protein was not functional, or the protein was not translated. Our phenotypic analyses also showed that all mutants exhibited impaired gravity responses at different development stages. At 3 days, a delay of response to gravity was observed during the first hour after gravistimulation. Mutant seedlings also had defects in an auxin transporter localization. At 40 days, we observed that the root cone angle of mutant plants was more open than that of wild-type plants. Two genes associated with auxin and several QTLs have been identified as contributing to this phenotype in rice. In the rest of our study, we therefore tried to identify new QTLs and genes involved in this morphological phenotype by a genome-wide association study in two Indica and Japonica panels. All accessions of the bulu ecotype from Indonesia and three South Asian temperate japonica had a very open root cone angle. Using a mixed model associated with a resampling technique, 55 QTLs were detected. The analysis of the underlying or neighbor (+/- 50kb) genes identified 539 genes, including 6 LRR-RLK, 5 genes related to auxin and 5 genes with a function validated in root development or architecture. A complementary approach by classical genetic mapping is proposed to identify genes involved in the mutation(s) involved in very open root cone angle. Prospective research lines are also presented to determine if the root cone angle phenotype , induced by DOCS1 or by newly identified genes, is linked with disruption of auxin fluxes.

Thesis advisor: Charles S. Hoffman / Glucose detection in yeast occurs via a cAMP signaling pathway that is similar to that of other signaling pathways in humans. The presence of glucose in the environment ultimately represses, as a result of cAMP signaling, the transcription of the gene fbp1. Adenylate cyclase is known to convert ATP to cAMP, and is thus a central protein in the propagation of the signal. Mutant forms of the adenylate cyclase gene (git2) have been found by the inability for the organism to repress fbp1 transcription in the presence of glucose. In this study, two questions were under investigation. The first was focused on the ability of the mutations to affect the dimerization of the catalytic domain. The second investigated multiple protein-protein interactions in the leucine rich-repeat (LRR) domain of adenylate cyclase. Both domains contain mutations that confer an activation defect, and they are thus are thought to have a relationship. / Thesis (BS) — Boston College, 2005. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Biology. / Discipline: College Honors Program.