Systemic fungal infection is a life-threatening problem. Anti-fungal drugs are the most effective clinical strategy to cure such infections. However, most current anti-fungal drugs either have high toxicity or have a narrow spectrum of effect. Meanwhile, anti-fungal drugs are losing their clinical efficacy due to emerging drug resistance. To protect us from these deadly pathogenic fungi, scientists need to study new drug targets and to solve problems related to drug resistance. The cell wall is essential for fungal cell survival and is absent from animal cells, so it is a promising reservoir for screening safe and effective drug targets. Alpha-1,3-glucan is one of the major cell wall carbohydrates and is important for the virulence of several pathogenic fungi. In this thesis, molecular biology and microscopy techniques were used to investigate the function and the synthesis process of α-1,3-glucan in the model fungus A. nidulans. My results showed that α-1,3-glucan comprises about 15% of A. nidulans cell wall dry weight, but also that α-1,3-glucan does not have an important role in cell wall formation and cell morphology. Deletion of α-1,3-glucan only affects conidial adhesion and cell sensitivity to calcofluor white. In contast, elevated α-1,3-glucan content can cause severe phenotypic defects. To study the α-1,3-glucan synthesis process, I systematically characterized four proteins, including two α-1,3-glucan synthases (AgsA and AgsB) and two amylase-like proteins (AmyD and AmyG). Results showed AgsA and AgsB are both functional synthases. AgsB is the major synthase due to its constant expression. AgsA mainly functions in conidiation stages. AmyG is a cytoplasmic protein that is critical for α-1,3-glucan synthesis, likely being required for an earlier step in the synthesis process. In contrast to the other three proteins, AmyD has a repressive effect on α-1,3-glucan accumulation. These results shed light on therapeutic strategies that might be developed against α-1,3-glucan. I also developed a strategy to investigate drug resistance mutations. The tractability of A. nidulans and the power of next generation sequencing enabled an easy approach to isolate single mutation strains and to identify the causal mutations from a genome scale efficiently. I suggest this strategy has applications to study the drug resistance mechanisms of current anti-fungal drugs and even possibly future ones.

Carbon catabolite repression (CCR) is a mechanism by which micro-organisms preferentially utilize more easily metabolizable carbon sources in comparison to less easily metabolizable carbon sources. It prevents the organisms from unnecessary expenditure of energy and enables them to exploit the nutrients in appropriate manner. It represents a complex system of gene regulation. The main aim of this study was to study the intracellular localization of proteins involved in CCR including CreA, CreB, CreC and CreD in A. nidulans in repressing and derepressing conditions. The major regulatory protein involved in CCR in A. nidulans is CreA. It is a DNA-binding repressor, but very little is known about the molecular events that allow CreA function to result in appropriate regulation in response to carbon source. To determine the amount and localization of CreA in different carbon sources, strains were made over-expressing GFP and HA tagged CreA. Western analysis showed that high levels of full length CreA can be present in cells that show normal responses to carbon catabolite repression, whether they are grown in repressing or derepressing media. Hence the amount of CreA is similar in both the conditions and thus degradation of CreA is not a key step in carbon catabolite repression. Fluorescence microscopy studies have shown that CreA is in the nucleus under repressing and derepressing carbon conditions and this is not affected by the absence of CreB or CreD, the other important proteins in A. nidulans. Thus mere localization of CreA in nucleus is not sufficient to cause carbon catabolite repression and there is some modification process involved for CreA to act as a repressor protein in CCR. CreB is a deubiquitinating protein and CreC is a protein containing five WD 40 repeats, a putative nuclear localization signal (NLS) and a proline rich region and both the proteins are present in the cell in a complex. CreB was localized using strains that over-expresses GFP tagged CreB and fluorescence microscopy. CreB is present mainly in the cytoplasm in both repressing and derepressing conditions. Moreover, intracellular localization of CreB is unaffected by the presence or absence of CreD. However, the amount of CreB was higher in a creD+ background as compared to a creD34 mutant background, implying that the presence of CreD affects the amount of CreB in the cell. CreC was localized by using strain that over-expresses YFP tagged CreC and it is also present mainly in the cytoplasm. CreD contains arrestin domains and PY motifs and is highly similar to the Rod1p and Rog3p from S. cerevisiae. CreD is proposed to be involved in ubiquitination process in CCR in A. nidulans. Localization studies have shown that CreD is present throughout the cell in a punctate pattern with more in the cytoplasm than in the nucleus. CreB and CreD co-localize in some regions of the cell whereas in other regions either CreB or CreD is present. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1346526 / Thesis (Ph.D.) - University of Adelaide, School of Molecular and Biomedical Science, 2008

Erratum pasted onto front end-paper. / Copies of author's previously published article inserted. / Bibliography: leaves 167-180. / 180 leaves, [51] leaves of plates : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Reanalyses the effects of the absence of CreA in the cell, raises antibodies for the detection of CreA and identifies new loci involved in carbon catabolite repression by using different genetic selection methods. / Thesis (Ph.D.)--University of Adelaide, Dept. of Genetics, 1999?

Carbon catabolite repression (CCR) is a mechanism by which micro-organisms preferentially utilize more easily metabolizable carbon sources in comparison to less easily metabolizable carbon sources. It prevents the organisms from unnecessary expenditure of energy and enables them to exploit the nutrients in appropriate manner. It represents a complex system of gene regulation. The main aim of this study was to study the intracellular localization of proteins involved in CCR including CreA, CreB, CreC and CreD in A. nidulans in repressing and derepressing conditions. The major regulatory protein involved in CCR in A. nidulans is CreA. It is a DNA-binding repressor, but very little is known about the molecular events that allow CreA function to result in appropriate regulation in response to carbon source. To determine the amount and localization of CreA in different carbon sources, strains were made over-expressing GFP and HA tagged CreA. Western analysis showed that high levels of full length CreA can be present in cells that show normal responses to carbon catabolite repression, whether they are grown in repressing or derepressing media. Hence the amount of CreA is similar in both the conditions and thus degradation of CreA is not a key step in carbon catabolite repression. Fluorescence microscopy studies have shown that CreA is in the nucleus under repressing and derepressing carbon conditions and this is not affected by the absence of CreB or CreD, the other important proteins in A. nidulans. Thus mere localization of CreA in nucleus is not sufficient to cause carbon catabolite repression and there is some modification process involved for CreA to act as a repressor protein in CCR. CreB is a deubiquitinating protein and CreC is a protein containing five WD 40 repeats, a putative nuclear localization signal (NLS) and a proline rich region and both the proteins are present in the cell in a complex. CreB was localized using strains that over-expresses GFP tagged CreB and fluorescence microscopy. CreB is present mainly in the cytoplasm in both repressing and derepressing conditions. Moreover, intracellular localization of CreB is unaffected by the presence or absence of CreD. However, the amount of CreB was higher in a creD+ background as compared to a creD34 mutant background, implying that the presence of CreD affects the amount of CreB in the cell. CreC was localized by using strain that over-expresses YFP tagged CreC and it is also present mainly in the cytoplasm. CreD contains arrestin domains and PY motifs and is highly similar to the Rod1p and Rog3p from S. cerevisiae. CreD is proposed to be involved in ubiquitination process in CCR in A. nidulans. Localization studies have shown that CreD is present throughout the cell in a punctate pattern with more in the cytoplasm than in the nucleus. CreB and CreD co-localize in some regions of the cell whereas in other regions either CreB or CreD is present. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1346526 / Thesis (Ph.D.) - University of Adelaide, School of Molecular and Biomedical Science, 2008

University, Diss., 2002--Göttingen.

A humanidade tem aumentado drasticamente o uso de antibióticos, antifúngicos, inseticidas, herbicidas e agentes quimioterápicos para tratar infecções, câncer e obter ganho econômico com a produção agrícola e industrial. O repetido uso destas substâncias leva freqüentemente à sua ineficiência devido à seleção de organismos resistentes ou tolerantes, com graves conseqüências econômicas e sociais. Os mecanismos envolvidos no processo de resistência à antifúngicos são pouco conhecidos. A compreensão destes mecanismos auxiliará no desenvolvimento de estratégias para a identificação de isolados clínicos resistentes, no tratamento de infecções fúngicas, na prevenção do surgimento de isolados resistentes, na definição de novas estratégias de utilização de antifúngicos, na revelação de novos alvos terapêuticos e portanto, no controle dos patógenos. Para o entendimento das bases moleculares da resistência à acriflavina e outros agentes inibidores em fungos nós clonamos, por transformação, um gene que confere esta resistência em Aspergillus nidulans e o caracterizamos molecularmente. Construímos uma biblioteca a partir de uma linhagem duplo-resistente e isolamos um clone que se mostrou capaz de transformar uma linhagem receptora sensível em resistente à acriflavina. A seqüência deste clone proveniente do mutante resistente, e de seu alelo selvagem revelou um gene de aproximadamente 2276 nucleotídeos traduzido em 697 aminoácidos, com alta similaridade com a trealose sintase/fosforilase (glicosiltransferase) de vários organismos. Esta seqüência foi depositada no “GenBanK” (AY102266). As enzimas trealose sintase e fosforilase participam da síntese da trealose que, além de ser fonte de carbono, está relacionada com a proteção das proteínas de membrana e das enzimas, e contra o estresse térmico e oxidativo em fungos filamentosos. As seqüências nucleotídicas dos alelos selvagem e mutante não apresentaram diferenças nas regiões estruturais ou promotoras. No entanto, a seqüência do cDNA da linhagem selvagem apresenta um íntron extra quando comparada com o cDNA da linhagem mutante. Portanto, o mRNA do gene da linhagem mutante não estaria sendo adequadamente processado, provavelmente por uma alteração no mecanismo envolvido neste processamento, inviabilizando a funcionalidade da trealose sintase / fosforilase produzida. O nocaute deste gene e a análise do fenótipo dos mutantes nulos na presença de acriflavina ou brometo de etídio confirmaram que ele não é essencial para o fungo. Através de genética clássica verificou-se que não há interação gênica ou sinergismo entre as mutações acrA1, que confere resistência à acriflavina e a outros inibidores, e tebA1, que confere resistência ao antimicótico terbinafina no fungo A. nidulans. / Mankind has drastically increased the use of antibiotics, antifungals, insecticides, herbicides and chemotherapeutic agents to treat infections and cancer and to obtain economic gains with agricultural and industrial production. The continuous use of these substances frequently leads to their inefficiency due to the selection of resistant or tolerant organisms, with serious economic and social consequences. The mechanisms involved in the process of antifungal resistance are little known. Understanding these mechanisms will help in the development of strategies for the identification of resistant clinical isolates, the treatment of fungal infections, the prevention of the occurrence of resistant isolates, the definition of new strategies for the use of antifungal agents, and the discovery of new therapeutic targets, and therefore the control of pathogens. To better understand the molecular basis of resistance to acriflavine and other inhibitory agents among fungi we cloned by transformation a gene that confers this resistance to Aspergillus nidulans and characterized it molecularly. We constructed a library from a double-resistant strain and isolated a clone that proved to be able to transform a receptor strain sensitive into an acriflavine-resistant strain. The sequence of this clone obtained from the resistant mutant and of its wild allele revealed a gene of approximately 2276 nucleotides translated into 697 amino acids, with high similarity to the trehalose synthase/phosphorylase (glycosyltransferase) of various organisms. This sequence was deposited in GenBanK (AY102266). The enzymes trehalose synthase and trehalose phosphorylase are related to the synthesis of trehalose, which in addition to being a carbon source is related to protection of the membrane proteins and of the enzymes against thermal and oxidative stress in filamentous fungi. The nucleotide sequences of the wild and mutant alleles did not show differences in the structural or promoter regions. However, the cDNA sequence of the wild strain presents an extra intron compared to the cDNA of the mutant strain. Thus, the mRNA of the gene of the mutant strain may not be adequately processed, probably due to an alteration in the mechanism involved in this processing, leading to inviability of the functionality of the trehalose synthase/phosphorylase produced. Knock out of this gene and analysis of the null mutant phenotypes in the presence of acriflavine or ethidium bromide confirmed that this gene is not essential for the fungus. Using classical Genetics, no gene interaction or synergism was observed between the acrA1 mutation, which confers resistance to acriflavine and to other inhibitors, and the tebA1 mutation, which confers resistance to the antimycotic agent terbinafine in the fungus A. nidulans.

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