Annual Report 2018 of the Computer Center, University of Wuerzburg

Eine Übersicht über die Aktivitäten des Rechenzentrums im Jahr 2018

A Histone Acetyltransferase Inhibitor with Antifungal Activity against CTG clade Candida Species

Candida species represent one of the most frequent causes of hospital-acquired infections in immunocompromised patient cohorts. Due to a very limited set of antifungals available and an increasing prevalence of drug resistance, the discovery of novel antifungal targets is essential. Targeting chromatin modifiers as potential antifungal targets has gained attention recently, mainly due to their role in regulating virulence in Candida species. Here, we describe a novel activity for the histone acetyltransferase inhibitor Cyclopentylidene-[4-(4-chlorophenyl)thiazol-2-yl)hydrazone (CPTH2) as a specific inhibitor of CTG clade Candida species. Furthermore, we show that CPTH2 has fungicidal activity and protects macrophages from Candida-mediated death. Thus, this work could provide a starting point for the development of novel antifungals specific to CTG clade Candida species

Annual Report 2017 of the Computer Center, University of Wuerzburg

Eine Übersicht über die Aktivitäten des Rechenzentrums im Jahr 2017

The Paralogous Histone Deacetylases Rpd3 and Rpd31 Play Opposing Roles in Regulating the White-Opaque Switch in the Fungal Pathogen Candida albicans

Chromatin modifications affect gene regulation in response to environmental stimuli in numerous biological processes. For example, N-acetyl-glucosamine and CO2 induce a morphogenetic conversion between white (W) and opaque (O) cells in MTL (mating-type locus) homozygous and heterozygous (a/α) strains of the human fungal pathogen Candida albicans. Here, we identify 8 histone-modifying enzymes playing distinct roles in the regulation of W/O switching in MTL homozygous and heterozygous strains. Most strikingly, genetic removal of the paralogous genes RPD3 and RPD31, both of which encode almost identical orthologues of the yeast histone deacetylase (HDAC) Rpd3, reveals opposing roles in W/O switching of MTLa/α strains. We show that Rpd3 and Rpd31 functions depend on MTL genotypes. Strikingly, we demonstrate that Rpd3 and Rpd31, which are almost identical except for a divergent C-terminal extension present in Rpd31, exert their functions in distinct regulatory complexes referred to as CaRpd3L and CaRpd31S complexes. Moreover, we identify the Candida orf19.7185 product Ume1, the orthologue of yeast Ume1, as a shared core subunit of CaRpd3L and CaRpd31S. Mechanistically, we show that the opposing roles of Rpd3 and Rpd31 require their deacetylase activities. Importantly, CaRpd3L interacts with the heterodimeric transcriptional repressor a1/α2, thus controlling expression of WOR1 encoding the master regulator of W/O switching. Thus, our work provides novel insight about regulation mechanisms of W/O switching in MTLa/α strains. This is the first example of two highly conserved HDACs exerting opposing regulatory functions in the same process in a eukaryotic cell

GroEL Plays a Central Role in Stress-Induced Negative Regulation of Bacterial Conjugation by Promoting Proteolytic Degradation of the Activator Protein TraJ▿

Transcription of DNA transfer genes is a prerequisite for conjugative DNA transfer of F-like plasmids. Transfer gene expression is sensed by the donor cell and is regulated by a complex network of plasmid- and host-encoded factors. In this study we analyzed the effect of induction of the heat shock regulon on transfer gene expression and DNA transfer in Escherichia coli. Raising the growth temperature from 22°C to 43°C transiently reduced transfer gene expression to undetectable levels and reduced conjugative transfer by 2 to 3 orders of magnitude. In contrast, when host cells carried the temperature-sensitive groEL44 allele, heat shock-mediated repression was alleviated. These data implied that the chaperonin GroEL was involved in negative regulation after heat shock. Investigation of the role of GroEL in this regulatory process revealed that, in groEL(Ts) cells, TraJ, the plasmid-encoded master activator of type IV secretion (T4S) system genes, was less susceptible to proteolysis and had a prolonged half-life compared to isogenic wild-type E. coli cells. This result suggested a direct role for GroEL in proteolysis of TraJ, down-regulation of T4S system gene expression, and conjugation after heat shock. Strong support for this novel role for GroEL in regulation of bacterial conjugation was the finding that GroEL specifically interacted with TraJ in vivo. Our results further suggested that in wild-type cells this interaction was followed by rapid degradation of TraJ whereas in groEL(Ts) cells TraJ remained trapped in the temperature-sensitive GroEL protein and thus was not amenable to proteolysis

The Candida albicans HIR histone chaperone regulates the yeast-to-hyphae transition by controlling the sensitivity to morphogenesis signals.

Morphological plasticity such as the yeast-to-hyphae transition is a key virulence factor of the human fungal pathogen Candida albicans. Hyphal formation is controlled by a multilayer regulatory network composed of environmental sensing, signaling, transcriptional modulators as well as chromatin modifications. Here, we demonstrate a novel role for the replication-independent HIR histone chaperone complex in fungal morphogenesis. HIR operates as a crucial modulator of hyphal development, since genetic ablation of the HIR complex subunit Hir1 decreases sensitivity to morphogenetic stimuli. Strikingly, HIR1-deficient cells display altered transcriptional amplitudes upon hyphal initiation, suggesting that Hir1 affects transcription by establishing transcriptional thresholds required for driving morphogenetic cell-fate decisions. Furthermore, ectopic expression of the transcription factor Ume6, which facilitates hyphal maintenance, rescues filamentation defects of hir1Δ/Δ cells, suggesting that Hir1 impacts the early phase of hyphal initiation. Hence, chromatin chaperone-mediated fine-tuning of transcription is crucial for driving morphogenetic conversions in the fungal pathogen C. albicans

Pour un développement territorial durable : l'aménagement des terroirs villageois au Niger : cas du projet Dallol Bosso Sud (1989-1994)

Depuis le milieu des années 1980, sur le continent africain, l'approche «aménagement des terroirs villageois» a émergé comme une réponse concrète aux problèmes de développement et de gestion des ressources naturelles au sein des communautés villageoises. Cette approche, qui est désormais inscrite comme option officielle de développement rural dans tous les pays du Sahel mérite d'être évaluée. Notre thèse se veut une contribution à l'évaluation de cette approche «d'aménagement des terroirs villageois». Elle porte sur la stratégie de développement territorial durable au Niger et centrée sur l'analyse et l'interprétation des résultats du premier projet du genre appliqué dans la région du Dallol Bosso Sud (1989-1994). Notre recherche emprunte une démarche interdisciplinaire et s'appuie sur les théories du développement territorial, du développement durable, de l'éco-aménagement et de l'écodéveloppement. Nous en parlerons comme étant une approche de développement territorial durable. C'est l'objet de la première partie de la thèse axée sur l'analyse théorique de cette notion de développement territorial durable. La deuxième partie porte sur l'étude empirique du projet nigérien d'aménagement des terroirs villageois du Dallol Bosso Sud. L'enquête terrain a été réalisée entre mars et juin 1999 auprès des acteurs-clés impliqués dans le projet. Cette enquête a porté sur l'appréciation et l'analyse des résultats et des impacts du projet (sociaux, économiques, écologiques et politiques) et sur l'appropriation (socio-politique, technique, financière) de la démarche du projet par les populations concernées. L'analyse a été réalisée à la fois à partir d'entretiens, d'observation directe sur terrain et par l'approche documentaire. Nos résultats révèlent que l'approche «aménagement des terroirs villageois» est porteuse d'orientations de développement territorial durable, n s'agit en effet d'une approche globale, multidimensionnelle et centrée sur la réalisation simultanée de plusieurs activités qui ont des impacts sociaux, économiques, écologiques, politiques et spatiaux très concrets pour les populations et leurs territoires. L'étude démontre par contre que la population n'a pas pu s'approprier suffisamment les différentes techniques, technologies et méthodes proposées par le projet à cause de l'imbrication malheureuse de certains facteurs conjoncturels et structurels. Notre recherche va ainsi au-delà de certaines idées reçues, voulant incriminer les populations dans un refus d'appropriation alors que les enjeux véritables sont de l'ordre des défis d'un métissage culturel majeur entre des manières d'être et de produire différenciées

The histone chaperone HIR maintains chromatin states to control nitrogen assimilation and fungal virulence

Adaptation to changing environments and immune evasion is pivotal for fitness of pathogens. Yet, the underlying mechanisms remain largely unknown. Adaptation is governed by dynamic transcriptional re-programming, which is tightly connected to chromatin architecture. Here, we report a pivotal role for the HIR histone chaperone complex in modulating virulence of the human fungal pathogen Candida albicans. Genetic ablation of HIR function alters chromatin accessibility linked to aberrant transcriptional responses to protein as nitrogen source. This accelerates metabolic adaptation and increases the release of extracellular proteases, which enables scavenging of alternative nitrogen sources. Furthermore, HIR controls fungal virulence, as HIR1 deletion leads to differential recognition by immune cells and hypervirulence in a mouse model of systemic infection. This work provides mechanistic insights into chromatin-coupled regulatory mechanisms that fine-tune pathogen gene expression and virulence. Furthermore, the data point toward the requirement of refined screening approaches to exploit chromatin modifications as antifungal strategies