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Considerable information has accumulated recently about specific genes of Histoplasma capsulatum that are expressed during the process of adaptation when the organism undergoes morphological transition at the onset of infection. The study of these genes is crucial to identify targets for the development of novel antifungal agents.

Resume L’analyse des depenses que les menages francais consacrent aux biens et aux services culturels et de communication permet de prendre la mesure des evolutions au cours des annees 2000. Si elles ont diminue en 2006 par rapport a 2001 et ne representent plus que 4 % du budget disponible contre 4,5 % cinq ans plus tot, la structure des depenses culture-medias s’est considerablement transformee. La numerisation des biens culturels a amplifie la transition vers une industrie de services. L’analyse confirme l’influence de l’âge, du niveau d’etudes, de la categorie socioprofessionnelle et de la taille de la commune de residence dans la part des depenses qu’un menage francais consacre aux depenses culturelles. Une approche typologique des depenses identifie trois univers de consommation culturelle : la culture « traditionnelle », la culture de l’ecran et la culture « jeune ».

Histoplasma capsulatum is the causative agent of histoplasmosis, a systemic fungal disease world-wide in occurrence and the most common respiratory mycotic infection affecting humans and animals. This organism, that consists of a pathogenic yeast phase present in human tissue and a saprobic mycelial phase found in soil, represents at a molecular level, the most extensively studied of the dimorphic pathogenic fungi (Maresca and Kobayashi, 1989). In culture, the transition from one phase to the other can be triggered reversibly by shifting the temperature of incubation between 25° (mycelia) and 37°C (yeast). This implies that each growth phase is an adaptation to two remarkably different environments. Therefore, it is likely that the temperature-induced phase transition and the events in the establishment of infection are intimately interrelated and, unlike the case in higher eukaryotes, the differentiation process in dimorphic fungi represents an adaptation to a new environment. In fact, the organism must face challenges that may not be strictly related to dimorphism to proceed towards phase transition (e.g., higher temperature, different redox potential and nutrients, presence of new degradative enzymes, etc.).

Fungal morphogenesis, in particular dimorphism in pathogenic fungi, has intrigued clinicians and medical mycologists since its discovery at the turn of the century. Numerous reviews have been written on this subject. Using Histoplasma capsulatum as a model to study host-parasite interaction at the biochemical and molecular level, we have attempted to relate the clinical spectrum of histoplasmosis to natural variations in the characteristics of H. capsulatum and to the adaptations this organism must make as a saprobe and a parasite.

The heat shock response is a general homeostatic mechanism that protects cells and the entire organism from the deleterious effects of environmental stress. It has been shown that heat shock proteins play major roles in many cellular processes and have a unique role in several areas of cell biology, from chronic degenerative diseases to immunology and from cancer research to interactions between host and parasite. In this review, Bruno Maresca and Luisella Carratu deal with some of the unique characteristics of the heat shock response in parasitic organisms.

Changes in temperature and a variety of other stimuli coordinately induce transcription of a specific set of heat-shock genes in all organisms. In the human fungal pathogen Histoplasma capsulatum, a temperature shift from 25 to 37 °C acts not only as a signal that causes transcription of heat-shock genes, but also triggers a morphological mycelium-to yeast-phase transition. The temperature-induced morphological transition may be viewed as a heat-shock response followed by cellular adaptation to a higher temperature. We have found that by inducing thermotolerance, i.e., an initial incubation at 34 °C, the thermosensitive attenuated Downs strain of H. capsulatum can be made to resemble those of the more temperature-tolerant G222B strain with respect to mitochondrial ATPase activity and electron transport efficiency at elevated temperatures. Furthermore, if the heat-shock response is first elicited by preincubation at milder temperatures or stress, transcription of heat-shock mRNA in mycelial cells of Downs strain that shifted to 37 °C proceeds at rates comparable to those of the virulent strains.Key words: heat shock, thermotolerance, ATPase, 70-kilodalton heat-shock protein, fungal morphogenesis.

The complex molecular response of cells to sudden temperature changes is a well-characterized phenomenon. Although it is clear that the induction of heat shock proteins provides protection from heat in all of the organisms so far tested, very little is known about the role that this set of proteins plays in cellular homeostasis. Recently, putative roles for hsp 60 and hsp 70-like proteins have been proposed in Saccharomyces cerevisiae . hsp 70-like proteins have been shown to be necessary for translocation of precursor polypeptides into mitochondria and endoplasmic reticulum, while hsp 60 is required for the assembly of precursor polypeptides into oligomeric complexes following incorporation into the mitochondrial matrix. In this paper, we report that a brief temperature shock (44 °C) impairs coupling of oxidative phosphorylation in S. cerevisiae as measured indirectly by the CI-CCP/oligomycin assay. Furthermore, at high temperature oligomycin stimulates rather than inhibits oxygen uptake under nonthermotolerant conditions. Pretreatment of cells for a short period of time at 37 °C, prior to exposure to higher temperatures rescues the capacity to maintain coupling between oxidative phosphorylation and electron transport. Inhibition of cytoplasmic RNA or protein synthesis during heat shock prevents the protection of this mitochondrial activity. We propose that one of the roles of the induction of heat shock proteins (or related activities) is to protect mitochondrial ATPase activity under conditions of further increase in temperature.

Histoplasma capsulatum is the causative agent of histoplasmosis, a systemic fungal disease worldwide in occurrence, and the most common respiratory mycotic infection affecting humans and animals (Schwarz 1981). Several fungi, in particular those pathogenic such as H.capsulatum, Blastomyces dermatitidis, Paracoccidioides brasiliensis etc., can assume a filamentous or unicellular morphology in response to changes in the environmental conditions (Maresca and Kobayashi 1989). H.capsulatum grows as mycelia in soil while the yeast phase is the only form present in patients. In laboratory conditions, dimorphism is directly and reversibly controlled by temperature changes. The temperature-induced transition and the events in establishment of infection seem to be intimately correlated. In fact, the temperature works not only as a signal for adaptation through the induction of a heat shock-like phenomenon, but also in triggering the phase transition. The role that the heat shock response plays during the differentiation process and in the adaptation to high temperature in H.capsulatum will be discussed here.

Histoplasmosis is an important systemic mycotic infection with a wide geographic distribution. Its occurrence has been mostly studied in the US (6) and in Central America (6), but very little is known about its distribution in Africa, where a specific variant exists. Skin test surveys in the Democratic Republic of Somali indicate that Histoplasma capsulatum or a closely related agent has a focus in this east African country. © 1987 Martinus Nijhoff/Dr W. Junk Publishers.

A cysteine dioxygenase, cysteine oxidase (EC 1.13.11.20), has been purified from the cytosolic fraction of yeast phase cells of the dimorphic fungus Histoplasma capsulatum. The cysteine oxidase is an iron-containing dioxygenase with a molecular weight of 10500 (±1500) and is present only in the yeast phase of the fungus. The enzyme is highly specific for l-cysteine, with a Km of 2 × 10−5 M in vitro. The product of cysteine oxidation is cysteinesulfinic acid, as analyzed by thin-layer chromatography and mass spectroscopy. To our knowledge, this is the first cysteine oxidase isolated from a fungus, and it probably plays an important role in the mycelial to yeast phase transition of H. capsulatum during which redox potential and cysteine levels are crucial factors. © 1983, American Chemical Society. All rights reserved.

Several fungi can assume either a filamentous or a unicellular morphology in response to changes in environmental conditions. This process, known as dimorphism, is a characteristic of several pathogenic fungi, e.g., Histoplasma capsulatum, Blastomyces dermatitidis, and Paracoccidioides brasiliensis, and appears to be directly related to adaptation from a saprobic to a parasitic existence. H. capsulatum is the most extensively studied of the dimorphic fungi, with a parasitic phase consisting of yeast cells and a saprobic mycelial phase. In culture, the transition of H. capsulatum from one phase to the other can be triggered reversibly by shifting the temperature of incubation between 25 degrees C (mycelia) and 37 degrees C (yeast phase). Mycelia are found in soil and never in infected tissue, in contrast to the yeast phase, which is the only form present in patients. The temperature-induced phase transition and the events in establishment of the disease state are very likely to be intimately related. Furthermore, the temperature-induced phase transition implies that each growth phase is an adaptation to two critically different environments. A fundamental question concerning dimorphism is the nature of the signal(s) that responds to temperature shifts. So far, both the responding cell component(s) and the mechanism(s) remain unclear. This review describes the work done in the last several years at the biochemical and molecular levels on the mechanisms involved in the mycelium to yeast phase transition and speculates on possible models of regulation of morphogenesis in dimorphic pathogenic fungi.

Organo-sulfur compounds favor the transition of mycelia of Histoplasma capsulatum to the yeast form (6, 8). Investigation of the role of cystine in the transition revealed that the two phases concentrated this amino acid at comparable rates and that mutants defective in the uptake of cystine were still able to undergo the transition normally. Uptake of cystine is therefore probably not a requirement for transition to or maintenance of the yeast phase. Both phases contained a reduced nicotinamide adenine dinucleotide phosphate-dependent glutathione reductase; but a reduced nicotinamide adenine dinucleotide-dependent cystine reductase was detectable only in the yeast phase. The cystine reductase appeared early in the transition of mycelium to yeast. Treatment of mycelia with p-chloromercuriphenylsulfonic acid, which prevented the transition to yeast, had no effect on cystine uptake but strongly inhibited the cystine reductase. These results suggest that cystine reductase may provide reduced sulfhydryl groups involved in the transition of mycelium to yeast.

1. The oxidative phosphorylation and the temperature dependence of mitochondria prepared from the outer compact layer and the inner spongy layer of adult tuna heart ventricle have been examined. 2. Mitochondria of the inner layer show higher succinoxidase and NADH-oxidase activities as compared with those of the outer layer. 3. Arrhenius plots for succinate oxidation by phosphorylating mitochondria show that the temperature dependence of the inner layer is higher than that of the outer layer. 4. Experiments performed with disrupted non-phosphorylating mitochondria demonstrate that this difference in temperature dependence of the two cardiac compartments depends on the integrity of the mitochondrial membranes. 5. These findings are discussed in relation to the physiology of the fish.

Three stages can be distinguished in the temperature-induced mycelial-to-yeast phase transition of Histoplasma capsulatum. Stage one is characterized by a progressive decrease in the respiration rate and in the intracellular concentrations of cysteine and other amino acids. By stage two, respiration has ceased completely and free cysteine has fallen to low levels. Exogenous cysteine is required during the second stage for activation of mitochondrial respiration (stage three) and completion of the morphological transition. Mitochondria isolated from cells in the second stage show no respiration with NADH, succinate, or other substrates unless they are first incubated with cysteine. In addition, a novel, cytosolic cysteine oxidase appears during the latter part of the second stage. In stage three, the respiration rate rises, intracellular concentrations of free cysteine and other amino acids increase to levels characteristic of yeast, and the morphological transition is completed. The results support the idea that alterations in cysteine metabolism play a key role in this differentiation process.

p-Chloromercuriphenylsulfonic acid (PCMS), a sulfhydryl inhibitor, prevented the mycelial-to-yeast transition of the dimorphic fungal pathogen, Histoplasma capsulatum. The effect of PCMS was specific for the mycelial-to-yeast transformation; it had no effect on growth of either the yeast or mycelial forms or on the yeast-to-mycelial transition. The failure of PCMS-treated mycelia to transform to yeast was permanent and irreversible. PCMS-treated mycelia could not infect mice but could stimulate resistance to infection by a pathogenic strain of Histoplasma capsulatum. These results suggest a new general strategy for vaccine development in diseases caused by dimorphic pathogens.

1. 1. The restriction patterns of three different Antarctic fish DNA ( P. bernacchi, N. rossi and C. kathleene ) have been analysed. 2. 2. The restricted DNAs have been probed for the presence of the heat shock 70 sequence (hsp70) by using the corresponding Drosophila sequence. The three patterns are closely related for the presence of several bands in common, though a closer arrangement for the hsp70 gene is present in P. bernacchi and N. rossi . The analysis with different stringency conditions has also suggested that in these fishes more than one copy of hsp70 per genome is present. 3. 3. Poly-A RNA analysis with Northern blot have shown that the hsp70 gene is transcribed, upon temperature increase, between 5 and 12°C with a maximum of expression at 8°C.

Histoplasma capsulatum, the etiological agent of histoplasmosis, is a dimorphic pathogenic fungus. The disease histoplasmosis occurs in many different parts of the world, but has a particularly high prevalence in temperate and subtropical zones such as the Ohio and Mississippi river valleys of the United States, South and Central America, parts of the Mediterranean basin, and West Africa (P. Q. Edwards and Billings, 1971). The epidemiology of H. capsulatum and problems related to human infection have been extensively studied (Sweany, 1960; Ajello et al., 1971; Schwarz, 1981). The nature of dimorphism in H. capsulatum has also received a great deal of interest ever since the fungus was observed in tissue and cultured in vitro and discovered to have a saprophytic hyphal phase and a parasitic yeast phase (DeMonbreun, 1934).

The response to heat shock has been examined In two strains of the dimorphic pathogenic fungus Histoplasma capsulatum, which differ considerably in thermotolerance and pathogenicity. The gene for the 70 kD heat shock protein (hsp70) was isolated using a Drosophila hsp70 gene to screen a cosmid library of the DNA from the temperature‐sensitive Downs strain (low level of thermotolerance for mice). Using the cloned gene as a probe, we have measured the transcription of the endogenous hsp70 gene at 25°C and in response to temperature shift to 34°, 37° and 40°C, temperatures that trigger the mycelial to yeast phase transition in this fungus. The gene is constitutively transcribed at low levels, both in the yeast and the mycelial stages. Synthesis of hsp70 mRNA was transiently increased 1 to 3 h after the temperature shifts. By Northern analysis, peak levels of transcription were shown to occur at 34°C in the Downs strain and at 37°C in the more pathogenic G222B strain. Our results are consistent with reports in which it has been shown that heat shock gene expression is part of temperature adaptation and probably developmental processes. The low levels of transcription of the hsp70 gene in the Downs strain at 37°C correlate with its greater temperature sensitivity and low level of virulence. Copyright © 1987, Wiley Blackwell. All rights reserved

The transition from yeast to mycelia of Histoplasma capsulatum could be accomplished by shifting the temperature of incubation from 37 to 25 degrees C. It was accompanied by many changes in cellular metabolism, including changes in respiration, intracellular cyclic adenosine 3',5'-monophosphate (cAMP) levels, and activities of two enzymes specific for the yeast phase, cystine reductase (EC 1.6.4.1) and cysteine oxidase (EC 1.13.11.20). Even at 37 degrees C, the yeast to mycelial transition could be induced by cAMP and agents which raise the intracellular levels of cAMP (theophylline, acetylsalicylic acid, prostaglandin E1, and nerve growth factor). During this morphogenesis the same pattern of changes occurred as in the temperature-induced transition. Therefore, these changes were not simply dependent on a shift in temperature, but rather were part of the process of the phase transition.

Plasma membrane vesicles from the yeast and mycelial phases of Histoplasma capsulatum have been purified and characterized. The method of purification involved differential centrifugation of ballistically fractured cells followed by sedimentation through discontinuous sucrose density gradient and equilibrium centrifugation. Purity of the preparation was assessed by electron microscopy. The protein composition of the membrane preparations from the yeast and mycelial phases of the fungus was analyzed by polyacrylamide gels. A comparison of the two morphologic phases revealed quantitative and qualitative differences in the expressions of several membrane-specific proteins. Physical differences in the appearance of the membranes were also observed by electron micrography of membrane preparations. Alteration in membrane fluidity may be one of the many causes for differences in the appearance of membrane vesicles in the two phases.

We compared the mycelial to yeast transitions of the Downs strain of Histoplasma capsulatum (low level of virulence) with those of G184A and G222B, two more virulent strains having different levels of pathogenicity for mice. When the morphological transitions are initiated by a temperature shift from 25 degrees to 37 degrees C, all three strains undergo similar physiological changes, but these are less severe in G184A and G222B than in the Downs strain. The transitions from mycelial to yeast morphology in both of the more virulent strains are also one-third more rapid than in Downs. We also find that the differences in temperature sensitivity of the three strains can be correlated with the temperature required for complete uncoupling of oxidative phosphorylation. The differences in sensitivity to elevated temperatures extend to the growth of yeast cells of all three strains. Considered together, our results suggest that sensitivity to elevated temperatures may be a key factor accounting for differences in virulence and that uncoupling of oxidative phosphorylation may be the primary event in the morphological transition in all three strains.

Respiration in the yeast and mycelial phases of Histoplasma capsulatum proceeds via a cytochrome system and an alternate oxidase, both present constitutively. The mycelial cytochrome system is distinguished by an additional partial shunt around the antimycin-sensitive site.

Histoplasma capsulatum is a dimorphic pathogenic fungus which is the causative agent of the disease histoplasmosis. The disease is worldwide in occurrence and approximately 40 million people have been infected in the USA1. In soil the fungus is filamentous, but in the infected host it exists as a budding yeast and it is believed that the phase transition is important in the pathogenicity. In the laboratory, the mycelial form can convert to the yeast phase when the temperature of incubation is shifted from room temperature (25 °C) to body temperature (37 °C). In this report we show that the elevated temperature initiates a series of reactions leading to changes in the intracellular level of 3′, 5′-cyclic adenosine monophosphate (cyclic AMP);the shifts in intracellular cyclic AMP levels are an important determinant of the morphological phase of the organism and therefore of its disease producing potential.

La complexité de l'environnement sonore urbain est aujourd'hui reconnue. L'évolution récente des recherches en la matière a montré qu'on ne peut désormais plus l'aborder d'un point de vue exclusivement acoustique : le problème consiste plutôt à articuler et croiser les données physiques avec les données sociologiques ou culturelles. De même, l'environnement sonore ne peut plus être réduit à une thématique de la nuisance : à la problématique de la gêne se substitue aujourd'hui des réflexions portant sur le confort sonore. La question du silence dans la ville, pour aussi difficile et délicate qu'elle soit, constitue sans doute un bon analyseur des discours sur la qualité sonore des espaces habités. A cet égard, trois orientations principales seront brièvement évoquées :- les propriétés fondamentales du silence et les principes de conception qui peuvent en résulter.