Cyclic AMP-induced tyrosinase synthesis in Neurospora crassa

Comparative transcriptomics of infectious spores from the fungal pathogen Histoplasma capsulatum reveals a core set of transcripts that specify infectious and pathogenic states

Histoplasma capsulatum is a fungal pathogen that infects both healthy and immunocompromised hosts. In regions where it is endemic, H. capsulatum grows in the soil and causes respiratory and systemic disease when inhaled by humans. An interesting aspect of H. capsulatum biology is that it adopts specialized developmental programs in response to its environment. In the soil, it grows as filamentous chains of cells (mycelia) that produce asexual spores (conidia). When the soil is disrupted, conidia aerosolize and are inhaled by mammalian hosts. Inside a host, conidia germinate into yeast-form cells that colonize immune cells and cause disease. Despite the ability of conidia to initiate infection and disease, they have not been explored on a molecular level. We developed methods to purify H. capsulatum conidia, and we show here that these cells germinate into filaments at room temperature and into yeast-form cells at 37°C. Conidia internalized by macrophages germinate into the yeast form and proliferate within macrophages, ultimately lysing the host cells. Similarly, infection of mice with purified conidia is sufficient to establish infection and yield viable yeast-form cells in vivo. To characterize conidia on a molecular level, we performed whole-genome expression profiling of conidia, yeast, and mycelia from two highly divergent H. capsulatum strains. In parallel, we used homology and protein domain analysis to manually annotate the predicted genes of both strains. Analyses of the resultant data defined sets of transcripts that reflect the unique molecular states of H. capsulatum conidia, yeast, and mycelia.

Extensive alteration of fungal gene transcript accumulation and elevation of G-protein-regulated cAMP levels by a virulence-attenuating hypovirus

Persistent infection of the chestnut blight fungus Cryphonectria parasitica with the prototypic hypovirus CHVI-713 results in attenuation of fungal virulence (hypo-virulence) and reduced accumulation of the GTP-binding (G) protein a subunit CPG-1. Transgenic cosuppression of CPG-1 accumulation in the absence of virus infection also confers hypovirulence. We now report the use of mRNA differential display to examine the extent to which virus infection alters fungal gene transcript accumulation and to assess the degree to which modification of CPG-1 signal transduction contributes to this alteration. More than 400 PCR products were identified that either increased (296 products) or decreased (127 products) in abundance as a result of virus infection. Significantly, 65% of these products exhibited similar changes as a result of CPG-1 cosuppression in the absence of virus infection. We also report that both virus infection and CPG-1 cosuppression elevate cAMP levels 3- to 5-fold. Additionally, it was possible to mimic the effect of virus infection and CPG-1 cosuppression on transcript accumulation for representative fungal genes by drug-induced elevation of cAMP levels. These results strengthen and extend previous indications that hypovirus infection causes a significant and persistent alteration of fungal gene expression/transcript accumulation. They further show that this alteration is primarily mediated through modification of the CPG-1 signaling pathway and suggest that, similar to mammalian Gi alpha subunits, CPG-1 functions as a negative modulator of adenylyl cyclase. Finally, these results suggest a role for G-protein-regulated cAMP accumulation in hypovirus-mediated alteration of fungal gene expression.

ATP-induced protyrosinase synthesis and carboxyl-terminal processing in Neurospora crassa

The effects of 3'-5' cyclic AMP and ATP upon tyrosinase induction in Neurospora crassa were examined. Northern analysis of total cellular RNA revealed rapid de novo synthesis of protyrosinase after addition of these substances to stationary-phase mycelia. The maturation of protyrosinase in crude extracts of mycelia was followed by Western analysis. Polyclonal rabbit antiserum directed against the denatured carboxyl-terminal extension of protyrosinase does recognize the proform and several intermediate forms of different molecular weight but not mature tyrosinase. Disruption of ATP-induced mycelia in sodium phosphate buffer (pH 6.0) demonstrate processing at the carboxyl-terminal end of protyrosinase. The activity assays revealed that protyrosinase is an inactive precursor and that at least two active forms of slightly different molecular weight are present in crude extracts. Maturation of protyrosinase thus involves specific and sequential proteolytic cleavage at the carboxyl-terminus. These results suggest the presence of a tyrosinase activator in Neurospora crassa mycelia, which is kept apart from protyrosinase in the intact mycelium.

The phenoloxidases of the ascomycete Podospora anserina. XIII. Action and interaction of genes controlling the formation of laccase

1. Eight mutants were isolated following mutagen treatment which are deficient in laccase formation. Seven of these had a pleiotropic effect and exhibited defects in growth rate and in mycelial and sexual morphology. 2. By means of tetrad analysis the mutations were assigned to 6 loci. Three mutations were in the incolora locus, the others were non-allelic. Only two of these loci were closely linked. 3. All genes exhibit numerous interactions. These concern the morphological expression of the laccase genes and also the laccase spectra. 4. The mutants could be separated into four classes on the basis of the amount and type of laccase produced. 5. Five of the loci studied appear to be structural genes because mutations alters the physical properties of the laccase protein. The sixth gene has a regulatory role.

Regulation of thymidine metabolism in Neurospora crassa

The utilization of thymidine by Neurospora crassa is initiated by the pyrimidine deoxyribonucleoside 2'-hydroxylase reaction and the consequent formation of thymine and ribose. Thymine must then be oxidatively demethylated by the thymine 7-hydroxylase and uracil-5-carboxylic acid decarboxylase reactions. This article shows that the 2'-hydroxylase reaction can be regulated differently than the oxidative demethylation process and suggests that the 2'-hydroxylase has, in addition to the role of salvaging the pyrimidine ring, the role of providing ribose not only for the utilization of the demethylated pyrimidine but also for other metabolic processes. One way that this difference in regulation was observed was with the uc-1 mutation developed by Williams and Mitchell. The present communication shows that this mutation increases the activities of the 7-hydroxylase and the decarboxylase but has no comparable effect on the 2'-hydroxylase. Qualitatively similar effects on these enzymes were bought about by growth of wild-type Neurospora in media lacking ammonium ion, such as the Westergaard-Mitchell medium. The 2'-hydroxylase and 7-hydroxylase are also differently affected by the carbon dioxide content of the atmosphere above the growing culture and the growth temperature. Studies with inhibitors indicated that the carbon dioxide effect is dependent on protein synthesis.

Control of differentiation in streptomycetes: involvement of extrachromosomal deoxyribonucleic acid and glucose repression in aerial mycelia development

When Streptomyces alboniger spores were grown in Hickey-Tresner broth containing 5 muM ethidium bromide, a high frequency of permanently cured aerial mycelia-negative (am-) colonies was recovered. The appearance an am- colonies was time dependent: a very low frequency (0.3%) at zero time, a maximum (9 to 21%) after 2 to 5 days of growth, and a decline again to low frequencies later in the growth cycle. On agar, cured am- colonies of S. alboniger still produced puromycin. The development of aerial mycelia in S. alboniger, S. scabies, and S. coelicolor was also sensitive to glucose repression. Colonies grown on Hickey-Tresner agar containing 2% glucose remained phenotypically am- throughout the observation period. Adenine (2.5 mM or greater), and to a lesser extent adenosine and guanosine, specifically reversed the repression. The accumulation of undissociated organic acids appears to be involved in glucose repression of aerial mycelia formation. However, this does not appear to be the case with puromycin production in S. alboniger; glucose repression was observed over the pH range 5.0 to 7.5.