Opposing signaling pathways regulate morphology in response to temperature in the fungal pathogenHistoplasma capsulatum

Abstract

19 20 21 22 23 2 24 25 ABSTRACT26 Phenotypic switching between two opposing cellular states is a fundamental aspect of biology, 27 and fungi provide facile systems to analyze the interactions between regulons that control this 28 type of switch. A long-standing mystery in fungal pathogens of humans is how thermally 29 dimorphic fungi switch their developmental form in response to temperature. These fungi, 30 including the subject of this study, Histoplasma capsulatum, are temperature-responsive 31 organisms that utilize unknown regulatory pathways to couple their cell shape and associated 32 attributes to the temperature of their environment. H. capsulatum grows as a multicellular hypha 33 in the soil that switches to a pathogenic yeast form in response to the temperature of a 34 mammalian host. These states can be triggered in the laboratory simply by growing the fungus 35 either at room temperature (where it grows as hyphae) or at 37ºC (where it grows as yeast). Prior 36 worked revealed that 15-20% of transcripts are differentially expressed in response to 37 temperature, but it is unclear which transcripts are linked to specific phenotypic changes such as 38 cell morphology or virulence. To elucidate temperature-responsive regulons, we previously 39 identified four transcription factors (Ryp1-4) that are required for yeast-phase growth at 37ºC; in 40 each ryp mutant, the fungus grows constitutively as hyphae regardless of temperature and the 41 cells fail to express genes that are normally induced in response to growth at 37ºC. Here we 42 perform the first genetic screen to identify genes required for hyphal growth of H. capsulatum at 43 room temperature and find that disruption of the signaling mucin MSB2 results in a yeast-locked 44 phenotype. RNAseq experiments reveal that MSB2 is not required for the majority of gene 45 expression changes that occur when cells are shifted to room temperature. However, a small 46 subset of temperature-responsive genes is dependent on MSB2 for its expression, thereby 3 47 implicating these genes in the process of filamentation. Disruption or knockdown of an Msb2-48 dependent MAP kinase (HOG2) and an APSES transcription factor (STU1) prevents hyphal 49 growth at room temperature, validating that the Msb2 regulon contains genes that control 50 filamentation. Notably, the Msb2 regulon shows conserved hyphal-specific expression in other 51 dimorphic fungi, suggesting that this work defines a small set of genes that are likely to be 52 conserved regulators and effectors of filamentation in multiple fungi. In contrast, a few yeast-53 specific transcripts, including virulence factors that are normally expressed only at 37ºC, are 54 inappropriately expressed at room temperature in the msb2 mutant, suggesting that expression of 55 these genes is coupled to growth in the yeast form rather than to temperature. Finally, we find 56 that the yeast-promoting transcription factor Ryp3 associates with the MSB2 promoter and 57 inhibits MSB2 transcript expression at 37ºC, whereas Msb2 inhibits...

Actual problems of mycoses caused by dimorphic pathogens

“…Идентифицированы некоторые ключевые молекулярные регуляторы диморфизма. Установ-лено, что взаимная трансформация обеих фаз критически важна для выживания возбудителей ООМ в окружающей среде и в организме млекопитающих [56][57][58][59][60][61].…”