A few shared up-regulated genes may influence conidia to yeast transformation in dimorphic fungal pathogens

Transcriptional Analysis of Coccidioides immitis Mycelia and Spherules by RNA Sequencing

Coccidioides immitis and C. posadasii are dimorphic fungi that transform from mycelia with internal arthroconidia in the soil to a tissue form known as a spherule in mammals. This process can be recapitulated in vitro by increasing the temperature, CO₂ and changing other culture conditions. In this study, we have analyzed changes in gene expression in mycelia and young and mature spherules. Genes that were highly upregulated in young spherules include a spherule surface protein and iron and copper membrane transporters. Genes that are unique to Coccidioides spp. are also overrepresented in this group, suggesting that they may be important for spherule differentiation. Enriched GO terms in young spherule upregulated genes include oxidation-reduction, response to stress and membrane proteins. Downregulated genes are enriched for transcription factors, especially helix–loop–helix and C2H2 type zinc finger domain-containing proteins, which is consistent with the dramatic change in transcriptional profile. Almost all genes that are upregulated in young spherules remain upregulated in mature spherules, but a small number of genes are differentially expressed in those two stages of spherule development. Mature spherules express more Hsp31 and amylase and less tyrosinase than young spherules. Some expression of transposons was detected and most of the differentially expressed transposons were upregulated in spherules.

Characterizing in vitro spherule morphogenesis of multiple strains of both species of Coccidioides

The disease San Joaquin Valley Fever (coccidioidomycosis) is caused by the inhalation of Coccidioides arthroconidia. In vivo, arthroconidia transform into pathogenic structures termed spherules. Exposure to the host milieu triggers spherule development; however, the molecular mechanisms responsible for the morphological shift are not well characterized. This study compared the morphogenesis of five strains of both species of Coccidioides in two media types to improve the in vitro model of dimorphism that can be easily reproduced, and is amenable to tissue culture. We also sought to establish a modern record of the morphological switch among commonly used lab strains through a detailed account of growth under various conditions. Spherules from five strains were grown in standard (Converse) and experimental media (RPMI-sph). Strain behavior was quantified by median spherule size and spherule concentration, beginning 3 days after inoculation and followed for 10 days of growth. There were significant differences observed among Coccidioides immitis and C. posadasii strains, as well as differences between the in vitro systems.

Analysis of Transposable Elements in Coccidioides Species

Coccidioides immitis and C. posadasii are primary pathogenic fungi that cause disease in immunologically-normal animals and people. The organism is found exclusively in arid regions of the Southwestern United States, Mexico, and South America, but not in other parts of the world. This study is a detailed analysis of the transposable elements (TE) in Coccidioides spp. As is common in most fungi, Class I and Class II transposons were identified and the LTR Gypsy superfamily is the most common. The minority of Coccidioides Gypsy transposons contained regions highly homologous to polyprotein domains. Phylogenetic analysis of the integrase and reverse transcriptase sequences revealed that many, but not all, of the Gypsy reverse transcriptase and integrase domains clustered by species suggesting extensive transposition after speciation of the two Coccidiodies spp. The TEs were clustered and the distribution is enriched for the ends on contigs. Analysis of gene expression data from C. immitis found that protein-coding genes within 1 kB of hAT or Gypsy TEs were poorly expressed. The expression of C. posadasii genes within 1 kB of Gypsy TEs was also significantly lower compared to all genes but the difference in expression was smaller than C. immitis. C. posadasii orthologs of C. immitis Gyspsy-associated genes were also likely to be TE-associated. In both C. immitis and C. posadasii the TEs were preferentially associated with genes annotated with protein kinase gene ontology terms. These observations suggest that TE may play a role in influencing gene expression in Coccidioides spp. Our hope is that these bioinformatic studies of the potential TE influence on expression and evolution of Coccidioides will prompt the development of testable hypotheses to better understand the role of TEs in the biology and gene regulation of Coccidioides spp.

Coccidioides immitis and posadasii; A review of their biology, genomics, pathogenesis, and host immunity

Coccidioides immitis and C. posadasii are two highly pathogenic dimorphic fungal species that are endemic in the arid areas of the new world, including the region from west Texas to southern and central California in the USA that cause coccidioidomycosis (also known as Valley Fever). In highly endemic regions such as southern Arizona, up to 50% of long term residents have been infected. New information about fungal population genetics, ecology, epidemiology, and host-pathogen interactions is becoming available. However, our understanding of some aspects of coccidioidomycosis is still incomplete, including the extent of genetic variability of the fungus, the genes involved in virulence, and how the changes in gene expression during the organism's dimorphic life cycle are related to the transformation from a free-living mold to a parasitic spherule. Unfortunately, efforts to develop an effective subunit vaccine have not yet been productive, although two potential live fungus vaccines have been developed.