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Cloning and analysis of mold-specific genes in the dimorphic fungus Histoplasma capsulatum
1Biological Sciences Department, Center for Molecular and Cellular Biosciences, University of Southern Mississippi, Hattiesburg, MS 39406-5018, USA.
Abstract:
A critical feature in the pathogenesis of the respiratory pathogen Histoplasma capsulatum is the conversion from the mold form (found in soil) to the yeast form in the lungs of the host. Little is known about the molecular biology of Histoplasma dimorphism. In particular, the possible roles of genes which are transcriptionally silent in yeast (i.e. mold-specific) have not been studied. We have produced a cDNA library highly enriched for mold-upregulated clones by fragmenting cDNA and removing yeast-specific and common sequences with a highly efficient enzyme degrading subtraction method. Screening of randomly selected clones identified cDNA fragments representing 16 different mold-upregulated genes. Because multiple cDNA fragments can be treated as alleles in a genetic screen, we were able to apply probability analysis to estimate the total number of mold-upregulated genes. We estimate that there are 27 upregulated genes; cDNA fragments of 16 have been isolated. Here we report the first isolation and analysis of cDNA from two mold-specific genes, MS8 (GenBank AF292398) and MS88 (GenBank AF357882). The MS8 transcript was very strongly expressed in mold but not detected on Northern blots with yeast RNA. The putative MS8 protein was predicted to be 21.3 kDa (203 aa), very rich in glutamine and glycine and had a calculated pI of 6.76. The MS88 transcript was weakly expressed in mold and not detected in yeast. The putative MS88 protein was predicted to be 22.5 kDa (219 aa) with a pI of 4.46. GenBank similarity searches revealed that the putative MS8 protein was similar to a glutamine-rich protein, of unknown function, from the fungus Colletotrichum gloeosporioides (GenBank U94186). No significant matches were found for the putative MS88 protein.
Insights
Researchers identified two novel mold-specific genes, MS8 and MS88, in Histoplasma capsulatum. This study advances understanding of fungal dimorphism and pathogenesis by characterizing these unique mold-specific genes.
Area of Science:
- Mycology
- Molecular Biology
- Pathogenesis
Background:
- Histoplasma capsulatum exhibits dimorphism, switching from mold to yeast form during infection.
- The molecular mechanisms underlying this transition, particularly mold-specific genes, remain largely uncharacterized.
Purpose of the Study:
- To identify and analyze mold-specific genes in Histoplasma capsulatum.
- To investigate the roles of these genes in fungal dimorphism.
Main Methods:
- Construction of a cDNA library enriched for mold-upregulated genes using subtractive hybridization.
- Screening of the library to identify unique cDNA fragments.
- Isolation and characterization of two mold-specific genes, MS8 and MS88.
- Bioinformatic analysis of predicted protein sequences and homology searches.
Main Results:
- Identification of 16 unique mold-upregulated genes, with an estimated total of 27.
- Isolation and characterization of two novel mold-specific genes: MS8 and MS88.
- MS8 transcript strongly expressed in mold, absent in yeast; putative protein is glutamine/glycine-rich.
- MS88 transcript weakly expressed in mold, absent in yeast; putative protein shows no significant homology.
Conclusions:
- This study provides the first isolation and analysis of mold-specific genes in Histoplasma capsulatum.
- The identified genes, MS8 and MS88, offer new targets for understanding fungal dimorphism and pathogenesis.
- Further research into these genes could elucidate critical aspects of Histoplasma capsulatum infection.
