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Published on: June 18, 2013
A novel quantitative mating assay for the fungal pathogen Cryptococcus neoformans provides insight into signalling
Hui Dong1, William Courchesne1
1Department of Microbiology, School of Medicine, University of Nevada, Reno, NV 89557-0046, USA.
Abstract:
Cryptococcus neoformans is a fungal pathogen that causes a lethal meningitis in immunocompromised individuals. Several factors are associated with virulence of this fungus, including its mating type; however, the mechanism by which mating type affects virulence is unknown. C. neoformans is a basidiomycete that exists in two mating types called a and alpha that can fuse to form an a/alpha dikaryon. A mating assay was developed that allowed a quantitative analysis of cryptococcal mating physiology. Interestingly, the efficiency of mating appeared to be dependent on temperature, being highest at 30 degrees C and almost completely absent at 37 degrees C. Thus, while mating type itself may be associated with virulence (which must occur at 37 degrees C), the ability to mate is probably not a virulence factor. Mating efficiency was increased by altering the carbon or nitrogen sources to give so-called starvation media. The addition of various drugs also seemed to alter the frequency of mating, depending on the composition of mating medium. The data suggested that cAMP, 8-bromo-cAMP and caffeine increased mating on starvation medium but only cAMP and 8-bromo-cAMP stimulated mating on rich medium; caffeine was unable to stimulate mating on rich medium. Aluminium fluoride, an activator of heterotrimeric GTP-binding proteins (G-proteins), was also found to stimulate mating, suggesting the involvement of a G-protein that may regulate the level of cAMP.
Insights
Cryptococcus neoformans mating type influences virulence, but mating itself is not a virulence factor. Mating efficiency is temperature-dependent and affected by nutrient availability and drug treatments.
Area of Science:
- Mycology
- Infectious Diseases
- Molecular Biology
Background:
- Cryptococcus neoformans causes lethal meningitis in immunocompromised individuals.
- Mating type is a known virulence factor, but the underlying mechanisms remain unclear.
- C. neoformans exists in two mating types, 'a' and 'alpha', which can form a/alpha dikaryons.
Purpose of the Study:
- To investigate the relationship between mating type and virulence in C. neoformans.
- To develop a quantitative assay for cryptococcal mating physiology.
- To explore factors influencing fungal mating efficiency.
Main Methods:
- Development of a quantitative mating assay for C. neoformans.
- Assessment of mating efficiency across different temperatures (30°C vs. 37°C).
- Evaluation of mating efficiency under varying nutrient conditions (starvation vs. rich media) and in the presence of drugs.
Main Results:
- Mating efficiency was highest at 30°C and significantly reduced at 37°C, suggesting mating is unlikely to be a virulence factor occurring at host temperature.
- Mating efficiency increased under nutrient-deprived (starvation) conditions.
- Specific compounds like cAMP, 8-bromo-cAMP, and caffeine modulated mating frequency, with aluminium fluoride suggesting G-protein involvement in cAMP regulation.
Conclusions:
- While mating type is linked to C. neoformans virulence, the direct ability to mate is not a virulence factor due to temperature sensitivity.
- Nutrient availability and specific signaling molecules (cAMP) play crucial roles in regulating cryptococcal mating.
- G-protein signaling pathways may be involved in controlling mating processes in C. neoformans.
