capsulatum. Additionally, the strain UC1 can be used to study cleistothecia Blasticidin S nmr formation in H. capsulatum. The cleistothecia formed by the pairing of UC1 and UH3 appear empty. We were unable to detect the presence of asci or ascospores inside the cleistothecia,

indicating that the mating process was arrested at some point. The strain UC1 is, therefore, unable to complete the mating process in spite of its ability to form see more cleistothecia. UC1 does not, however, lose the ability to form empty cleistothecia over time in culture, making it a unique strain that is well suited for studying the molecular and morphological stages of cleistothecia formation. At this time, it is unclear whether or not hyphal fusion can occur between UC1 and UH3. It is thought that hyphal fusion precedes cleistothecia formation

during normal mating in H. capsulatum [1], but hyphal fusion may or may CX-6258 chemical structure not be required for the formation of coiling and branching peridial hyphae comprising the outer structure of the cleistothecia. It is, therefore, unknown at what point the mating process is arrested during the UC1/UH3 cross. The property of the strain UC1 to form empty cleistothecia when crossed with a freshly isolated MAT1-2 strain affords the opportunity to dissect the relationship between hyphal fusion and the formation of the outer cleistothecia structure, as well as the contribution of each strain to the mating structure. Although UC1 contains a functional GFP gene, its expression is under control of the calcium binding protein gene

promoter and is therefore limited to expression in yeast phase organisms. Because mating occurs in the mycelial phase, an additional derivative of UC1 expressing a fluorescent marker in the mycelial phase would need to be generated to answer these questions. There is no clear pattern of pheromone and pheromone receptor expression under standard growth conditions in the H. capsulatum strains studied here. In S. cerevisiae, MATa strains secrete a pheromone and express the alpha pheromone receptor STE2, while MATalpha strains secrete alpha pheromone and express the a pheromone receptor STE3 [36]. There are also, however, examples of fungi such as Neurospora crassa in which both pheromone receptors are constitutively expressed [37]. In the current study, STE2 RNA levels were elevated in the established laboratory strain G217B, Linifanib (ABT-869) while STE3 levels were undetectable. The fact that STE2 but not STE3 is detected in G217B would indicate that organisms of MAT1-1 mating type are responsive to alpha pheromone. This would confirm previous studies, which showed MAT1-1-1 RNA levels in a clinical H. capsulatum strain were responsive to an extract enriched for alpha pheromone [2]. If MAT1-1 strains respond to alpha pheromone, they would be expected to produce a pheromone. However UC1, the strain capable of empty cleistothecia formation, produces elevated RNA levels of alpha pheromone.