Sexual Cycle of Cryptococcus neoformans var. grubii and Virulence of Congenic a and α Isolates

Abstract

Cryptococcus neoformans is a human-pathogenic fungus that has evolved into three distinct varieties that infect most prominently the central nervous system. A sexual cycle involving haploid cells of a and ␣ mating types has been reported for two varieties (C. neoformans var. neoformans, serotype D, and C. neoformans var. gattii, serotypes B and C), yet the vast majority of infections involve a distinct variety (C. neoformans var. grubii, serotype A) that has been thought to be clonal and restricted to the ␣ mating type. We recently identified the first serotype A isolate of the a mating type which had been thought to be extinct (strain 125.91). Here we report that this unusual strain can mate with a subset of pathogenic serotype A strains to produce a filamentous dikaryon with fused clamp connections, basidia, and viable recombinant basidiospores. One meiotic segregant mated poorly with the serotype A reference strain H99 but robustly with a crg1 mutant that lacks a regulator of G protein signaling and is hyperresponsive to mating pheromone. This meiotic segregant was used to create congenic a and ␣ mating type serotype A strains. Virulence tests with rabbit and murine models of cryptococcal meningitis showed that the serotype A congenic a and ␣ mating type strains had equivalent virulence in animal models, in contrast to previous studies linking the ␣ mating type to increased virulence in congenic serotype D strains. Our studies highlight a role for sexual recombination in the evolution of a human fungal pathogen and provide a robust genetic platform to establish the molecular determinants of virulence.

Gib2, A Novel Gβ-like/RACK1 Homolog, Functions as a Gβ Subunit in cAMP Signaling and Is Essential in Cryptococcus neoformans

“…Whereas Gpa1 is known to function in a conserved cAMP signaling pathway, functions of Gpa2 and Gpa3 remain unreported. We have recently identified a regulator of the G protein signaling protein, Crg1, as one of the key regulators for mating and virulence in C. neoformans (51,52) and have shown that Crg1 functions as a GTPase activating protein specific to Gpa2. 4 To expand our studies on regulators of G protein signaling, we performed a yeast two-hybrid screen using Gpa1 as bait.…”

Nitrogen Metabolite Repression of Metabolism and Virulence in the Human Fungal Pathogen Cryptococcus neoformans

“…Mating assays: Mating assays were conducted as described previously (Nielsen et al 2003). Briefly, strains were pregrown on YPD plates for 2 days, after which a small amount of cells was removed using a flat-end toothpick and patched onto V8 and MS mating media (pH 5.0) either alone or mixed in equal proportions with a strain of the opposite mating-type (MAT ) (Kwon-Chung et al 1982;Xue et al 2007).…”

Cryptococcus neoformans var. grubii isolates recovered from persons with AIDS demonstrate a wide range of virulence during murine meningoencephalitis that correlates with the expression of certain virulence factors

“…grubii) by a slide agglutination test (Crypto-Check kit, Iatron) and mating type a by PCR with specific primers that amplify portions of the STE20a or STE20a allele (Nielsen et al, 2003). We determined the LD 50 for each of the isolates at 15 days following the intracranial (i.c.)…”