Nielsen Kirsten, Cox Gary M, Wang Ping, Toffaletti Dena L, Perfect John R, Heitman Joseph
Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Infect Immun. 2003 Sep;71(9):4831-41. doi: 10.1128/IAI.71.9.4831-4841.2003.
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 alpha 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 alpha 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 alpha mating type serotype A strains. Virulence tests with rabbit and murine models of cryptococcal meningitis showed that the serotype A congenic a and alpha mating type strains had equivalent virulence in animal models, in contrast to previous studies linking the alpha 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.
新型隐球菌是一种人类致病真菌，已进化为三个不同的变种，其中枢神经系统感染最为突出。据报道，两个变种（新型隐球菌变种新型隐球菌，血清型D，以及新型隐球菌变种格特变种，血清型B和C）存在涉及a和α交配型单倍体细胞的有性循环，但绝大多数感染涉及一个独特的变种（新型隐球菌变种格鲁比变种，血清型A），该变种被认为是克隆性的，且仅限于α交配型。我们最近鉴定出了首个被认为已灭绝的a交配型血清型A分离株（菌株125.91）。在此我们报告，这个不寻常的菌株可以与一部分致病性血清型A菌株交配，产生具有融合夹状连接、担子和有活力的重组担孢子的丝状双核体。一个减数分裂分离株与血清型A参考菌株H99交配不佳，但与一个缺乏G蛋白信号调节因子且对交配信息素反应过度的crg1突变体交配良好。这个减数分裂分离株被用于创建同基因的a和α交配型血清型A菌株。用兔和小鼠隐球菌性脑膜炎模型进行的毒力测试表明，血清型A同基因的a和α交配型菌株在动物模型中的毒力相当，这与之前将α交配型与同基因血清型D菌株毒力增加相关的研究形成对比。我们的研究突出了有性重组在人类真菌病原体进化中的作用，并提供了一个强大的遗传平台来确定毒力的分子决定因素。
