Lin Xiaorong, Litvintseva Anastasia P, Nielsen Kirsten, Patel Sweta, Floyd Anna, Mitchell Thomas G, Heitman Joseph
Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, North Carolina, USA.
PLoS Genet. 2007 Oct;3(10):1975-90. doi: 10.1371/journal.pgen.0030186.
Cryptococcus neoformans is a ubiquitous human fungal pathogen that causes meningoencephalitis in predominantly immunocompromised hosts. The fungus is typically haploid, and sexual reproduction involves two individuals with opposite mating types/sexes, alpha and a. However, the overwhelming predominance of mating type (MAT) alpha over a in C. neoformans populations limits alpha-a mating in nature. Recently it was discovered that C. neoformans can undergo same-sex mating under laboratory conditions, especially between alpha isolates. Whether same-sex mating occurs in nature and contributes to the current population structure was unknown. In this study, natural alpha AD alpha hybrids that arose by fusion between two alpha cells of different serotypes (A and D) were identified and characterized, providing definitive evidence that same-sex mating occurs naturally. A novel truncated allele of the mating-type-specific cell identity determinant SXI1 alpha was also identified as a genetic factor likely involved in this process. In addition, laboratory-constructed alpha AD alpha strains exhibited hybrid vigor both in vitro and in vivo, providing a plausible explanation for their relative abundance in nature despite the fact that AD hybrids are inefficient in meiosis/sporulation and are trapped in the diploid state. These findings provide insights on the origins, genetic mechanisms, and fitness impact of unisexual hybridization in the Cryptococcus population.
新型隐球菌是一种普遍存在的人类真菌病原体，主要在免疫功能低下的宿主中引起脑膜脑炎。这种真菌通常是单倍体，有性繁殖涉及两个具有相反交配型/性别的个体，即α和a。然而，在新型隐球菌群体中，交配型（MAT）α相对于a的压倒性优势限制了自然界中的α-a交配。最近发现，新型隐球菌在实验室条件下可以进行同性交配，特别是在α分离株之间。同性交配是否在自然界中发生并对当前的群体结构有贡献尚不清楚。在这项研究中，通过不同血清型（A和D）的两个α细胞融合产生的天然αADα杂种被鉴定和表征，提供了同性交配在自然界中自然发生的确凿证据。一种新型的交配型特异性细胞身份决定因子SXI1α的截短等位基因也被鉴定为可能参与这一过程的遗传因素。此外，实验室构建的αADα菌株在体外和体内都表现出杂种优势，这为它们在自然界中相对丰富提供了一个合理的解释，尽管AD杂种在减数分裂/孢子形成方面效率低下并被困在二倍体状态。这些发现为隐球菌群体中孤雌生殖杂交的起源、遗传机制和适应性影响提供了见解。
