Australian Infectious Diseases Research Centre, University of Queensland, Brisbane, Australia.
mBio. 2012 Feb 28;3(2). doi: 10.1128/mBio.00310-11. Print 2012.
The accumulation of genomic structural variation between closely related populations over time can lead to reproductive isolation and speciation. The fungal pathogen Cryptococcus is thought to have recently diversified, forming a species complex containing members with distinct morphologies, distributions, and pathologies of infection. We have investigated structural changes in genomic architecture such as inversions and translocations that distinguish the most pathogenic variety, Cryptococcus neoformans var. grubii, from the less clinically prevalent Cryptococcus neoformans var. neoformans and Cryptococcus gattii. Synteny analysis between the genomes of the three Cryptococcus species/varieties (strains H99, JEC21, and R265) reveals that C. neoformans var. grubii possesses surprisingly few unique genomic rearrangements. All but one are relatively small and are shared by all molecular subtypes of C. neoformans var. grubii. In contrast, the large translocation peculiar to the C. neoformans var. grubii type strain is found in all tested subcultures from multiple laboratories, suggesting that it has possessed this rearrangement since its isolation from a human clinical sample. Furthermore, we find that the translocation directly disrupts two genes. The first of these encodes a novel protein involved in metabolism of glucose at human body temperature and affects intracellular levels of trehalose. The second encodes a homeodomain-containing transcription factor that modulates melanin production. Both mutations would be predicted to increase pathogenicity; however, when recreated in an alternate genetic background, these mutations do not affect virulence in animal models. The type strain of C. neoformans var. grubii in which the majority of molecular studies have been performed is therefore atypical for carbon metabolism and key virulence attributes.
The fungal pathogen Cryptococcus is a major cause of mortality among the immunocompromised population, primarily in AIDS patients of sub-Saharan Africa. Most research into the particular variety of Cryptococcus responsible for the vast majority of infections, Cryptococcus neoformans var. grubii, is performed using the type strain isolated in 1978 from a Hodgkin's disease patient from North Carolina. We have determined that this particular isolate contains a chromosomal translocation that directly interrupts two genes, which all descendants of this strain from various research laboratories appear to possess. Disruption of these two genes affects multiple virulence factors of Cryptococcus, particularly the ability to grow at human body temperature, which could have wide-ranging implications for molecular genetic studies and virulence assays using this important strain.
随着时间的推移，密切相关的种群中基因组结构变异的积累会导致生殖隔离和物种形成。真菌病原体隐球菌最近被认为发生了多样化，形成了一个包含具有不同形态、分布和感染病理学特征的成员的种复合体。我们研究了区分最具致病性的变种、新型隐球菌 var. grubii 与临床发病率较低的新型隐球菌 var. neoformans 和格特隐球菌的基因组结构变化，如倒位和易位。对三个隐球菌种/变种（菌株 H99、JEC21 和 R265）基因组之间的同线性分析表明，新型隐球菌 var. grubii 仅具有极少数独特的基因组重排。所有这些重排都相对较小，并且存在于新型隐球菌 var. grubii 的所有分子亚型中。相比之下，新型隐球菌 var. grubii 株的大型易位仅存在于来自多个实验室的所有测试亚培养物中，这表明它自从人类临床样本中分离出来就具有这种重排。此外，我们发现易位直接破坏了两个基因。第一个基因编码一种参与人在体温下葡萄糖代谢的新型蛋白，影响海藻糖的细胞内水平。第二个基因编码一种含有同源结构域的转录因子，调节黑色素的产生。这两种突变都会增加致病性；然而，当在替代遗传背景中重建时，这些突变不会影响动物模型中的毒力。因此，在进行了大多数分子研究的新型隐球菌 var. grubii 株的类型是碳代谢和关键毒力特征的非典型代表。
真菌病原体隐球菌是免疫功能低下人群（主要是撒哈拉以南非洲地区的艾滋病患者）死亡率的主要原因。对负责绝大多数感染的隐球菌特定变种，新型隐球菌 var. grubii 的大部分研究都是使用 1978 年从北卡罗来纳州一名霍奇金病患者中分离出的株型进行的。我们已经确定，这个特定的分离株含有一个染色体易位，该易位直接中断了两个基因，而来自各个研究实验室的该株的所有后代似乎都拥有这两个基因。这两个基因的破坏影响了隐球菌的多个毒力因子，特别是在人体温度下生长的能力，这可能对使用这种重要菌株进行分子遗传学研究和毒力测定产生广泛影响。
