A tetraploid intermediate precedes aneuploid formation in yeasts exposed to fluconazole.
A tetraploid intermediate precedes aneuploid formation in yeasts exposed to fluconazole.
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DOI：
10.1371/journal.pbio.1001815
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发表时间：
2014-03
期刊：
影响因子：
9.8
通讯作者：
Berman J
中科院分区：
文献类型：
--
作者：
Harrison BD;Hashemi J;Bibi M;Pulver R;Bavli D;Nahmias Y;Wellington M;Sapiro G;Berman J
当暴露于抗真菌药物氟康唑时，白色念珠菌会发生异常生长，形成三叶的“三聚体”。这些非整倍体三聚体产生了具有不同数量染色体的遗传变异后代，增加了产生耐药菌株的几率。 白色念珠菌是最常见的人类真菌病原体，通常是二倍体。然而，对最广泛使用的抗真菌剂氟康唑（FLC）耐药的菌株中有50%是非整倍体，并且一些非整倍体可以赋予FLC耐药性。为了询问FLC暴露是否导致或仅选择非整倍性，我们使用流式细胞术和落射荧光显微镜分析了暴露于FLC期间的二倍体菌株。FLC暴露引起了正常细胞周期调节的一致偏离：核和纺锤体周期在芽出现之前开始，导致“三聚体”，即由母亲、女儿和孙女芽组成的三个连接的细胞。最初双核，三聚体进行协调核分裂产生四个子核，其中两个进行有丝分裂崩溃，形成一个四倍体细胞与额外的纺锤体组件。在随后的细胞周期中，异常数目的纺锤体导致不平等的DNA分离和可行的非整倍体后代。研究了C.白色念珠菌的非整倍性非常令人联想到人类肿瘤发生的早期阶段，因为非整倍性是通过四倍体中间体和随后的由多个纺锤体驱动的不均等DNA分离产生的，所述多个纺锤体与随后的选择优势结合，所述选择优势由至少一些非整倍性在应激下生长期间赋予。最后，三聚体的形成被检测到响应于其他唑类抗真菌剂，在相关念珠菌属物种，并在念珠菌感染的体内模型，这表明非整倍体的出现由于唑类治疗的几种致病性酵母菌，这可能会发生在感染过程中。真菌感染是一个特别具有挑战性的问题，在医学上，由于有效的抗真菌药物的数量很少。氟康唑是最常用的抗真菌药物，它可以阻止细胞生长，但不会杀死它们，这给了真菌种群一个产生耐药性的机会。白色念珠菌是最常见的真菌病原体，临床上已分离出许多这种微生物的氟康唑耐药菌株。耐氟康唑的分离株通常含有异常数量的染色体（一种称为非整倍性的状态），这些染色体上的耐药基因的额外拷贝使细胞能够绕过药物。念珠菌细胞如何获得异常的染色体数目是一个非常重要的医学问题--非整倍体仅仅是被动选择的，还是药物治疗主动诱导的？在这项研究中，我们发现氟康唑和其他相关的唑类抗真菌药诱导异常的细胞周期进程，其中母细胞和子细胞在染色体分离后不能分离。在进一步的生长周期后，这些细胞形成一种不寻常的细胞类型，我们称之为“三聚体”-具有两个核的三叶细胞。三聚体中异常的染色体分离动力学产生染色体数目是正常数目两倍的后代。在这些后代中的不平等的染色体分离导致在人群中的非整倍体的患病率增加。我们推测，非整倍体的增加大大增加了发展耐药性的几率。
When exposed to the antifungal drug fluconazole, Candida albicans undergoes abnormal growth, forming three-lobed “trimeras.” These aneuploid trimeras turn out genetically variable progeny with varying numbers of chromosomes, increasing the odds of creating a drug-resistant strain. Candida albicans, the most prevalent human fungal pathogen, is generally diploid. However, 50% of isolates that are resistant to fluconazole (FLC), the most widely used antifungal, are aneuploid and some aneuploidies can confer FLC resistance. To ask if FLC exposure causes or only selects for aneuploidy, we analyzed diploid strains during exposure to FLC using flow cytometry and epifluorescence microscopy. FLC exposure caused a consistent deviation from normal cell cycle regulation: nuclear and spindle cycles initiated prior to bud emergence, leading to “trimeras,” three connected cells composed of a mother, daughter, and granddaughter bud. Initially binucleate, trimeras underwent coordinated nuclear division yielding four daughter nuclei, two of which underwent mitotic collapse to form a tetraploid cell with extra spindle components. In subsequent cell cycles, the abnormal number of spindles resulted in unequal DNA segregation and viable aneuploid progeny. The process of aneuploid formation in C. albicans is highly reminiscent of early stages in human tumorigenesis in that aneuploidy arises through a tetraploid intermediate and subsequent unequal DNA segregation driven by multiple spindles coupled with a subsequent selective advantage conferred by at least some aneuploidies during growth under stress. Finally, trimera formation was detected in response to other azole antifungals, in related Candida species, and in an in vivo model for Candida infection, suggesting that aneuploids arise due to azole treatment of several pathogenic yeasts and that this can occur during the infection process. Fungal infections are a particularly challenging problem in medicine due to the small number of effective antifungal drugs available. Fluconazole, the most commonly prescribed antifungal, prevents cells from growing but does not kill them, giving the fungal population a window of opportunity to become drug resistant. Candida albicans is the most prevalent fungal pathogen, and many fluconazole-resistant strains of this microbe have been isolated in the clinic. Fluconazole-resistant isolates often contain an abnormal number of chromosomes (a state called aneuploidy), and the additional copies of drug resistance genes on those chromosomes enable the cells to circumvent the drug. How Candida cells acquire abnormal chromosome numbers is a very important medical question—is aneuploidy merely passively selected for, or is it actively induced by the drug treatment? In this study, we found that fluconazole and other related azole antifungals induce abnormal cell cycle progression in which mother and daughter cells fail to separate after chromosome segregation. Following a further growth cycle, these cells form an unusual cell type that we have termed “trimeras”—three-lobed cells with two nuclei. The aberrant chromosome segregation dynamics in trimeras produce progeny with double the normal number of chromosomes. Unequal chromosome segregation in these progeny leads to an increase in the prevalence of aneuploidy in the population. We postulate that the increase in aneuploidy greatly increases the odds of developing drug resistance.
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影响因子：
4.5
作者：
Hill JA;Ammar R;Torti D;Nislow C;Cowen LE
通讯作者：
Cowen LE
压力改变白色念珠菌中杂合性丧失的速率和类型。
影响因子：
6.4
作者：
Forche A;Abbey D;Pisithkul T;Weinzierl MA;Ringstrom T;Bruck D;Petersen K;Berman J
通讯作者：
Berman J
影响因子：
9.2
作者：
Burrack, Laura S.;Applen, Shelly E.;Berman, Judith
通讯作者：
Berman, Judith
影响因子：
9.8
作者：
Forche A;Alby K;Schaefer D;Johnson AD;Berman J;Bennett RJ
通讯作者：
Bennett RJ
影响因子：
11.4
作者：
Bennett, RJ;Johnson, AD
通讯作者：
Johnson, AD