Chromosome loss in the fungal pathogen C. albicans

描述(申请人提供)：白色念珠菌是最常见的真菌病原体，可引起黏膜和全身感染，特别是在免疫功能低下的人中。直到最近，这种机会主义的病原体还被认为是无性的，只以二倍体有机体的形式存在。然而，一个交配型(MTL)基因座被鉴定出来，对它的遗传操作导致了白念珠菌交配能力菌株的实验室构建。交配的产物是四倍体品系，如果要实现完整的有性周期，必须经过减数分裂才能返回到二倍体状态。在白色念珠菌中，这种减数分裂(从四倍体到二倍体)可以通过一种涉及一致染色体丢失的非减数分裂机制发生。由此产生的二倍体本身就具有交配能力，从而在这种有机体中完成了一个无性生殖循环。 本研究的目的是确定白念珠菌染色体协同丢失的机制，并了解其在生物体生命周期中的作用，特别是其在感染过程中可能发挥的作用。四倍体菌株的染色体丢失模式将通过提取染色体丢失的中间产物并将它们的DNA与念珠菌微阵列杂交来绘制。这将揭示某些染色体是否优先丢失，以及它们是否按规定的顺序丢失。染色体丢失也将通过显微镜直接观察经历染色体丢失的细胞来检查。如果发生染色体不分离，则可观察到有丝分裂器官的缺陷。二倍体和四倍体菌株的转录图谱也将进行比较。特别强调了解四倍体菌株在染色体丢失过程中的转录程序。这些研究的一个主要目标是研究四倍体和染色体丢失在感染中的作用。因此，白念珠菌四倍体菌株的毒力将与二倍体菌株的毒力进行比较，并在感染模型中观察染色体丢失。最后，这些研究将通过构建等位基因微阵列直接解决念珠菌在其二倍体基因组中是否包含隐性致死等位基因的问题。这也将使发生在白念珠菌性旁性周期中的重组事件被识别出来。

DESCRIPTION (provided by applicant): Candida albicans is the most common fungal pathogen, causing both mucosal and systemic infections, particularly in immunocompromised people. Until recently, this opportunistic pathogen was thought to be asexual, existing only as a diploid organism. However, a mating-type-like (MTL) locus was identified and genetic manipulation of it led to the laboratory construction of mating-competent strains of C. albicans. The products of mating are tetraploid strains that must undergo a reductional division to return to the diploid state if a complete sexual cycle is to be achieved. In C. albicans, this reductional division (from tetraploid to diploid) can occur by a non-meiotic mechanism involving concerted chromosome loss. The resultant diploids are themselves mating-competent, thereby completing a parasexual cycle in this organism. The goal of this study is to determine the mechanism of concerted chromosome loss in C. albicans, and to understand the role it plays in the life-cycle of the organism, with special emphasis on its possible role during infection. The pattern of chromosome loss from tetraploid strains will be mapped by taking intermediates in chromosome loss and hybridizing their DNA to Candida microarrays. This will reveal if certain chromosomes are lost preferentially, and whether they are lost in a prescribed order. Chromosome loss will also be examined by directly visualizing cells undergoing chromosome loss by microscopy. If chromosome non-disjunction is occurring then defects in the mitotic apparatus may be observed. The transcriptional profiles of diploid and tetraploid strains will also be compared. Particular emphasis will be placed on understanding the transcriptional program of tetraploid strains during chromosome loss. A major goal of these studies is to examine the role of the tetraploid and chromosome loss in infection. Therefore, the virulence of the tetraploid strain of C. albicans will be compared to that of diploid strains, and chromosome loss will be followed in models of infection. Finally, these studies will directly address whether Candida contains recessive lethal alleles in its diploid genome by construction of an allelic microarray. This will also allow recombination events that take place during the parasexual cycle of C. albicans to be identified.