白念珠菌a/αOpaque菌株交配、White-Opaque表型转换机制及其与致病性的关系

Since Hull and Johnson identified the mating type-like (MTL) locus in C.albicans' genome in 1999, after more than 10 years investigation, it is now becoming evident that C. albicans exhibits an unique sexual cycle, including a phenotypic transition called "White-Opaque" switching. In nature, most C.albicans strains were a/α?strains, in which two alleles existed in the mating type locus, MTLa and MTLα. Before Mating, an a/αstrain would have to undergo homozygosis to a/a or α/α, and then undergo a complex phenotypic transition from the white to the opaque phase. This reversible transition was between the normal yeast morphology (white) to an elongated cell type opaque, which is the mating-cometent form of this fungus..We found an interesting phenomenon that higher percentage of a/α?opaque cells were observed in clinical isolates than natural isolates. Because opaque was mating-competent cells, based on our partial preliminary liboratory data, we hypothesized that opaque a/α ?strain would be mating in host niche..In this context, this research focused on the difference in mating type and white-opaque phase between natural strain and clinical strain, study the microbiologic characteristics, switch mechanism of opaque a/α?cell and the relationship between this phenomenon and pathogenesis in host.

大部分白念珠菌为a/α菌株，同时具备MTLa位点和MTLα位点，交配的发生率很低。白念珠菌的a/α菌株必须首先在MTL 位点上形成纯合状态，形成a/a或α/α菌株，再通过重要的White-Opaque转换步骤，才具备交配能力。研究者在临床分离的白念珠菌中观察到有趣的现象即与自然环境分离株相比，临床分离株中存在较高的a/α菌株Opaque表型。鉴于Opaque表型是具有交配能力的表型及部分前期实验结果，我们推测Opaque表型a/α白念珠菌在人体内环境中也能进行交配。基于上述假设，本研究针对白念珠菌自然株及临床分离株中Mating type及White-Opaque表型差异，研究白念珠菌临床分离a/α菌株中Opaque表型的细胞特征、White-Opaque表型转换机制及对于白念珠菌致病性的影响，对于解开白念珠菌有性生殖生活周期之谜，及交配对于白念珠菌致病性的作用具有非常重要的意义。

项目背景.白念珠菌是一种常见的人体共生菌，可以定植于健康人群的口腔、消化道、外生殖道黏膜及皮肤，也可引起免疫受损人群的表浅甚至系统性感染。..主要研究内容.我们的研究结果报道了231株白念珠菌临床菌株的CAI和MTL基因型，以及white-opaque转换和酵母相-菌丝相表型。..重要结果.（1）我们在231株菌株中发现65种CAI基因型，并且某些部位定植的菌株具有特定CAI基因型。例如，阴道感染患者定植菌株的优势基因型为CAI 30-44和30-45。血液系统感染患者定植菌株以CAI 21-26为优势基因型，系统性感染以11-11、18-26和21-21为优势基因型。（2）白念珠菌具有多种不同的表型，包括酵母形态、菌丝形态、white细胞以及opaque细胞。我们同样观察了CAI基因型与表型转换之间的关系。结果发现CAI基因型中具有较长的CAA/G重复序列的菌株更易于发生white-opaque转换。这种相关性可能是由于CAI所在的RLM1基因对white-opaque表型的调节作用。（3）MTL纯合菌株散在分布于各CAI组中，提示MTL与CAI基因型的相关性不大。（4）以往研究认为white-opaque转换多发生于MTL纯合型菌株，并且多发生于菌株培养于含氮乙酰葡糖胺的培养基上。然而我们的研究结果发现一些MTL杂合型菌株也可发生white-opaque转换，并且转换也可发生于常规培养基，即以葡萄糖作为碳源的培养基上。（5）我们并未发现CAI和MTL基因型与菌丝发生之间的关系。..科学意义.我们的结果说明白念珠菌临床菌株具有较为丰富的基因型和表型多态性，且基因型与表型之间具有一定的相关性。