https://scholars.lib.ntu.edu.tw/handle/123456789/96205
標題: | 人體病原真菌隱球菌生殖,菌絲生長及致病分子機制之探討(III) | 作者: | 沈偉強 | 關鍵字: | 隱球菌;費洛蒙反應機制;費洛蒙傳費;洛蒙傳送蛋白質;G 蛋白質α及β次單元;Cryptococcus neoformans;pheromone response pathway;pheromone;pheromone transporter;heterotrimeric GTP binding protein α and ß subunit | 公開日期: | 2004 | 出版社: | 臺北市:國立臺灣大學植物病理與微生物學系暨研究所 | 摘要: | 隱球菌(Cryptococcus neoformans)為一 伺機性人體病原真菌,對免疫缺陷之族 群,具致命性真菌性腦膜炎之威脅。隱球 菌病原性之研究顯示,該菌主要致病因子 包括,莢膜(capsule)、黑色素(melanin)、能 生長於37℃或更高之溫度,以及其交配型 基因位點(mating type locus)。隱球菌交配型 α 基因位點已被選殖出,其大小超過100 kb,其上包含20 個以上之基因,其中包含 三個費洛蒙基因。研究費洛蒙基因突變株 發現,在交配型α 的菌株中,可能存有費 洛蒙自我調控之機轉(autocrine signaling loop)存在,並可能為交配型α 的菌株具較 高病原性之成因。本計畫之目的,乃在進 一步瞭解隱球菌血清型D 型菌之費洛蒙反 應機制,探討交配型基因位點與致病機制 及其他生理調控之關係,主要分為兩個方 向,一為找出費洛蒙反應機制之下游基因 STE6,以進一步確認費洛蒙自我調控之機 轉與有性生殖、致病性之關係。二為針對 隱球菌血清型D 型菌之G 蛋白質複合體β 次單元,進行其生理角色之探討。 為了進一步探討此自我調控機轉之作 用機制,吾人在隱球菌之基因體序列中, 找到了一個和S. cerevisiae a 費洛蒙外送蛋 白基因 STE6 之同源基因。分析STE6 基因 突變株之性狀顯示,在隱球菌的兩種不同 交配型細胞中,缺乏此費洛蒙傳輸蛋白會 明顯降低其有性生殖之效率。但若以兩不 同交配型之突變株細胞進行交配時,則其 有性生殖之過程將完全阻絕,無法完成。 而令人意料的,交配型α ste6 突變株仍然保 有進行 haploid fruiting 之功能。因此,吾 人推測在交配型α 細胞中,費洛蒙自我調 控之機轉(autocrine signaling loop),MFα費 洛蒙分子不需要經由 STE6 外泌至細胞 外, 在刺激交配型α細胞進行haploid fruiting 或其他生理反應;換言之,MFα 費洛蒙可能經由細胞內未知標的蛋白之作 用,在交配型α 細胞內引起對 MFα 費洛蒙 之反應。此外,在探討G 蛋白之功能方面, G 蛋白α 與 β次單元基因亦於隱球菌基因 體中找到,經由突變株性狀之分析顯示, 該二基因應為費洛蒙反應上游G 蛋白複合 體之次單元,G 蛋白α次單元基因GPA3 負 向調控隱球有性生殖及 haploid fruiting 之 反應;G 蛋白 β次單元基因GPB1 為有性生 殖之正向調控因子。 Cryptococcus neoformans, an opportunistic human fungal pathogen, causes the life-threatening meningoencephalitis mainly in individuals with compromised immune functions. Studies of the pathogenesis in C. neoformans have revealed several important virulence factors such as 2 capsule, melanin, ability to grow at 37 ℃ or higher temperature, and interestingly the mating type locus. The MATα locus of C. neoformans has been identified and characterized. It has unusual large size of over 100 kb and contains more than 20 genes. Three copies of pheromone precursor genes are identified in the MATα locus. Characterization of pheromone gene triple deletion mutant strains suggested an autocrine signaling loop may function and contribute to the virulence of the MATα cells (Shen et al., 2002). The purpose of this proposal is to characterize the components in the pheromone response pathway of C. neoformans serotype D strain and further address how mating type locus regulates the virulence and how the autocrine signaling loop functions in C. neoformans. To further address the role of pheromones in the signaling loop, we have identified the STE6 homologue, the S. cerevisiae a-factor exporter, in the C. neoformans genome and begun to dissect its function. By disrupting the STE6, we found that ste6 mutants in either MATα or MATa background showed partially impaired mating function. However, when ste6 MATα and MATa mutants bilaterally cross with each other, the mating process was completely abolished. Surprisingly, MATα ste6 mutant does not exhibit a defect in haploid fruiting, which implicates that the pheromone molecules could induce the signaling response intracellularly in MATα cells. We conclude that Ste6 is evolutionally conserved for mating and is not required for monokaryotic fruiting in C. neoformans. Additionally, we have also characterized the α and β subunits of heterotrimeric G protein complex. Phenotypic characterization of respective mutants suggests that they possibly form the G protein complex functioning in the upstream of the pheromone response pathway. G protein α subunit gene, GPA3, negatively regulates mating and haploid fruiting in C. neoformans. G protein βsubunit gene, GPB1, positively regulates mating in C. neoformans. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/17691 | 其他識別: | 922311B002094 | Rights: | 國立臺灣大學植物病理與微生物學系暨研究所 |
顯示於: | 植物病理與微生物學系 |
檔案 | 描述 | 大小 | 格式 | |
---|---|---|---|---|
922311B002094.pdf | 447.54 kB | Adobe PDF | 檢視/開啟 |
在 IR 系統中的文件,除了特別指名其著作權條款之外,均受到著作權保護,並且保留所有的權利。