探討剔除白色念珠菌 CaPTR2、CaPTR3、CaPTR22 對白色念珠菌型態變化之影響

Abstract

白色念珠菌(Candida albicans)是一種伺機性的二倍體病源真菌，通常共生於人體中，當宿主免疫功能低下或缺損時，白色念珠菌就會引起嚴重感染甚至造成死亡。白色念珠菌具有型態之間轉換的能力，一般有三種型態：酵母菌型、假菌絲型、菌絲型。其致病力與型態轉換能力被認定為有關聯性的。在菌絲生成的調控路徑上，主要是由Cph1p和Efg1p進行調控。實驗證明cph1/cph1 efg1/efg1雙基因剔除株，無法在實驗室條件下生成菌絲型態且在小鼠中失去致病能力。故可由研究白色念珠菌的型態變化能力再進而推測其與致病性的關聯。白色念珠菌可將蛋白質降解成為多肽鏈並吸收含氮的養分以利生長。菌體會分泌天冬胺酸蛋白酶降解蛋白質，再經由特定的胜肽轉運載體吸收至細胞內，其中CaPTR2和 CaPTR22已被研究出是表現胜肽轉運載體的基因，但該PTR家族中的CaPTR3仍屬未知。由於氮的濃度會影響到白色念珠菌的型態變化，故本研究欲測試CaPTR基因失去功能時對型態轉變能力的影響。本研究利用SAT1 flipper cassette構築CaPTR2、CaPTR3和CaPTR22之剔除株及其雙基因組成之剔除株，並測試其性狀。在結果中發現：Captr2和Captr22及其雙基因突變株和野生株並無明顯差異。但是在Captr3及其有關的雙基因突變株中，菌落生成型態及菌落侵犯力和cph1/cph1 efg1/efg1雙基因剔除株較相似。因此CaPTR3對型態變化確實有影響，但詳細的調控路徑以及其與含氮營養源運輸上的角色，仍需要更進一步的研究。

Candida albicans is a commensal diploid fungus found in human. However, it is an opportunistic pathogen. It can cause serious infections, even death, especially in immunocompromised patients. The hyphal formation was regulatd by the transcription factors CaCph1p and CaEfg1p. The cph1/cph1 efg1/efg1 double mutant was defective in filamentous growth, and became avirulent in a mouse model. Therefore, investigating the morphogenesis may infer the virulence of Candida albicans. Candida albicans can use proteins as the sole source of nitrogen for growth. The secretion of aspartic proteinases allows the fungus to digest host proteins to produce peptides for cells to take up via specific transporters. PTR family is known to affect the up-take of peptides. CaPTR2 and CaPTR22 have been verified as peptide transporters, while the function of CaPTR3 is unknown. The concentrations of nitrogen affect the formation of filaments. In this study, I determined the effect of CaPTR null mutation on the morphogenesis of C. albicans, to investigate the connection of virulence and transport of nitrogen source. I used the SAT1 flipper cassette to construct null mutant and double mutant strains of CaPTR2、CaPTR3 and CaPTR22 .Then I determined the effect on the morphogenesis. The results showed that Captr2/Captr2, Captr22/Captr22 and their double mutant strains showed no difference to the wild-type strain. The Captr3/Captr3 null mutant and it’s double mutant strains showed similar phenotypes to cph1/cph1 efg1/efg1 in invasion test and colony morphology. Therefore, CaPTR3 affects the morphogenesis, but the pathway and the roles of CaPTR3 in nitrogen source transporter need to be investigated further.