Dual roles of Spätzle-6 in the immune responses and development in the mosquito, Aedes aegypti

• Main Authors: Chun-Hao Huang, 黃俊豪
• Other Authors: 蕭信宏
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/73712478135965313604

碩士 === 國立臺灣大學 === 微生物學研究所 === 98 === Mosquitoes are major vectors of several devastating human diseases, such as malaria, Dengue fever, West Nile encephalitis, Japanese encephalitis and filariasis. In addition to developing new drugs and vaccines and controlling these diseases researcher have also been devoted to combat the vector-borne diseases by developing new genetic engineering approaches. Therefore, studies of the regulation machinery of mosquito innate immunity against pathogens and development provide new insights on vector-born disease control. In this study, we use the major vector of Dengue fever, the mosquito Aedes aegypti, as our experimental model. Microarray analysis in Anopheles gambiae showed that several immune responsive genes, including Spätzle-6(Spz6), were up-regulated upon immune stimulation including Inhibitor of Apoptosis-2(IAP2). IAP2 was shown to be an important component participated in the regulation of antimicrobial peptides in the mosquito. In addition, studies in Drosophila melanogaster showed that Spz gene family plays important roles in egulating Toll signaling pathway and the production of antimicrobial peptides. These studies trigger our interest to study the role of Spz6 in the mosquito Aedes aegypti. To understand the role of Aedes aegypti Spz6 in response to invading pathogens, we used RNA interference(RNAi) approach to inhibit the expression of Aedes aegypti Spz6. Survival assay was performed following the challenge of Beauveria bassiana, Staphylococcus aureus or Escherichia coli. The results showed that Aedes aegypti were significantly resistant to E. coli challenge in the absence of Spz6, suggesting that Spz6 acted as an inhibitory regulator in the IMD pathway. Next, we are intrigued to know the effects of Spz6 to the downstream targets of IMD pathway. Therefore, we examined the transcriptional expression profiles of Cecropin A and Defencin A in the absence of Spz6. Interestingly, both Cecropin A and Defencin A showed relatively higher expressional pattern upon S. aureus and E. coli challenge in the absence of Spz6. We further analyzed the Spz6 expressional pattern in different tissues. To our surprise, Spz6 was highly expressed in the mosquito midgut, whereas other Spz members were expressed in the mosquito ovary. On the other hand, we found that Spz6 is highly expressed in the black pupae stage. Therefore, we performed RNAi approach to inhibit the expression of the Spz6 in white pupae stage. We observed the significant reduction of the emerging rate of the adult mosquito in the absence of Spz6. Interestingly, we found that Spz6 process alternative splicing during metamorphosis. The oviposition rate was also reduced in the absence of Spz6. Taken together, our results showed that Spz6 is a negative regulator in the IMD pathway and participate in the vitellogenesis and development. Detail analysis of Spz6 will benefit the development of new strategies for the control of the vector-borne disease.