Identification of a Yorkie homolog from Litopenaeus vannamei as a negative regulator in anti- WSSV immune response.

Hippo signaling pathway is a serine threonine kinase cascade that is evolutionary conserved with well-established roles in organ size control, development, tumorigenesis and immunity. As its core molecule, Yorkie also plays an important role against pathogen. In this study, we cloned and characterized a Yorkie homolog from Litopenaeus vannamei, designed as LvYKI, which has a 1650 bp open reading frame. It has the characterized domains of Yokie family, and displayed to be close to the insects and crustacean. Quantitative Real-time PCR showed that LvYKI had different regulatory mechanisms in different tissues. The transcriptional level of Lvyki was down-regulated in gill, while up-regulated in hepatopancreas post white spot syndrome virus (WSSV) infection. Moreover, the expression and phosphorylation of LvYKI was reduced upon WSSV infection, which indicated that LvYKI was involved in WSSV infection. Furthermore, RNAi was performed to evaluate the role of LvYKI in shrimp immune responses. Knocking down of Lvyki resulted in inhibition of the transcription of WSSV gene ie1 and vp28, and delayed mortality of shrimp post WSSV infection. Meanwhile, the apoptosis of hemocyte was increased as well. All results suggested that shrimp can promote apoptosis to resist WSSV infection mediated by down-regulation of LvYKI. In addition, it was found that LvYKI could interact with Lvβ-catenin, which cross-linked the Wnt and Hippo signaling pathway in innate immunity. Conclusively, our study provided clues that LvYKI plays an important role in the interaction between shrimp and virus. It will promote our understanding of the molecular mechanism in innate immunity.