A newly identified Hippo homologue from the oriental river prawn Macrobrachium nipponense is involved in the antimicrobial immune response.

The Hippo signalling pathway plays a vital role in organ size control, cell proliferation, apoptosis, and immune regulation. In this study, a Hippo homologue with three isoforms (named MnHippo-a, MnHippo-b, and MnHippo-c) was isolated and characterized for the first time from the freshwater prawn Macrobrachium nipponense. The deduced amino acid sequences of MnHippo-a (698 aa), MnHippo-b (688 aa), and MnHippo-c (656 aa) were highly similar, and they all contained an N-terminal S_TKc (serine/threonine protein kinase catalytic) domain and a C-terminal Mst1_SARAH (Sav/Rassf/Hpo) domain. MnHippo-a and MnHippo-c were derived from alternative splicing. Phylogenetic analysis was performed, and the results revealed that MnHippo was a member of the clade containing STPK4 and Hippo of Penaeus vannamei. The expression distribution showed that MnHippo was constitutively expressed in various tissues of uninfected prawns and highly expressed in the hepatopancreas and intestine. In prawns challenged with Vibrio parahaemolyticus and Staphylococcus aureus, the expression of MnHippo in haemocytes was significantly upregulated. Furthermore, in MnHippo-knockdown prawns injected with V. parahaemolyticus or S. aureus, the transcription levels of five antimicrobial peptides were downregulated. MnHippo silencing weakened the clearance of V. parahaemolyticus and S. aureus in prawns. The survival rate of the MnHippo-dsRNA group was obviously decreased from 2 to 6 days post-injection with V. parahaemolyticus or S. aureus. Hence, MnHippo might be involved in the antibacterial immune defence of M. nipponense.