Yorkie involves in immune response under hypoxia stress in Chinese mitten crab (Eriocheir sinensis)

Oxygen is essential for the survival of aquatic animals. Hypoxia constitutes a critical environmental stressor that fundamentally impacts immune homeostasis in aquatic crustaceans. However, the immune regulatory mechanisms of crustaceans under hypoxia stress require further exploration. Yorkie (Yki), a key downstream effector of the Hippo signaling pathway, has been implicated in innate immunity regulation, its precise functional mechanisms during hypoxic conditions in Eriocheir sinensis remain unclear. This study investigated the expression characteristics and immune regulation of Yki in response to hypoxia stress in E. sinensis. The mRNA expression of Yki and its downstream target gene, Cactus in haemocytes were significantly increased from 3 h to 6 h post hypoxia stress, and then decreased to slightly lower than that of the control. The Yki phosphorylation level under hypoxia stress was significantly decreased. Meanwhile, the positive green signal of Yki translocated from the cytoplasm to the nucleus under hypoxia stress. The Yki and Cactus transcripts were significantly increased after Aeromonas hydrophila injection under hypoxic conditions. A. hydrophila stimulation inhibited and promoted the phosphorylation level and nuclear translocation of Yki post hypoxia stress, respectively. Furthermore, after the reduction of Yki mRNA expression by RNAi, the mRNA expression levels of lipopolysaccharide factors (ALFs) in haemocytes were significantly up-regulated post A. hydrophila stimulation under hypoxia stress, whereas they significantly decreased after the inhibition of Yki phosphorylation by CA3 injection. Our findings collectively suggested that hypoxia could activate Yki, and Yki was involved in regulating ALFs expression in E. sinensis, which enrich the understanding of regulatory mechanisms underlying immune defense in crustaceans under hypoxia stress.