The anti-inflammatory cytokine IL-22 exhibited a proinflammatory effect in the ovary aiding with the parturition of ovoviviparous black rockfish (Sebastes schlegelii)

IntroductionAs a unique type of immunological process, pregnancy and subsequent parturition are associated with a series of inflammatory events. As an anti-inflammatory cytokine, IL-22 has been proven to participate in the parturition process in mammals. However, less is known about ovoviviparous teleosts. To investigate the role of IL-22 in fish parturition, black rockfish, an ovoviviparous teleost, was used. This fish is unique in that it provides over 60% nutrition supply for over 50 thousand embryos at the same time though a placenta-like structure during pregnancy while delivering all fries in two hours.MethodsSequence alignment, phylogenetic tree analysis and homology modeling were performed on IL-22 and its receptor. In situ hybridization demonstrated ovarian localization of il22 and il22r1. The protein of rIL-22 was obtained through the prokaryotic expression. RNA-seq analysis was performed on black rockfish ovarian cells treated with rIL-22.ResultsIn situ hybridization results showed that both il22 and il22ra1 were localized in the perinatal follicle layer and embryonic envelope. The il22 expression level was significantly increased during parturition compared to before and after parturition (P