MicroRNA expression profile in Lampetra morii upon Vibrio anguillarum infection and miR-4561 characterization targeting lip.

As a critical evolutionary pivot between invertebrates and vertebrates, lampreys provide rich genetic information. Lamprey immune protein (LIP) is a key immune regulator. MicroRNAs, well-conserved in the response to immunological stress, remain understudied in lamprey immunity. We generated a lamprey microRNA expression atlas, using deep sequencing, upon Vibrio anguillarum infection. Using comparative methods, we found that miR-4561 potentially regulates innate immunity via interaction with lip. We found a sequence in the 3′-UTR region of LIP mRNA complementary to the miR-4561 seed region; miR-4561 expression was negatively correlated with LIP. During V. anguillarum infection, miR-4561 inhibited LIP expression and bacterial clearance. Notably, LIP expression in supraneural body cells was necessary for the Gram-negative immune response. Additionally, we observed that overexpression of miR-4561 induced apoptosis in embryonic cells, suggesting a role in embryonic development. Collectively, we show lamprey microRNAs may significantly affect gene regulation and provide new insights on LIP-mediated immune regulation. Ma et al characterise differentially expressed miRNAs in Lamprey upon bacterial infection. They identify miR-4561 as being decreased after infection and show that it targets the 3′UTR of the mRNA encoding lamprey immune protein (LIP) involved in lamprey innate immunity and regulates survival in lamprey embryos.