GCN2-eIF2α signaling pathway negatively regulates the growth of triploid crucian carp

GCN2-eIF2α signaling pathway plays crucial roles in cell growth,development, and protein synthesis. However, in polyploid fish, the function of this pathway is rarely understood. In this study, genes associated with the GCN2-eIF2α pathway (pkr, pek, gcn2, eif2α) are founded lower expression levels in the triploid crucian carp (3nCC) muscle compared to that of the red crucian carp (RCC). In muscle effect stage embryos of the 3nCC, the mRNA levels of this pathway genes are generally lower than those of RCC, excluding hri and fgf21. Inhibiting gcn2 in 3nCC embryos downregulates downstream gene expression (eif2α, atf4, fgf21), accelerating embryonic development. In contrast, overexpressing of eif2α can alter the expression levels of downstream genes (atf4 and fgf21), and decelerates the embryonic development. These results demonstrate the GCN2-eIF2α pathway's regulatory impact on 3nCC growth, advancing understanding of fish rapid growth genetics and offering useful molecular markers for breeding of excellent strains.

microRNA-27c negatively regulates NF-κB and IRF3 signaling pathway via targeting MITA in miiuy croaker

As a non-coding RNA with regulatory functions, microRNAs(miRNAs) can regulate gene expression and participate in a variety of physiological and pathological processes. In recent years, although there have been many studies on miRNA, the regulation mechanisms of miRNA in teleost fish have not been fully elucidated. In this study, it was first predicted that MITA is the target of miR-27c through bioinformatics, and it was confirmed by dual fluorescence experiments. Then we found that miR-27c can inhibit the expression of MITA at the mRNA and protein levels, thereby promoting the NF-κB or IRF3 pathway. It is speculated that miR-27c plays an important role in the innate immunity of teleost fish. This study will help to further understand miRNAs regulatory mechanism in teleost fish.

microRNA-122 regulates NF-κB signaling pathway by targeting IκBα in miiuy croaker, Miichthys miiuy

The inhibitory protein IκBα plays a key role in the inflammatory process and immune response by regulating the activity of the transcription factor NF-κB. microRNA (miR) is a small non-coding RNA that can regulate many biochemical processes, such as cell growth, proliferation, and immune response. In this study, it was first predicted that IκBα is the target of miR-122 through bioinformatics, and it was confirmed by dual fluorescence experiments. Then we found that miR-122 can inhibit the expression of IκBα at the mRNA and protein levels, thereby promoting the p65-activated NF-κB pathway. It is speculated that miR-122 plays an important role in the innate immunity of teleost fish. This study will help to further understand miRNAs regulatory mechanism in teleost fish.

Cloning and functional analysis of SNX8 from grass carp (Ctenopharyngodon idellus)

Sorting nexin 8 (SNX8), a member of sorting nexin protein family, plays important roles in endocytosis, endosomal sorting, and innate immune response. To date, a few homologs of SNX8 have been found in fish except in mammals. In this study, a teleost SNX8 cDNA was identified from grass carp (Ctenopharyngodon idellus). CiSNX8 was up-regulated significantly after infection with poly I:C or GCRV. We found that SNX8 was mainly distributed in the endoplasmic reticulum (ER) in CIK cells. Further analysis indicated that CiSNX8 might negatively regulate RLR signaling pathway that is quite distinct from mammalian SNX8. In addition, CiSNX8 could interact with MAVS, STING, TBK1, IRF3 and IRF7. Either wild type CiSNX8 or mutants of N-terminal PX domain (aa 1-245) and C-terminal BAR domain (aa 256-519) could associate with STING. These results suggested that fish SNX8 participated in innate immune response through different molecular mechanisms.

microRNA-128 inhibits the inflammatory responses by targeting TAB2 in miiuy croaker, Miichthysmiiuy

The inflammatory response is a self-defense process that fights the pathogen invasion by eliminating harmful stimuli. However, excessive inflammation may disrupt immune homeostasis, even causing chronic inflammation or autoimmune diseases. MicroRNAs (miRNAs) are a crucial regulator that can negatively regulate gene expression and participate in multiple biological processes of growth, development, and immune response in organisms. However, the miRNA-mediated modulation networks of inflammatory responses remain largely unclear in lower vertebrates. In this study, miR-128 was identified as a negative regulator to participate in the NF-κB signaling pathway by targeting TAB2 in miiuy croaker. First, we predicted target genes of miR-128 through the bioinformatics software programs and found that TAB2 is a direct target of miR-128. We also found that miR-128 can inhibit TAB2 expression at the mRNA and protein levels. Besides, upon LPS stimulation, miR-128 inhibits the expression of inflammatory cytokines by targeting TAB2 to avoid excessive inflammation. Particularly, we found that miR-128 can regulate TAB2-mediated NF-κB signaling pathways. In summary, our results indicate that miR-128 plays a critical role in suppressing inflammatory responses by regulating the TAB2-mediated NF-κB signaling pathway in miiuy croaker.

IRF1 negatively regulates NF-κB signaling by targeting MyD88 for degradation in teleost fish

MyD88 is considered as one of the most crucial adaptors in TLR signaling pathway. MyD88 may be influential to interferon regulatory factors (IRFs), while the way that IRFs regulate MyD88 is not fully understood. In this study, we demonstrated that the member of IRF family named IRF1 in miiuy croaker played a role as a negative regulator of MyD88-mediated NF-κB signaling and promoted the degradation of MyD88. Firstly, we found the strong inhibitory effect of IRF1 on MyD88-mediated NF-κB signaling pathway. Secondly, we confirmed that IRF1 could enhance the degradation of MyD88, while the knockdown of IRF1 presented an opposite result. Furthermore, the DBD domain of IRF1 was necessary for the inhibition to MyD88. In addition, it could be found that IRF1 could promote MyD88 degradation through ubiquitin-proteasome pathway. Our findings suggest that miiuy croaker IRF1 negatively regulates the cellular response by targeting MyD88 for degradation, which provides new insights into the regulatory mechanism in teleost.

microRNA-144 regulates the NF-κB signaling in miiuy croaker via targeting IL1β

microRNAs have been demonstrated to be critical regulators of the immune responses. While, the miRNA-mediate the detail regulatory mechanism response is still not clear in fish species. In this research, the regulation of miRNA to the NF-κB signaling through decreasing the target gene mRNAs was discussed in miiuy croaker. We first used the bioinformatics predicted miR-144 has a direct negative regulatory affect on IL1β in miiuy croaker, further the luciferase assays were used to probe the functions of miR-144. The overexpression of miR-144 mimics and pre-miR-144 plasmid all showed the dose-dependent pattern on IL1β. Moreover, the inhibition of luciferase activity was attenuated after co-transfected with miR-144 inhibitors. In addition, we observed that the miR-144 could negative regulate to the nuclear factor kappaB (NF-κB) signaling in miiuy croaker by targeting IL1β. In conclusion, our studies on miR-144 will enlarge knowledge of its functions in regulation of immune response, further provide a new insight to research on the immune regulation mechanism in teleost fish.

microRNA-375 modulates the NF-κB pathway in miiuy croaker by targeting DUSP1 gene

microRNAs (miRNAs) are highly conserved, small non-coding endogenous molecule, and can participate in a variety of biological processes in organisms such as development, growth and immune response. Dual-Specificity Phosphatases (DUSPs) are enzymes that can remove phosphate groups from phosphatases. Research found that DUSP1 is an important molecule in the process of MAPK regulation. However, as a significant regulatory factor, the study of DUSP1 was very few in fish. Consequently, in this study, the regulatory role of miRNAs on DUSP1 has been verified through dual-luciferase reporter assay and western blotting analysis. Furethermore, we found that miR-375 mimics and pre-miR-375 plasmid can negatively regulate the target gene DUSP1 in miiuy croaker through combining with 3'untranslated region of DUSP1 gene. These experiment results directly indicate the negative regulatory function of miR-375 to DUSP1. Moreover, miR-375 can negatively regulate NF-κB signaling pathway via target to DUSP1. This study can increase our knowledge and help us to understand complexity of genomic and complex gene expression regulatory networks in teleost fish.

microRNA-145 regulates the RLR signaling pathway in miiuy croaker after poly(I:C) stimulation via targeting MDA5

MicroRNAs (miRNAs) are endogenous small non-coding RNAs that participate in diverse biological processes via degrading the target mRNAs or repressing translation. In this study, the regulation of miRNA to the RLR (RIG-I-like receptor) signaling pathway by degrading the target mRNAs was researched in miiuy croaker. MDA5, a microRNA-145-5p (miR-145-5p) putative target gene, was predicted by bioinformatics, and the target sites from the 3'untranslated region of MDA5 transcripts were confirmed using luciferase reporter assays. Pre-miR-145 was more effective in inhibiting MDA5 than miR-145-5p mimic, and the effect was dose- and time-dependent. The expression patterns of miR-145-5p and MDA5 were analyzed in liver and kidney from miiuy croaker. Results implied that miR-145-5p may function via degrading the MDA5 mRNAs, thereby regulating the RLR signaling pathway. Studies on miR-145-5p will enrich knowledge of its functions in immune response regulation in fish, as well as offer a basis for regulatory networks that are composed of numerous miRNAs.