Recognition of the non-self signature of invading pathogens is a crucial step for the initiation of the innate immune mechanisms of the host. The host response to viral and bacterial infection involve Show more
Recognition of the non-self signature of invading pathogens is a crucial step for the initiation of the innate immune mechanisms of the host. The host response to viral and bacterial infection involves sets of pattern recognition receptors (PRRs), which bind evolutionarily conserved pathogen structures, known as pathogen-associated molecular patterns (PAMPs). Recent advances in the identification of different types of PRRs in teleost fish revealed a number of cytosolic sensors for recognition of viral and bacterial nucleic acids. These are DExD/H-box RNA helicases including a group of well-characterized retinoic acid inducible gene I (RIG-I)-like receptors (RLRs) and non-RLR DExD/H-box RNA helicases (e.g., DDX1, DDX3, DHX9, DDX21, DHX36 and DDX41) both involved in recognition of viral RNAs. Another group of PRRs includes cytosolic DNA sensors (CDSs), such as cGAS and LSm14A involved in recognition of viral and intracellular bacterial dsDNAs. Moreover, dsRNA-sensing protein kinase R (PKR), which has a role in antiviral immune responses in higher vertebrates, has been identified in fish. Additionally, fish possess a novel PKR-like protein kinase containing Z-DNA binding domain, known as PKZ. Here, we review the current knowledge concerning cytosolic sensors for recognition of viral and bacterial nucleic acids in teleosts. Show less
Numerous cytosolic DNA sensors (CDSs), which are very important for recognizing cytosolic dsDNA derived from intracellular viruses and bacteria, exist in mammals. However, teleost CDSs are poorly unde Show more
Numerous cytosolic DNA sensors (CDSs), which are very important for recognizing cytosolic dsDNA derived from intracellular viruses and bacteria, exist in mammals. However, teleost CDSs are poorly understood. In this study, four CDSs, including the cyclic GMP-AMP synthase (cGAS), Sm-like protein 14 homolog A (LSm14A), DEAH-box helicase (DHX) 9, and DHX36 genes were identified in Japanese medaka, Oryzias latipes, and their expression patterns were elucidated. The expression of these genes was upregulated in the intestines and kidney of CpG-ODN-stimulated medaka. The cGAS and LSm14A genes were significantly induced in the intestines, kidney, and spleen of formalin-killed Edwardsiella tarda-treated medaka; the DHX9 and DHX36 genes were not. cGAS gene expression was induced only in the intestines of live E. tarda-treated medaka. These results suggest that the transcription of four CDS genes of medaka responds to dsDNA stimulation, and cGAS is probably more important for the immune response against E. tarda infection. Show less