Channel Catfish Virus Infection And Immune Features Of Catfish (Channel Catfish And Chinese Yellow Catfish)

Catfish are distributed to every continent except Antarctica and have been cultured for many centuries around the world. Catfish are considered important species of the world fish industry because of high market value. The farming of catfish suffers from severe outbreaks of viral and bacterial diseases, which cause extensive economic loss to the yield of this species. Many researchers reported several viral and bacterial diseases that cause significant mortality and morbidity in different species of catfish. Further it is established that fish respond to the invading microbes via physical and biochemical immune systems. However, immune system that consists of complex components,enzymes and signaling pathways, confer significant protection to the fish body. Many immune-relevant proteins and enzymes have been isolated from catfish and their immunological activity was elucidated in various organs including the mucosal layer and secretion. This study reports the immune response of channel catfish after infection with the channel catfish virus (CCV) and stating the discovery and anti-bacterial response of recombination activating gene 2 (RAG2) in Chinese yellow catfish. Furthermore, an inflammatory factor cyclophilin A (CypA) was detected and its immunological role was studied in mucosal secretion of Chinese yellow catfish.The channel catfish virus (CCV) can cause lethal hemorrhagic infection in juvenile channel catfish, thereby resulting in a huge economic loss to the fish industry. The genome of the CCV has been fully sequenced, and its prevalence is well documented.However, less is known about the molecular mechanisms and pathogenesis of the CCV.Herein, the channel catfish ovary cells (CCO) were infected with CCV and their transcriptomic sketches were analyzed using an RNA sequencing technique. In total,72,686,438 clean reads were obtained from 73,231,128 sequence reads, which were further grouped into 747,168 contigs. These contigs were assembled into 49,119 unigenes,of which 20,912 and 18,333 unigenes were found in Nr and SwissProt databases and matched 15,911 and 14,625 distinctive proteins, respectively. From these, 3,641 differentially expressed genes (DEGs), comprising 260 up-regulated and 3,381 down-regulated genes, were found compared with the control (non-infected) cells. For verification, 16 DEGs were analyzed using qRT-PCR. The analysis of the DEGs and their related cellular signaling pathways revealed that substantial DEGs successfully associated in the propagation of apoptosis pathway induced by CCV infection. The apoptosis pathways were further elucidated using standard apoptosis assays. The results showed that CCV could induce a tumor necrosis factor (TNF)-mediated extrinsic apoptosis pathway(instead of a mitochondrial intrinsic apoptosis pathway) in CCO cells. This study helps our understanding of the pathogenesis of CCV and contributes to the prevention of CCV infection in channel catfish.Recombination activating gene 2 (RAG2), associates with RAG1 and regulates the V(D)J recombination of immunoglobulin (Ig) and T-cell receptor (TCR) genes. Being a key player in the adaptive immune response of vertebrates, RAG2 functional characterization in yellow catfish was beneficial for understanding its biological response to pathogens. In the current study, RAG2 gene from yellow catfish was cloned and characterized and the expression pattern was studied. The results depicted that the open reading frame (ORF) of yellow catfish RAG2 (YC-RAG2) was 1596 bp encoding a polypeptide of 531 amino acids and 59.86 kDa. The multiple alignment and phylogenetic analysis of YC-RAG2 with other species showed the conserved regions and classical taxonomy and evolution. The YC-RAG2 protein was expressed and specific anti-RAG2 polyclonal antibody was generated in rabbit. Subsequently, YC-RAG2 transcript and protein were detected in different tissues with relative high expression level in the thymus tissues, spleen and head kidney tissues. Moreover, the temporal expression of YC-RAG2,Interleukin 1 beta (IL-1?) and tumour necrosis factor-alpha (TNF-a) were observed in the lymphoid tissues after Edwardsiella ictaluri infection. Our finding suggests that YC-RAG2 was potentially involved in immunological response against bacterial infection in yellow catfish.Fish skin mucus is a dynamic barrier for invading pathogens with a variety of anti-microbial enzymes, including cyclophilin A (CypA), a multi-functional protein with peptidyl-prolyl cis/trans isomerase (PPIase) activity. Beside various other immunological functions, CypA induces leucocytes migration in vitro in teleost. In the current study, we have discovered several novel immune-relevant proteins in yellow catfish skin mucus by mass spectrometry (MS). The CypA present among them was further detected by Western blot. Moreover, the CypA present in the skin mucus displayed strong chemotactic activity for yellow catfish leucocytes. Interestingly, asparagine (like arginine in mammals) at position 69 was the critical site in yellow catfish CypA involved in leucocyte attraction.These novel efforts do not only highlight the enzymatic texture of skin mucus, but signify CypA to be targeted for anti-inflammatory therapeutics.