Genome-wide characterization of gap junction (connexins and pannexins) genes in turbot (Scophthalmus maximus L.): evolution and immune response following Vibrio anguillarum infection

The role of antifreeze genes in the tolerance of cold stress in the Nile tilapia (Oreochromis niloticus)

BACKGROUND

Tilapia is one of the most essential farmed fishes in the world. It is a tropical and subtropical freshwater fish well adapted to warm water but sensitive to cold weather. Extreme cold weather could cause severe stress and mass mortalities in tilapia. The present study was carried out to investigate the effects of cold stress on the up-regulation of antifreeze protein (AFP) genes in Nile tilapia (Oreochromis niloticus). Two treatment groups of fish were investigated (5 replicates of 15 fish for each group in fibreglass tanks/70 L each): 1) a control group; the fish were acclimated to lab conditions for two weeks and the water temperature was maintained at 25 °C during the whole experimental period with feeding on a commercial diet (30% crude protein). 2) Cold stress group; the same conditions as the control group except for the temperature. Initially, the temperature was decreased by one degree every 12 h. The fish started showing death symptoms when the water temperature reached 6-8 °C. In this stage the tissue (muscle) samples were taken from both groups. The immune response of fish exposed to cold stress was detected and characterized using Differential Display-PCR (DD-PCR).

RESULTS

The results indicated that nine different up-regulation genes were detected in the cold-stressed fish compared to the control group. These genes are Integrin-alpha-2 (ITGA-2), Gap junction gamma-1 protein-like (GJC1), WD repeat-containing protein 59 isoform X2 (WDRP59), NUAK family SNF1-like kinase, G-protein coupled receptor-176 (GPR-176), Actin cytoskeleton-regulatory complex protein pan1-like (PAN-1), Whirlin protein (WHRN), Suppressor of tumorigenicity 7 protein isoform X2 (ST7P) and ATP-binding cassette sub-family A member 1-like isoform X2 (ABCA1). The antifreeze gene type-II amplification using a specific PCR product of 600 bp, followed by cloning and sequencing analysis revealed that the identified gene is antifreeze type-II, with similarity ranging from 70 to 95%. The in-vitro transcribed gene induced an antifreeze protein with a molecular size of 22 kDa. The antifreeze gene, ITGA-2 and the WD repeat protein belong to the lectin family (sugar-protein).

CONCLUSIONS

In conclusion, under cold stress, Nile tilapia express many defence genes, an antifreeze gene consisting of one open reading frame of approximately 0.6 kbp.

Genome-wide identification of gap junction (connexins and pannexins) genes in black rockfish (Sebastes schlegelii): Evolution and immune response mechanism following challenge

Cell-to-cell communication through gap junction channels is very important to coordinate the functions of cells in all multicellular biological tissues. It allows the direct exchange of ions and small molecules (including second messengers, such as Ca²⁺, IP3, cyclic nucleotides, and oligonucleotides). In this study, a total of 48 members of the gap junction (GJ) protein family were identified from Sebastes schlegelii. In S. schlegelii, GJ proteins were classified into two types, connexin, and pannexin, and then connexins were divided into five subfamilies. The naming of 48 genes was verified through phylogenetic analysis and syntenic analysis. The connexin proteins contained four transmembrane fragments and two extracellular loops, the lengths of the intracellular loop and C-terminal was quite different, and the C-terminal region was highly variable after post-translational modification. PPI analysis showed that GJs interacted with tight junctions, adhesive junctions, and cell adhesions to form a complex network and participated in cell-cell junction organization, ATP binding, ion channel, voltage-gated conduction, wnt signaling pathway, Fc-γ receptor signaling pathway, and DNA replication. In addition, the S. schlegelii GJ protein was highly expressed in intestinal tissues and remarkably regulated after Edwardsiella tarda and Streptococcus iniae infection. The expression of GJs in intestinal cells of S. schlegelii was significantly regulated by LPS and poly (I:C), which was consistent with the results of intestinal tissue stimulation by pathogens. In conclusion, this study can provide valuable information for further research on the function of S. schlegelii GJ proteins.

Characterization of Pannexin1, Connexin32, and Connexin43 in Spotted Sea Bass (Lateolabrax maculatus): They Are Important Neuro-Related Immune Response Genes Involved in Inflammation-Induced ATP Release

Many immunological diseases can be treated by regulating neurobehavior, in which extracellular ATP is a vital member of endogenous danger-associated molecular pattern signaling molecule that plays a crucial part in innate neuro-related immunity. It is actively released through pannexin (Panx) and connexin (Cx) hemichannels from activated or stressed cells during inflammation, injury, or apoptosis. In addition to participating in ATP release, Panxs and Cxs also have crucial immune functions. In this study, pannexin1, three connexin32 isoforms and connexin43 were identified and characterized in spotted sea bass (Lateolabrax maculatus), which were named LmPanx1, LmCx32.2, LmCx32.3, LmCx32.7, and LmCx43. Their similar topological structures were discovered by sequence analysis: a relatively unconserved C-terminal region and four highly conserved transmembrane (TM) domains, and so on. Each extracellular (ECL) region of Panx1 has two conserved cysteine residues. Unlike Panx1, each ECL region of Cx32 and Cx43 contains three conserved cysteine residues, forming two conserved motifs: CX6CX3C motif in ECL1 and CX4CX5C motif in ECL2. Furthermore, Panx1 and Cx43 share similar genomic organization and synteny with their counterparts in selected vertebrates. Cx32 and CX43 were located in the same locus in fish, but diverged into two loci from amphibian. Moreover, despite varying expression levels, the identified genes were constitutively expressed in all examined tissues. All genes were upregulated by PAMP [lipopolysaccharide and poly(I:C)] stimulation or bacterial infection in vivo and in vitro, but they were downregulated in the brain at 6 or 12 h after stimulation. Especially, the three LmCx32 isoforms and LmCx43 were upregulated by ATP stimulation in primary head kidney leukocytes; however, downregulation of LmCx32.3 and LmCx43 expression were noted at 12 h. Conversely, ATP treatment inhibited the expression of LmPanx1. Importantly, we showed that the spotted sea bass Panx1, Cx43, and Cx32 were localized on the cellular membrane and involved in inflammation-induced ATP release. Taken together, our results demonstrated that Panx1, Cx32, and Cx43 are important neuro-related immune response genes involved in inflammation-induced ATP release.