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As one important member of the two-pore-domain potassium channel (K 2P ) family, potassium channel subfamily K member 3 (KCNK3) has been reported for thermogenesis regulation, energy homeostasis , membrane potential conduction, and pulmonary hypertension in mammals. However, its roles in fishes are far less examined and published. In the present study, we identified two kcnk3 genes (kcnk3a and kcnk3b ) in an euryhaline fish, Nile tilapia ( Oreochromis niloticus ), by molecular cloning , genomic survey and laboratory experiments to investigate their potential roles for osmoregulation . We obtained full-length coding sequences of the kcnk3a and kcnk3b genes (1209 and 1173 bp), which encode 402 and 390 amino acids, respectively. Subsequent multiple sequence alignments , putative 3D-structure model prediction, genomic survey and phylogenetic analysis confirmed that two kcnk3 paralogs are widely presented in fish genomes. Interestingly, a DNA fragment inversion of a kcnk3a cluster was found in Cypriniforme in comparison with other fishes. Quantitative real-time PCRs demonstrated that both the tilapia kcnk3 genes were detected in all the examined tissues with a similar distribution pattern, and the highest transcriptions were observed in the heart. Meanwhile, both kcnk3 genes in the gill were proved to have a similar transcriptional change pattern in response to various salinity of seawater, implying that they might be involved in osmoregulation. Furthermore, three predicted transcription factors (arid3a, arid3b, and arid5a) of both kcnk3 genes also showed a similar pattern as their target genes in response to the various salinity, suggesting their potential positive regulatory roles. In summary, we for the first time characterized the two kcnk3 genes in Nile tilapia , and demonstrated their potential involvement in osmoregulation for this economically important fish.

Elongases of very long-chain fatty acids (Elovls) catalyze the rate-limiting step of the elongation pathway that results in net two‑carbon elongation of pre-existing fatty acyl chains. As a set of crucial enzymes involved in the long-chain polyunsaturated fatty acids (LC-PUFA) biosynthesis, Elovls of fish have been investigated extensively in recent years. In the present study, we first identified two novel fish-specific elovl genes (named as elovl8a and elovl8b) from the herbivorous marine teleost rabbitfish (Siganus canaliculatus) by genomic survey and molecular cloning methods. Subsequently, their functional characteristics, tissue distribution patterns and transcriptional changes in response to different nutritional states were investigated. Full-length coding sequences of the elovl8a and elovl8b genes were 804 and 792 bp, encoding 267 and 263 amino acids, respectively. Multiple alignment, genomic synteny and phylogenetic analyses further suggested that elovl8 genes were unique to teleosts. Functional characterization by heterologous expression in yeast showed that Elovl8b could elongate C18 (18:2n-6, 18:3n-3 and 18:4n-3) and C20 (20:4n-6 and 20:5n-3) polyunsaturated fatty acids (PUFAs) to longer-chain polyunsaturated fatty acids (LC-PUFAs) whereas Elovl8a lacked this ability. In vitro, the expression of elovl8b but not elovl8a in rabbitfish hepatocytes was significantly up-regulated by incubation with 18:2n-6, 18:3n-3, 20:4n-6 and 20:5n-3, respectively. In vivo, compared with fish oil, dietary vegetable oil enriched in C18 PUFA enhanced the expression of elovl8b in rabbitfish brain, liver, intestine and gill tissues. These findings suggest that elovl8b but not elovl8a is a novel active member of the Elovl protein family involved in the LC-PUFAs biosynthesis pathway in rabbitfish, and provide novel insight into the mechanisms of LC-PUFAs biosynthesis in teleost.

The present study was conducted to investigate the effect of fish meal replacement with Clostridium autoethanogenum protein (CAP) on growth performance, haemato-biochemistry, digestive capacity, antioxidant index, and histopathological examination of liver and intestine in largemouth bass (Micropterus salmoides). Seven experimental diets were formulated with CAP replacement of 0% (CAP0), 15% (CAP15), 27% (CAP27), 39% (CAP39), 51% (CAP51), 63% (CAP63) and 75% (CAP75) fish meal, respectively. Results showed that replacement of fish meal by CAP did not affect SR, FBW, WGR, SGR and CF. While the fish fed diets containing CAP displayed a higher PER and a lower FCR than the control group (P 0.05). Additionally, The ADC of dry matter and protein were improved by addition of CAP (P 0.05). The lipase and amylase activities were not dramatically altered in stomach (P > 0.05), but were significantly increased in intestine with dietary substitution level up to 39% (P

Toll-like receptor 5 (TLR5) is an important pathogen recognition receptor (PRR) that recognizes the flagellin protein of pathogenic bacteria and plays a fundamental role in activating the innate immune response. In this study, full-length pvTLR5m (membrane) and pvTLR5s (soluble) genes were cloned from darkbarbel catfish Pelteobagrus vachellii, and their expression and that of downstream genes were analyzed following exposure to the Aeromonas hydrophila pathogen. The 3009 bp pvTLR5m cDNA includes a 2652 bp open reading frame (ORF) encoding 884 amino acids. The 2422 bp pvTLR5s cDNA includes a 1944 bp ORF encoding a predicted protein of 648 amino acids. The genes are most closely related to TLR5m (75%) and TLR5s (69%) from Ictalurus punctatus, respectively, and both have a typical TLR structure. Both genes were constitutively expressed in all examined tissues, and most abundantly in the head kidney and spleen. Following pathogen challenge, pvTLR5m and pvTLR5s expression was increased significantly (P0.05) and peaked at 24 and 12 h post-exposure in the liver, 24 and 12 h in the head kidney, and 48 and 24 h in the spleen, respectively. The downstream genes interleukin-1β (IL-1β), IL-12 and tumor necrosis factor-alpha (TNF-α) were significantly up-regulated following pathogen exposure in spleen, and the NF-kB inhibitor (IκB) was down-regulated. These findings indicated that pvTLR5 may play an important role in the immune responses to A. hydrophila. These results provide new insight to elucidate the immune signalling pathways of fish TLR.

The complement components C8α and C8β mediate the formation of the membrane attack complex (MAC) to resist pathogenic bacteria and play important roles in innate immunity. Full-length complement C8α (Pv-C8α) and C8β (Pv-C8β) cDNA were identified in the darkbarbel catfish Pelteobagrus vachellii, and their mRNA expression levels were analyzed after ammonia-N and pathogen treatment. The Pv-C8α gene contained 1983 bp, including a 1794-bp open reading frame (ORF) encoding 598 amino acids. The Pv-C8β gene contained 1952 bp, including a 1761-bp ORF encoding 587 amino acids. Pv-C8α and Pv-C8β had the highest amino acid identity with rainbow trout Oncorhynchus mykiss C8α (62%) and Japanese flounder Paralichthys olivaceus C8β (83%), respectively. Sequence analysis indicated that both Pv-C8α and Pv-C8β contained a thrombospondin type-1 (TSP1) domain, a low-density lipoprotein receptor class A (LDLR-A) domain, a membrane attack complex/perforin (MACPF) domain and an epidermal growth factor-like (EGF-like) domain. In addition, Pv-C8α and Pv-C8β were mainly distributed in the liver, head kidney, spleen, and eggs. Under ammonia-N stress, the Pv-C8α and Pv-C8β mRNA levels significantly decreased (P

As one of the most important enzyme families, the caspase family works effectively in immunization reactions, and many of its members mediate programmed cell death and pathogen immunity through complicated molecular pathways. However, studies on the genes of caspase family is very limited in invertebrates. In this work, we examined their nucleotide sequences, three-dimensional structures, molecular evolution, and potential functions in the world-famous whiteleg shrimp (Litopenaeus vannamei) in a systematic manner. The deduced protein sequences were revealed to have a potential active site (QACRG pentapeptide), which seems to be conserved in most caspases. However, protein conserved domains and three-dimensional structures present notable variances, implying that these caspase proteins may play various roles in invertebrates and vertebrates. Conserved domain prediction and phylogenetic analysis of multiple species suggest that caspase-3 may be an intermediate transitional form of caspase genes during the evolution from invertebrates to vertebrates. The up-regulation of caspase-1, -2, -3 transcripts in the hepatopancreas tissue of whiteleg shrimp after iridescent virus infection implies that these proteins are involved in the immune response to the virus. Our transcriptome data also support in-depth understanding of the molecular evolution, as well as the physiological roles of the caspase family in the whiteleg shrimp when this invertebrate species was infected by exogenous viral pathogens.

Elongation of very long-chain fatty acids 4 (Elovl4) proteins, belong to the fatty acyl elongase families that are involved in long-chain polyunsaturated fatty acids (LC-PUFA) biosynthesis in animals. Thus far, very little is known about the roles of Elovl4 in fish. Previously, we reported an elovl4 gene named as elovl4b in rabbitfish (Siganus canaliculatus). In this study, a novel elovl4-like gene with a 957-bp open reading frame encoding a 318 amino-acid protein, which shared 67.3% similarity with rabbitfish Elovl4b and more than 80% similarity with Elovl4a from other teleost, was identified in S. canaliculatus, and thus was termed as elovl4a. Multiple protein sequences alignment, gene synteny and phylogenetic analysis indicated that two obviously different elovl4 genes are widespread in various teleost. Different with elovl4b (mainly expressed in eye and slightly expressed in brain), rabbitfish elovl4a was primarily distributed in brain, slightly examined in eye and gonad tissues while hardly detectable in other tissues. The transcription of cerebral elovl4a was significantly higher in fishes cultured in seawater (32‰) than that of those maintained at a brackish water environment (15‰), when fishes were fed with a vegetable oil (VO) enriched diet. However, the transcriptional pattern was totally inverse when fishes were fed with a fish oil (FO) enriched diet. In the brackish water, diet types had no effect on the transcription of cerebral elovl4a. Whereas in seawater, the transcription of cerebral elovl4a was significantly higher in fishes fed with the VO diet in comparison with those fed with the FO diet. Our findings suggest that elovl4a can be regulated by both nutritional and osmotic factors, and it may play an important role in endogenous biosynthesis of LC-PUFA in the neural system of rabbitfish. This study may help us to understand the effects of nutritional and osmotic factors on the LC-PUFA biosynthesis, as well as contribute to the optimization or enhancement of LC-PUFA biosynthesis in teleost.