Molecular cloning of two kcnk3 genes from the Northern snakehead (Channa argus) for quantification of their transcriptions in response to fasting and refeeding

Characterization of three lamp genes from largemouth bass (Micropterus salmoides): molecular cloning, expression patterns, and their transcriptional levels in response to fast and refeeding strategy

Lysosomes-associated membrane proteins (LAMPs), a family of glycosylated proteins and major constituents of the lysosomal membranes, play a dominant role in various cellular processes, including phagocytosis, autophagy and immunity in mammals. However, their roles in aquatic species remain poorly known. In the present study, three lamp genes were cloned and characterized from Micropterus salmoides. Subsequently, their transcriptional levels in response to different nutritional status were investigated. The full-length coding sequences of lamp1, lamp2 and lamp3 were 1251bp, 1224bp and 771bp, encoding 416, 407 and 256 amino acids, respectively. Multiple sequence alignment showed that LAMP1-3 were highly conserved among the different fish species, respectively. 3-D structure prediction, genomic survey, and phylogenetic analysis were further confirmed that these genes are widely existed in vertebrates. The mRNA expression of the three genes was ubiquitously expressed in all selected tissues, including liver, brain, gill, heart, muscle, spleen, kidney, stomach, adipose and intestine, lamp1 shows highly transcript levels in brain and muscle, lamp2 displays highly expression level in heart, muscle and spleen, but lamp3 shows highly transcript level in spleen, liver and kidney. To analyze the function of the three genes under starvation stress in largemouth bass, three experimental treatment groups (fasted group and refeeding group, control group) were established in the current study. The results indicated that the expression of lamp1 was significant induced after starvation, and then returned to normal levels after refeeding in the liver. The expression of lamp2 and lamp3 exhibited the same trend in the liver. In addition, in the spleen and the kidney, the transcript level of lamp1 and lamp2 was remarkably increased in the fasted treatment group and slightly decreased in the refed treatment group, respectively. Collectively, our findings suggest that three lamp genes may have differential function in the immune and energetic organism in largemouth bass, which is helpful in understanding roles of lamps in aquatic species.

MRAP2 Interaction with Melanocortin-4 Receptor in SnakeHead (Channa argus)

The melanocortin-4 receptor (MC4R) plays an important role in the regulation of food intake and energy expenditure. Melanocortin-2 receptor accessory protein 2 (MRAP2) modulates trafficking, ligand binding, and signaling of MC4R. The Northern snakehead (Channa argus) is an economically important freshwater fish native to East Asia. To explore potential interaction between snakehead MC4R and MRAP2, herein we cloned snakehead mc4r and mrap2. The snakehead mc4r consisted of a 984 bp open reading frame encoding a protein of 327 amino acids, while snakehead mrap2 contained a 693 bp open reading frame encoding a protein of 230 amino acids. Synteny analysis indicated that mc4r was highly conserved with similar gene arrangement, while mrap2 contained two isoforms in teleost with different gene orders. Snakehead mc4r was primarily expressed in the brain, whereas mrap2 was expressed in the brain and intestine. Snakehead mc4r and mrap2 expression was modulated by fasting and refeeding. Further pharmacological experiments showed that the cloned snakehead MC4R was functional, capable of binding to peptide agonists and increasing intracellular cAMP production in a dose-dependent manner. Snakehead MC4R exhibited high constitutive activity. MRAP2 significantly decreased basal and agonist-stimulated cAMP signaling. These findings suggest that snakehead MC4R might be involved in energy balance regulation by interacting with MRAP2. Further studies are needed to elucidate MC4R in regulating diverse physiological processes in snakehead.

Characterization of two kcnk3 genes in rabbitfish (Siganus canaliculatus): Molecular cloning, distribution patterns and their potential roles in fatty acids metabolism and osmoregulation

KCNK3 is a two-pore-domain (K_2P) potassium channel involved in maintaining ion homeostasis, mediating thermogenesis, controlling breath and modulating electrical membrane potential. Although the functions of this channel have been widely described in mammals, its roles in fishes are still rarely known. Here, we identified two kcnk3 genes from the euryhaline rabbitfish (Siganus canaliculatus), and their roles related to fatty acids metabolism and osmoregulation were investigated. The open reading frames of kcnk3a and kcnk3b were 1203 and 1176 bp in length, encoding 400 and 391 amino acids respectively. Multiple sequences alignment and phylogenetic analysis revealed that the two isotypes of kcnk3 were extensively presented in fishes. Quantitative real-time PCRs indicated that both genes were widely distributed in examined tissues but showed different patterns. kcnk3a primary distributed in adipose, eye, heart, and spleen tissues, while kcnk3b was mainly detectable in heart, kidney, muscle and spleen tissues. In vivo experiments showed that fish fed diets with fish oil as dietary lipid (rich in long chain polyunsaturated fatty acids, LC-PUFA) induced higher mRNA expression levels of kcnk3 genes in comparison with fish fed with plant oil diet at two different salinity environments (32 and 15‰). Meanwhile, the expression levels of kcnk3 genes were higher in seawater (32‰) than that in brackish water (15‰) when fishes were fed with both types of feeds. In vitro experiments with rabbitfish hepatocytes showed that LC-PUFA significantly improved hepatic kcnk3a expression level compared with treatment of linolenic acid. These results suggest that two kcnk3 genes are widely existed and they might be functionally related to fatty acids metabolism and osmoregulation in the rabbitfish.

Molecular characterization of two leptin genes and their transcriptional changes in response to fasting and refeeding in Northern snakehead (Channa argus)

Leptin has been proved to play critical roles in energy metabolism, body weight regulation, food intake, reproduction and immunity in mammals. However, its roles are still largely unclear in fish. Here, we report two leptin genes (lepA and lepB) from the Northern snakehead (Channa argus) and their transcriptions in response to different feeding status. The snakehead lepA is 781 bp in length and contains a 480 bp open reading frame (ORF) encoding a 159-aa protein, while the snakehead lepB is 553 bp in length and contains a 477 bp ORF encoding a 158-aa protein. Multi-sequences alignment, three-dimensional (3D) model prediction, syntenic and genomic comparison, and phylogenetic analysis confirm two leptin genes are widely existing in teleost. Tissue distribution revealed that the two leptin genes exhibit different patterns. In a post-prandial experiment, the hepatic lepA and brain lepB showed a similar transcription pattern. In a long-term (2-week) fasting and refeeding experiment, the hepatic lepA and brain lepB showed a similar transcription change pattern induced by food deprivation stimulation but differential changes after refeeding. These findings suggest snakehead lepA and lepB are differential both in tissue distribution and molecular functions, and they might play as an important regulator in energy metabolism and food intake in fish, respectively.

Characterization of two kcnk3 genes in Nile tilapia (Oreochromis niloticus): Molecular cloning, tissue distribution, and transcriptional changes in various salinity of seawater

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.