Molecular characterization and expression of three preprosomatostatin genes and their association with growth in common carp (Cyprinus carpio)

Recent advances in neuropeptide-related omics and gene editing: Spotlight on NPY and somatostatin and their roles in growth and food intake of fish

Feeding and growth are two closely related and important physiological processes in living organisms. Studies in mammals have provided us with a series of characterizations of neuropeptides and their receptors as well as their roles in appetite control and growth. The central nervous system, especially the hypothalamus, plays an important role in the regulation of appetite. Based on their role in the regulation of feeding, neuropeptides can be classified as orexigenic peptide and anorexigenic peptide. To date, the regulation mechanism of neuropeptide on feeding and growth has been explored mainly from mammalian models, however, as a lower and diverse vertebrate, little is known in fish regarding the knowledge of regulatory roles of neuropeptides and their receptors. In recent years, the development of omics and gene editing technology has accelerated the speed and depth of research on neuropeptides and their receptors. These powerful techniques and tools allow a more precise and comprehensive perspective to explore the functional mechanisms of neuropeptides. This paper reviews the recent advance of omics and gene editing technologies in neuropeptides and receptors and their progresses in the regulation of feeding and growth of fish. The purpose of this review is to contribute to a comparative understanding of the functional mechanisms of neuropeptides in non-mammalians, especially fish.

Differential expression of somatostatin genes in the central nervous system of the sea lamprey

The identification of three somatostatin (SST) genes (SSTa, SSTb, and SSTc) in lampreys (Tostivint et al. Gen Comp Endocrinol 237:89-97 https://doi.org/10.1016/j.ygcen.2016.08.006 , 2016) prompted us to study their expression in the brain and spinal cord of the sea lamprey by in situ hybridization. These three genes were only expressed in equivalent neuronal populations in the hypothalamus. In other regions, SST transcripts showed clear differential expression. In the telencephalon, SSTc-positive cells were observed in the medial pallium, ventral part of the lateral pallium, striatum, subhippocampal lobe, and preoptic region. In the diencephalon, SSTa-positive cells were observed in the thalamus and SSTc-positive cells in the prethalamus, posterior tubercle, pretectal area, and nucleus of the medial longitudinal fascicle. In the midbrain, SSTc-positive cells were observed in the torus semicircularis, lateral reticular area, and perioculomotor tegmentum. Different SSTa- and SSTc-positive populations were observed in the isthmus. SSTc neurons were also observed in the rostral octavolateralis area and caudal rhombencephalon. In the spinal cord, SSTa was expressed in cerebrospinal-fluid-contacting (CSF-c) neurons and SSTc in non-CSF-c interneurons. Comparison with previous immunohistochemical studies using anti-SST-14 antibodies strongly suggests that SST-14-like neurons correspond with the SSTa populations. Thus, the SSTc populations were not reported previously in immunohistochemical studies. Cluster-based analyses and alignments of mature peptides suggested that SSTa is an ortholog of SST1 and that SSTb is closely related to SST2 and SST6. These results provide important new insights into the evolution of the somatostatinergic system in vertebrates.

Polymorphisms of the growth hormone gene and their association with growth traits and sex in Sarcocheilichthys sinensis

The growth hormone gene (gh) of Sarcocheilichthys sinensis was cloned and characterized in this study. The cDNA length of gh was 973 bp, containing a 5'-UTR of 15 bp, a 3'-UTR of 325 bp and an open reading frame of 633 bp. The genomic DNA of gh was 2135 bp in length containing five exons and four introns. The precursor peptide of gh contained 210 amino acids (aa), including a signal peptide of 22 aa (Met¹-Ala²²) and a mature region of 188 aa (Ser²³-Leu²¹⁰). The similarity and identity ranges of the gh precursor peptide with those of other cyprinids were 88.6%-99.0% and 84.8%-98.6%, respectively. The gh of S. sinensis expressed at the highest level in the pituitary, and its expression was also detected in muscle and brain. Six polymorphic sites were detected in intron 1 (g.51InDel, g.64InDel and g.242InDel), intron 2 (g.864T>C), intron 3 (g.1017InDel) and intron 4 (g.1541A>G). Among these sites, g.242InDel was significantly associated with condition factor, g.1541A>G was associated with all six growth traits, while g.864T>C was associated with sex. The data obtained herein provide useful information for further studies on the regulation mechanisms of growth and sexual growth differences in S. sinensis.

Identification, Expression, and Functions of the Somatostatin Gene Family in Spotted Scat (Scatophagus argus)

Somatostatins (SSTs) are a family of proteins consisting of structurally diverse polypeptides that play important roles in the growth regulation in vertebrates. In the present study, four somatostatin genes (SST1, SST3, SST5, and SST6) were identified and characterized in the spotted scat (Scatophagus argus). The open reading frames (ORFs) of SST1, SST3, SST5, and SST6 cDNA consist of 372, 384, 321, and 333 bp, respectively, and encode proteins of 123, 127, 106, and 110 amino acids, respectively. Amino acid sequence alignments indicated that all SST genes contained conserved somatostatin signature motifs. Real-time PCR analysis showed that the SST genes were expressed in a tissue specific manner. When liver fragments were cultured in vitro with synthetic peptides (SST1, SST2, or SST6 at 1 μM or 10 μM) for 3 h or 6 h, the expression of insulin-like growth factor 1 and 2 (Igf-1 and Igf-2) in the liver decreased significantly. Treatment with SST5 had no significant effect on Igf-1 and Igf-2 gene expression. This study provides an enhanced understanding of the gene structure and expression patterns of the SST gene family in S. argus. Furthermore, this study provides a foundation for future exploration into the role of SST genes in growth and development.

Genome-Wide Association Study of Growth and Body-Shape-Related Traits in Large Yellow Croaker (Larimichthys crocea) Using ddRAD Sequencing

Large yellow croaker (Larimichthys crocea) is an economically important marine fish species of China. Due to overfishing and marine pollution, the wild stocks of this croaker have collapsed in the past decades. Meanwhile, the cultured croaker is facing the difficulties of reduced genetic diversity and low growth rate. To explore the molecular markers related to the growth traits of croaker and providing the related SNPs for the marker-assisted selection, we used double-digest restriction-site associated DNA (ddRAD) sequencing to dissect the genetic bases of growth traits in a cultured population and identify the SNPs that associated with important growth traits by GWAS. A total of 220 individuals were genotyped by ddRAD sequencing. After quality control, 27,227 SNPs were identified in 220 samples and used for GWAS analysis. We identified 13 genome-wide significant associated SNPs of growth traits on 8 chromosomes, and the beta P of these SNPs ranged from 0.01 to 0.86. Through the definition of candidate regions and gene annotation, candidate genes related to growth were identified, including important regulators such as fgf18, fgf1, nr3c1, cyp8b1, fabp2, cyp2r1, ppara, and ccm2l. We also identified SNPs and candidate genes that significantly associated with body shape, including bmp7, col1a1, col11a2, and col18a1, which are also economically important traits for large yellow croaker aquaculture. The results provided insights into the genetic basis of growth and body shape in large yellow croaker population and would provide reliable genetic markers for molecular marker-assisted selection in the future. Meanwhile, the result established a basis for our subsequent fine mapping and related gene study.

Molecular identification, tissue distribution and functional analysis of somatostatin receptors (SSTRs) in red-spotted grouper (Epinephelus akaara)

In the present study, four full-length cDNAs of somatostatin receptor (sstr) were cloned from the forebrain and pituitary of red-spotted grouper. The four full-length cDNAs were designated 2292, 1522, 1873 and 1789 bp and identified as sstr1, sstr2, sstr3, and sstr5 by BLAST analysis; the corresponding sizes of the open reading frames (ORFs) were 1155, 1113, 1467 and 1503 bp, which encoding 384, 370, 488 and 500 aa, respectively. The four receptors have seven transmembrane structures and contain the YANSCANPI/VLY sequence, which is the conserved amino acid sequence of the SSTR family. A tissue distribution study showed that the four sstrs had different expression patterns, suggesting that they may play different roles in regulating different physiological processes. The four receptors mediate ERK1/2 phosphorylation by SS-14 in HEK293 cells, and SS-14 promotes ATK and ERK1/2 phosphorylation in primary hepatocytes of red-spotted grouper. These results facilitate the study of SSTRs-mediated intracellular signaling pathways.

Identification of novel genes significantly affecting growth in catfish through GWAS analysis

Growth is the most important economic trait in aquaculture. Improvements in growth-related traits can enhance production, reduce costs and time to produce market-size fish. Catfish is the major aquaculture species in the United States, accounting for 65% of the US finfish production. However, the genes underlying growth traits in catfish were not well studied. Currently, the majority of the US catfish industry uses hybrid catfish derived from channel catfish female mated with blue catfish male. Interestingly, channel catfish and blue catfish exhibit differences in growth-related traits, and therefore the backcross progenies provide an efficient system for QTL analysis. In this study, we conducted a genome-wide association study for catfish body weight using the 250 K SNP array with 556 backcross progenies generated from backcross of male F1 hybrid (female channel catfish × male blue catfish) with female channel catfish. A genomic region of approximately 1 Mb on linkage group 5 was found to be significantly associated with body weight. In addition, four suggestively associated QTL regions were identified on linkage groups 1, 2, 23 and 24. Most candidate genes in the associated regions are known to be involved in muscle growth and bone development, some of which were reported to be associated with obesity in humans and pigs, suggesting that the functions of these genes may be evolutionarily conserved in controlling growth. Additional fine mapping or functional studies should allow identification of the causal genes for fast growth in catfish, and elucidation of molecular mechanisms of regulation of growth in fish.

Identification of three somatostatin genes in lampreys

Somatostatins (SSs) are a structurally diverse family of neuropeptides that play important roles in the regulation of growth, development and metabolism in vertebrates. It has been recently proposed that the common ancestor of gnathostomes possessed three SS genes, namely SS1, SS2 and SS5. SS1 and SS2 are still present in most extant gnathostome species investigated so far while SS5 primarily occurs in chondrichthyes, actinopterygians and actinistia but not in tetrapods. Very little is known about the repertoire of SSs in cyclostomes, which are extant jawless vertebrates. In the present study, we report the cloning of the cDNAs encoding three distinct lamprey SS variants that we call SSa, SSb and SSc. SSa and SSb correspond to the two SS variants previously characterized in lamprey, while SSc appears to be a totally novel one. SSa exhibits the same sequence as gnathostome SS1. SSb differs from SSa by only one substitution (Thr¹²→Ser). SSc exhibits a totally unique structure (ANCRMFYWKTMAAC) that shares only 50% identity with SSa and SSb. SSa, SSb and SSc precursors do not exhibit any appreciable sequence similarity outside the C-terminal region containing the SS sequence. Phylogenetic analyses failed to clearly assign orthology relationships between lamprey and gnathostome SS genes. Synteny analysis suggests that the SSc gene arose before the split of the three gnathostome genes SS1, SS2 and SS5.

Molecular Characterization and Growth Association of Two Apolipoprotein A-Ib Genes in Common Carp (Cyprinus carpio)

Apolipoprotein A-I (ApoA-I) is functionally involved in the transportation and metabolism of lipids in vertebrates. In this study, two isoforms of apoA-Ib in common carp (Cyprinus carpio L.) were characterized. Sequence comparison and phylogenetic analysis showed that C. carpio ApoA-Ib is relatively conserved within cyprinid fishes. During embryonic development, C. carpioapoA-Ib was first expressed at the stage of multi-cells, and the highest mRNA level was observed at the stage of optic vesicle. A ubiquitous expression pattern was detected in various tissues with extreme predominance in the liver. Significantly different expression levels were observed between light and heavy body weight groups and also in the compensatory growth test. Seventeen and eight single-nucleotide polymorphisms (SNPs) were identified in matured mRNA of the C. carpioapoA-Ib.1 and apoA-Ib.2, respectively. Two of these SNPs (apoA-Ib.2-g.183A>T and apoA-Ib.2-g.1753C>T) were significantly associated with body weight and body length in two populations of common carp. These results indicate that apoA-Ib may play an important role in the modulation of growth and development in common carp.

Cloning, Expression, and Characterization of Capra hircus Golgi α-Mannosidase II

Golgi α-mannosidase II (GMII), a key glycosyl hydrolase in the N-linked glycosylation pathway, has been demonstrated to be closely associated with the genesis and development of cancer. In this study, we cloned cDNA-encoding Capra hircus GMII (chGMII) and expressed it in Pichia pastoris expression system. The chGMII cDNA contains an open reading frame of 3432 bp encoding a polypeptide of 1144 amino acids. The deduced molecular mass and pI of chGMII was 130.5 kDa and 8.04, respectively. The gene expression profile analysis showed GMII was the highest expressed gene in the spleen. The recombinant chGMII showed maximum activity at pH 5.4 and 42 °C and was activated by Fe(2+), Zn(2+), Ca(2+), and Mn(2+) and strongly inhibited by Co(2+), Cu(2+), and EDTA. By homology modeling and molecular docking, we obtained the predicted 3D structure of chGMII and the probable binding modes of chGMII-GnMan5Gn, chGMII-SW. A small cavity containing Tyr355 and zinc ion fixed by residues Asp290, His176, Asp178, and His570 was identified as the active center of chGMII. These results not only provide a clue for clarifying the catalytic mechanism of chGMII but also lay a theoretical foundation for subsequent investigations in the field of anticancer therapy for mammals.