Identification of Insulin-like Growth Factor (IGF) Family Genes in the Golden Pompano, Trachinotus ovatus: Molecular Cloning, Characterization and Gene Expression.

Insulin-like growth factors (IGFs) are hormones that primarily stimulate and regulate animal physiological processes. In this study, we cloned and identified the open reading frame (ORF) cDNA sequences of IGF family genes: the insulin-like growth factor 1 (IGF1), insulin-like growth factor 2 (IGF2), and insulin-like growth factor 3 (IGF3). We found that IGF1, IGF2, and IGF3 have a total length of 558, 648, and 585 base pairs (bp), which encoded a predicted protein with 185, 215, and 194 amino acids (aa), respectively. Multiple sequences and phylogenetic tree analysis showed that the mature golden pompano IGFs had been conserved and showed high similarities with other teleosts. The tissue distribution experiment showed that IGF1 and IGF2 mRNA levels were highly expressed in the liver of female and male fish. In contrast, IGF3 was highly expressed in the gonads and livers of male and female fish, suggesting a high influence on fish reproduction. The effect of fasting showed that IGF1 and mRNA expression had no significant difference in the liver but significantly decreased after long-term (7 days) fasting in the muscles and started to recover after refeeding. IGF2 mRNA expression showed no significant difference in the liver but had a significant difference in muscles for short-term (2 days) and long-term fasting, which started to recover after refeeding, suggesting muscles are more susceptible to both short-term and long-term fasting. In vitro incubation of 17ß-estradiol (E2) was observed to decrease the IGF1 and IGF3 mRNA expression level in a dose- (0.1, 1, and 10 µM) and time- (3, 6, and 12 h) dependent manner. In addition, E2 had no effect on IGF2 mRNA expression levels in a time- and dose-dependent manner. The effect of 17α-methyltestosterone (MT) in vitro incubation was observed to significantly increase the IGF3 mRNA expression level in a time- and dose-dependent manner. MT had no effect on IGF2 mRNA but was observed to decrease the IGF1 mRNA expression in the liver. Taken together, these data indicate that E2 and MT may either increase or decrease IGF expression in fish; this study provides basic knowledge and understanding of the expression and regulation of IGF family genes in relation to the nutritional status, somatic growth, and reproductive endocrinology of golden pompano for aquaculture development.

Phenotypic sorting of individual male and female intersex Cherax quadricarinatus and analysis of molecular differences in the gonadal transcriptome.

Cherax quadricarinatus exhibit sexual dimorphism, with males outpacing females in size specification and growth rate. However, there is limited understanding of the molecular mechanisms underlying sex determination and sex differentiation in crustaceans. To study the differences between intersex individuals and normal individuals, this study counted the proportion of intersex individuals in the natural population, collected the proportion of 7 different phenotypes in 200 intersex individuals, and observed the differences in tissue sections. RNA-seq was used to study the different changes in the transcriptome of normal and intersex gonads. The results showed that: the percentage of intersex in the natural population was 1.5 %, and the percentage of different types of intersex ranged from 0.5 % to 22.5 %; the sections revealed that the development of normal ovaries was stagnant at the primary oocyte stage when intersex individuals with ovaries were present; We screened for pathways and genes that may be associated with gonadal development and sex, including ovarian steroid synthesis, estrogen signaling pathway, oocyte meiosis, progesterone-mediated oocyte maturation, etc. Relevant genes including tra2a, dmrta2, ccnb2, foxl2, and smad4. This study provides an important molecular basis for sex determination, sex-controlled breeding, and unisex breeding in red crayfish.

Molecular cloning of estrogen receptor and its function on vitellogenesis in pompano (Trachinotus ovatus).

Estrogen receptors (ERs) play a critical role in vitellogenesis (Vtgs). However, the contribution of each ER for the regulation of vtgs expression was not analyzed clearly in teleosts. In the present study, three ers isoforms (erα, erß1, and erß2) were cloned in pompano (Trachinotus ovatus). Real-time PCR and enzyme-linked immunosorbent assay (ELISA) was used to detect the effects of 17ß-estradiol (E2) on ERs and Vtgs in the liver of pompano. In vivo injection experiments showed that E2 significantly increased the expressions of ers and vtgs. ER broad spectrum antagonist Fulvestrant significantly attenuated the E2- induced up-regulation of ers and vtgs in a dose-dependent manner. ERα antagonist Methyl-piperidino pyrazole (MPP) significantly attenuated the up-regulation of erα, erß2, vtg-B and vtg-C, and promoted the expressions of erß1 and vtg-A. ERß antagonist Cyclofenil significantly inhibited the expressions of erß1, erß2, vtg-A and vtg-C, and promoted the expressions of erα and vtg-B. In addition, E2 significantly increased the protein level of Vtg, while Fulvestrant, MPP and Cyclofenil significantly inhibited the protein level of Vtg in a dose-dependent manner. Our results indicate that E2 may regulate the expression of each vtg with different subtypes of ERs, and shows a distinct compensatory expression effect on the regulation for ers and vtgs, which provides a theoretical basis for reproductive endocrinology study in pompano.

Comparative Transcriptome Analysis Reveals the Effect of Aurantiochytrium sp. on Gonadal Development in Zebrafish.

Aurantiochytrium sp. has received much attention as a potential resource for mass production of omega-3 fatty acids, which contribute to improved growth and reproduction in aquatic animals. In this study, we evaluated the gonadal index changes in zebrafish supplemented with 1-3% Aurantiochytrium sp. crude extract (TE) and the effects of ex vivo environmental Aurantiochytrium sp. on oocytes. 1% TE group showed significant improvement in the gonadal index, and both in vitro incubation and intraperitoneal injection promoted the maturation of zebrafish oocytes. In contrast, the transcriptome revealed 576 genes that were differentially expressed between the 1% TE group and the control group, including 456 up-regulated genes and 120 down-regulated genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) pathway analysis of differentially expressed genes indicated that Aurantiochytrium sp. potentially affects pathways such as lipid metabolism, immune regulation, and oocyte development in zebrafish. The results of this study enriched the knowledge of Aurantiochytrium sp. in regulating gonadal development in zebrafish and provided a theoretical basis for its application in aquaculture.

Analysis of circRNA and miRNA expression profiles in IGF3-induced ovarian maturation in spotted scat (Scatophagus argus).

Insulin-like growth factor 3 (IGF3) induces ovarian maturation in teleosts; however, research on its molecular regulatory mechanism remains deficient. Circular RNAs (circRNAs) and microRNAs (miRNAs) are involved in various biological processes, including reproduction. In this study, circRNAs and miRNAs involved in IGF3-induced ovarian maturation were evaluated in spotted scat (Scatophagus argus). In ovarian tissues, we identified 176 differentially expressed (DE) circRNAs and 52 DE miRNAs between IGF3 treatment and control groups. Gene Ontology (GO) enrichment analyses showed that host genes of DE circRNAs and target genes of DE miRNAs were enriched for various processes with a high degree of overlap, including cellular process, reproduction, reproductive process, biological adhesion, growth, extracellular region, cell junction, catalytic activity, and transcription factor activity. Enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways included cell adhesion molecules, ECM-receptor interaction, regulation of actin cytoskeleton, focal adhesion, cell cycle, Hedgehog signaling pathway, phosphatidylinositol signaling system, PI3K-Akt signaling pathway, Apelin signaling pathway, Notch signaling pathway, insulin signaling pathway, and Rap1 signaling pathway. A circRNA-miRNA-mRNA regulatory network was constructed, including DE genes involved in reproduction (e.g., oocyte maturation, oocyte meiosis, and ECM remodeling), such as ccnd2, hecw2, dnm2, irs1, adam12, and cdh13. According to the regulatory network and tissue distribution, we identified one circRNA (Lachesis_group5:6245955|6270787) and three miRNAs (novel_miR_622, novel_miR_980, and novel_miR_64) that may exert regulatory effects in IGF3-induced ovarian maturation in S. argus. Taken together, this study provides a novel insight into the molecular mechanisms by which IGF3 functions in ovaries and highlights the effects of circRNAs and miRNAs in reproduction in S. argus.

Effects of Dietary Supplementation with Aurantiochytrium sp. on Zebrafish Growth as Determined by Transcriptomics.

The marine protist Aurantiochytrium produces several bioactive chemicals, including EPA (eicosapentaenoic acid), DHA (docosahexaenoic acid), and other critical fish fatty acids. It has the potential to improve growth and fatty acid profiles in aquatic taxa. This study evaluated zebrafish growth performance in response to diets containing 1% to 3% Aurantiochytrium sp. crude extract (TE) and single extract for 56 days. Growth performance was best in the 1% TE group, and therefore, this concentration was used for further analyses of the influence of Aurantiochytrium sp. Levels of hepatic lipase, glucose-6-phosphate dehydrogenase, acetyl-CoA oxidase, glutathione peroxidase, and superoxide dismutase increased significantly in response to 1% TE, while malic enzyme activity, carnitine lipid acylase, acetyl-CoA carboxylase, fatty acid synthase, and malondialdehyde levels decreased. These findings suggest that Aurantiochytrium sp. extract can modulate lipase activity, improve lipid synthesis, and decrease oxidative damage caused by lipid peroxidation. Transcriptome analysis revealed 310 genes that were differentially expressed between the 1% TE group and the control group, including 185 up-regulated genes and 125 down-regulated genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) pathway analyses of the differentially expressed genes revealed that Aurantiochytrium sp. extracts may influence liver metabolism, cell proliferation, motility, and signal transduction in zebrafish.

Physiological Effects and Transcriptomic Analysis of sbGnRH on the Liver in Pompano (Trachinotus ovatus).

Pompano (Trachinotus ovatus) is one of the important economic marine fishes in the south coast of China. At present, the research on the basic biology of pompano is relatively weak, which has seriously affected the development of this economic important fish. The liver is an important digestive and metabolic organ of fish which plays an important regulatory role in its growth and development. It is necessary to clarify the effects of sea bream gonadotropin releasing hormone (sbGnRH) on liver physiology and metabolic enzyme activity. The effects of sbGnRH peptides (10 ng/gbw) on the physiological and biochemical indices and metabolic enzyme activities of pompano liver were studied. It was found that after injection of 10 ng/gbw sbGnRH peptides, the contents of albumin, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, glucose, creatine kinase, iron, magnesium, aspartate aminotransferase, alanine aminotransferase and creatinine increased, while of cholesterol and calcium contents decreased. The activities of amylase, lipase, pyruvate kinase, acyl CoA oxidase, superoxide dismutase, phospholipid hydroperoxide glutathione peroxidase, catalase, glucose-6-phosphate dehydrogenase, fatty acid synthase and lipoprotein lipase increased, while the activities of malic enzyme, carnitine acyl, carnitine translocation, acetyl CoA carboxylase and malondialdehyde decreased. Three hours after the injection of different concentrations of sbGnRH peptides (0 and 10 ng/gbw), the transcriptome sequences of the two groups of livers were sequenced. After quality control and removal of some low-quality data, clean reads of 21,283,647、19,427,359、21,873,990、21,732,174、23,660,062 and 21,592,338 were obtained respectively. In this study, 99 genes were screened and identified as differentially expressed genes, including 77 up-regulated genes and 22 down-regulated genes. According to the Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) pathway analyses, these pathways and the typical genes involved can be divided into cellular processes, environmental information processing, genetic information processing, diseases, metabolism and organismal systems. The results from this study provide a the oretical basis for studying the effects of sbGnRH on the physiology, biochemistry and metabolic enzyme activities of liver in pompano.

Effects of probiotics on digestive enzymes of fish (finfish and shellfish); status and prospects: a mini review.

Digestive enzymes are found in the digestive tract of animals which assist in the breakdown of larger food molecules into more easily absorbed particles that can then be used by the body. The ability of fish to break down a diet is highly dependent on the availability of suitable digestive enzymes which mediate specific degradation pathways and on both the physical and chemical nature of food. Probiotics are known to produce helpful enzymes that aid in digestion and protect the gastrointestinal tract (GIT) of animals. When applied appropriately, probiotics improve intestinal microbial balance which also improves digestive enzyme activities, food absorption, and decrease pathogenic issues in the GIT. They work hand-in-hand with the digestive enzymes in the GIT of animals as supplements thereby improvings nutrition. This in turn leads to higher feed efficiency and growth as well as the prevention of antinutritional factors present in the ingredients, intestinal disorders, and pre-digestion. This review seeks to present summaries of the results of research findings on the application of probiotics on the activities of digestive enzymes including amylase, lipase, and protease. Further, this review points out gaps in available literature and suggests ideas that could be explored in further investigations to better understand and enhance the activities of these digestive enzymes to increase feed and nutrient utilization and the production of aquaculture species.

Identification and functional characterization of gonadotropin -releasing hormone in pompano (Trachinotus ovatus).

Gonadotropin-releasing hormone (GnRH) is an important neuropeptide in the reproductive system. Although GnRH analogues have been used to artificially spawn pompano (Trachinotus sp.), the native forms of GnRH have not been described in this species. In this study three GnRH subtypes [sea bream GnRH (sbGnRH), chicken GnRH-Ⅱ (cGnRH-Ⅱ) and salmon GnRH (sGnRH)] were identified in pompano (Trachinotus ovatus). cgnrh-Ⅱ and sgnrh were mainly expressed in the brain of male and female fish, showing a tissue-specific expression pattern, while sbgnrh was expressed at different transcriptional levels in all tested tissues. In vivo injection experiment showed that sbGnRH significantly increased fsh and lh genes expression in a dose-dependent manner, but a high concentration of sbGnRH could desensitize the expression of lh. High concentrations of cGnRH-Ⅱ and sGnRH could induce the expression of fsh and lh. In addition, the results of in vitro incubation experiments showed that the high concentration of sbGnRH peptide could induce the expression of fsh and lh, while cGnRH-Ⅱ and sGnRH peptides could only induce the expression of fsh. 17ß-estradiol (E2) and 17α-methyltestosterone (MT) significantly inhibited sbgnrh mRNA expression in a dose-dependent manner, but did not affect the expression of cgnrh-Ⅱ and sgnrh mRNA. sbGnRH is the main GnRH subtype in pompano. E2 and MT can play a negative role in the regulation of sbgnrh. This study provides a theoretical basis for the reproductive endocrinology of pompano.

De Novo Transcriptomic Characterization Enables Novel Microsatellite Identification and Marker Development in Betta splendens.

The wild populations of the commercially valuable ornamental fish species, Betta splendens, and its germplasm resources have long been threatened by habitat degradation and contamination with artificially bred fish. Because of the lack of effective marker resources, population genetics research projects are severely hampered. To generate genetic data for developing polymorphic simple sequence repeat (SSR) markers and identifying functional genes, transcriptomic analysis was performed. Illumina paired-end sequencing yielded 105,505,486 clean reads, which were then de novo assembled into 69,836 unigenes. Of these, 35,751 were annotated in the non-redundant, EuKaryotic Orthologous Group, Swiss-Prot, Kyoto Encyclopedia of Genes and Genomes and Gene Ontology databases. A total of 12,751 SSR loci were identified from the transcripts and 7970 primer pairs were designed. One hundred primer pairs were randomly selected for PCR validation and 53 successfully generated target amplification products. Further validation demonstrated that 36% (n = 19) of the 53 amplified loci were polymorphic. These data could not only enrich the genetic information for the identification of functional genes but also effectively facilitate the development of SSR markers. Such knowledge would accelerate further studies on the genetic variation and evolution, comparative genomics, linkage mapping and molecular breeding in B. splendens.

Comparative Physiological and Transcriptomic Profiling Offers Insight into the Sexual Dimorphism of Hepatic Metabolism in Size-Dimorphic Spotted Scat (Scatophagus argus).

The spotted scat (Scatophagus argus) is an economically important cultured marine fish that exhibits a typical sexual size dimorphism (SSD). SSD has captivated considerable curiosity for farmed fish production; however, up till now the exact underlying mechanism remains largely unclear. As an important digestive and metabolic organ, the liver plays key roles in the regulation of fish growth. It is necessary to elucidate its significance as a downstream component of the hypothalamic-pituitary-liver axis in the formation of SSD. In this study, the liver physiological differences between the sexes were evaluated in S. argus, and the activity of several digestive and metabolic enzymes were affected by sex. Females had higher amylase, protease, and glucose-6-phosphate dehydrogenase activities, while males exhibited markedly higher hepatic lipase and antioxidant enzymes activities. A comparative transcriptomics was then performed to characterize the responsive genes. Illumina sequencing generated 272.6 million clean reads, which were assembled into 79,115 unigenes. A total of 259 differentially expressed genes were identified and a few growth-controlling genes such as igf1 and igfbp1 exhibited female-biased expression. Further analyses showed that several GO terms and pathways associated with metabolic process, particularly lipid and energy metabolisms, were significantly enriched. The male liver showed a more active mitochondrial energy metabolism, implicating an increased energy expenditure associated with reproduction. Collectively, the female-biased growth dimorphism of S. argus may be partially attributed to sexually dimorphic metabolism in the liver. These findings would facilitate further understanding of the nature of SSD in teleost fish.

The Roles of Neuropeptide Y (Npy) and Peptide YY (Pyy) in Teleost Food Intake: A Mini Review.

Neuropeptide Y family (NPY) is a potent orexigenic peptide and pancreatic polypeptide family comprising neuropeptide Y (Npy), peptide YYa (Pyya), and peptide YYb (Pyyb), which was previously known as peptide Y (PY), and tetrapod pancreatic polypeptide (PP), but has not been exhaustively documented in fish. Nonetheless, Npy and Pyy to date have been the key focus of countless research studies categorizing their copious characteristics in the body, which, among other things, include the mechanism of feeding behavior, cortical neural activity, heart activity, and the regulation of emotions in teleost. In this review, we focused on the role of neuropeptide Y gene (Npy) and peptide YY gene (Pyy) in teleost food intake. Feeding is essential in fish to ensure growth and perpetuation, being indispensable in the aquaculture settings where growth is prioritized. Therefore, a better understanding of the roles of these genes in food intake in teleost could help determine their feeding regime, regulation, growth, and development, which will possibly be fundamental in fish culture.

A Chromosome-Level Genome Assembly of the Spotted Scat (Scatophagus argus).

The spotted scat, Scatophagus argus is a member of the family Scatophagidae found in Indo-Pacific coastal waters. It is an emerging commercial aquaculture species, particularly in East and Southeast Asia. In this study, the first chromosome-level genome of S. argus was constructed using PacBio and Hi-C sequencing technologies. The genome is 572.42 Mb, with a scaffold N50 of 24.67 Mb. Using Hi-C data, 563.28 Mb (98.67% of the genome) sequences were anchored and oriented in 24 chromosomes, ranging from 12.57 Mb to 30.38 Mb. The assembly is of high integrity, containing 94.26% conserved single-copy orthologues, based on BUSCO analysis. A total of 24,256 protein-coding genes were predicted in the genome, and 96.30% of the predicted genes were functionally annotated. Evolutionary analysis showed that S. argus diverged from the common ancestor of Japanese puffer (Takifugu rubripes) approximately 114.8 Ma. The chromosomes of S. argus showed significant correlation to T. rubripes chromosomes. A comparative genomic analysis identified 49 unique and 90 expanded gene families. These genomic resources provide a solid foundation for functional genomics studies to decipher the economic traits of this species.

Comparison of Gonadal Transcriptomes Uncovers Reproduction-Related Genes with Sexually Dimorphic Expression Patterns in Diodon hystrix.

Diodon hystrix is a new and emerging aquaculture species in south China. However, due to the lack of understanding of reproductive regulation, the management of breeding and reproduction under captivity remains a barrier for the commercial aquaculture of D. hystrix. More genetic information is needed to identify genes critical for gonadal development. Here, the first gonadal transcriptomes of D. hystrix were analyzed and 151.89 million clean reads were generated. All reads were assembled into 57,077 unigenes, and 24,574 could be annotated. By comparing the gonad transcriptomes, 11,487 differentially expressed genes were obtained, of which 4599 were upregulated and 6888 were downregulated in the ovaries. Using enrichment analyses, many functional pathways were found to be associated with reproduction regulation. A set of sex-biased genes putatively involved in gonad development and gametogenesis were identified and their sexually dimorphic expression patterns were characterized. The detailed transcriptomic data provide a useful resource for further research on D. hystrix reproductive manipulation.

Chromosomal-Level Genome Assembly of Silver Sillago (Sillago sihama).

Silver sillago, Sillago sihama is a member of the family Sillaginidae and found in all Chinese inshore waters. It is an emerging commercial marine aquaculture species in China. In this study, high-quality chromosome-level reference genome of S. sihama was first constructed using PacBio Sequel sequencing and high-throughput chromosome conformation capture (Hi-C) technique. A total of 66.16 Gb clean reads were generated by PacBio sequencing platforms. The genome-scale was 521.63 Mb with 556 contigs, and 13.54 Mb of contig N50 length. Additionally, Hi-C scaffolding of the genome resulted in 24 chromosomes containing 96.93% of the total assembled sequences. A total of 23,959 protein-coding genes were predicted in the genome, and 96.51% of the genes were functionally annotated in public databases. A total of 71.86 Mb repetitive elements were detected, accounting for 13.78% of the genome. The phylogenetic relationships of silver sillago with other teleosts showed that silver sillago was separated from the common ancestor of Sillago sinica ∼7.92 Ma. Comparative genomic analysis of silver sillago with other teleosts showed that 45 unique and 100 expansion gene families were identified in silver sillago. In this study, the genomic resources provide valuable reference genomes for functional genomics research of silver sillago.

Fish Feed Intake, Feeding Behavior, and the Physiological Response of Apelin to Fasting and Refeeding.

Feed is one of the most important external signals in fish that stimulates its feeding behavior and growth. The intake of feed is the main factor determining efficiency and cost, maximizing production efficiency in a fish farming firm. The physiological mechanism regulating food intake lies between an intricate connection linking central and peripheral signals that are unified in the hypothalamus consequently responding to the release of appetite-regulating genes that eventually induce or hinder appetite, such as apelin; a recently discovered peptide produced by several tissues with diverse physiological actions mediated by its receptor, such as feed regulation. Extrinsic factors have a great influence on food intake and feeding behavior in fish. Under these factors, feeding in fish is decontrolled and the appetite indicators in the brain do not function appropriately thus, in controlling conditions which result in the fluctuations in the expression of these appetite-relating genes, which in turn decrease food consumption. Here, we examine the research advancements in fish feeding behavior regarding dietary selection and preference and identify some key external influences on feed intake and feeding behavior. Also, we present summaries of the results of research findings on apelin as an appetite-regulating hormone in fish. We also identified gaps in knowledge and directions for future research to fully ascertain the functional importance of apelin in fish.

Transcriptome analysis of liver provides insight into metabolic and translation changes under hypoxia and reoxygenation stress in silver sillago (Sillago sihama).

Hypoxia can lead to adverse effects on growth, reproduction, behavioral activities and survival in fish, and is one of the most critical factors in the aquatic environment. The liver is an important target organ for reducing toxin accumulation and hypoxia in fish. In this study, silver sillago (Sillago sihama) was exposed to normoxia (dissolved oxygen, DO = 8.0 mg/L), hypoxia for 1 h (hypoxia 1 h, DO = 1.5 mg/L), hypoxia for 4 h (hypoxia 4 h, DO = 1.5 mg/L) and reoxygenation for 4 h after hypoxia 4 h (reoxygenation 4 h, DO = 8.0 mg/L). Results showed that the expression of 506, 1721, and 1230 differentially expressed genes (DEGs) (|log2(fold change) > 1.0| and padj < 0.05) were identified at hypoxia 1 h, hypoxia 4 h, and reoxygenation 4 h in the liver, respectively. The enrichment analysis showed that the DEGs were significantly enriched in metabolic and translation changes pathways, including mapk signaling pathway, p53 signaling pathway, fatty acid metabolism, protein export, ribosome biogenesis in eukaryotes. The DEGs of 17 genes validated the RNA-seq results by quantitative real-time PCR (qRT-PCR). This study provides a comprehensive understanding of the transcriptional changes that occur in different hypoxia and insights into the mechanisms of hypoxia adaptation of the liver in S. sihama.

Identification, functional characterization, and estrogen regulation on gonadotropin-releasing hormone in the spotted scat, Scatophagus argus.

Gonadotropin-releasing hormone (GnRH) is a key neuropeptide of the reproductive system. However, little is known about the role of GnRH in the spotted scat (Scatophagus argus). Here, three GnRH subtypes (cGnRH-II, sGnRH, and sbGnRH) were identified in the spotted scat. cGnRH-II and sGnRH were only expressed in the brains and gonads of both male and female fish, exhibiting a tissue-specific expression pattern, while sbGnRH was expressed at different transcription levels in all examined tissues. During ovarian maturation, hypothalamus-associated sbGnRH was upregulated, while the expression of sGnRH was variable and cGnRH-II first increased and then decreased. In vivo experiments showed that sbGnRH significantly promoted the expression of fsh and lh genes in a dose-dependent manner and exhibited a desensitization effect on lh expression at high concentrations. For sGnRH and cGnRH-II, only high concentrations could induce fsh and lh expression. Furthermore, treatment with highly concentrated sbGnRH peptide also induced fsh and lh expression, whereas the sGnRH and cGnRH-II peptides only induced fsh expression in vitro. 17ß-Estradiol (E2) significantly inhibited the expression of sbGnRH mRNA in a dose-dependent manner and did not impact sGnRH and cGnRH-II mRNA levels in vivo or in vitro. The inhibitory effect of E2 on sbGnRH expression was attenuated by the estrogen receptor (ER) broad-spectrum antagonist (fulvestrant) and the ERα-specific antagonist (methyl-piperidinopyrazole), respectively, implying that the feedback regulation on sbGnRH is mediated via ERα. This study provides a theoretical basis for the reproductive endocrinology of the spotted scat by studying GnRH.

Comparative Transcriptomic Analysis Uncovers Genes Responsible for the DHA Enhancement in the Mutant Aurantiochytrium sp.

Docosahexaenoic acid (DHA), a n-3 long-chain polyunsaturated fatty acid, is critical for physiological activities of the human body. Marine eukaryote Aurantiochytrium sp. is considered a promising source for DHA production. Mutational studies have shown that ultraviolet (UV) irradiation (50 W, 30 s) could be utilized as a breeding strategy for obtaining high-yield DHA-producing Aurantiochytrium sp. After UV irradiation (50 W, 30 s), the mutant strain X2 which shows enhanced lipid (1.79-fold, 1417.37 mg/L) and DHA (1.90-fold, 624.93 mg/L) production, was selected from the wild Aurantiochytrium sp. Instead of eicosapentaenoic acid (EPA), 9.07% of docosapentaenoic acid (DPA) was observed in the mutant strain X2. The comparative transcriptomic analysis showed that in both wild type and mutant strain, the fatty acid synthesis (FAS) pathway was incomplete with key desaturases, but genes related to the polyketide synthase (PKS) pathway were observed. Results presented that mRNA expression levels of CoAT, AT, ER, DH, and MT down-regulated in wild type but up-regulated in mutant strain X2, corresponding to the increased intercellular DHA accumulation. These findings indicated that CoAT, AT, ER, DH, and MT can be exploited for high DHA yields in Aurantiochytrium.

ddRADseq-assisted construction of a high-density SNP genetic map and QTL fine mapping for growth-related traits in the spotted scat (Scatophagus argus).

BACKGROUND: Scatophagus argus is a popular farmed fish in several countries of Southeast Asia, including China. Although S. argus has a highly promising economic value, a significant lag of breeding research severely obstructs the sustainable development of aquaculture industry. As one of the most important economic traits, growth traits are controlled by multiple gene loci called quantitative trait loci (QTLs). It is urgently needed to launch a marker assisted selection (MAS) breeding program to improve growth and other pivotal traits. Thus a high-density genetic linkage map is necessary for the fine mapping of QTLs associated with target traits. RESULTS: Using restriction site-associated DNA sequencing, 6196 single nucleotide polymorphism (SNP) markers were developed from a full-sib mapping population for genetic map construction. A total of 6193 SNPs were grouped into 24 linkage groups (LGs), and the total length reached 2191.65 cM with an average marker interval of 0.35 cM. Comparative genome mapping revealed 23 one-to-one and 1 one-to-two syntenic relationships between S. argus LGs and Larimichthys crocea chromosomes. Based on the high-quality linkage map, a total of 44 QTLs associated with growth-related traits were identified on 11 LGs. Of which, 19 significant QTLs for body weight were detected on 9 LGs, explaining 8.8-19.6% of phenotypic variances. Within genomic regions flanking the SNP markers in QTL intervals, we predicted 15 candidate genes showing potential relationships with growth, such as Hbp1, Vgll4 and Pim3, which merit further functional exploration. CONCLUSIONS: The first SNP genetic map with a fine resolution of 0.35 cM for S. argus has been developed, which shows a high level of syntenic relationship with L. crocea genomes. This map can provide valuable information for future genetic, genomic and evolutionary studies. The QTLs and SNP markers significantly associated with growth-related traits will act as useful tools in gene mapping, map-based cloning and MAS breeding to speed up the genetic improvement in important traits of S. argus. The interesting candidate genes are promising for further investigations and have the potential to provide deeper insights into growth regulation in the future.