Explore the vast range of titles available.

Variation in the TGF-β signaling pathway is emerging as an important mechanism by which gonadal sex determination is controlled in teleosts. Here we show that amhy, a Y-specific duplicate of the anti-Müllerian hormone (amh) gene, induces male sex determination in Nile tilapia. amhy is a tandem duplicate located immediately downstream of amhΔ-y on the Y chromosome. The coding sequence of amhy was identical to the X-linked amh (amh) except a missense SNP (C/T) which changes an amino acid (Ser/Leu92) in the N-terminal region. amhy lacks 5608 bp of promoter sequence that is found in the X-linked amh homolog. The amhΔ-y contains several insertions and deletions in the promoter region, and even a 5 bp insertion in exonVI that results in a premature stop codon and thus a truncated protein product lacking the TGF-β binding domain. Both amhy and amhΔ-y expression is restricted to XY gonads from 5 days after hatching (dah) onwards. CRISPR/Cas9 knockout of amhy in XY fish resulted in male to female sex reversal, while mutation of amhΔ-y alone could not. In contrast, overexpression of Amhy in XX fish, using a fosmid transgene that carries the amhy/amhΔ-y haplotype or a vector containing amhy ORF under the control of CMV promoter, resulted in female to male sex reversal, while overexpression of AmhΔ-y alone in XX fish could not. Knockout of the anti-Müllerian hormone receptor type II (amhrII) in XY fish also resulted in 100% complete male to female sex reversal. Taken together, these results strongly suggest that the duplicated amhy with a missense SNP is the candidate sex determining gene and amhy/amhrII signal is essential for male sex determination in Nile tilapia. These findings highlight the conserved roles of TGF-β signaling pathway in fish sex determination.

Studies of gene function in non-model animals have been limited by the approaches available for eliminating gene function. The CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR associated) system has recently become a powerful tool for targeted genome editing. Here, we report the use of the CRISPR/Cas9 system to disrupt selected genes, including nanos2, nanos3, dmrt1, and foxl2, with efficiencies as high as 95%. In addition, mutations in dmrt1 and foxl2 induced by CRISPR/Cas9 were efficiently transmitted through the germline to F1. Obvious phenotypes were observed in the G0 generation after mutation of germ cell or somatic cell-specific genes. For example, loss of Nanos2 and Nanos3 in XY and XX fish resulted in germ cell-deficient gonads as demonstrated by GFP labeling and Vasa staining, respectively, while masculinization of somatic cells in both XY and XX gonads was demonstrated by Dmrt1 and Cyp11b2 immunohistochemistry and by up-regulation of serum androgen levels. Our data demonstrate that targeted, heritable gene editing can be achieved in tilapia, providing a convenient and effective approach for generating loss-of-function mutants. Furthermore, our study shows the utility of the CRISPR/Cas9 system for genetic engineering in non-model species like tilapia and potentially in many other teleost species.

Background Spotted scat, a marine aquaculture fish, has variable body color development stages during their ontogenesis. However, the regulatory mechanism of body color patterns formation was poorly understood. Thyroid hormones (TH) function as an important endocrine factor in regulating metamorphosis. In this study, exogenous thyroid hormones 3,5,3′-L-triiodothyronine (T3) and its inhibitor thiourea (TU) were used to treat spotted scat juveniles during the metamorphosis stage (from 60 to 90 dpf). The function and molecular mechanism of thyroid hormone signaling in regulating body color patterns formation was revealed, using the micro-observation of pigments cells distribution, colorimetric evaluation and carotenoids concentration measurement by spectrophotometry, and comparative transcriptome analysis. Results Spotted scat body color patterns consisted of whole body black color, black bar, black and red spots, and its final pattern was formed through the metamorphosis. When spotted scat were treated with the inhibitor TU to disrupt thyroid hormone signaling, the levels of T3 and T4 were significantly decreased, the melanophores numbers were significantly increased, as well as the expression of genes involved in melanin synthesis and melanophore differentiation ( tyr , tyrp1 , dct , mitf, pmel , oca2 , slc24a5 , and erbb3 ) was significantly increased. Besides, the expression of genes associated with carotenoids and pteridine metabolism ( apod , pnpla2 , rdh12 , stard10 , xdh , abca1 , retsat , scarb1 , rgs2 , and gch1 ) and carotenoids accumulation were stimulated, when thyroid hormone signaling was disrupted by TU. On the contrary, the levels of T3 and T4 were significantly elevated in spotted scat treated with T3, which could weaken the skin redness and reduce the number of black spots and melanophores, as well as the number and diameter of larval erythrophores. Notably, unlike melanophores and erythrophores, the differentiation of iridophore was promoted by thyroid hormones, gene related to iridophore differentiation ( fhl2-l , fhl2 , ltk , id2a , alx4 ) and guanine metabolism ( gmps , hprt1 , ppat , impdh1b ) were up-regulated after T3 treatment, but they were down-regulated after TU treatment. Conclusions Above results showed that thyroid hormone signaling might play critical roles in regulation pigments synthesis and deposition, thereby affecting pigment cells (melanophores, iridophores and erythrophores) formation and body color patterns. The mechanisms of hyperthyroid and hypothyroid on different pigment cells development were different. Excess thyroid hormone might impact the rearrangement of melanophore by regulating cell cycle, resulting in the abnormalities of black spots in spotted scat. Meanwhile, the excessed thyroid hormone could reduce the number and diameter of larval erythrophores, as well as weaken the skin redness of juvenile erythrophores, but they were enhanced by the disruption of thyroid hormone. However, the formation of iridophore differentiation and guanine synthesis genes expression were stimulated by thyroid hormones. These findings provide new insights for exploring the formation of body color patterns in fish, and help to elucidate the molecular mechanism of thyroid hormone in regulating pigment cell development and body coloration, and may also contribute to selective breeding of ornamental fish.

Meiosis is a process unique to the differentiation of germ cells. Retinoic acid (RA) is the key factor controlling the sex-specific timing of meiotic initiation in tetrapods; however, the role of RA in meiotic initiation in teleosts has remained unclear. In this study, the genes encoding RA synthase aldh1a2 and catabolic enzyme cyp26a1 were isolated from Nile tilapia ( Oreochromis niloticus ), a species without stra8 . The expression of aldh1a2 was up-regulated and expression of cyp26a1 was down-regulated before the meiotic initiation in ovaries and in testes. Treatment with RA synthase inhibitor or disruption of Aldh1a2 by CRISPR/Cas9 resulted in delayed meiotic initiation, with simultaneous down-regulation of cyp26a1 and up-regulation of sycp3 . By contrast, treatment with an inhibitor of RA catabolic enzyme and disruption of cyp26a1 resulted in earlier meiotic initiation, with increased expression of aldh1a2 and sycp3 . Additionally, treatment of XY fish with estrogen (E2) and XX fish with fadrozole led to sex reversal and reversion of meiotic initiation. These results indicate that RA is indispensable for meiotic initiation in teleosts via a stra8 independent signaling pathway where both aldh1a2 and cyp26a1 are critical. In contrast to mammals, E2 is a major regulator of sex determination and meiotic initiation in teleosts.

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.

Sex determination and differentiation in teleosts are governed by complex genetic regulatory networks that include evolutionarily conserved mechanisms. In this study, we investigated Boleophthalmus pectinirostris, a Gobiidae species lacking heterogametic sex chromosomes, using comparative gonadal transcriptome analysis to identify sex differentially expressed genes (DEGs). RNA sequencing of ovarian and testicular tissues identified 17,214 DEGs, including 14,302 upregulated in males and 2912 upregulated in females. These DEGs were primarily associated with male (e.g., dmrt1, amh, amhr2) or female (e.g., bmp15, gdf9, rspo1) sex determination and differentiation, steroidogenesis (e.g., hsd17b1, hsd3b1, cyp17a1), and meiosis (e.g., cyp26b1, aldh1a2, piwil2). Functional enrichment analysis revealed that male upregulated DEGs were involved in spermatogenesis pathways such as calcium signaling, while female upregulated DEGs were associated with oogenesis pathways including oocyte meiosis and progesterone-mediated oocyte maturation. Conserved regulators, notably dmrt1 and amh, were predicted to act as key hubs in protein–protein interaction networks, being primarily associated with reproductive processes and sex differentiation in B. pectinirostris. The amh gene produces two alternatively spliced isoforms that differ by a partial deletion in the second exon, both expressed in ovaries and testes. Collectively, this study provides the first comprehensive molecular framework of sex determination and differentiation in Gobiidae species, offering critical insights into the regulatory mechanisms of B. pectinirostris reproductive development.

Spotted scat (Scatophagus argus) can tolerate a wide range of salinity fluctuations. It is a good model for studying environmental salinity adaptation. Lipid metabolism plays an important role in salinity adaptation in fish. To elucidate the mechanism of lipid metabolism in the osmoregulation, the liver transcriptome was analyzed after 22 d culture with a salinity of 5 ppt (Low-salinity group: LS), 25 ppt (Control group: Ctrl), and 35 ppt (High-salinity group: HS) water by using RNA sequencing (RNA-seq) in spotted scat. RNA-seq analysis showed that 1276 and 2768 differentially expressed genes (DEGs) were identified in the LS vs. Ctrl and HS vs. Ctrl, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the pathways of steroid hormone biosynthesis, steroid biosynthesis, glycerophospholipid metabolism, glycerolipid metabolism, and lipid metabolism were significantly enriched in the LS vs. Ctrl. The genes of steroid biosynthesis (sqle, dhcr7, and cyp51a1), steroid hormone biosynthesis (ugt2a1, ugt2a2, ugt2b20, and ugt2b31), and glycerophospholipid metabolism (cept1, pla2g4a, and ptdss2) were significantly down-regulated in the LS vs. Ctrl. The pathways related to lipid metabolisms, such as fatty acid metabolism, fatty acid biosynthesis, peroxisome proliferator-activated receptor (PPAR) signaling pathway, adipocytokine signaling pathway, fatty acid degradation, and unsaturated fatty acid biosynthesis, were significantly enriched in the HS vs. Ctrl. The genes of unsaturated fatty acid biosynthesis (scd1, hacd3, fads2, pecr, and elovl1) and adipocytokine signaling pathway (g6pc1, socs1, socs3, adipor2, pck1, and pparα) were significantly up-regulated in the HS vs. Ctrl. These results suggest that the difference in liver lipid metabolism is important to adapt to low- and high-salinity stress in spotted scat, which clarifies the molecular regulatory mechanisms of salinity adaptation in euryhaline fish.

The Scatophagus argus (S. argus) is a valuable aquaculture species in southern China, with females exhibiting significantly faster growth rates than males. However, the limited understanding of its sex determination and differentiation mechanisms poses challenges for sex-controlled breeding. MicroRNAs (miRNAs), key post-transcriptional regulators, are known to modulate critical pathways governing sex determination and differentiation across several vertebrates. However, there is currently no research on miRNAs related to sex determination and differentiation in S. argus. In this study, we analyzed the expression profiles of miRNA and mRNA in the gonads of adult S. argus using high-throughput sequencing. Our analysis identified 2210 miRNAs, including 482 differentially expressed miRNAs (DEMs) between sexes. These DEMs targeted 3340 differentially expressed genes (DEGs), generating 13,773 regulatory interaction pairs. The expression of some DEGs related to sex determination and differentiation was found to be either positively or negatively correlated with expression of DEMs that might regulate them. The novel_miR_110/Foxl2, novel_miR_802/Gdf9, and novel_miR_1263/Gdf9 show opposing differential expression trends, whereas sar-miR-143-5p-4/Gsdf, sar-miR-143-5p-5/Gsdf, and novel_miR_379/Sox3 show consistent trends. The regulatory relationship between miRNA and gene in the gonads does not seem to be conserved among different fish species. This work advances our understanding of the molecular mechanisms underlying the sexual dimorphism of gonadal gene expression in S. argus. The identified miRNA–gene interactions may serve as potential targets for future sex-control strategies, contributing to advancements in aquaculture practices for this species.

Salinity significantly affects physiological and metabolic activities, breeding, development, survival, and growth of marine fish. The greater amberjack (Seriola dumerili) is a fast-growing species that has immensely contributed to global aquaculture diversification. However, the tolerance, adaptation, and molecular responses of greater amberjack to salinity are unclear. This study reared greater amberjack juveniles under different salinity stresses (40, 30, 20, and 10 ppt) for 30 days to assess their tolerance, adaptation, and molecular responses to salinity. RNA sequencing analysis of gill tissue was used to identify genes and biological processes involved in greater amberjack response to salinity stress at 40, 30, and 20 ppt. Eighteen differentially expressed genes (DEGs) (nine upregulated and nine downregulated) were identified in the 40 vs. 30 ppt group. Moreover, 417 DEGs (205 up-regulated and 212 down-regulated) were identified in the 20 vs. 30 ppt group. qPCR and transcriptomic analysis indicated that salinity stress affected the expression of genes involved in steroid biosynthesis (ebp, sqle, lss, dhcr7, dhcr24, and cyp51a1), lipid metabolism (msmo1, nsdhl, ogdh, and edar), ion transporters (slc25a48, slc37a4, slc44a4, and apq4), and immune response (wnt4 and tlr5). Furthermore, KEGG pathway enrichment analysis showed that the DEGs were enriched in steroid biosynthesis, lipids metabolism, cytokine–cytokine receptor interaction, tryptophan metabolism, and insulin signaling pathway. Therefore, this study provides insights into the molecular mechanisms of marine fish adaptation to salinity.

The fish brain is crucial for adjusting to environmental changes. Metabolic changes play a vital role in the adaptation to salinity change in aquatic animals. However, few studies have evaluated the responses of the fish brain to salinity changes. To evaluate the response to various salinities, spotted scat ( Scatophagus argus ) was cultured in water with salinity levels of 5 (low salinity: LS), 25 (control group: Ctrl), and 35 (high salinity group: HS) for 22 days. The brain transcriptome was analyzed. In total, 1698 differentially expressed genes (DEGs) were identified between the HS and Ctrl groups, and 841 DEGs were identified between the LS and Ctrl groups. KEGG analysis showed that the DEGs in the HS vs . Ctrl comparison were involved in steroid biosynthesis, terpenoid backbone biosynthesis, fatty acid biosynthesis, ascorbate and aldarate metabolism, other types of O-glycan biosynthesis, and fatty acid metabolism. Glyoxylate and dicarboxylate metabolism, one carbon pool by folate, steroid biosynthesis, and cysteine and methionine metabolism were significantly enriched in the LS vs . Ctrl comparison. Additionally, the genes related to metabolism ( acc, fas, hmgcr, hmgcs1, mvd, soat1, nsdhl, sqle, cel, fdft1, dnmt3a and mtr ) were significantly up-regulated in the HS vs . Ctrl comparison. The genes related to metabolism ( lipa, sqle, acc, fas, bhmt, mpst, dnmt3a, mtr, hao2, LOC111225351 and hmgcs1 ) were significantly up-regulated, while hmgcr and soat1 were significantly down-regulated in the LS vs . Ctrl compparison. These results suggest that salinity stress affects signaling pathways and genes’ expressions involved in metabolic processes in the brain, and the differences in metabolism play an important role in adaptation to hyperhaline or hypohaline environments in spotted scat. This research provides a comprehensive overview of transcriptional changes in the brain under hyperhaline or hypohaline conditions, which is helpful to understand the mechanisms underlying salinity adaptation in euryhaline fishes.