Genomic structure, polymorphism and expression analysis of the growth hormone (GH) gene in female and male Half-smooth tongue sole (Cynoglossus semilaevis)

Development of DNA Insertion-specific Markers Based on the Intergenic Region of Oplegnathus punctatus Cdkn1/srsf3 for Sex Identification

Spotted knifejaw (Oplegnathus punctatus) is a marine economic fish with high food and ecological value, and its growth process has obvious male and female sexual dimorphism, with males growing significantly faster than females. However, the current sex identification technology is not yet mature, which will limit the growth rate of O. punctatus aquaculture and the efficiency of separate sex breeding, so the development of efficient sex molecular markers is imperative. This study identified a 926 bp DNA insertion fragment in the cdkn1/srsf3 intergenic region of O. punctatus males through whole-genome scanning, comparative genomics, and structural variant analysis. A pair of primers was designed based on the insertion information of the Y chromosome intergenic region in male individuals. Agarose gel electrophoresis revealed the amplification of two DNA fragments, 1118 bp and 192 bp, in male O. punctatus individuals. The 926 bp fragment was identified as the insertion in the intergenic region of cdkn1/srsf3 in males, while only a single 192 bp DNA fragment was amplified in females. The biological sex of the individuals identified in this manner was consistent with their known phenotypic sex. In this study, we developed a method to detect DNA insertion variants in the intergenic region of O. punctatus. Additionally, we introduced a new DNA marker for the rapid identification of the sex of O. punctatus, which enhances detection efficiency. The text has important reference significance and application value in sex identification, all-male breeding, and lineage selection. It provides new insights into the regulation of variation in the intergenic region of cdkn1/srsf3 genes and the study of RNA shearing.

CircRNA Identification and CircRNA-miRNA-mRNA Network in Cynoglossus semilaevis Sexual Size Dimorphism

Sexual size dimorphism (SSD), which is the sexual differences in body size, has been widely reported in various species including fishes. For Chinese tongue sole (Cynoglossus semilaevis), a flatfish exhibiting typically female-biased SSD, little is known for its epigenetic regulation mechanism, especially the role of circRNAs. Here, we identified the differently expressed abundances of circRNAs in females, males, and pseudo-males to explore the potential functions of circRNAs in Chinese tongue sole SSD. In total, 14,745 novel circRNAs were screened, among which 1461 DE circRNAs were identified from the brain, gonad, liver, and muscle in female, male, and pseudo-male individuals. The ceRNA network was subsequently constructed, including 10 circRNAs, 26 mRNAs, and 11 miRNAs. These DE mRNAs were mainly related to the mRNA surveillance pathway, metabolic pathways, and cellular senescence. Importantly, the ceRNA network has revealed that several circRNAs such as novel_circ_004374 and novel_circ_014597 may regulate homeodomain interacting protein kinase 2 (hipk2) expression by sponging miR-130-x. It is also worth exploring whether or how novel_circ_008696 regulates SET Domain Containing 2, histone lysine methyltransferase (setd2), which in turn affects the epigenetic patterns of different sexual individuals. The present study not only enriches the knowledge on the potential roles of circRNA in the physiological process, but also provides new clues for the explanation of fish SSD. In future studies, the precise function and involvement of circRNAs in female-biased SSD will require more efforts.

Identification of Male-Specific Molecular Markers by Recombination of RhoGEF10 Gene in Spotted Knifejaw (Oplegnathus punctatus)

The spotted knifejaw (Oplegnathus punctatus) is a marine economic fish with high ecological value, food value, and fishing value, and its growth has obvious sex dimorphism. The rapid identification of its sex is beneficial to the development of sex determination and breeding. In this study, the method of comparative genomics and PCR amplification was used to further establish a rapid detection method for the recombinant RhoGEF10 gene in O. punctatus, which can quickly, accurately, and efficiently identify the sex of the O. punctatus to be tested. The homologous comparison results of male and female individuals showed that the DNA fragment length of the RhoGEF10 gene on the X1 chromosome was 326 bp, and the DNA fragment length on the Y chromosome was 879 bp. Therefore, it can be concluded that there is an insert fragment of 553 bp on the Y chromosome. PCR amplification results showed that the two DNA fragments of 879 bp and 326 bp were amplified in the Y chromosome and X1 chromosome of the male O. punctatus (X1X2Y), respectively, and the 879 bp fragment was a unique marker fragment of the recombinant RhoGEF10 gene; The female O. punctatus (X1X1X2X2) only a single DNA fragment of 326 bp was amplified. At the same time, the inserted fragment of the male individual resulted in partial inactivation of the RhoGEF10 protein, which in turn resulted in a slowing of peripheral nerve conduction velocity and thinning of the myelin sheath in male O. punctatus. The method shortens the time for accurate identification of the O. punctatus RhoGEF10 gene recombination and improves the detection efficiency. It is of great significance and application value in the research of nerve conduction and myelin development, male and female sex identification, the preparation of high male seedlings, and family selection based on the RhoGEF10 gene in the O. punctatus.

Identification of crucial factors involved in Cynoglossus semilaevis sexual size dimorphism by GWAS and demonstration of zbed1 regulatory network by DAP-seq

Sexual size dimorphism (SSD), whereby females and males exhibit different body sizes, are widely documented in animals. To explore crucial regulators implicated in female-biased SSD of Chinese tongue sole (Cynoglossus semilaevis), GWAS was conducted on 350 females and 59 males. Twenty SNPs and 25 genes including zbed1, nsd3, cdc45, klhl29, and smad4 with -log(p) > 7 were screened, mainly mapping to sex chromosome. The chromosome W-linked gene zbed1 attracted particular attention because it is a master key for cell proliferation. Thus, the regulatory network of zbed1 in C. semilaevis was explored by DAP-seq and 1352 peaks were discovered in the female brain. Moreover, zbed1 potentially regulated hippo signaling pathway, cell cycle, translation, and PI3k-Akt signaling pathway in C. semilaevis. These findings identify crucial SNPs and genes associated with female-biased SSD in C. semilaevis, also provide the first genome-wide survey for the zbed1 regulatory network in fish species.

Integration of Transcriptome and Methylome Highlights the Roles of Cell Cycle and Hippo Signaling Pathway in Flatfish Sexual Size Dimorphism

Sexual size dimorphism (SSD) is the difference in segments or body size between sexes prevalent in various species. Understanding the genetic architecture of SSD has remained a significant challenge owing to the complexity of growth mechanisms and the sexual influences among species. The Chinese tongue sole (Cynoglossus semilaevis), which exhibits a female-biased SSD and sex reversal from female to pseudomale, is an ideal model for exploring SSD mechanism at the molecular level. The present study aimed to integrate transcriptome and methylome analysis to unravel the genetic and epigenetic changes in female, male, and pseudomale C. semilaevis. The somatotropic and reproductive tissues (brain, liver, gonad, and muscle) transcriptomes were characterized by RNA-seq technology. Transcriptomic analysis unravelled numerous differentially expressed genes (DEGs) involved in cell growth and death-related pathways. The gonad and muscle methylomes were further employed for screening differentially methylated genes (DMGs). Relatively higher DNA methylation levels were observed in the male and pseudomale individuals. In detail, hypermethylation of the chromosome W was pronounced in the pseudomale group than in the female group. Furthermore, weighted gene co-expression network analysis showed that turquoise and brown modules positively and negatively correlated with the female-biased SSD, respectively. A combined analysis of the module genes and DMGs revealed the female-biased mRNA transcripts and hypomethylated levels in the upstream and downstream regions across the cell cycle-related genes. Moreover, the male and pseudomale-biased gene expression in the hippo signaling pathway were positively correlated with their hypermethylation levels in the gene body. These findings implied that the activation of the cell cycle and the inhibition of the hippo signaling pathway were implicated in C. semilaevis female-biased SSD. In addition, the dynamic expression pattern of the epigenetic regulatory factors, including dnmt1, dnmt3a, dnmt3b, and uhrf1, among the different sexes correspond with their distinct DNA methylation levels. Herein, we provide valuable clues for understanding female-biased SSD in C. semilaevis.

Ecology and population structure of some indigenous geese breeds and the impact of four GH and Pit-1 SNPs on their body weights

This study aims to determine the genetic correlation using nine microsatellite markers to reconstruct the history of some indigenous geese populations, along with the use of four single nucleotides polymorphisms (SNPs) to investigate their correlation with the geese body weight. Microsatellite markers are mainly used to provide updated information on changes in the population structure of geese breeds. The eight goose populations reported 24% private alleles specific for each population. Expected heterozygosity (He) ranged from 0.46 to 0.70. Three breeds were reported highly polymorphic. Inbreeding coefficient (Fis) revealed that three breeds were in a minimum level of extinction danger, while one breed was in a potential endangered situation. Phylogenetic tree, principal component analysis (PCA), and self-organizing map (SOM) were constructed using MATLAB to study the population distribution and relationship among these breeds. Four SNPs were detected, two SNPs at GH gene exon (C123T and C158T), and two SNPs at Pit-1 gene exons (G161A and T282G). Four SNP loci were reported to have a significant effect on geese body weight. They were CT genotype for C123T locus, TT genotype for C158T locus, GG genotype for G161A locus, and GG genotype for T282G locus.

The linkage of cell cycle and DNA replication with growth difference in female Chinese tongue sole (Cynoglossus semilaevis): Analysis from transcriptomic study and WGCNA

In addition to the typical sexual size dimorphism, considerable size differences within the female population of the Chinese tongue sole (Cynoglossus semilaevis) have become a further bottleneck of the improvement of sole aquaculture. To identify the internal mechanism, transcriptomic analysis and weighted gene co-expression network analysis (WGCNA) were employed simultaneously. Transcriptomic analyses of brain, pituitary gland, liver, gonad, and muscle tissues from two female groups with size differences identified 109, 698, 1325, 2299, and 2141 differentially expressed genes (DEGs), respectively. The results of these enrichment analyses suggest that the up-regulation of neuroactive ligand-receptor interaction, cell cycle, DNA replication, and MAPK signaling pathway in the group with larger females may be involved in the regulation of the observed growth differences. WGCNA of DEGs showed that cell cycle and DNA replication might be crucial pathways for accelerating cell growth in the groups with larger females. Finally, a series of hub genes including 6-phosphofructokinase type C (pfkp), ribosome biogenesis protein (wdr12), bleomycin hydrolase (blmh), and semaphorin-3A (sema3a) were recognized by the illustrated network map of modules. The linkage of cell cycle, DNA replication, and hub genes in the growth regulation of C. semilaevis provides further information for a better understanding of growth differences in fish.

Nutrient regulation of somatic growth in teleost fish. The interaction between somatic growth, feeding and metabolism

This review covers the current knowledge on the regulation of the somatic growth axis and its interaction with metabolism and feeding regulation. The main endocrine and neuroendocrine factors regulating both the growth axis and feeding behavior will be briefly summarized. Recently discovered neuropeptides and peptide hormones will be mentioned in relation to feeding control as well as growth hormone regulation. In addition, the influence of nutrient and nutrient sensing mechanisms on growth axis will be highlighted. We expect that in this process gaps of knowledge will be exposed, stimulating future research in those areas.

Effects of feeding frequency on juvenile Chinese sturgeon Acipenser sinensis

In this study, the effects of different feeding frequencies on the growth and the expression of genes in the GH/IGF axis were assessed in juvenile Chinese sturgeon. The newly hatched Chinese sturgeons were bred for 38 days at three different feeding frequencies groups (feeding frequency of two times a day, TWD; three times a day, THD; and four times a day, FOD), and the expression levels of the GH/IGF axis responses to feeding frequency were determined by quantitative real-time PCR. In addition, the full-length of the Coding Sequences of IGF I and IGF II genes (489-bp and 660-bp, respectively), were cloned and analyzed from Chinese sturgeon the first time. Multiple sequence alignments of IGFs revealed that Chinese sturgeon are high sequence identity to IGFs from other species. The phylogenetic relationships based on the IGF I and IGF II amino acid sequences were consistent with the traditional classification. After 38 days of growth, the three different feeding frequencies groups of Chinese sturgeon had no significant difference of body length, body weight, specific growth rate, the survival rate, the rate of weight gain and the condition factor. However, the relative expression of Chinese sturgeon GH in the pituitary decreased with increasing feeding frequency. The relative expression of Chinese sturgeon GHR in liver and skeletal muscle was deceased with increasing feeding frequency, while the relative expression of GHR in stomach and intestines at THD group was significantly higher than that of at TWD group and FOD group (p < 0.05). The relative expression of Chinese sturgeon IGF I in liver increased significantly with increasing feeding frequency (p < 0.05). The relative expression of IGF I in stomach and skeletal muscle was similar at the three groups. The relative expression of IGF I in intestines was significantly higher at FOD group than at TWD group and THD group (p < 0.05). The relative expression of Chinese sturgeon IGF II in liver at TWD group was significantly higher than that at THD group and FOD group (p < 0.05). However, the relative expression of IGF II in stomach, intestines and skeletal muscle at THD group was higher than that at TWD group and FOD group. Based on these previous studies that liver IGF I is regarded as a biomarker of growth performance, this result suggested that the juvenile Chinese sturgeon is better for growth when feeding four times daily compared to twice and thrice daily.

Molecular identification and developmental expression patterns of growth hormone and its receptors in yellowtail kingfish (Seriola lalandi)

In fish and other vertebrates, growth hormone (GH) is an essential polypeptide required for normal growth and development. In an attempt to understand growth regulation in yellowtail kingfish (YTK), the full-length cDNA sequences encoding gh and its receptors (ghr1 and ghr2) were cloned, characterized and the expression profiles of these three genes were investigated during embryonic development. The full-length cDNA sequences of GH and its receptors were obtained by RT-PCR combined with RACE methord. YTK gh cDNA sequence was 852 base pairs (bp) that comprised an open reading frame (ORF) of 615 bp encoding a 204-amino acids (aa) precursor. The preprohormone compassed a signal peptide (17 aa) and the mature peptide (187 aa). YTK GHR1 protein consisted of a signal peptide (28 aa), an extracellular domain (222 aa), a single transmembrane domain (23 aa) and an intracellular domain (361 aa). GHR2 protein included 18 aa, 223 aa, 23 aa, and 321 aa, respectively. Tissue distribution analysis showed that the maximal level of gh expression was observed in the pituitary, and ghr1 mRNA was mainly detected in the liver, while ghr2 transcripts were most abundant in the gonad. Moreover, both ghr1 and ghr2 mRNAs were expressed in all embryonic stages and displayed different gene expression profiles. Overall, these results provide initial evidences for the involvement of the GH/GHR system in the early ontogeny of yellowtail kingfish.

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.

Stat5b Regulates Sexually Dimorphic Gene Expression in Zebrafish Liver

Sexual size dimorphism is an interesting phenomenon occurred in many fish species. Wildtype zebrafish exhibits a significant sexual dimorphism in body size at the adult stage. Previous studies indicated that sexual size dimorphism was eliminated in stat5b-mutated zebrafish. Herein, the comparative transcriptome analysis was conducted to observe the genes and pathways involved in sexual size dimorphism. The number of male-biased and female-biased genes was much less in the liver of stat5b mutant zebrafish than in wildtype. Gene ontology (GO) enrichment and Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis indicated that multiple pathways related to metabolism were affected upon loss of stat5b function. qRT-PCR results also validated that sexually dimorphic expression of a set of genes was lost when stat5b was mutated. Furthermore, the weighted correlation network analysis (WGCNA) detected many candidate genes related to the growth traits and stat5b function, such as greb1, lepr, and igf2b. Our data suggest that stat5b should regulate the sexually dimorphic gene expression in zebrafish liver and add in understanding of the molecular mechanisms underlying sexual size dimorphism in fish species.

Sexually Dimorphic Gene Expression Associated with Growth and Reproduction of Tongue Sole (Cynoglossus semilaevis) Revealed by Brain Transcriptome Analysis

In this study, we performed a comprehensive analysis of the transcriptome of one- and two-year-old male and female brains of Cynoglossus semilaevis by high-throughput Illumina sequencing. A total of 77,066 transcripts, corresponding to 21,475 unigenes, were obtained with a N50 value of 4349 bp. Of these unigenes, 33 genes were found to have significant differential expression and potentially associated with growth, from which 18 genes were down-regulated and 12 genes were up-regulated in two-year-old males, most of these genes had no significant differences in expression among one-year-old males and females and two-year-old females. A similar analysis was conducted to look for genes associated with reproduction; 25 genes were identified, among them, five genes were found to be down regulated and 20 genes up regulated in two-year-old males, again, most of the genes had no significant expression differences among the other three. The performance of up regulated genes in Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis was significantly different between two-year-old males and females. Males had a high gene expression in genetic information processing, while female’s highly expressed genes were mainly enriched on organismal systems. Our work identified a set of sex-biased genes potentially associated with growth and reproduction that might be the candidate factors affecting sexual dimorphism of tongue sole, laying the foundation to understand the complex process of sex determination of this economic valuable species.

Sex biased expression of ghrelin and GHSR associated with sexual size dimorphism in yellow catfish

Sexual size dimorphism has been observed in many cultivable fish species including yellow catfish, in which male fish grow much faster than female fish. Ghrelin is a potent stimulator of pituitary growth hormone (GH) release and known to potentially promote food intake and body weight gain. In order to investigate the molecular mechanism of sexual size dimorphism in yellow catfish (Pelteobagrus fulvidraco), ghrelin and its functional receptor, growth hormone secretagogue receptor (GHSR) cDNAs were cloned. Real-time PCR indicated that both ghrelin and GHSR were more highly expressed in hypothalamus and gut of male fish than female. During normal larval development, expression of ghrelin and GHSR genes was significantly higher in males than in females. 17a-Methyltestosterone (MT) treatment enhanced the expression of ghrelin in female larval fish and GHSR in both sexes, whereas the expression of ghrelin in male larval fish increased in the beginning, then decreased as the treatment time prolonged. Furthermore, the expression of ghrelin and GHSR in male juvenile was significantly increased compared with female juvenile, in short and long term fasting periods, suggesting that male fish may have a better appetite than female during fasting. Our results demonstrate that sex difference in the expression of ghrelin and GHSR may be involved in sexual size dimorphism by regulating feeding and GH/IGF signaling in yellow catfish.

Molecular characterization of three gonadotropin subunits and their expression patterns during ovarian maturation in Cynoglossus semilaevis

The endocrine regulation of reproduction in a multiple spawning flatfish with an ovary of asynchronous development remains largely unknown. The objectives of this study were to monitor changes in mRNA expression patterns of three gonadotropin hormone (GTH) subunits (FSHβ, LHβ and CGα) and plasma GTH levels during ovarian maturation of half-smooth tongue sole Cynoglossus semilaevis. Cloning and sequence analysis revealed that the cDNAs of FSHβ, LHβ and CGα were 541, 670 and 685 bp in length, and encode for peptides of 130, 158 and 127 amino acids, respectively. The number of cysteine residues and potential N-linked glycosylation sites of the flatfish GTHs were conserved among teleosts. However, the primary structure of GTHs in Pleuronectiformes appeared to be highly divergent. The FSHβ transcriptional level in the pituitary remained high during the vitellogenic stage while plasma levels of FSH peaked and oocyte development was stimulated. The LHβ expression in the pituitary and ovary reached the maximum level during oocyte maturation stages when the plasma levels of LH peaked. The brain GTHs were expressed at the different ovarian stages. These results suggested that FSH and LH may simultaneously regulate ovarian development and maturation through the brain-pituitary-ovary axis endocrine system in tongue sole.

Association of polymorphisms of exon 2 of the growth hormone gene with production performance in Huoyan goose

Primers based on the cDNA sequence of the goose growth hormone (GH) gene in GenBank were designed to amplify exon 2 of the GH gene in Huoyan goose. A total of 552 individuals were brooded in one batch and raised in Liaoning and Jiangsu Provinces, China. Single nucleotide polymorphisms (SNPs) of exon 2 in the GH gene were detected by the polymerase chain reaction (single strand conformation polymorphism method). Homozygotes were subsequently cloned, sequenced and analyzed. Two SNP mutations were detected, and 10 genotypes (referred to as AA, BB, CC, DD, AB, AC, AD, BC, BD and CD) were obtained. Allele D was predominant, and the frequencies of the 10 genotypes fit the Hardy-Weinberg equilibrium in the male, female and whole populations according to the chi-square test. Based on SNP types, the 10 genotypes were combined into three main genotypes. Multiple comparisons were carried out between different genotypes and production traits when the geese were 10 weeks old. Some indices of production performance were significantly (p < 0.05) associated with the genotype. Particularly, geese with genotype AB or BB were highly productive. Thus, these genotypes may serve as selection markers for production traits in Huoyan geese.

Genetic differentiation and efficient sex-specific marker development of a pair of Y- and X-linked markers in yellow catfish

Pf62-Y and Pf62-X is a pair of allelic Y chromosome-linked and X chromosome-linked markers, and have been used to identify YY super-males, XY males and XX females for commercial production of all-male populations in yellow catfish (Pelteobagrus fulvidraco). However, the SCAR primers used previously have only two nucleotide difference, which restricts the wide utility because of nucleotide polymorphism. In this study, a continuous 8102 bp Pf62-Y sequence and a 5362 bp Pf62-X sequence have been cloned by genome walking, and significant genetic differentiation has been revealed between the corresponding X and Y chromosome allele sequences. Moreover, three pairs of primers were designed to efficiently identify YY super-males, XY males and XX females in an artificial breeding population, and to distinguish XY males and XX females in various wild populations. Together, the three new sex-specific genetic markers develop a highly stable and efficient method for genetic sex identification and sex control application in sustainable aquaculture of all-male yellow catfish.

Evaluation of reference genes for quantitative real-time RT-PCR analysis of gene expression in Nile tilapia (Oreochromis niloticus)

Quantitative real-time reverse-transcriptase polymerase chain reaction (RT-qPCR) has been used frequently to study gene expression related to fish immunology. In such studies, a stable reference gene should be selected to correct the expression of the target gene. In this study, seven candidate reference genes (glyceraldehyde-3-phosphate dehydrogenase (GADPH), ubiquitin-conjugating enzyme (UBCE), 18S ribosomal RNA (18S rRNA), beta-2-microglobulin (B2M), elongation factor 1 alpha (EF1A), tubulin alpha chain-like (TUBA) and beta actin (ACTB)), were selected to analyze their stability and normalization in seven tissues (liver, spleen, kidney, brain, heart, muscle and intestine) of Nile tilapia (Oreochromis niloticus) challenged with Streptococcus agalactiae or Streptococcus iniae, respectively. The results showed that all the candidate reference genes exhibited tissue-dependent transcriptional variations. With PBS injection as a control, UBCE was the most stable and suitable single reference gene in the intestine, liver, brain, kidney, and spleen after S. iniae infection, and in the liver, kidney, and spleen after S. agalactiae infection. EF1A was the most suitable in heart and muscle after S. iniae or S. agalactiae infection. GADPH was the most suitable gene in intestine and brain after S. agalactiae infection. In normal conditions, UBCE and 18S rRNA were the most stably expressed genes across the various tissues. These results showed that for RT-qPCR analysis of tilapia, selecting two or more reference genes may be more suitable for cross-tissue analysis of gene expression.

The co-existence of two growth hormone receptors and their differential expression profiles between female and male tongue sole (Cynoglossus semilaevis)

Growth hormone receptor (Ghr) is a single-transmembrane pass protein which is important in initiating the ability of growth hormone (Gh) to regulate development and somatic growth in vertebrates. In this study, molecular cloning, expression analysis of two different ghr genes (ghr1 and ghr2) in the tongue sole (Cynoglossus semilaevis) was conducted. As a result, the ghr1 and ghr2 cDNA sequences are 2364 bp and 3125 bp, each of which encodes a transmembrane protein of 633 and 561 amino acids (aa), respectively. Besides, the ghr1 gene includes nine exons and eight introns. The sex-specific tissue expression was analyzed by using 14 tissues from females, normal males and extra-large male adults. Both the ghr1 and ghr2 were predominantly expressed in the liver, and the ghr1 expression level in normal males was 1.6 and 1.4 times as much as those in females and extra-large males, while the ghr2 mRNA expression level in normal males was 1.1 and 1.2 times as much as those in females and extra-large males, respectively. Ontogenetic expression analysis at early life stages indicated that the ghr1 and ghr2 mRNAs were detected at all of the 35 sampling points (from oosphere to 410days-old). Furthermore, the sex differences in ghr mRNA expressions were also examined by using a full-sib family of C. semilaevis. Significantly higher levels of ghr1 mRNA were observed in males than in females at most stages of the sampling period (P<0.01). The ghr2 mRNA expression at most stages exhibited a significant sexual difference at each sampling point (P<0.01) without any variation trend related with the sexes during the whole sampling period.