Seminal Plasma Exosomes: Promising Biomarkers for Identification of Male and Pseudo-Males in Cynoglossus semilaevis

Identification and Functional Analysis of Cynoglossus semilaevis Z-Linked E3 Ubiquitin Ligase rnf34

The high proportion of males in C. semilaevis hinders their industrial development. The genetic ZW individual can become a pseudomale by sex reversal. And the pseudomale can produce Z-sperm (with epigenetic information to cause sex reversal) while W-sperm is absent, which leads to an even higher male proportion in offspring. Recently, with the development of transcriptomic technologies, research on spermatogenesis in C. semilaevis has been focused on the ubiquitination pathway. In this study, we analyzed the function of the ubiquitin ligase rnf34 gene on the Z chromosome. A qPCR experiment showed that its expression level in the gonad was the highest among different tissues. In the ovary, the expression gradually increased with development from 40 days post-hatching (dph) to 1.5 years post-hatching (yph). In the testis, rnf34 showed increased expression from 40 dph to 6 months post-hatching (mpf) and stabilized up until 1.5 ypf. In situ hybridization showed that the mRNA of rnf34 was mainly distributed in the germ cells of the testis and the ovary. In vivo siRNA-mediated knockdown of the rnf34 gene in male fish affected the expression of a series of genes related to sex differentiation and spermatogenesis. These results provide genetic data on the molecular mechanisms of gonadal development and spermatogenesis in C. semilaevis.

MicroRNA Regulation in Infectious Diseases and Its Potential as a Biosensor in Future Aquaculture Industry: A Review

An infectious disease is the most apprehensive problem in aquaculture as it can lead to high mortality in aquatic organisms and massive economic loss. Even though significant progress has been accomplished in therapeutic, prevention, and diagnostic using several potential technologies, more robust inventions and breakthroughs should be achieved to control the spread of infectious diseases. MicroRNA (miRNA) is an endogenous small non-coding RNA that post-transcriptionally regulates the protein-coding genes. It involves various biological regulatory mechanisms in organisms such as cell differentiation, proliferation, immune responses, development, apoptosis, and others. Furthermore, an miRNA also acts as a mediator to either regulate host responses or enhance the replication of diseases during infection. Therefore, the emergence of miRNAs could be potential candidates for the establishment of diagnostic tools for numerous infectious diseases. Interestingly, studies have revealed that miRNAs can be used as biomarkers and biosensors to detect diseases, and can also be used to design vaccines to attenuate pathogens. This review provides an overview of miRNA biogenesis and specifically focuses on its regulation during infection in aquatic organisms, especially on the host immune responses and how miRNAs enhance the replication of pathogens in the organism. In addition to that, we explored the potential applications, including diagnostic methods and treatments, that can be employed in the aquaculture industry.

Sex-Inclined Piwi-Interacting RNAs in Serum Exosomes for Sex Determination in the Greater Amberjack (Seriola dumerili)

The greater amberjack (Seriola dumerili) is a gonochoristic fish with no sexual dimorphism in appearance, making sex identification difficult. Piwi-interacting RNAs (piRNAs) function in transposon silencing and gametogenesis and are involved in various physiological processes, including sex development and differentiation. Exosomal piRNAs can be indicators for the determination of sex and physiological status. In this study, four piRNAs were differentially expressed in both serum exosomes and gonads between male and female greater amberjack. Three piRNAs (piR-dre-32793, piR-dre-5797, and piR-dre-73318) were significantly up-regulated and piR-dre-332 was significantly down-regulated in serum exosomes and gonads of male fish, compared to female fish, consistent with the serum exosomal results. According to the relative expression of four marker piRNAs derived from the serum exosomes of greater amberjack, the highest relative expression of piR-dre-32793, piR-dre-5797, and piR-dre-73318 in seven female fish and that of piR-dre-332 in seven male fish can be used as the standard for sex determination. The method of sex identification can ascertain the sex of greater amberjack by blood collection from the living body, without sacrificing fish. The four piRNAs did not show sex-inclined expression in the hypothalamus, pituitary, heart, liver, intestine, and muscle tissue. A piRNA-target interaction network involving 32 piRNA-mRNA pairs was generated. Sex-related target genes were enriched in sex-related pathways, including oocyte meiosis, transforming growth factor-beta signaling pathway, progesterone-mediated oocyte maturation, and gonadotropin releasing hormone signaling pathway. These results provide a basis for sex determination in greater amberjack and improve our understanding of the mechanisms underlying sex development and differentiation in the species.

The feasibility of skin mucus replacing exosome as a pool for bacteria-infected markers development via comparative proteomic screening in teleost

In fish, skin mucus forms a protective barrier between the body surface and the external water environment, thus providing the most direct and intuitive clues to monitor the subject's health condition. To explore the impact of the Vibrio harveyi pathogen on teleost, the proteome of epidermal mucus from control and sick Cynoglossus semilaevis were screened through iTRAQ followed with LC-MS/MS. 1531 credible proteins were obtained relating to structural, metabolic and immunological functions. 335 different expressed proteins (DEPs) were identified, with 166 up-regulated and 169 down-regulated in MS. 62 proteins were characterized, including 22 up-regulated proteins and 40 down-regulated proteins. Integrated analysis of DE-miRNAs and DEPs from miRomics and proteomics were conducted to show the indirect regulatory relationship. Comparative analysis of DEPs between mucus and exosomes demonstrated that exosomes contributed the most DEPs of all mucus DEPs. 125 proteins are DEPs only in exosomes, which presented minor difference in total mucus. Expression of Aminopeptidase (anpep), Calcium-transporting ATPase, Histone H2B and H2A confirmed implied fine discriminative power with infected C. semilaevis, among which Calcium-transporting ATPase and H2B also appeared in list of exosomal markers. This study might shed the light on effective biomarker digging at other extended screening scenarios.

Developmental RNA-Seq transcriptomics of haploid germ cells and spermatozoa uncovers novel pathways associated with teleost spermiogenesis

In non-mammalian vertebrates, the molecular mechanisms involved in the transformation of haploid germ cells (HGCs) into spermatozoa (spermiogenesis) are largely unknown. Here, we investigated this process in the marine teleost gilthead seabream (Sparus aurata) through the examination of the changes in the transcriptome between cell-sorted HGCs and ejaculated sperm (SPZEJ). Samples were collected under strict quality controls employing immunofluorescence microscopy as well as by determining the sperm motion kinematic parameters by computer-assisted sperm analysis. Deep sequencing by RNA-seq identified a total of 7286 differentially expressed genes (DEGs) (p-value < 0.01) between both cell types, of which nearly half were upregulated in SPZEJ compared to HCGs. In addition, approximately 9000 long non-coding RNAs (lncRNAs) were found, of which 56% were accumulated or emerged de novo in SPZEJ. The upregulated transcripts are involved in transcriptional and translational regulation, chromatin and cytoskeleton organization, metabolic processes such as glycolysis and oxidative phosphorylation, and also include a number of ion and water channels, exchangers, transporters and receptors. Pathway analysis conducted on DEGs identified 37 different signaling pathways enriched in SPZEJ, including 13 receptor pathways, from which the most predominant correspond to the chemokine and cytokine, gonadotropin-releasing hormone receptor and platelet derived growth factor signaling pathways. Our data provide new insight into the mRNA and lncRNA cargos of teleost spermatozoa and uncover the possible involvement of novel endocrine mechanisms during the differentiation and maturation of spermatozoa.

Exosome-derived small non-coding RNAs reveal immune response upon grafting transplantation in Pinctada fucata (Mollusca)

Exosomes, a subset of small extracellular vesicles, carry various nucleic acids, proteins, lipids, amino acids and metabolites. They function as a mode of intercellular communication and molecular transfer. Exosome cargo molecules, including small non-coding RNAs (sncRNAs), are involved in the immune response in various organisms. However, the role of exosome-derived sncRNAs in immune responses in molluscs remains unclear. Here, we aimed to reveal the sncRNAs involved in the immune response during grafting transplantation by the pearl oyster Pinctada fucata. Exosomes were successfully extracted from the P. fucata haemolymph during graft transplantation. Abundant microRNAs (miRNAs) and PIWI-interacting RNAs (piRNAs) were simultaneously discovered in P. fucata exosomes by small RNA sequencing. The expression patterns of the miRNAs and piRNAs at the grafting and initial stages were not substantially different, but varied significantly between the initial and later stages. Target prediction and functional analysis indicate that these miRNAs and piRNAs are related to immune response upon grafting transplantation, whereas piRNAs may also be associated with transposon silencing by targeting with genome transposon elements. This work provides the basis for a functional understanding of exosome-derived sncRNAs and helps to gain further insight into the PIWI/piRNA pathway function outside of germline cells in molluscs.

Evidence for a Novel Antiviral Mechanism of Teleost Fish: Serum-Derived Exosomes Inhibit Virus Replication through Incorporating Mx1 Protein

Exosomes are associated with cancer progression, pregnancy, cardiovascular diseases, central nervous system-related diseases, immune responses and viral pathogenicity. However, study on the role of exosomes in the immune response of teleost fish, especially antiviral immunity, is limited. Herein, serum-derived exosomes from mandarin fish were used to investigate the antiviral effect on the exosomes of teleost fish. Exosomes isolated from mandarin fish serum by ultra-centrifugation were internalized by mandarin fish fry cells and were able to inhibit Infectious spleen and kidney necrosis virus (ISKNV) infection. To further investigate the underlying mechanisms of exosomes in inhibiting ISKNV infection, the protein composition of serum-derived exosomes was analyzed by mass spectrometry. It was found that myxovirus resistance 1 (Mx1) was incorporated by exosomes. Furthermore, the mandarin fish Mx1 protein was proven to be transferred into the recipient cells though exosomes. Our results showed that the serum-derived exosomes from mandarin fish could inhibit ISKNV replication, which suggested an underlying mechanism of the exosome antivirus in that it incorporates Mx1 protein and delivery into recipient cells. This study provided evidence for the important antiviral role of exosomes in the immune system of teleost fish.

miR-23a-3p is involved in drug resistance by directly targeting the influx drug transporter organic anion-transporting polypeptide 2

OBJECTIVE

Drug transporters are involved in the drug resistance of individuals with drug-resistant epilepsy by influencing the intracerebral transport of antiepileptic drugs (AEDs). The expression of drug transporters is associated with microRNAs. We previously revealed that miR-23a-3p levels were elevated in the blood of patients with intractable epilepsy. Additionally, the influx drug transporter organic anion-transporting polypeptide 2 (Oatp2) is involved in the intracerebral transport of valproic acid (VPA), the most commonly used AED; repeated seizures lead to decreased expression of Oatp2. However, the role of miR-23a-3p in the expression of Oatp2 and in the development of drug resistance has not been established. Herein, we aimed to determine the potential role of miR-23a-3p in VPA-resistant epilepsy through in vivo and in vitro experiments.

METHODS

Epilepsy was elicited after status epilepticus (SE) was induced by lithium-pilocarpine in adult Sprague-Dawley rats, followed by VPA treatment to select rats with VPA resistance. The expression of miR-23a-3p was detected by immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR). A miR-23a-3p inhibitor was intracerebrally injected into VPA-resistant rats, and histological staining and Morris water maze tests were performed to evaluate brain damage and learning/memory functions in these rats. Subsequently, a dual-luciferase reporter assay and a VPA uptake assay were performed in brain microvascular endothelial cells (BMECs) to investigate the underlying mechanism of action of miR-23a-3p.

RESULTS

Our results indicated that compared to that in control rats, miR-23a-3p was elevated in VPA-resistant rats. Intracerebral injection of a miR-23a-3p inhibitor reduced brain damage and the associated deficits in learning and memory functions in rats with VPA resistance. Further investigation indicated that Oatp2 was the direct target of miR-23a-3p, and it was negatively regulated by miR-23a-3p in the brain and BMECs. Furthermore, we demonstrated that miR-23a-3p reduced VPA uptake in BMECs by regulating Oatp2 expression.

CONCLUSIONS

miR-23a-3p is involved in VPA resistance in epilepsy by directly targeting the influx drug transporter Oatp2, indicating that miR-23a-3p could be a potential therapeutic target for intractable epilepsy.

Proteomics of mucosal exosomes of Cynoglossus semilaevis altered when infected by Vibrio harveyi

The cargo of exosomes contains proteins with various functions, which might be promising biomarkers for disease diagnosis and prognosis. To explore the impact of the Vibrio harveyi pathogen on Cynoglossus semilaevis from a different perspective and develop promising biomarkers for infection, the exosomes from epidermal mucus of healthy controls（EC）and sick fish（ES）were extracted and identified, coupled with proteomic screening through iTRAQ followed with LC-MS/MS. 1531 credible proteins were obtained relating to structural, metabolic and immunological functions. 359 different expressed proteins (DEPs) (FC > 2 or FC < 0.5) were found, with 161 up-regulated and 198 down-regulated in ES. Based on the database of C. semilaevis on Uniprot, 71 proteins were characterized as concrete names, including 19 up-regulated proteins and 52 down-regulated proteins, and were selected as subjects for further studies. Ferritin, Toll-like receptor 5S protein and Calcium-transporting ATPase were upregulated, while Histone H2B and Eukaryotic translation initiation factor 5A were downregulated, consistent with the expression levels of related mRNAs in skin tissue verified by qRT-PCR. The integrated analysis between miRomics and proteomics also provided possible regulatory relationships mediated by mucous exosomes during infection. The signature proteins in mucosal exosomes could make sense in the explanation of the infection defending mechanism and the development of biomarkers which can differentiate diseased and healthy C. semilaevis individuals.

Sex bias miRNAs in Cynoglossus semilaevis could play a role in transgenerational inheritance

Alterations of non-coding RNA profiling in spermatozoa are candidate mechanisms related to changes in paternal environment and progeny. Transgenerational inheritance of sex in pseudomales of Cynoglossus semilaevis, a fish with significant sex dimorphism, is a typical example of non-Mendelian inheritance. In the present study, miRNA profiles of spermatozoa were compared between male and pseudomale of C. semilaevis. Differential miRNAs in sperm from F0 and F1 generation also provides clues for revealing the possible role of non-coding RNA mediated transgenerational inheritance. Four sexual bias miRNAs, dre-miR-26a-5p, dre-miR-27b-3p, dre-miR-125b-5p,pol-199a-5p, were identified and verified in F0 and F1 generation of C. semilaevis. All of them were highly expressed in male sperm compared with pseudomale sperm. Function of target genes indicates that target genes of these differential RNAs are highly correlated with sex differentiation, gametogenesis and maintenance of secondary sexual characteristics. In a word, identification of epigenetic markers in gametes has great prospects in predicting susceptibility and properties in offsprings, and providing an indicator of parentalgenetic property.

A simple and rapid method for fish sex identification based on recombinase-aided amplification and its use in Cynoglossus semilaevis

Fish sex identification is a basic technique of great importance for both fish genetic studies and fisheries. Due to the sexual reversal phenomenon in many fish species, a simple and rapid molecular identification method for fish genetic sex is urgently needed to suit versatile detection scenarios, such as point-of-need applications. In this study, we took Cynoglossus semilaevis as an example, established a recombinase-aided amplification (RAA)-based method for sex identification, and combined the RAA-detection with two result visualization approaches with distinct features, capillary electrophoresis (CE) and lateral flow dipstick (LFD). Specific primers and probe were designed to specifically detect the sex chromosome W of C. semilaevis in order to distinguish the genetic sex between males, pseudo-males and females. To evaluate the performance of our methods, the genetic sex for twenty-eight males, sixty-eight pseudo-males and fifty-four females were examined with the RAA-based method and classical PCR-based genotyping method, demonstrating the consistent results of sex identification between both methods. The RAA-LFD method is operationally simple, rapid (~ 30 min) and holds great potential for point-of-need applications of fish sex identification, including fishery fields. The method presented here could be effective for identifying fish gender with the ZW karyotype.

Extracellular vesicles piwi-interacting RNAs from skin mucus for identification of infected Cynoglossus semilaevis with Vibrio harveyi

Extracellular vesicles play a regulatory role in intracellular and intercellular transmission through a variety of biological information molecules, including mRNA, small RNAs and proteins. piRNAs are one kind of regulatory small RNAs in the vesicles at the post transcriptional level. Hereby, we isolated the extracellular vesicles from skin mucus and screened the piRNA profiles of these vesicles, aiming at developing biomarkers related to bacterial infections in Cynoglossus semilaevis. The different profilings of piRNAs in mucous extracellular vesicles of C. semilaevis were compared through small RNA sequencing, between fish infected with Vibrio harveyi and healthy ones. The number of clean reads on the alignment of exosome sick (ES) group was 105, 345 and that of exosome control (EC) group was 455, 144. GO and KEGG pathway enrichment analysis showed that most of the target genes were involved in cellular process, response to stimulus, biological regulation, immune system process and signal transduction, signal molecular and interaction, transport and catabolism. The 45 final candidate piRNAs related to immunity or infectious diseases included 20 piRNAs with high expression in the ES group and 25 piRNAs with a low expression in the ES group. After verification by qRT-PCR, there was significant difference of five piRNAs expression level between infected fish and healthy fish, in line with the sequencing. The expression level of piR-mmu-16401212, piR-mmu-26829319 and piR-gga-244092 in infected fish were significantly lower than that of control group, while piR-gga-71717 and piR-gga-99034 were higher, which implying that these piRNAs in mucous extracellular vesicles can be used to identify diseased fish from normal ones. This work supplied a novel class of biomarker for infection diagnosis in fish, and it will be benefit for screening disease resistant breeding of C. semilaevis.

Novel molecular marker for RAA-LFD visual detection of Cynoglossus semilaevis sex

Due to the significant sex dimorphism, Cynoglossus semilaevis has long been a species of research interest in the field of artificial sex manipulation. The existence of pseudo-males both in the natural habitat and aquaculture enterprises also is indicative of the importance for identification of the genetic sex in this species. In the present study, there was elucidation of a novel molecular marker for utilizing the recombinase aided amplification-lateral flow dipstick (RAA-LFD) visual system to identify the genetic sex of C. semilaevis. This 533 bp novel marker is a differential single copy fragment between the Z and W chromosome of C. semilaevis and exists only in the W chromosome. After primer designing and probe labeling, this marker has been utilized in a RAA isothermal amplification system. There were 49 C. semilaevis specimens evaluated for genetic sex identification using both PCR-agarose gel electrophoresis based InDel marker detection and the novel RAA-LFD system. The results from conducting evaluations with the two methods were consistent in all samples. Also, results from sensitivity analysis with use of the RAA-LFD system indicated the detection system was effective and reliable from 10⁸ copy number to 10¹. With use of the RAA reaction, there was only need to utilize a constant temperature of 37 ℃ for specific DNA amplification within 30 min. The combination use of RAA with LFD resulted in more efficient and convenient sex determination with there being a lesser technical threshold.

Detecting Cynoglossus semilaevis infected with Vibrio harveyi using micro RNAs from mucous exosomes

Exosomes are important mediators of vesicle transportation and contain microRNAs (miRNAs) that mediate transcriptional gene knockout and silencing in biological processes. Moreover, exosomic miRNAs are promising biomarkers for disease diagnosis and physiological status indication in many species, including fish. The impact of the Vibrio harveyi pathogen on Cynoglossus semilaevis aquaculture is becoming more and more serious as the industry expands. To overcome this challenge, miRNAs in mucous exosomes were screened by small RNA sequencing and verified by quantitative real-time PCR to develop biomarkers. This is the first capture of exosomes from flatfish mucus coupled with miRNA profiling. The results revealed significant differences in expression levels of some miRNAs between infected and healthy fish. Three unique miRNAs were identified for V. harveyi infection diagnosis; expression levels of dre-miR-205-5p and dre-miR-205-5p in infected fish were significantly lower than controls, while dre-miR-100-5p expression was higher. These miRNAs in mucous exosomes could be used to differentiate diseased and healthy fish in an early screening method with practical value for breeding disease-resistant C. semilaevis.

A combination of genome-wide association study screening and SNaPshot for detecting sex-related SNPs and genes in Cynoglossus semilaevis

Chinese tongue sole (Cynoglossus semilaevis) males and females exhibit great differences in growth rate and appearance. The species is heterogametic (ZW/ZZ) and has sex-reversed "pseudomales" that are genetically female and physiologically male. In this study, we identified eight sex-specific single nucleotide polymorphism (SNP) markers for the sex identification of C. semilaevis by using a combination of genome-wide association study (GWAS) screening and SnaPshot validation. Candidate SNPs were screened using genotyping by sequencing to perform GWAS of the differential SNPs between the sexes of C. semilaevis. The SNP loci were amplified using a multiplex PCR system and detected via SNaPshot, which enables multiplexing of up to 30-40 SNPs in a single assay and ensures high accuracy of the results. The molecular markers detected in our study were used to successfully identify normal males and pseudomales from 45 caught and 40 cultured C. semilaevis specimens. Linkage disequilibrium analysis showed that the eight SNP loci were related to each other, with a strong linkage. Moreover, we investigated the expression of prdm6 mRNA containing a missense SNP and confirmed that the gene is differentially expressed in the gonads of the different sexes of C. semilaevis; the expression of prdm6 mRNA was significantly higher in the males than in the females and pseudomales. This means prdm6 may be related to sex differentiation in C. semilaevis.

Large scale SNP unearthing and genetic architecture analysis in sea-captured and cultured populations of Cynoglossus semilaevis

Knowledge on population structure and genetic diversity is a focal point for association mapping studies and genomic selection. Genotyping by sequencing (GBS) represents an innovative method for large scale SNP detection and genotyping of genetic resources. Here we used the GBS approach for the genome-wide identification of SNPs in a collection of Cynoglossus semilaevis and for the assessment of the level of genetic diversity in C. semilaevis genotypes. GBS analysis generated a total of 55.12 Gb high-quality sequence data, with an average of 0.63 Gb per sample. The total number of SNP markers was 563, 109. In order to explore the genetic diversity of C. semilaevis and to select a minimal core set representing most of the total genetic variation with minimum redundancy, C. semilaevis sequences were analyzed using high quality SNPs. Based on hierarchical clustering, it was possible to divide the collection into 2 clusters. The marine fishing populations were clustered and clearly separated from the cultured populations, and the cultured populations from Hebei was also distinct from the other two local populations. These analyses showed that genotypes were clustered based on species-related features. Differential significant SNPs were also captured and validated by GBS and SNaPshot, with linkage disequilibrium and haplotype analysis, seven SNPs have been confirmed to have obvious differentiation in two populations, which may be used as the characteristic evaluation sites of sea-captured and cultured Cynoglossus semilaevis populations. And SNP markers and information on population structure developed in this study will undoubtedly support genome-wide association mapping studies and marker-assisted selection programs. These differential SNPs could be also employed as the characteristic evaluation sites of sea-captured and cultured Cynoglossus semilaevis populations in future.

Identification and characterization of the melanocortin 1 receptor gene (MC1R) in hypermelanistic Chinese tongue sole (Cynoglossus semilaevis)

The Chinese tongue sole (Cynoglossus semilaevis) is a flatfish with distinctive asymmetry in its body coloration. The melanism (hyperpigmentation) in both the blind side and ocular side of C. semilaevis gives it an extremely low commercial value. However, the fundamental molecular mechanism of this melanism remains unclear. Melanocortin 1 receptor (MC1R), a GTP-binding protein-coupled receptor, is considered to play a vital role in the physiology of the vertebrate pigment system. In order to confirm the contribution of MC1R to the body coloration of C. semilaevis, the expression levels of Mc1r mRNA were measured in seven tissue types at different developmental stages of normal and melanistic C. semilaevis. The expression levels of Mc1r mRNA in the heart, brain, liver, kidney, ocular-side skin, and blind-side skin of melanistic C. semilaevis were significantly higher than that of normal C. semilaevis in all developmental stages. Moreover, the knocking down of Mc1r in the C. semilaevis liver cell line (HTLC) increased the expression of the downstream genes microphthalmia transcription factor (Mitf) and tyrosinase-related protein 1 (Tyrp1) in the pigmentation pathway. Thus, the present data suggest that MC1R might play important roles in Tyrp1- and Mitf-mediated pigment synthesis in C. semilaevis.

Identification and application of piwi-interacting RNAs from seminal plasma exosomes in Cynoglossus semilaevis

BACKGROUND

Piwi-interacting RNAs (piRNAs) have been linked to epigenetic and post-transcriptional gene silencing of retrotransposons in germ line cells, particularly in spermatogenesis. Exosomes are important mediators of vesicle transport, and the piRNAs in exosomes might play an important role in cell communication and signal pathway regulation. Moreover, exosomic piRNAs are promising biomarkers for disease diagnosis and physiological status indication. We used Cynoglossus semilaevis because of its commercial value and its sexual dimorphism, particularly the sex reversed "pseudomales" who have a female karyotype, produce sperm, and copulate with normal females to produce viable offspring.

RESULTS

To determine whether piRNAs from fish germ line cells have similar features, seminal plasma exosomes from half-smooth tongue sole, C. semilaevis, were identified, and their small RNAs were sequenced and analysed. We identified six signature piRNAs as biomarkers in exosomes of seminal plasma from males and pseudomale C. semilaevis. Bioinformatic analysis showed that all six signatures were sex-related, and four were DNA methylation-related and transposition-related piRNAs. Their expression profiles were verified using real-time quantitative PCR. The expression of the signature piRNAs was markedly higher in males than in pseudomales. The signature piRNAs could be exploited as male-specific biomarkers in this fish.

CONCLUSIONS

These signatures provide an effective tool to explore the regulatory mechanism of sex development in C. semilaevis and may provide guidance for future research on the function of piRNAs in the generative mechanism of sex reversed "pseudomales" in C. semilaevis.