Molecular characterization and expression of Piwil1 and Piwil2 during gonadal development and treatment with HCG and LHRH-A 2 in Odontobutis potamophila

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.

Immunolocalization of Vasa, PIWI, and TDRKH proteins in male germ cells during spermatogenesis of the teleost fish Poecilia reticulata

Vasa, PIWI and TDRKH are conserved components of germ granules that in metazoans are involved in germline specification and differentiation, as documented by mutational experiments in some model animals. So far, investigations on PIWI during spermatogenesis of fish has been limited to a few species, and no information is available for TDRKH, another protein involved in the piRNA pathway. In this study, the immunolocalization of these three germline determinants was analyzed in male gonads of the teleost fish Poecilia reticulata to document their localization pattern in the different stages of germ cell differentiation. To analyze their distribution pattern during the different stages of spermatogenesis we performed immunohistochemistry (IHC) and immunofluorescence (IF) assays using primary polyclonal antibodies after testing their specificity with Western Blot. Moreover, sections of testis stained with haematoxylin and eosin clarified the structural organization of P. reticulata testis, while the use of the confocal microscope and the nuclear staining clarified the different stages of germ cell differentiation during spermatogenesis. The results showed that Vasa, PIWI and TDRKH were specifically immunolocalized in the germ cells of P. reticulata, with no specific signal detected in Sertoli cells and in other somatic cells of the gonad. These markers were detected in all stages of differentiation from early spermatogonia to advanced spermatids. Vasa staining was the strongest in spermatogonia, and then decreases throughout differentiation. Instead, both PIWI and TDRKH staining increases during differentiation, and their distribution pattern, similar to what observed in the mouse, suggests their concerted participation in the piRNA pathway also in this fish.

Mucus piRNAs profiles of Vibrio harveyi-infected Cynoglossus semilaevis: A hint for fish disease monitoring

The half-smooth tongue sole, Cynoglossus semilaevis, is an important cultured flatfish species. Vibrio harveyi is a common pathogen to this fish, which may result in great economic loss to C. semilaevis culture industry. piRNAs, a non-coding RNAs with 26-32 nt, have been regarded as promising biomarkers for cancer diagnosis and fish diseases. Here, we extracted the RNA from mucus of C. semilaevis and constructed the differential expression profiles of piRNAs between the sick fish (MS) and healthy fish (MC). We identified 45,696 differentially expressed piRNAs including 22,735 up-regulated piRNAs and 22,961 down-regulated piRNAs in MS group compared with MC group. The GO enrichment and KEGG pathway enrichment analyses of the differential piRNAs were carried out. The result showed immunity-related target genes mainly involved in immune system process, response to stimulus, cell killing, immune system, infectious diseases and cell growth and death. The 10 most differentially expressed piRNAs were chosen to perform the qRT-PCR, while only seven piRNAs were consistent with the sequence result. Compared with MC group, the expression levels of piR-mmu-72173>piR-rno-62831>piR-xtr-704880, piR-dme-15546979, piR-mmu-49941660, piR-mmu-29283297 and piR-mmu-1758399 were significantly lower, and piR-gga-10574 and piR-gga-134812 were significantly higher in MS group. These piRNAs may be potential biomarkers during the V. harveyi infection of C. semilaevis. This study could provide a new method to identify the infection status of C. semilaevis and understand better about the innate and adaptive immune system in C. semilaevis during bacterial infection.

Functional role of piRNAs in animal models and its prospects in aquaculture

The recent advances in the field of aquaculture over the last decade has helped the cultured‐fish industry production sector to identify problems and choose the best approaches to achieve high‐volume production. Understanding the emerging roles of non‐coding RNA (ncRNA) in the regulation of fish physiology and health will assist in gaining knowledge on the possible applications of ncRNAs for the advancement of aquaculture. There is information available on the practical considerations of epigenetic mechanisms like DNA methylation, histone modification and ncRNAs, such as microRNA in aquaculture, for both fish and shellfish. Among the non‐coding RNAs, PIWI‐interacting RNA (piRNA) is 24–31 bp long transcripts, which is primarily involved in silencing the germline transposons. Besides, the burgeoning reports and studies establish piRNAs' role in various aspects of biology. Till date, there are no reviews that summarize the recent findings available on piRNAs in animal models, especially on piRNAs biogenesis and biological action. To gain a better understanding and get an overview on the process of piRNA genesis among the different animals, this work reviews the literature available on the processes of piRNA biogenesis in animal models with special reference to aquatic animal model zebrafish. This review also presents a short discussion and prospects of piRNA’s application in relevance to the aquaculture industry.

The influence of environmental calcium on the branchial morphology in a catadromous fish

Eels are exposed to Ca²⁺ changes during migration between seawater and freshwater. The gill is the main organ of active calcium transport and has a large surface area to be particularly sensitive to environmental changes in the aquatic environment. In this research, we focused on the morphological changes of gill tissues when eels are faced with the environmental calcium challenges. Based on the results of hematoxylin and eosin (HE) staining and immunohistochemistry, compared with the control group (normal Ca²⁺ environment), the filament and lamella lengths and lamellar frequency (LF) appeared higher in high calcium environment and lower in deficient calcium environment, while the lamella width and filamental lamellar surface area (SA_FL) decreased in high calcium environment and increased in deficient calcium environment. And there was no difference in the number filaments in first right gill arch in the three Ca²⁺ water environment. Transmission electron microscopy was employed to examine the ultrastructural changes in gills in different Ca²⁺ water environment. The nucleus and endoplasmic reticulum had a tendency to expand in calcium-deficient water, but had a tendency to shrink in high-calcium water comparing with the control group. This study provides the support that branchial surface areas are regulated in different Ca²⁺ waters through a list of calcium transporters including CACNB2.

Effect of ovarian stimulation on the expression of piRNA pathway proteins

PIWI-interacting RNAs (piRNAs) play an important role in gametogenesis, fertility and embryonic development. The current study investigated the effect of different doses of pregnant mare serum gonadotrophin/human chorionic gonadotrophin (PMSG/hCG) and repeated ovarian stimulation (OS) on the expression of the Mili, Miwi, Mael, Tdrd1, Tdrd9, qnd Mitopld genes, which have crucial roles in the biogenesis and function of piRNAs. Here, we found that after treatment with 7.5 I.U. PMSG/hCG and two repeated rounds of OS, both the mRNA and protein levels of Tdrd9, Tdrd1 and Mael showed the greatest decrease in the ovarian tissue, but the plasma E₂ levels showed the strongest increases (p<0.05). However, we found that the Mitopld, Miwi and Mili gene levels were decreased significantly after treatment with 12.5 I.U. PMSG/hCG. Our results suggested that exogenous gonadotropin administration leads to a significant decrease in the expression of the Mili, Miwi, Mael, Tdrd1, Tdrd9 and Mitopld genes, which are critically important in the piRNA pathway, and the changes in the expression levels of Tdrd9, Tdrd1 and Mael may be associated with plasma E₂ levels. New comprehensive studies are needed to reduce the potential effects of OS on the piRNA pathway, which silences transposable elements and maintains genome integrity, and to contribute to the safety of OS.

Integrated analysis of proteomics and metabolomics reveals the potential sex determination mechanism in Odontobutis potamophila

Odontobutis potamophila is a valuable species for aquaculture in China, which shows asexually dimorphic growth pattern. In this study, the integrated proteomics and metabolomics were used to analyze the sex determination mechanism. A total of 2781 significantly different regulated proteins were identified by proteomics and 2693 significantly different expressed metabolites were identified by metabolomics. Among them, 2560 proteins and 1701 metabolites were significantly up-regulated in testes, whereas 221 proteins and 992 metabolites were significantly up-regulated in ovaries. Venn diagram analysis showed 513 proteins were differentially regulated at both protein and metabolite levels. Correlation analysis of differentially-regulated proteins and metabolites were identified by Gene Ontology annotation and Kyoto Encyclopedia of Genes and Genomes pathway analysis. The results showed lipid metabolism plays an important role in sex determination. The metabolites decanoyl-CoA, leukotriene, 3-dehydrosphinganine, and arachidonate were the biomarkers in testes, whereas estrone and taurocholate were the biomarkers in ovaries. Interaction networks of the significant differentially co-regulated proteins and metabolites in the process of lipid metabolism showed arachidonic acid metabolism and steroid hormone biosynthesis were the most important pathways in sex determination. The findings of this study provide valuable information for selective breeding of O. potamophila. SIGNIFICANCE OF THE STUDY: The male O. potamophila grows substantially larger and at a quicker rate than the female. Thus, males have greater economic value than females. However, limited research was done to analyze the sex determination mechanism of O. potamophila, which seriously hindered the development of whole-male O. potamophila breeding. In this study, four key proteins (Ctnnb1, Piwil1, Hsd17b1, and Dnali1), six most important biomarkers (decanoyl-CoA, leukotriene, 3-dehydrosphinganine, arachidonate, estrone, and taurocholate) and two key pathways (arachidonic acid metabolism and steroid hormone biosynthesis) in sex determination of O. potamophila were found by integrated application of iTRAQ and LC-MS techniques. The results give valuable information for molecular breeding of O. potamophila in aquaculture.

Roles of piwil1 gene in gonad development and gametogenesis in Japanese flounder, Paralichthys olivaceus

PIWI family member piwil1, which associates with Piwi-interacting RNA (piRNA), is responsible in regulation of germ cell differentiation and maintenance of reproductive stem cells. In this study, we analyzed the piwil1 gene in Paralichthys olivaceus. Bioinformatics analysis and structure prediction showed that piwil1 had the conserved domains: PAZ domain and PIWI domain. Expression analysis during embryonic development implied that piwil1 gene was maternally inherited. The tissue distribution showed a sexually dimorphic gene expression pattern, with higher expression level in testis than ovary. In situ hybridization results demonstrated that piwil1 was predominantly distributed in oogonia, oocytes, sertoli cells and spermatocytes. A CpG island was predicted in the 5'-flanking region of piwil1 gene, and its methylation levels showed significant disparity between males and females, indicating that the sexually dimorphic expression of piwil1 gene might be regulated by methylation. Furthermore, we explored the distinct roles of human chorionic gonadotropin and 17α-methyltestosterone in regulating the expression of piwil1, and found that piwil1 was interacting with the HPG axis hormones. These results indicated that piwil1 might play a crucial role in gonadal development and gametogenesis in Paralichthys olivaceus.