Suppression effect of LHRH-A and hCG on Piwi expression in testis of Nile tilapia Oreochromis niloticus

The regulatory effects of water probiotic supplementation on the blood physiology, reproductive performance, and its related genes in Red Tilapia (Oreochromis niloticus X O. mossambicus)

Probiotics are becoming increasingly popular as eco-friendly alternatives in aquaculture. However, there is limited research on their impacts on the reproductive efficiency of Red Tilapia (Oreochromis niloticus x O. mossambicus) broodstock. Therefore, this experiment aimed to explore the combined effects of selective probiotics Bacillus subtilis and B. licheniformis (BSL; 1:1) added to water on blood hematology, serum metabolites, gonadal histology, reproductive performance, and reproductive associated genes in Red Tilapia broodstock. Tilapia broodfish weighing 140-160 g were stocked in four treatment groups: control (T0), and the other three groups were added different levels of BSL to the water as follows: T1 (0.01 g/m3), T2 (0.02 g/m3), and T3 (0.03 g/m3), respectively. Results indicate that BSL administration significantly improved RBCs, hemoglobin, hematocrit, MCH, and MCHC, with the highest improvement seen in the T3 group (P < 0.05). BSL added to the fish water significantly enhanced serum protein fractions (total protein, albumin, and globulins), while AST, ALT, ALP, creatinine, uric acid, and glucose were significantly diminished in a dose-dependent way (P < 0.05). Adding 0.02-0.03 g/ m3 of BSL resulted in higher antioxidant status (superoxide dismutase and catalase) compared to other groups (P < 0.05). Testosterone levels were higher in T3 than in other groups (P < 0.05). All female hormones (LH, FSH, estradiol, and progesterone) were substantially augmented by the addition of BSL. Additionally, the BSL groups exhibited higher GSI, HSI, VSI (male only), egg diameter (mm), mean number of fry/fish, and mean fry weight (g) compared to the control group (P < 0.05). Expression of reproductive-associated genes (vasa, nanos1a, nanos2, dnd1, pum1, AMH, and vtg) were significantly up-regulated in the gonads of fish in the 0.03 g/m3 treatment. The histological gonadal structure exhibited that BSL improved gonad maturation in both genders of Tilapia fish. Overall, adding a mixture of B. subtilis and B. licheniformis (0.03 g/m3 water) can accelerate reproductive performance in Red Tilapia through up-regulation of reproductive genes and enhance the health profile.

Effects of four hormones on the mitigation of ovarian damage in tilapia (Oreochromis niloticus) after copper and cadmium exposure

Female tilapia of the Genetic Improvement of Farmed Tilapia (GIFT) strain were selected as an animal model to study the effects of four hormonal drugs in mitigating ovarian damage following exposure to copper and cadmium. After combined exposure to copper and cadmium in aqueous phase for 30 d, tilapia were randomly injected with oestradiol (E2), human chorionic gonadotropin (HCG), luteinizing hormone releasing hormone (LHRH), or coumestrol and raised in clear water for 7 d Ovarian samples were collected after combined exposure to heavy metals for 30 d and after recovery for 7 d Gonadosomatic index (GSI), copper and cadmium levels in the ovary, reproductive hormone levels in serum, and mRNA expression of key reproductive regulatory factors were determined. After 30 d of exposure to the combined copper and cadmium in aqueous phase, the Cd²⁺ content in tilapia ovarian tissue increased by 1,242.46% (p < 0.05), whereas the Cu²⁺ content, body weight, and GSI decreased by 68.48%, 34.46%, and 60.00% (p < 0.05), respectively. Additionally, E2 hormone levels in tilapia serum decreased by 17.55% (p < 0.05). After drug injection and recovery for 7 d, compared to the negative control group, the HCG group exhibited an increase of 39.57% (p < 0.05) in serum vitellogenin levels. Increases of 49.31%, 42.39%, and 45.91% (p < 0.05) in serum E2 levels were observed, and mRNA expression of 3β-HSD increased by 100.64%, 113.16%, and 81.53% (p < 0.05) in the HCG, LHRH, and E2 groups, respectively. The mRNA expression of CYP11A1 in tilapia ovaries increased by 282.26% and 255.08% (p < 0.05) and mRNA expression of 17β-HSD increased by 109.35% and 111.63% in the HCG and LHRH groups, respectively (p < 0.05). All four hormonal drugs, particularly HCG and LHRH, promoted the restoration of tilapia ovarian function to varying degrees after injury induced by combined exposure to copper and cadmium. This study presents the first hormonal treatment protocol for the mitigation of ovarian damage in fish exposed to combined aqueous phases of copper and cadmium as a strategy to prevent and treat fish ovarian damage induced by heavy metals.

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.

Quercetin inhibits testicular toxicity induced by the mixture of three commonly used phthalates in rats

BACKGROUND

Phthalates (PEs), such as butyl benzyl phthalate, dibutyl phthalate and di(2-ethylhexyl) phthalate, are one of the most widely used plasticizers, and humans are increasingly exposed to them. Phytochemical quercetin (Que) is a typical flavonoid with several biological effects, such as antioxidative and anti-inflammatory. The present study was designed to explore the effect of Que on testicular toxicity caused by the mixture of three commonly used PEs (MPEs), and the underlying mechanism. Forty male Sprague-Dawley rats were randomly and equally divided into five groups (n = 8). Rats in control the group were orally treated with the excipient. Rats in the MPEs group were orally administered with 900 mg kg^-1  day^-1 MPEs, whereas rats in the MPEs+L-Que, MPEs+M-Que and MPEs+H-Que groups were simultaneously treated with 900 mg kg^-1  day^-1 MPEs and, respectively, 10, 30 and 90 mg kg^-1  day^-1 Que for 30 days.

RESULTS

Compared with the control group, the testes weight, epididymides weight, serum testosterone, luteinizing hormone, follicle-stimulating hormone and estradiol levels, and anogenital distance in the MPEs group were significantly decreased (P < 0.05). The testicular tissues were injured with atrophy of seminiferous tubules, hyperplasia of Leydig cells and arrest of spermatogenesis in the MPEs group. Testicular steroidogenic proteins (StAR, P450scc, CYP17A1 and 17β-HSD, P450arom) were up-regulated, whereas P-element-induced wimpy testis proteins (PIWIL1 and PIWIL2) were down-regulated in the MPEs group (P < 0.05). However, the alterations of these parameters were inhibited in the MPEs+M-Que and MPEs+H-Que groups.

CONCLUSION

MPEs disturbed steroid hormone metabolism and caused testicular injuries. Que could inhibit testicular toxicity of MPEs, which might relate to the improved regulation of steroid hormone metabolism. © 2022 Society of Chemical Industry.

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.

An ex vivo Approach to Study Hormonal Control of Spermatogenesis in the Teleost Oreochromis niloticus

As the male reproductive organ, the main task of the testis is the production of fertile, haploid spermatozoa. This process, named spermatogenesis, starts with spermatogonial stem cells, which undergo a species-specific number of mitotic divisions until starting meiosis and further morphological maturation. The pituitary gonadotropins, luteinizing hormone, and follicle stimulating hormone, are indispensable for vertebrate spermatogenesis, but we are still far from fully understanding the complex regulatory networks involved in this process. Therefore, we developed an ex vivo testis cultivation system which allows evaluating the occurring changes in histology and gene expression. The experimental circulatory flow-through setup described in this work provides the possibility to study the function of the male tilapia gonads on a cellular and transcriptional level for at least 7 days. After 1 week of culture, tilapia testis slices kept their structure and all stages of spermatogenesis could be detected histologically. Without pituitary extract (tilPE) however, fibrotic structures appeared, whereas addition of tilPE preserved spermatogenic cysts and somatic interstitium completely. We could show that tilPE has a stimulatory effect on spermatogonia proliferation in our culture system. In the presence of tilPE or hCG, the gene expression of steroidogenesis related genes (cyp11b2 and stAR2) were notably increased. Other testicular genes like piwil1, amh, or dmrt1 were not expressed differentially in the presence or absence of gonadotropins or gonadotropin containing tilPE. We established a suitable system for studying tilapia spermatogenesis ex vivo with promise for future applications.

Temperature-induced testicular germ cell loss and recovery in Nile tilapia Oreochromis niloticus

Water temperature is a critical external factor influencing gonadal development in fish. This research aimed to study the impact of elevated temperature on testicular germ cell survival and reproductive capacity of Nile tilapia. Male Nile tilapia were exposed to high temperatures of either 36 (HT1) or 37 °C (HT2) for 3000 degree-days (DD) and thereafter returned to the control temperature of 27 °C (CT) for 2200 DD. The deleterious effects on testicular germ and somatic cells were observed histologically, characterised by vacuolisation, atrophy and the loss of spermatogenic cells in testes with a more severe impact of HT2 compared to HT1. Interestingly, serum 11-ketotestosterone (11-KT) and testosterone (T) levels tended to be higher during the heat treatments than CT. Expression levels of germline-specific genes piwil1, piwil2 and nanos2 and Bcl-2 family genes, bcl-xLb and baxa were significantly reduced during the heat treatment compared to CT, more so in the HT2, while the levels of nanos3 and gfra1 transcripts were only significantly reduced in HT2, implying a significant loss of spermatogonial stem cell (SSC) and spermatogonia in HT2. The effect of HT2 is further evidenced by the significantly reduced sperm density and fertilisation rate compared to CT and HT1 at the end of the recovery period but complete sterility was not induced by HT2. Overall, the present study showed significant effects of HT2 on germ cell survival with histological changes in testes, reduced milt quality, increased 11-KT, and decreased expression of germline-specific genes, SSC marker genes and Bcl-2 family genes in testes which could therefore be potential target genes for sterilisation by genome editing.

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.

Evolutionary conservation and divergence of Vasa, Dazl and Nanos1 during embryogenesis and gametogenesis in dark sleeper (Odontobutis potamophila)

Germline-specific genes, Vasa, Dazl and Nanos1, have highly conserved functions in germline development and fertility across animal phyla. In this study, the full-length sequences of Opvasa, Opdazl and Opnanos1 were cloned and characterized from the dark sleeper (Odontobutis potamophila). Gonad-specific expression patterns of Opvasa and Opdazl were confirmed in adult tissues by quantitative real-time PCR (qRT-PCR). Different from Opvasa and Opdazl, the expression of Opnanos1 was ubiquitously detected in all examined tissues except for the liver and spleen. Time-course dynamic expressions during embryogenesis were assessed, and all three genes (Opvasa, Opdazl and Opnanos1) persisted at a high level until gastrulation. qRT-PCR and Western blotting analyses revealed that all three genes were highly expressed throughout gametogenesis. In testis, the expressions of all three genes at the mRNA and protein levels were down-regulated during spermatogenesis. In ovary, different expression patterns were found, and all three genes had a differential role in translational regulation during oogenesis. The expressions of Opvasa, Opdazl and Opnanos1 at the mRNA but not the protein level were high in stage IV. Different expression patterns were found in premeiotic gonads treated by HPG axis hormones (HCG and LHRH-A). Immunolocalization analysis demonstrated that in testis, Opvasa, Opdazl and Opnanos1 were detected in spermatogonia and spermatocytes but absent in the meiotic products, such as spermatids and spermatozoa. In ovary, Opvasa, Opdazl and Opnanos1 persisted at a high level throughout oogenesis. These findings indicated that Opvasa, Opdazl and Opnanos1 played an important role in mitotic and early meiotic phases of oogenesis and spermatogenesis, and they functioned as maternal factors in early embryogenesis. Their proteins could be used as three new markers for germ cells during gametogenesis in O. potamophila gonad. Our data laid a good foundation for improving the breeding efficiency of O. potamophila.

Piwil1 gene is regulated by hypothalamic-pituitary-gonadal axis in turbot (Scophthalmus maximus): A different effect in ovaries and testes

As constituent factors of Piwi-interacting RNA (piRNA) pathways, Piwi proteins are essential for germline maintenance and gonadal development. Previous studies show that Piwi-piRNA pathways could be regulated by hypothalamic-pituitary-gonadal (HPG) axis, however, related studies have not been reported in marine species. Here we reported the identification of turbot (Scophthalmus maximus) piwil1 gene, which was abundantly expressed in testis and ovary in a tissue-specific manner. Phylogenetic and genomic structure analyses revealed that piwil1 was conserved in its sequence and function during vertebrate evolution. We also investigated the effects of HPG axis hormones, including human chorionic gonadotropin (hCG), estradiol-17β (E2) and 17α-methyltestosterone (MT), on gonadal piwil1 expression via in vivo and in vitro approaches. In ovary, hCG and E2 suppressed piwil1 expression both in vivo and in vitro, and MT increased piwil1 expression in vivo. In testis, hCG had upregulating effects on piwil1 expression in vivo and in vitro, and MT also increased piwil1 expression in vitro. In addition, E2 suppressed expression of piwil1 in vivo. These results indicated that the decreased or increased expression of piwil1 regulated by hormones might play a crucial role during gonadal differentiation and development in S. maximus.

Identification and expression of piwil2 in turbot Scophthalmus maximus, with implications of the involvement in embryonic and gonadal development

Piwil2, a member of the Argonaute family, is involved in the biogenesis of PIWI-interacting RNAs (piRNAs) and plays an important role in regulating gametogenesis. In the present study, we identified turbot Scophthalmus maximus piwil2 gene, named Smpiwil2, which contained a PAZ domain and a PIWI domain. Sequence comparison, genomic structure and phylogenetic analyses showed that Smpiwil2 is homologous to that of teleosts and tetrapods. The Smpiwil2 transcript showed higher expression in the ovary than in the testis, demonstrating a sexually dimorphic gene expression pattern. In situ hybridization (ISH) showed that Smpiwil2 was expressed in the oogonia and all the stages of oocytes in the ovary as well as in spermatogonia and spermatocytes in the testis. Embryonic expression profile revealed that Smpiwil2 was maternally inherited, and its level was higher from the zygote to the blastula stage and subsequently decreased until hatching. Moreover, a CpG island was predicted to locate in the 5'-flanking region of Smpiwil2 gene, and its methylation levels detected by sodium bisulfite sequencing showed significant disparity between females and males, implying that the sexually dimorphic expression of Smpiwil2 might be regulated by methylation. These results indicated that Smpiwil2 had potentially vital functions in embryonic and gonadal development in this species. In addition, the temporal and sex differences in Smpiwil2 expression indicated that this gene may play different roles in gonadal development of different sexes.