Differential expression of vasa homologue gene in the germ cells during oogenesis and spermatogenesis in a teleost fish, tilapia, Oreochromis niloticus

Cryopreservation and transplantation of spermatogonia stem cells in piracanjuba Brycon orbignyanus (Characiformes: Characidae), an endangered fish species

Piracanjuba (Brycon orbignyanus) is an endangered fish species from the Neotropical region. The establishment of a cryobank using spermatogonial stem cells (SSCs) and subsequent production of a germline chimera is thus a promising strategy for such species. In the present work, procedures for the isolation and cryopreservation of piracanjuba SSCs and subsequent transplantation into sterile recipients were established. The piracanjuba SSCs were obtained by Percoll density gradient centrifugation and differential plating. SSC fractions were evaluated by relative ddx4 expression, alkaline phosphatase activity, and light microscopy. SSC cryopreservation was performed using five cryoprotectants at three different concentrations. The mix of the cells from the 20% and 30% Percoll density gradients showed 58.35 ± 0.03% purity of SSCs. The purity of SSCs increased to 66.00 ± 0.01% after differential plating. The relative ddx4 expression was 3.5 times higher in cells from the Percoll density gradient centrifugation than in the gonad and cells after differential plating. Propanediol (1 M) was the most effective cryoprotector evaluated (P = 1.000), showing 90.75 ± 1.85% cell viability. Freshly isolated and cryopreserved cells from the Percoll density gradient centrifugation were transplanted into a sterile male adult triploid hybrid with germ cell-less gonads. SSCs were observed in the germinal epithelium of the testes of recipients 20 days after transplantation. The results are promising for obtaining functional germline chimeras in Neotropical fish. Consequently, although the number of males used for the experiment was borderline, the procedures established here can be applied in future actions for the conservation and reconstitution of the piracanjuba in case of extinction.

Characteristics of the Vasa Gene in Silurus asotus and Its Expression Response to Letrozole Treatment

The identification and expression of germ cells are important for studying sex-related mechanisms in fish. The vasa gene, encoding an ATP-dependent RNA helicase, is recognized as a molecular marker of germ cells and plays a crucial role in germ cell development. Silurus asotus, an important freshwater economic fish species in China, shows significant sex dimorphism with the female growing faster than the male. However, the molecular mechanisms underlying these sex differences especially involving in the vasa gene in this fish remain poorly understood. In this work, the vasa gene sequence of S. asotus (named as Savasa) was obtained through RT-PCR and rapid amplification of cDNA end (RACE), and its expression in embryos and tissues was analyzed using qRT-PCR and an in situ hybridization method. Letrozole (LT) treatment on the larvae fish was also conducted to investigate its influence on the gene. The results revealed that the open reading frame (ORF) of Savasa was 1989 bp, encoding 662 amino acids. The SaVasa protein contains 10 conserved domains unique to the DEAD-box protein family, showing the highest sequence identity of 95.92% with that of Silurus meridionalis. In embryos, Savasa is highly expressed from the two-cell stage to the blastula stage in early embryos, with a gradually decreasing trend from the gastrula stage to the heart-beating stage. Furthermore, Savasa was initially detected at the end of the cleavage furrow during the two-cell stage, later condensing into four symmetrical cell clusters with embryonic development. At the gastrula stage, Savasa-positive cells increased and began to migrate towards the dorsal side of the embryo. In tissues, Savasa is predominantly expressed in the ovaries, with almost no or lower expression in other detected tissues. Moreover, Savasa was expressed in phase I-V oocytes in the ovaries, as well as in spermatogonia and spermatocytes in the testis, implying a specific expression pattern of germ cells. In addition, LT significantly upregulated the expression of Savasa in a concentration-dependent manner during the key gonadal differentiation period of the fish. Notably, at 120 dph after LT treatment, Savasa expression was the lowest in the testis and ovary of the high concentration group. Collectively, findings from gene structure, protein sequence, phylogenetic analysis, RNA expression patterns, and response to LT suggest that Savasa is maternally inherited with conserved features, serving as a potential marker gene for germ cells in S.asotus, and might participate in LT-induced early embryonic development and gonadal development processes of the fish. This would provide a basis for further research on the application of germ cell markers and the molecular mechanisms of sex differences in S. asotus.

Dmrt1 is the only male pathway gene tested indispensable for sex determination and functional testis development in tilapia

Sex is determined by multiple factors derived from somatic and germ cells in vertebrates. We have identified amhy, dmrt1, gsdf as male and foxl2, foxl3, cyp19a1a as female sex determination pathway genes in Nile tilapia. However, the relationship among these genes is largely unclear. Here, we found that the gonads of dmrt1;cyp19a1a double mutants developed as ovaries or underdeveloped testes with no germ cells irrespective of their genetic sex. In addition, the gonads of dmrt1;cyp19a1a;cyp19a1b triple mutants still developed as ovaries. The gonads of foxl3;cyp19a1a double mutants developed as testes, while the gonads of dmrt1;cyp19a1a;foxl3 triple mutants eventually developed as ovaries. In contrast, the gonads of amhy;cyp19a1a, gsdf;cyp19a1a, amhy;foxl2, gsdf;foxl2 double and amhy;cyp19a1a;cyp19a1b, gsdf;cyp19a1a;cyp19a1b triple mutants developed as testes with spermatogenesis via up-regulation of dmrt1 in both somatic and germ cells. The gonads of amhy;foxl3 and gsdf;foxl3 double mutants developed as ovaries but with germ cells in spermatogenesis due to up-regulation of dmrt1. Taking the respective ovary and underdeveloped testis of dmrt1;foxl3 and dmrt1;foxl2 double mutants reported previously into consideration, we demonstrated that once dmrt1 mutated, the gonad could not be rescued to functional testis by mutating any female pathway gene. The sex reversal caused by mutation of male pathway genes other than dmrt1, including its upstream amhy and downstream gsdf, could be rescued by mutating female pathway gene. Overall, our data suggested that dmrt1 is the only male pathway gene tested indispensable for sex determination and functional testis development in tilapia.

Determination of the timing of early gonadal differentiation in silver pomfret, Pampus argenteus

Silver pomfret is a species of global significance due to its high nutritional in fisheries sector. To accurately ascertain the timing of sex differentiation mechanism and mRNA level in this species, this study examined gonad morphology and patterns of gene expression related to sex differentiation in males and females from 51 to 180 days post hatch (dph), the temperature of water was maintained at 26 ± 1 ℃. Distinct morphological differentiation of the silver pomfret ovaries, marked by the emergence of primary oocytes, became apparent from 68 dph. By 108 dph, the testes began to differentiate, as evidenced by the appearance of the efferent duct. Early oocytes exhibited a diameter ranged from 0.077 mm to 0.682 mm, with an average diameter of 0.343 ± 0.051 mm. The proportions of various types of germ cells within the testes were subjected to analysis. The localization of Vasa during the early stages of sexual differentiation was a subject to analysis as well. Vasa was predominantly localized within the cytoplasm of gonocyte, peri-nucleolus stage oocytes, primary oocytes and type A spermatogonocytes, indicating that Vasa is involved in the early gonadal differentiation of silver pomfret. The study investigated the expression patterns of dmrt1, gsdf, amh, foxl2, cyp19a1a, cyp11a, sox3 and vasa, all of which are involved in the sex differentiation of teleosts. Among these genes, amh, gsdf, sox3, foxl2, vasa were indentified as crucial contributors to the early gonadal development of silver pomfret. Significant sex-related differences were observed in the expression patterns of amh, dmrt1, gsdf, cyp11a, sox3, cyp19a1a, vasa. This study provides novel insights into the timing of physiological changes associated with the sexual differentiation of silver pomfret. Collectively, the present data indicates that the differentiation of ovaries and testes take place approximately at 68 dph in females and 108 dph in males.

Effects of CRISPR/Cas9-mediated dnd1 knockout impairs gonadal development in striped catfish

Clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 technology allows for the generation of loss-of-function mutations to enable efficient gene targeting to produce desired phenotypes, such as the production of germ cell-free fish. This technology could provide several applications for aquaculture and conservation of fisheries resources, such as the prevention of overpopulation in fish culture and gene flow from escaped farmed fish into wild populations and the production of germ cell-free recipient larvae for germ cell transplantation. This study aimed to develop CRISPR/Cas9 mediated dead-end 1 (dnd1) knockout techniques for striped catfish (Pangasianodon hypophthalmus). To optimise CRISPR/Cas9-induced dnd1 knockout, three single-guide RNAs (sgRNAs) were designed to target upstream sequences of start codon of the dnd1 gene. A combination of two concentrations of each sgRNA (100 and 200 ng/µl) and three concentrations of Cas9 (100, 250, and 500 ng/µl) was microinjected into fertilised striped catfish eggs. These sgRNAs/Cas9 could induce indel mutations and lower the primordial germ cell (PGC) numbers. Histological analyses indicated that sgRNA3 targeting upstream and nearest to the start codon at 200 ng/µL and Cas9 at 500 ng/µL showed the lowest PGC number. The reduction in PGC number was confirmed by in situ hybridisation using antisense dnd1 and vasa probes. All sgRNA/Cas9 combinations reduced the expression of dnd1, cxcr4b, dazl, nanos1, nanos2, and vasa, and the lowest expression levels were observed in gonads obtained from fish injected with 200 ng/µL sgRNA3 and 500 ng/µL Cas9 (P < 0.05). In addition, at 1 year of age, a significantly lower gonadosomatic index was observed in fish injected with all sgRNA and Cas9 at 500 ng/µL. Moreover, compared to the control fish, the ovaries and testes presented different morphologies in the sgRNA/Cas9-injected fish, that is, few previtellogenic oocytes in the ovary and spermatogonial cell-less testes. In conclusion, CRISPR/Cas 9 targeting dnd1 knockout at the upstream sequences of start codon was achieved, which resulted in the downregulation of dnd1 and lowered PGC number.

Isolation of an Insulin-Like Receptor Involved in the Testicular Development of the Mud Crab Scylla paramamosain

Insulin-like androgenic gland hormone (IAG) is a key regulator of male sexual differentiation in crustaceans that plays important roles in secondary sexual characteristics and testicular development. As a hormone, IAG interacts with its membrane receptor to initiate downstream signal pathways to exert its biological functions. In this study, we isolated a full-length cDNA of an insulin-like receptor (Sp-IR) from the mud crab Scylla paramamosain. Sequence analysis revealed that this receptor consists of a Fu domain, two L domains, three FN-III domains, a transmembrane domain, and a tyrosine kinase domain, classifying it as a member of the tyrosine kinase insulin-like receptors family. Our results also suggested that Sp-IR was highly expressed in the testis and AG in males. Its expression in the testis peaked in stage I but significantly decreased in stages II and III (p < 0.01). Next, both short- and long-term RNA interference (RNAi) experiments were performed on males in stage I to explore Sp-IR function in mud crabs. The results showed that Sp-vasa and Sp-Dsx expression levels in the testis were significantly down-regulated after the specific knockdown of Sp-IR by RNAi. Additionally, the long-term knockdown of Sp-IR led to a considerable decrease in the volume of seminiferous tubules, accompanied by large vacuoles and a reduced production of secondary spermatocytes and spermatids. In conclusion, our results indicated that Sp-IR is involved in testicular development and plays a crucial role in transitioning from primary to secondary spermatocytes. This study provided a molecular basis for the subsequent analysis of the mechanism on male sexual differentiation in Brachyuran crabs.

Silencing of the Vasa gene by RNA Interference Affects Embryonic Development and Reproductive Output in the Sea Louse Caligus rogercresseyi

The sea louse Caligus rogercresseyi is a major ectoparasitic copepod that causes significant economic losses in the salmon farming industry. Despite recent advancements, the mechanisms underlying germline and embryo development in this species remain poorly understood. The Vasa gene encodes a highly conserved DEAD box helicase that is required for germ cell formation and function in many species. In this study, the Vasa gene was characterized in C. rogercresseyi, and its expression and function were analyzed. Phylogenetic analysis showed that the Cr-Vasa gene product formed clusters in clades with Vasa proteins from closely related species of crustaceans. Cr-Vasa gene expression patterns were assessed by qPCR, and the results showed a significantly higher relative expression level in adult females compared to copepodid, chalimus, and adult male stages. Tissue-specific localization of Cr-Vasa mRNA in C. rogercresseyi was determined using chromogenic in situ hybridization, and strong positive signal was observed in male testes, but also in the intestine and cuticle, while in females, it was observed in the ovaries, oocytes, cuticle, intestine, and egg strings. RNAi-mediated gene silencing of Cr-Vasa impacted embryonic development and reproductive output in adult female lice. Females from the dsVasa-treated group displayed unusual phenotypes, including shorter egg strings with numerous extra-embryonic inclusions, irregularly shaped abnormal embryos, and aborted egg strings. This study provides insights into the role of the Vasa gene in C. rogercresseyi embryonic development and reproductive output, which may have implications for the control of this parasitic copepod in the salmon farming industry.

RNA Helicase Vasa as a Multifunctional Conservative Regulator of Gametogenesis in Eukaryotes

Being a conservative marker of germ cells across metazoan species, DEAD box RNA helicase Vasa (DDX4) remains the subject of worldwide investigations thanks to its multiple functional manifestations. Vasa takes part in the preformation of primordial germ cells in a group of organisms and contributes to the maintenance of germline stem cells. Vasa is an essential player in the piRNA-mediated silencing of harmful genomic elements and in the translational regulation of selected mRNAs. Vasa is the top hierarchical protein of germ granules, liquid droplet organelles that compartmentalize RNA processing factors. Here, we survey current advances and problems in the understanding of the multifaceted functions of Vasa proteins in the gametogenesis of different eukaryotic organisms, from nematodes to humans.

Characterization of ddx4 and dnd Homologs in Snakeskin Gourami (Trichopodus pectoralis) and Their Expression Levels during Larval Development and in Gonads of Males and Females

The purpose of this study was to clone and characterize ddx4 and dnd1 homologs in snakeskin gourami (Trichopodus pectoralis) and to determine their expression levels during larval development and in the gonads of males and females. Both cDNAs contained predicted regions that shared consensus motifs with the ddx4 family in teleosts and the dnd family in vertebrates. Phylogenetic tree construction analysis confirmed that these two genes were clustered in the families of teleosts. Both ddx4 and dnd1 mRNAs were detectable only in the gonads, particularly in germ cells. These two genes were expressed during early larval development. The expression of ddx4 was high during early larval development and decreased with increasing developmental age, whereas dnd1 expression increased with developmental age. In adult fish, the expression levels of both genes were higher in the ovary than in the testis. Overall, these findings provide valuable molecular information on ddx4 and dnd, and can be applied in future reproductive biological studies relating to sex dimorphism in snakeskin gourami.

Vasa Is a Potential Germ Cell Marker in Leopard Coral Grouper (Plectropomus leopardus)

Vasa (Ddx4, DEAD box polypeptide 4), an extremely specific marker of germ cells in vivo, is an ATP-dependent RNA helicase that plays an essential role in germ cell development and gametogenesis. However, the expression and function information about this gene in groupers remains lacking. Here, vasa homolog termed Plvasa was isolated and identified Plvasa as a putative germ cell marker in the leopard coral grouper, (Plectropomus leopardus). Results indicated that Plvasa contained 17 exons in the genomic sequence and 9 conserved motifs of the DEAD-box protein by sequence analysis. The sequence comparison, phylogenetic analyses and synteny analyses showed that Plvasa was homologous with other teleosts. Additionally, the expression of Plvasa was significantly higher in gonads than in other tissues in adult individuals (p < 0.05). Further, the distribution of Plvasa revealed that it was only expressed in the germ cells, such as spermatids, germline stem cells and oocytes at different stages, and could not be detected in the somatic cells of gonads. The current study verified that the Plvasa gene is a valuable molecular marker of germ cells in leopard coral grouper, which potentially plays an important role in investigating the genesis and development of teleost germ cells.

A time-course transcriptome analysis of gonads from yellow catfish (Pelteobagrus fulvidraco) reveals genes associated with gonad development

Background

The yellow catfish, Pelteobagrus fulvidraco, is a commercially important fish species. It is widely distributed in the fresh water areas of China, including rivers, lakes, and reservoirs. Like many other aquaculture fish species, people have observed significant size dimorphism between male and female yellow catfish and it shows a growth advantage in males.

Results

Here, at the first time, the time-course transcriptome was used to explore the various expression profiles of genes in different gonad developmental stages and genders. A total of 2696 different expression genes (DEGs) were identified from different stages. Based on these DEGs, 13 gonad development related genes were identified which showed time-specific or sex biased expression patterns.

Conclusion

This study will provide the crucial information on the molecular mechanism of gonad development of female and male yellow catfish. Especially, during the different gonad development stages, these 13 gonad development related genes exhibit various expression patterns in female and male individual respectively. These results could inspire and facilitate us to understanding the various roles of these genes play in different gonad development stages and genders.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08651-0.

pitpβ_w Encoding Phosphatidylinositol Transfer Protein Is Involved in Female Differentiation of Chinese Tongue Sole, Cynoglossus semilaevis

Phosphatidylinositol transfer protein (pitp) plays an important role in phospholipid transfer in animals. A pitp variant (pitpβ_w) in Chinese tongue sole was identified by transcriptomic analysis for its female-biased expression. The coding sequence of pitpβ_w was 816 bp, encoding a 371-amino-acid protein. pitpβ_w showed female-biased expression and was relatively high in brain, muscle, and ovary tissues. In different developmental stages of the ovary, pitpβ_w could be detected from 40 days until 3 years post hatching, and the highest expression was observed at 90 days. In situ hybridization revealed that pitpβ_w was predominantly localized in early-stage oocytes (I-III stages). After siRNA-mediated knockdown of pitpβ_w in an ovarian cell line, the expression of sox9a was reduced, while that of figla_tv1 and sox9b was significantly increased. Our findings suggest that pitpβ_w might be involved in female differentiation and early oogenesis.

Identification and characterization of a new germline-specific marker vasa gene and its promoter in the giant freshwater prawn Macrobrachium rosenbergii

Vasa gene encodes a protein member of DEAD-box superfamily of ATP-dependent RNA helicases, which plays a key role in germline development in metazoans. In present study, we identified a new germline-specific marker Mrvasa in the prawn Macrobrachium rosenbergii, whose genomic DNA sequence consists of 14 exons and 13 introns. A 2516 bp of full-length Mrvasa cDNA encodes a protein of 603 amino acids. It contains nine conserved motifs, a zinc-finger motif, and RGG repeats. RT-PCR indicated that Mrvasa mRNA was specifically expressed in gonads. QPCR analysis further revealed that the expression of Mrvasa mRNA is much higher in testis than in ovary. In testis, the relative expression level of Mrvasa mRNA in late developing stage is significantly higher than that in early-middle developing stage. During ovarian development, no significant difference in expression was found. In situ hybridization demonstrated that Mrvasa mRNA was localized in germline cells including spermatogonia, spermatocytes, and spermatozoa in testes, and previtellogenic and vitellogenic oocytes in ovary. We then isolated the Mrvasa promoter and determined the transcription core region of this promoter. This is the first report on identification of vasa core promoter in crustaceans. Our results will provide a useful germline-specific marker Mrvasa for tracing germline cell formation and development in M. rosenbergii.

Cloning and Expression Profiling of the Gene vasa during First Annual Gonadal Development of Cobia (Rachycentron canadum)

The vasa gene is essential for germ cell development and gametogenesis both in vertebrates and in invertebrates. In the present study, vasa (Rcvasa) cDNA was cloned from cobia (Rachycentron canadum) using the RACE amplification method. We found that the full-length cDNA sequence of Rcvasa comprises 2571 bp, containing a 5′-UTR of 145 bp, a 3′-UTR of 341 bp, and an open reading frame (ORF) of 2085 bp, encoding a protein of 694 aa. The deduced amino acid sequence contains 8 conserved motifs of the DEAD-box protein family, 7 RGG repeats, and 10 RG repeats in the N-terminal region. Comparisons of the deduced amino acid sequence with those of other teleosts revealed the highest percentage identity (86.0%) with Seriola quinqueradiata. By using semiquantitative RT-PCR, Rcvasa appeared to be specifically expressed in the testis and ovary, among 13 tissues analyzed. In addition, annual changes in Rcvasa expression levels were examined in the gonads by quantitative real-time PCR (qRT-PCR). The expression of Rcvasa in the testis first increased significantly at 120 dph (stage II–III), then stabilized as the testis developed from 185 dph (stage III) to 360 dph (stage V). During the development of the ovary (stage I to II), the expression of Rcvasa first increased and reached the highest level at 210 dph (stage II), then decreased. Furthermore, the results of chromogenic in situ hybridization (CISH) revealed that Rcvasa mRNA was mainly expressed in germ cells and barely detected in somatic cells. In the testis, Rcvasa mRNA signal was concentrated in the periphery of spermatogonia, primary spermatocytes, and secondary spermatocytes and was significantly weaker in spermatids and spermatozoa. In the ovary, Rcvasa mRNA signal was uniformly distributed in the perinuclear cytoplasm and was intense in early primary oocytes (stage I and II). These findings could provide a reference for understanding the regulatory mechanisms of vasa expression during the development of germ cells in cobia.

Comparative transcriptomic analysis of gonadal development and renewal in the ovoviviparous black rockfish (Sebastes schlegelii)

BACKGROUND

The black rockfish (Sebastes schlegelii) has an ovoviviparous reproductive pattern and long-term sperm storage, resulting in asynchronous gonadal development between the sexes. However, the comprehensive understanding of gonadal development in black rockfish has not yet been achieved. Here, we studied gonadal development and germ cell renewal using histology and RNA-seq.

RESULTS

In this study, RNA-seq was performed on testes and ovaries to characterize key pathways and genes that are active during development and gamete maturation in black rockfish. Differentially expressed genes (DEGs) were identified and annotated in 4 comparisons (F_III vs. F_IV, F_IV vs. F_V, M_III vs. M_IV and M_IV vs. M_V). Based on analysis of DEGs enriched in the testis, 11 and 14 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were mapped to the M_III vs. M_IV group and the M_IV vs. M_V group, respectively. DEGs in ovarian development were also classified into 10 groups according to their biological functions. The expression patterns of the selected genes determined by qPCR were significantly correlated with the RNA-Seq results, supporting the reliability and accuracy of the RNA-Seq analysis. E2 levels showed down regulation from previtellogenesis to mature stage in female and T level showed down regulation from spermatogenesis to regressed stage in the male.

CONCLUSIONS

The categories "intercellular interaction and cytoskeleton", "molecule amplification" and "repair in the cell cycle" were revealed to be crucial in testis development and spermatogenesis, as was the biosynthesis of a series of metabolites. Our results provide comprehensive insight into black rockfish gonadal development and provide a basis for further study of reproductive physiology and molecular biology in ovoviviparity teleosts.

Establishment of a stem Leydig cell line capable of 11-ketotestosterone production

The deficiency or insufficiency of androgen can trigger a range of reproductive diseases as well as other symptoms. Stem Leydig cells (SLCs) are critical for the formation and maintenance of a functional androgen-producing cell (Leydig cell, LC) population throughout adult male life. However, to date, our knowledge about SLCs is poor. Here we report the derivation and characterisation of a clonal stem LC line (designated as TSL) capable of 11- ketotestosterone (11-KT) production from a 3-month-old Nile tilapia (Oreochromis niloticus) testis. The cells retained stable proliferation after 77 generations with normal karyotype and growth factor dependency. They expressed platelet-derived growth factor receptor-α (pdgfrα), nestin and chicken ovalbumin upstream promoter transcription factor II (coup-tfIIa), which are characteristic of SLCs. Upon induction in defined medium, TSLs could undergo differentiation into steroidogenically active LCs and produce 11-KT. When implanted into recipient Nile tilapia testes from which endogenous LCs had been eliminated by ethane dimethanesulphonate (EDS) treatment, the PKH26-labelled TSLs could colonise the interstitium, subsequently express steroidogenic genes and restore 11-KT production. Taken together, our data suggest that TSLs possess the ability of continuous proliferation and potential of differentiation into functional LCs invitro and invivo. To the best of our knowledge TSL might represent the first stem LC line capable of 11-KT production to date. Our study may offer new opportunities for investigating the self-renewal of SLCs and steroidogenesis invitro, and provide an invaluable invitro model for investigating endocrine disruptors.

Homozygous mutation of foxh1 arrests oogenesis causing infertility in female Nile tilapia†

Foxh1, a member of fox gene family, was first characterized as a transcriptional partner in the formation of the Smad protein complex. Recent studies have shown foxh1 is highly expressed in the cytoplasm of oocytes in both tilapia and mouse. However, its function in oogenesis remains unexplored. In the present study, foxh1-/- tilapia was created by CRISPR/Cas9. At 180 dah (days after hatching), the foxh1-/- XX fish showed oogenesis arrest and a significantly lower GSI. The transition of oocytes from phase II to phase III and follicle cells from one to two layers was blocked, resulting in infertility of the mutant. Transcriptomic analysis revealed that expression of genes involved in estrogen synthesis and oocyte growth were altered in the foxh1-/- ovaries. Loss of foxh1 resulted in significantly decreased Cyp19a1a and increased Cyp11b2 expression, consistent with significantly lower concentrations of serum estradiol-17β (E2) and higher concentrations of 11-ketotestosterone (11-KT). Moreover, administration of E2 rescued the phenotypes of foxh1-/- XX fish, as indicated by the appearance of phase III and IV oocytes and absence of Cyp11b2 expression. Taken together, these results suggest that foxh1 functions in the oocytes to regulate oogenesis by promoting cyp19a1a expression, and therefore estrogen production. Disruption of foxh1 may block the estrogen synthesis and oocyte growth, leading to the arrest of oogenesis and thus infertility in tilapia.

Germline sexual fate is determined by the antagonistic action of dmrt1 and foxl3/foxl2 in tilapia

Germline sexual fate has long been believed to be determined by the somatic environment, but this idea is challenged by recent studies of foxl3 mutants in medaka. Here, we demonstrate that the sexual fate of tilapia germline is determined by the antagonistic interaction of dmrt1 and foxl3, which are transcriptionally repressed in male and female germ cells, respectively. Loss of dmrt1 rescued the germ cell sex reversal in foxl3Δ7/Δ7 XX fish, and loss of foxl3 partially rescued germ cell sex reversal but not somatic cell fate in dmrt1Δ5/Δ5 XY fish. Interestingly, germ cells lost sexual plasticity in dmrt1Δ5/Δ5 XY and foxl3Δ7/Δ7 XX single mutants, as aromatase inhibitor (AI) and estrogen treatment failed to rescue the respective phenotypes. However, recovery of germ cell sexual plasticity was observed in dmrt1/foxl3 double mutants. Importantly, mutation of somatic cell-specific foxl2 resulted in testicular development in foxl3Δ7/Δ7 or dmrt1Δ5/Δ5 mutants. Our findings demonstrate that sexual plasticity of germ cells relies on the presence of both dmrt1 and foxl3. The existence of dmrt1 and foxl3 allows environmental factors to influence the sex fate decision in vertebrates.

Primordial Germ Cell Migration and Histological and Molecular Characterization of Gonadal Differentiation in Pachón Cavefish Astyanax mexicanus

The genetic regulatory network governing vertebrate gonadal differentiation appears less conserved than previously thought. Here, we investigated the gonadal development of Astyanax mexicanus Pachón cavefish by looking at primordial germ cells (PGCs) migration and proliferation, gonad histology, and gene expression patterns. We showed that PGCs are first detected at the 80% epiboly stage and then reach the gonadal primordium at 1 day post-fertilization (dpf). However, in contrast to the generally described absence of PGCs proliferation during their migration phase, PGCs number in cavefish doubles between early neurula and 8-9 somites stages. Combining both gonadal histology and vasa (germ cell marker) expression patterns, we observed that ovarian and testicular differentiation occurs around 65 dpf in females and 90 dpf in males, respectively, with an important inter-individual variability. The expression patterns of dmrt1, gsdf, and amh revealed a conserved predominant male expression during cavefish gonadal development, but none of the ovarian differentiation genes, i. e., foxl2a, cyp19a1a, and wnt4b displayed an early sexually dimorphic expression, and surprisingly all these genes exhibited predominant expression in adult testes. Altogether, our results lay the foundation for further research on sex determination and differentiation in A. mexicanus and contribute to the emerging picture that the vertebrate sex differentiation downstream regulatory network is less conserved than previously thought, at least in teleost fishes.

Amniotic fluid-derived exosomes improved spermatogenesis in a rat model of azoospermia

AIMS

This study aimed to explore the therapeutic effects of amniotic fluid-derived extracellular vesicles including exosomes (AF-Exos) on the recovery of sperm production capacity in a rat model of azoospermia.

MAIN METHODS

The non-obstructive azoospermia (NOA) was induced in rats using intratesticular administration of Busulfan. Azoospermia was confirmed by testis histology. AF-Exos samples containing 10 or 40 μg exosomal proteins were injected into testicular tissue of NOA rats. After two months, the recovery of spermatogenesis was monitored via histopathological staining, spermiogram, and hormonal analysis. Immunohistochemistry staining for OCT-3/4 was used to identify of spermatogonial progenitors. The expression of DAZL and VASA, was also measured.

KEY FINDINGS

AF-Exos exhibited sphere-shaped morphology with the mean diameter and zeta potential of 50 ± 7.521 nm and -7.16 mV. Immunoblots revealed that isolated nanoparticles were CD63, CD9, and CD81 positive. Histopathological evaluation revealed that spermatogenesis was improved significantly in NOA rats after AF-Exos injection. Data showed that the sperm parameters and spermatogenesis index were significantly improved after AF-Exos injection compared to azoospermic groups. OCT-3/4⁺ cells were increased in NOA rats after AF-Exos injection, showing the restoration of spermatogenesis. In the present study, both doses of exosome (10 and 40 μg) restored the testicular function of NOA rats. DAZL and VASA were increased significantly in animals who received 40 μg exosomal protein compared to azoospermic rats. Except in a high dose of AF-Exos (40 μg) for Testosterone and FSH, no statistically significant differences were found regarding hormones post-exosome injection.

SIGNIFICANCE

Our study demonstrated that AF-Exos regenerated spermatogenesis and improved sperm quality in NOA rats.

Cloning, expression and functional analysis of the desert hedgehog (dhh) gene in Chinese tongue sole (Cynoglossus semilaevis)

Desert hedgehog (dhh) is a gene that is crucial for spermatogenesis and Leydig cell differentiation, but little is known regarding its influence on gonadal differentiation and development in fish. To understand its function, we cloned and characterized the dhh gene from Cynoglossus semilaevis (csdhh). The full length csdhh cDNA was 2473 bp, including a 1386 bp open reading frame (ORF), a 475 bp 5'-UTR, and a 612 bp 3'-UTR, encoding a predicted protein of 461 amino acid residues. Phylogenetic analysis showed that the putative protein belongs to the hedgehog (HH) family, and contains typical HH-N and HH-C domains. Amino acid sequence analysis revealed that CsDhh shares many features with Dhh analogues in other teleost species. Real-time quantitative PCR showed that csdhh was detected in eight different tissues in male and female tongue sole. During early embryonic development, the relative expression of the csdhh was significantly higher in the neural stage than in other embryonic developmental stages (P < 0.05). csdhh was detected at 20 days after hatching (dah) and at the critical period of male gonadal differentiation (80-95 dah), the relative expression of the csdhh was significantly higher in the male gonads than the female gonads. In 5, 8, and 12 month old gonads, the relative expression of the csdhh was significantly higher in male and pseudo-male than in female fish. The in situ hybridization (ISH) results showed that the hybridization signal was strongly expressed in primary and secondary spermatocytes, spermatids, and sertoli cells of the 1-year-old fish testis, with only weak signal expression in the corresponding ovarian tissue. These results suggest that csdhh is highly conserved in evolution and plays an important role in spermatogenesis in males and pseudo-males.

Comparison of RNA m6A and DNA methylation profiles between mouse female germline stem cells and STO cells

N⁶-methyladenosine (m⁶A) methylation modification is the most prevalent and abundant internal modification of eukaryotic mRNAs. Increasing evidence has shown that mRNA m⁶A plays important roles in the development of stem cells. However, to the best of our knowledge, no reports about the roles of mRNA m⁶A in mouse female germline stem cells (mFGSCs) have been published. In this study, we compared the genome-wide profiles of mRNA m⁶A methylation and DNA methylation between FGSCs and sandosinbred mice (SIM) embryo-derived thioguanine and ouabain-resistant (STO) cells. qRT-PCR revealed that the expression levels of mRNA m⁶A-related genes (Mettl3, Alkbh5, Ythdf1, Ythdf2, Ythdc1, and Ythdc2) in FGSCs were significantly higher than those in STO cells. m⁶A RNA immunoprecipitation sequencing (MeRIP-seq) data further showed that the unique m⁶A-methylated mRNAs in FGSCs and STO cells were related to cell population proliferation and somatic development, respectively. Additionally, knockdown of Ythdf1 inhibited FGSC self-renewal. Comparison of methylated DNA immunoprecipitation sequencing (MeDIP-seq) results between FGSCs and STO cells identified that DNA methylation contributed to FGSC proliferation by suppressing the somatic program. These results suggested that m⁶A regulated FGSC self-renewal possibly through m⁶A binding protein YTHDF1, and DNA methylation repressed somatic programs in FGSCs to maintain FGSC characteristics.

Sex determination, gonadal sex differentiation, and plasticity in vertebrate species

A diverse array of sex determination (SD) mechanisms, encompassing environmental to genetic, have been found to exist among vertebrates, covering a spectrum from fixed SD mechanisms (mammals) to functional sex change in fishes (sequential hermaphroditic fishes). A major landmark in vertebrate SD was the discovery of the SRY gene in 1990. Since that time, many attempts to clone an SRY ortholog from nonmammalian vertebrates remained unsuccessful, until 2002, when DMY/dmrt1by was discovered as the SD gene of a small fish, medaka. Surprisingly, however, DMY/dmrt1by was found in only 2 species among more than 20 species of medaka, suggesting a large diversity of SD genes among vertebrates. Considerable progress has been made over the last 3 decades, such that it is now possible to formulate reasonable paradigms of how SD and gonadal sex differentiation may work in some model vertebrate species. This review outlines our current understanding of vertebrate SD and gonadal sex differentiation, with a focus on the molecular and cellular mechanisms involved. An impressive number of genes and factors have been discovered that play important roles in testicular and ovarian differentiation. An antagonism between the male and female pathway genes exists in gonads during both sex differentiation and, surprisingly, even as adults, suggesting that, in addition to sex-changing fishes, gonochoristic vertebrates including mice maintain some degree of gonadal sexual plasticity into adulthood. Importantly, a review of various SD mechanisms among vertebrates suggests that this is the ideal biological event that can make us understand the evolutionary conundrums underlying speciation and species diversity.

Germline Specific Expression of a vasa Homologue Gene in the Viviparous Fish Black Rockfish (Sebastes schlegelii) and Functional Analysis of the vasa 3 Untranslated Region

Germ cells play a key role in gonad development. As precursors, primordial germ cells (PGCs) are particularly important for germline formation. However, the origination and migration patterns of PGCs are poorly studied in marine fish, especially for viviparous economic species. The vasa gene has been widely used as a germ cell marker to identify a germline because vasa RNA is a component of germ plasm. In this study, we described the expression pattern of black rockfish (Sebastes schlegelii) vasa (Ssvas) in gonadal formation and development by in situ hybridization. The results showed that Ssvas failed in localization at the cleavage furrows until the late gastrula stage, when PGCs appeared and migrated to the genital ridge and formed elongated gonadal primordia at 10 days after birth. This study firstly revealed the PGCs origination and migration characteristics in viviparous marine fish. Furthermore, we microinjected chimeric mRNA containing EGFP and the 3′untranslated region (3′UTR) of Ssvas into zebrafish (Danio rerio) and marine medaka (Oryzias melastigma) fertilized eggs for tracing PGCs. We found that, although Sebastes schlegelii lacked early localization, similar to red seabream (Pagrus major) and marine medaka, only the 3′UTR of Ssvas vasa 3′UTR of black rockfish was able to label both zebrafish and marine medaka PGCs. In comparison with other three Euteleostei species, besides some basal motifs, black rockfish had three specific motifs of M10, M12, and M19 just presented in zebrafish, which might play an important role in labeling zebrafish PGCs. These results will promote germ cell manipulation technology development and facilitate artificial reproduction regulation in aquaculture.

Both of marine fish species Oryzias melastigma and Pagrus major all failing in early localization at embryo stage by vasa RNA

Germ cells are essential for gonadal development. As precursors of germ cells, primordial germ cells (PGCs) are particularly important for germline formation. However, the research on distribution patterns of PGCs in marine fish is very limited, especially for economic species. The vasa gene has been widely used as marker to identify PGCs origination and migration because of vasa RNA is a component of germ plasm. In this study, we isolated full-length vasa cDNA (Omvas and Pmvas) from marine medaka (Oryzias melastigma) and red seabream (Pagrus major), detected vasa transcripts in different tissues by RT-PCR and described vasa expression patterns during embryogenesis and gametogenesis by in situ hybridization. At the same time, we also explored the relationship between early distribution of germ plasm components and species evolution. The results demonstrated that deduced amino acid sequence of Omvas and Pmvas shared several conserved motifs of Vasa homologues and high identity with other teleost, and vasa transcripts were exclusively detected in early germ cells of gonad. During embryogenesis, vasa RNA of both fishes, like medaka (Oryzias latipes), failed to localize at cleavage furrows and distributed uniformly throughout each blastomere. This study firstly discovered that the marine economic fish, red seabream, lost vasa RNA early specific localization at cleavage furrows and distinctive distribution in germ cells. In addition, compared with other teleost, we found that early distribution of germ plasm might not relate to species evolution. This will improve our understanding of vasa localization modes in teleost, and facilitate fish germ cell manipulation.

Presence of the matrix metalloproteinases during the migration of the primordial germ cells in zebrafish gonadal ridge

In vertebrates, the primordial germ cells (PGCs) differentiate from extragonadal regions, migrating to gonadal ridge during the embryonic development. However, recent studies in mammals indicate that the PGCs originate from the epiblast and subsequently migrate into the yolk sac. Cell and molecular bases involved in routes during the migration of these cells are still not well understood. Thus, in an attempt to evaluate the participation of matrix metalloproteinases (MMPs) during the gonadal primordium formation in Danio rerio (zebrafish), the route of migration of PGCs was analyzed. In zebrafish, during the migration of the PGCs to the forming gonad, they bind by cytoplasmic processes to the extracellular matrix and migrate through amoeboid movements until they reach the gonadal ridge. During the epiboly, MMPs were not detected. However, after organogenesis, three MMP types were expressed in the somatic cells that were located ahead of the PGCs in the migration route. This expression was maintained throughout the mesentery and was not detected in the PGCs. Upon reaching the gonadal ridge, the PGCs and somatic cells express MMPs and epithelium begins to be formed. After the formation of the basement membrane, the germinal epithelium is delineated by the somatic cells, which remodeling the extracellular matrix. So, a PGC organization occurs through the tissue, forming the gonadal primordium. Concomitantly, granulocytes expressing different MMPs are present. This data in exposing the role of MMPs during the PGC migration to the forming gonad, may point a new way in understanding the reproductive biology of the vertebrates in general.

Expression of Vasa, Nanos2 and Sox9 during initial testicular development in Nile tilapia (Oreochromis niloticus) submitted to sex reversal

Sexual differentiation and early gonadal development are critical events in vertebrate reproduction. In this study, the initial testis development and expression of the Vasa, Nanos2 and Sox9 proteins were examined in Nile tilapia Oreochromis niloticus submitted to induced sex reversal. To that end, 150O. niloticus larvae at 5 days post-hatching (dph) were kept in nurseries with no hormonal addition (control group) and 150 larvae were kept with feed containing 17α-methyltestosterone to induce male sex reversal (treated group). Morphological sexual differentiation of Nile tilapia occurred between 21 and 25 dph and sex reversal resulted in 94% males, whereas the control group presented 53% males. During sexual differentiation, gonocytes (Gon) were the predominant germ cells, which decreased and disappeared after that stage in both groups. Undifferentiated spermatogonia (Aund) were identified at 21 dph in the control group and at 23 dph in the treated group. Differentiated spermatogonia (Adiff) were found at 23 dph in both groups. Vasa and Nanos2 occurred in Gon, Aund and Adiff and there were no significant differences between groups. Vasa-labelled Adiff increased at 50 dph in both groups and Nanos2 presented a high proportion of labelled germ cells during sampling. Sertoli cells expressed Sox9 throughout the experiment and its expression was significantly greater during sexual differentiation in the control group. The results indicate that hormonal treatment did not alter initial testis development and expression of Vasa and Nanos2 in Nile tilapia, although lower expression of Sox9 and a delay in sexual differentiation was detected in the treated group.

Physiological impact and comparison of mutant screening methods in piwil2 KO founder Nile tilapia produced by CRISPR/Cas9 system

The application of genome engineering techniques to understand the mechanisms that regulate germ cell development opens promising new avenues to develop methods to control sexual maturation and mitigate associated detrimental effects in fish. In this study, the functional role of piwil2 in primordial germ cells (PGCs) was investigated in Nile tilapia using CRISPR/Cas9 and the resultant genotypes were further explored. piwil2 is a gonad-specific and maternally deposited gene in Nile tilapia eggs which is known to play a role in repression of transposon elements and is therefore thought to be important for maintaining germline cell fate. A functional domain of piwil2, PIWI domain, was targeted by injecting Cas9 mRNA and sgRNAs into Nile tilapia embryos at 1 cell stage. Results showed 54% of injected mutant larvae had no or less putative PGCs compared to control fish, suggesting an essential role of piwil2 in survival of PGCs. The genotypic features of the different phenotypic groups were explored by next generation sequencing (NGS) and other mutant screening methods including T7 endonuclease 1 (T7E1), CRISPR/Cas-derived RNA-guided engineered nuclease (RGEN), high resolution melt curve analysis (HRMA) and fragment analysis. Linking phenotypes to genotypes in F0 was hindered by the complex mosacism and wide indel spectrum revealed by NGS and fragment analysis. This study strongly suggests the functional importance of piwil2 in PGCs survival. Further studies should focus on reducing mosaicism when using CRISPR/Cas9 system to facilitate direct functional analysis in F0.

Molecular approaches underlying the oogenic cycle of the scleractinian coral, Acropora tenuis

This study aimed to elucidate the physiological processes of oogenesis in Acropora tenuis. Genes/proteins related to oogenesis were investigated: Vasa, a germ cell marker, vitellogenin (VG), a major yolk protein precursor, and its receptor (LDLR). Coral branches were collected monthly from coral reefs around Sesoko Island (Okinawa, Japan) for histological observation by in situ hybridisation (ISH) of the Vasa (AtVasa) and Low Density Lipoprotein Receptor (AtLDLR) genes and immunohistochemistry (IHC) of AtVasa and AtVG. AtVasa immunoreactivity was detected in germline cells and ooplasm, whereas AtVG immunoreactivity was detected in ooplasm and putative ovarian tissues. AtVasa was localised in germline cells located in the retractor muscles of the mesentery, whereas AtLDLR was localised in the putative ovarian and mesentery tissues. AtLDLR was detected in coral tissues during the vitellogenic phase, whereas AtVG immunoreactivity was found in primary oocytes. Germline cells expressing AtVasa are present throughout the year. In conclusion, Vasa has physiological and molecular roles throughout the oogenic cycle, as it determines gonadal germline cells and ensures normal oocyte development, whereas the roles of VG and LDLR are limited to the vitellogenic stages because they act in coordination with lipoprotein transport, vitellogenin synthesis, and yolk incorporation into oocytes.

Meagre Argyrosomus regius (Asso, 1801) Stem Spermatogonia: Histological Characterization, Immunostaining, In Vitro Proliferation, and Cryopreservation

The meagre, Argyrosomus regius, is a valued fish species of which aquaculture production might be supported by the development of a stem germ cell xenotransplantation technology. Meagre males were sampled at a fish farm in the Ionian Sea (Italy) at the beginning and end of the reproductive season. Small and large Type A undifferentiated spermatogonia were histologically identified in the germinal epithelium. Among the tested stemness markers, anti-oct4 and anti-vasa antibodies labeled cells likely corresponding to the small single Type A spermatogonia; no labeling was obtained with anti-GFRA1 and anti-Nanos2 antibodies. Two types of single A spermatogonia were purified via density gradient centrifugation of enzymatically digested testes. Testes from fish in active spermatogenesis resulted in a more efficient spermatogonial stem cell (SSC) yield. After cell seeding, meagre SSCs showed active proliferation from Day 7 to Day 21 and were cultured up to Day 41. After cryopreservation in dimethyl-sulfoxide-based medium, cell viability was 28.5%. In conclusion, these results indicated that meagre SSCs could be isolated, characterized, cultured in vitro, successfully cryopreserved, and used after thawing. This is a first step towards the development of a xenotransplantation technology that might facilitate the reproduction of this valuable species in captivity.

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.

Germ plasm-related structures in marine medaka gametogenesis; novel sites of Vasa localization and the unique mechanism of germ plasm granule arising

Germ plasm, a cytoplasmic factor of germline cell differentiation, is suggested to be a perspective tool for in vitro meiotic differentiation. To discriminate between the: (1) germ plasm-related structures (GPRS) involved in meiosis triggering; and (2) GPRS involved in the germ plasm storage phase, we investigated gametogenesis in the marine medaka Oryzias melastigma. The GPRS of the mitosis-to-meiosis period are similar in males and females. In both sexes, five events typically occur: (1) turning of the primary Vasa-positive germ plasm granules into the Vasa-positive intermitochondrial cement (IMC); (2) aggregation of some mitochondria by IMC followed by arising of mitochondrial clusters; (3) intramitochondrial localization of IMC-originated Vasa; followed by (4) mitochondrial cluster degradation; and (5) intranuclear localization of Vasa followed by this protein entering the nuclei (gonial cells) and synaptonemal complexes (zygotene-pachytene meiotic cells). In post-zygotene/pachytene gametogenesis, the GPRS are sex specific; the Vasa-positive chromatoid bodies are found during spermatogenesis, but oogenesis is characterized by secondary arising of Vasa-positive germ plasm granules followed by secondary formation and degradation of mitochondrial clusters. A complex type of germ plasm generation, 'the follicle cell assigned germ plasm formation', was found in late oogenesis. The mechanisms discovered are recommended to be taken into account for possible reconstruction of those under in vitro conditions.

Visualization of Turbot (Scophthalmus maximus) Primordial Germ Cells in vivo Using Fluorescent Protein Mediated by the 3' Untranslated Region of nanos3 or vasa Gene

Primordial germ cells (PGCs) as the precursors of germ cells are responsible for transmitting genetic information to the next generation. Visualization of teleost PGCs in vivo is essential to research the origination and development of germ cells and facilitate further manipulation on PGCs isolation, cryopreservation, and surrogate breeding. In this study, artificially synthesized mRNAs constructed by fusing fluorescent protein coding region to the 3' untranslated region (3'UTR) of nanos3 or vasa (mCherry-Smnanos3 3'UTR or mCherry-Smvasa 3'UTR mRNA) were injected into turbot (Scophthalmus maximus) fertilized eggs for tracing PGCs. The results demonstrated that the fluorescent PGCs differentiated from somatic cells and aligned on both sides of the trunk at the early segmentation period, then migrated and located at the dorsal part of the gut where the gonad would form. In the same way, we also found that the zebrafish (Danio rerio) vasa 3'UTR could trace turbot PGCs, while the vasa 3'UTR s of marine medaka (Oryzias melastigma) and red seabream (Pagrus major) failed, although they could label the marine medaka PGCs. In addition, through comparative analysis, we discovered that some potential sequence elements in the3 'UTRs of nanos3 and vasa, such as GCACs, 62-bp U-rich regions and nucleotide 187-218 regions might be involved in PGCs stabilization. The results of this study provided an efficient, rapid, and specific non-transgenic approach for visualizing PGCs of economical marine fish in vivo.

Alternative splice variants and differential relative abundance patterns of vasa mRNAs during gonadal development in the Chinese mitten crab Eriocheir sinensis

Gonadal development usually involves alternative splicing of sex-related genes. Vasa, a highly conserved ATP-dependent RNA helicase present mainly in germ cells, has an important function in gonadal development. As an important sex-related gene, recent evidence indicates that different splice variants of vasa exist in many species. In this study, there was identification of two types of vasa splice variants in the Chinese mitten crab Eriocheir sinensis, termed Esvasa-l and Esvasa-s, respectively. Furthermore, splice variants of Esvasa-s were sub-divided into Esvasa-s1, Esvasa-s2, Esvasa-s3, Esvasa-s4, and Esvasa-s5, based on differing numbers of TGG repeats. Results from genomic structure analyses indicated that these forms are alternatively spliced transcripts from a single vasa gene. Results from tissue distribution assessments indicate the vasa splice variants were exclusively expressed in the gonads of male and female adult crabs. In situ hybridization results indicate Esvasa mRNA was mainly present in the cytoplasm of previtellogenic oocytes. As oocyte size increased, relative abundance of Esvasa mRNA decreased and became distributed near the cellular membrane. The Esvasa mRNA was not detectable in mature oocytes. In testis, Esvasa mRNA was detected in spermatids and spermatozoa, but not in spermatogonia and spermatocytes. Notably, results from qPCR analysis of Esvasa-l and Esvasa-s indicate there are different relative proportions during gametogenesis, implying that splice variants of the Esvasa gene may have different biological functions during crab gonadal development.

Dmrt1 (doublesex and mab-3-related transcription factor 1) expression during gonadal development and spermatogenesis in the Japanese eel

Dmrt1, doublesex- and mab-3-related transcription factor-1, has been suggested to play critical roles in male gonadogenesis, testicular differentiation and development, including spermatogenesis, among different vertebrates. Vasa is a putative molecular marker of germ cells in vertebrates. In this study, we cloned the full-length dmrt1 cDNA from Japanese eel, and the protein comprised 290 amino acids and presented an extremely conserved Doublesex and Mab-3 (DM) domain. Vasa proteins were expressed in gonadal germ cells in a stage-specific manner, and were expressed at high levels in PGC and spermatogonia, low levels in spermatocytes, and were absent in spermatids and spermatozoa of Japanese eels. Dmrt1 proteins were abundantly expressed in spermatogonia B cells, spermatocytes, spermatids, but not in spermatozoa, spermatogonia A and Sertoli cells. To our knowledge, this study is the first to show a restricted expression pattern for the Dmrt1 protein in spermatogonia B cells, but not spermatogonia A cells, of teleosts. Therefore, Dmrt1 might play vital roles at the specific stages during spermatogenesis from spermatogonia B cells to spermatids in the Japanese eel. Moreover, the Dmrt1 protein exhibited a restricted localization in differentiating oogonia in the early differentiating gonad (ovary-like structure) of male Japanese eels and in E2-induced feminized Japanese eels. We proposed that dmrt1 may be not only required for spermatogenesis but might also play a role in oogenesis in the Japanese eel.

Resveratrol Plays a Protective Role against Premature Ovarian Failure and Prompts Female Germline Stem Cell Survival

This study was designed to investigate the protective effect of resveratrol (RES) on premature ovarian failure (POF) and the proliferation of female germline stem cells (FGSCs) at the tissue and cell levels. POF mice were lavaged with RES, and POF ovaries were co-cultured with RES and/or GANT61 in vitro. FGSCs were pretreated with Busulfan and RES and/or GANT61 and co-cultured with M1 macrophages, which were pretreated with RES. The weights of mice and their ovaries, as well as their follicle number, were measured. Ovarian function, antioxidative stress, inflammation, and FGSCs survival were evaluated. RES significantly increased the weights of POF mice and their ovaries as well as the number of follicles, while it decreased the atresia rate of follicles. Higher levels of Mvh, Oct4, SOD2, GPx, and CAT were detected after treatment with RES in vivo and in vitro. RES treatment resulted in significantly lower TNF-α and IL-6 concentrations and an obviously higher IL-10 concentration in the ovaries. In FGSCs, higher Mvh, Oct4, and SOD2 concentrations and lower TNF-α, IL-6, and MDA concentrations were measured in the RES group. Blockage of the Hh signaling pathway reversed the protective effect of RES on FGSCs. In conclusion, RES effectively improved the ovarian function of the POF model and the productive capacity of FGSCs via relieving oxidative stress and inflammation and a mechanism involving the Hh signaling pathway, suggesting that RES is a potential agent against POF and can aid in the survival of FGSCs.

Hedgehog pathway inhibition causes primary follicle atresia and decreases female germline stem cell proliferation capacity or stemness

Background

Follicle depletion is one of the causes of premature ovarian failure (POF) and primary ovarian insufficiency (POI). Hence, maintenance of a certain number of female germline stem cells (FGSCs) is optimal to produce oocytes and replenish the primordial follicle pool. The mechanism that regulates proliferation or stemness of FGSCs could contribute to restoring ovarian function, but it remains uncharacterized in postnatal mammalian ovaries. This study aims to investigate the mechanism by which inhibiting the activity of the hedgehog (Hh) signaling pathway regulates follicle development and FGSC proliferation.

Methods and results

To understand the role of the Hh pathway in ovarian aging, we measured Hh signaling activity at different reproductive ages and the correlation between them in physiological and pathological mice. Furthermore, we evaluated the follicle number and development and the changes in FGSC proliferation or stemness after blocking the Hh pathway in vitro and in vivo. In addition, we aimed to explain one of the mechanisms for the FGSC phenotype changes induced by treatment with the Hh pathway-specific inhibitor GANT61 via oxidative stress and apoptosis. The results show that the activity of Hh signaling is decreased in the ovaries in physiological aging and POF models, which is consistent with the trend of expression levels of the germline stem cell markers Mvh and Oct4. In vitro, blocking the Hh pathway causes follicular developmental disorders and depletes ovarian germ cells and FGSCs after treating ovaries with GANT61. The proliferation or stemness of cultured primary FGSCs is reduced when Hh activity is blocked. Our results show that the antioxidative enzyme level and the ratio of Bcl-2/Bax decrease, the expression level of caspase 3 increases, the mitochondrial membrane potential is abnormal, and ROS accumulate in this system.

Conclusions

We observed that the inhibition of the Hh signaling pathway with GANT61 could reduce primordial follicle number and decrease FGSC reproductive capacity or stemness through oxidative damage and apoptosis.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1299-5) contains supplementary material, which is available to authorized users.

Evolutionarily conserved vasa identifies embryonic and gonadal germ cells in spinyhead croaker Collichthys lucidus

In this study, a 2198 bp full-length cDNA of spinyhead croaker Collichthys lucidus vasa gene encoding 616 amino-acid residues was obtained. Multiple alignment revealed that C. lucidus vasa has eight conserved characteristic motifs of the DEAD box protein family and has the highest identity to large yellow croaker Larimichthys croceas. Reverse-transcription (RT)-PCR and Western blot analyses indicated that the vasa messenger (m)RNA and Vasa protein are specifically expressed in the gonads in both sexes. In situ hybridisation (ISH) demonstrated that vasa RNA is exclusively detected in the germ cells in C. lucidus gonads and its temporospatial expression reveals a dynamic pattern during oogenesis. Surprisingly, C. lucidus vasa 3'UTR can direct stable and specific GFP expression in the primordial germ cells (PGC) of medaka Oryzias latipes embryos. Taken together, these results suggest that because C. lucidus vasa expression delineates critical stages of oogenesis, it may be a useful molecular marker for the identification of gonadal germ cells, facilitating the isolation and utilization of germ cells in future study.

MicroRNA-322 Regulates Self-renewal of Mouse Spermatogonial Stem Cells through Rassf8

Spermatogonial stem cells (SSCs) are essential for spermatogenesis and male fertility. MicroRNAs (miRs) are key regulators of gene expression involved in self-renewal, differentiation, and apoptosis. However, the function and mechanisms of individual miR in regulating self-renewal and differentiation of SSCs remain unclear. Here, we report for the first time that miR-322 regulates self-renewal of SSCs. Functional assays revealed that miR-322 was essential for SSC self-renewal. Mechanistically, miR-322 promoted SSC self-renewal by targeting RASSF8 (ras association domain family 8). Moreover, the WNT/β-catenin signaling pathway was involved in the miR-322-mediated regulation. Furthermore, miR-322 overexpression increased GFRα1, ETV5 and PLZF expression but decreased STRA8, C-KIT and BCL6 expression. Our study provides not only a novel insight into molecular mechanisms regulating SSC self-renewal but also a basis for the diagnosis, treatment, and prevention of male infertility.

Molecular characterization of vasa homologue in marbled goby, Oxyeleotris marmorata: Transcription and localization analysis during gametogenesis and embryogenesis

Identification of germ cell markers is important for investigating reproduction biology in fish. Vasa is one of the most studied germ cell markers in mammals and lower vertebrates including fish. Here, we characterized a vasa homologue from the fish marbled goby (Oxyeleotris marmorata), termed omvasa. The full length of omvasa cDNA is 2344 bp and encodes 658 amino acids, sharing high identities with Vasa homologues of other vertebrates. OmVasa protein contains 15 RG/RGG repeats at N-terminus, 2 ATPase motifs, as well as RNA unwinding and RNA binding domains at C-terminus. Phylogenetic tree showed that omVasa had the closest relationship with the Vasa homologue from the fish Boleophthalmus pectinirostris, the great blue-spotted mudskipper. qRT-PCR analysis indicated that omvasa was specifically transcribed in gonads, and the transcription level was gradually increased during oocyte development. The germ cell-specific distribution of omvasa mRNA was revealed by fluorescent in situ hybridization. In ovary, the signal of omvasa RNA displayed strong-weak-strong dynamics from oogonia over pre-vitellogenic oocytes to vitellogenic oocytes. In testis, omvasa signal was strong in spermatogonia, modest in spermatocytes but undetectable in spermatids and somatic cells. During embryogenesis, the transcription of omvasa mRNA was high at blastula stage, gradually decreased from gastrula stage and maintained at a low level in later developmental stages. Whole mount in situ hybridization indicated that omvasa mRNA was specific to primordial germ cells (PGCs). In summary, marbled goby vasa is a germ cell-specific transcript during gametogenesis, and can be used as an ideal marker for tracing PGC formation and migration, which is pivotal to germ cell manipulation in this species.

The autosomal Gsdf gene plays a role in male gonad development in Chinese tongue sole (Cynoglossus semilaevis)

Gsdf is a key gene for testicular differentiation in teleost. However, little is known about the function of Gsdf in Chinese tongue sole (Cynoglossus semilaevis). In this study, we obtained the full-length Gsdf gene (CS-Gsdf), and functional characterization revealed its potential participation during germ cell differentiation in testes. CS-Gsdf transcription was predominantly detected in gonads, while the levels in testes were significantly higher than those in ovaries. During the different developmental stages in male gonads, the mRNA level was significantly upregulated at 86 dph, and a peak appeared at 120 dph; then, the level decreased at 1 and 2 yph. In situ hybridization revealed that CS-Gsdf mRNA was mainly localized in the Sertoli cells, spermatogonia, and spermatids in mature testes. After CS-Gsdf knockdown in the male testes cell line by RNA interference, a series of sex-related genes was influenced, including several sex differentiation genes, CS-Wnt4a, CS-Cyp19a1a and CS-Star. Based on these data, we speculated that CS-Gsdf may play a positive role in germ differentiation and proliferation via influencing genes related to sex differentiation.

Genome-wide identification, evolution of DNA methyltransferases and their expression during gonadal development in Nile tilapia

DNA methyltransferases (dnmts) are responsible for DNA methylation and play important roles in organism development. In this study, seven dnmts genes (dnmt1, dnmt2, dnmt3aa, dnmt3ab, dnmt3ba, dnmt3bb.1, dnmt3bb.2) were identified in Nile tilapia. Comprehensive analyses of dnmts were performed using available genome databases from representative animal species. Phylogenetic analysis revealed that the dnmts family were highly conserved in teleosts. Based on transcriptome data from eight adult tilapia tissues, the dnmts were found to be dominantly expressed in the head kidney, testis and ovary. Analyses of the gonadal transcriptome data in different developmental stages revealed that all dnmts were expressed in both ovary and testis, and four de novo dnmts (dnmt3aa, dnmt3ab, dnmt3bb.1, dnmt3bb.2) showed higher expression in the testis than in the ovary. Furthermore, during sex reversal induced by Fadrozole, the expression of these four de novo dnmts increased significantly in treated group compared to female control group. By in situ hybridization, the seven dnmts were found to be expressed mainly in phase I and II oocytes of the ovary and spermatocytes of the testis. When gonads were incubated with a methyltransferase inhibitor (5-AzaCdR) in vitro, the expression of dnmts genes were down-regulated significantly, while the expression of cyp19a1a (a key gene in female pathway) and dmrt1 (a key gene in male pathway) increased significantly. Our results revealed the conservation of dnmts during evolution and indicated a potential role of dnmts in epigenetic regulation of gonadal development.

Characterization and localization of primordial germ cells in Totoaba macdonaldi

The totoaba, Totoaba macdonaldi, is an endangered fish of the Gulf of California with high economic and ecological potential. Therefore, our purpose was to characterize the Primordial Germ Cells (PGCs) of this Sciaenid with two objectives: (1) to provide the basis for PGCs cryopreservation to preserve the genetic resources and (2) to take the first step to know the gonadal genesis and sex differentiation of totoaba. Immunofluorescence analysis performed from 2-cell stage to 8-day after hatch (DAH) shows that Vasa protein is specific for PGCs. These cells were first observed in the peripheral and dorsal regions of the blastodisc at approximately the 50%-epiboly stage and migrated to both sides of embryo body during the development. Finally, at 7 DAH the PGCs of the hatching embryo reached the place where the gonad will be developed. Histology analysis of larvae showed a genital ridge with enclosed PGCs on the dorsal side of the peritoneum at 9 DAH, gonadal primordium growth was observed at 11 DAH as a result of the interaction between PGCs and somatic cells derived from the peritoneum. Results of qPCR showed that vasa expression was restricted to the embryonic and early larval development, highest values were observed in 2-cell and mid-blastula stage suggesting the maternal inheritance of vasa mRNA. These findings support the hypothesis of preformation in T. macdonaldi PGCs. The migration pattern of PGCs allow us to recommend the isolation and subsequent cryopreservation of these cells before 7 DAH when the embryonic and larval development is given at 21 °C.

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.

Transcriptome display during tilapia sex determination and differentiation as revealed by RNA-Seq analysis

Background

The factors determining sex in teleosts are diverse. Great efforts have been made to characterize the underlying genetic network in various species. However, only seven master sex-determining genes have been identified in teleosts. While the function of a few genes involved in sex determination and differentiation has been studied, we are far from fully understanding how genes interact to coordinate in this process.

Results

To enable systematic insights into fish sexual differentiation, we generated a dynamic co-expression network from tilapia gonadal transcriptomes at 5, 20, 30, 40, 90, and 180 dah (days after hatching), plus 45 and 90 dat (days after treatment) and linked gene expression profiles to both development and sexual differentiation. Transcriptomic profiles of female and male gonads at 5 and 20 dah exhibited high similarities except for a small number of genes that were involved in sex determination, while drastic changes were observed from 90 to 180 dah, with a group of differently expressed genes which were involved in gonadal differentiation and gametogenesis. Weighted gene correlation network analysis identified changes in the expression of Borealin, Gtsf1, tesk1, Zar1, Cdn15, and Rpl that were correlated with the expression of genes previously known to be involved in sex differentiation, such as Foxl2, Cyp19a1a, Gsdf, Dmrt1, and Amh.

Conclusions

Global gonadal gene expression kinetics during sex determination and differentiation have been extensively profiled in tilapia. These findings provide insights into the genetic framework underlying sex determination and sexual differentiation, and expand our current understanding of developmental pathways during teleost sex determination.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4756-0) contains supplementary material, which is available to authorized users.