Evaluation of Sycp3, Plzf and Cyclin B3 expression and suitability as spermatogonia and spermatocyte markers in zebrafish

Dissecting the dynamic cellular transcriptional atlas of adult teleost testis development throughout the annual reproductive cycle

Teleost testis development during the annual cycle involves dramatic changes in cellular compositions and molecular events. In this study, the testicular cells derived from adult black rockfish at distinct stages - regressed, regenerating and differentiating - were meticulously dissected via single-cell transcriptome sequencing. A continuous developmental trajectory of spermatogenic cells, from spermatogonia to spermatids, was delineated, elucidating the molecular events involved in spermatogenesis. Subsequently, the dynamic regulation of gene expression associated with spermatogonia proliferation and differentiation was observed across spermatogonia subgroups and developmental stages. A bioenergetic transition from glycolysis to mitochondrial respiration of spermatogonia during the annual developmental cycle was demonstrated, and a deeper level of heterogeneity and molecular characteristics was revealed by re-clustering analysis. Additionally, the developmental trajectory of Sertoli cells was delineated, alongside the divergence of Leydig cells and macrophages. Moreover, the interaction network between testicular micro-environment somatic cells and spermatogenic cells was established. Overall, our study provides detailed information on both germ and somatic cells within teleost testes during the annual reproductive cycle, which lays the foundation for spermatogenesis regulation and germplasm preservation of endangered species.

Characterization of potential spermatogonia biomarker genes in the European eel (Anguilla anguilla)

Identification of specific molecular markers for spermatogonial stem cells in teleost is crucial for enhancing the efficacy of reproductive biotechnologies in aquaculture, such as transplantation and surrogate production in fishes. Since it is not yet possible to distinguish spermatogonial stem cells of European eel (Anguilla anguilla) using specific molecular markers, we isolated spermatogonial cells from immature European eels to find these potential markers. We attempted this by studying three candidate genes: vasa, nanos2, and dnd1. Two vasa (vasa1 and vasa2) genes, nanos2, and dnd1 were identified, characterized, and studied in the muscle, testis, and isolated spermatogonia. Our results showed that vasa1 and vasa2 had the highest levels of expression when measured by qPCR. In situ hybridization and immunochemistry assays showed that the four genes were localized explicitly in type A spermatogonia. However, vasa1 and vasa2 exhibited stronger signals in the immature testicular tissue than the other two potential markers. According to this, vasa1 and vasa2 were found to be the most effective markers for spermatogonial cells in the European eel.

A Single-Cell Landscape of Spermioteleosis in Mice and Pigs

(1) Background: Spermatozoa acquired motility and matured in epididymis after production in the testis. However, there is still limited understanding of the specific characteristics of sperm development across different species. In this study, we employed a comprehensive approach to analyze cell compositions in both testicular and epididymal tissues, providing valuable insights into the changes occurring during meiosis and spermiogenesis in mouse and pig models. Additionally, we identified distinct gene expression signatures associated with various spermatogenic cell types. (2) Methods: To investigate the differences in spermatogenesis between mice and pigs, we constructed a single-cell RNA dataset. (3) Results: Our findings revealed notable differences in testicular cell clusters between these two species. Furthermore, distinct gene expression patterns were observed among epithelial cells from different regions of the epididymis. Interestingly, regional gene expression patterns were also identified within principal cell clusters of the mouse epididymis. Moreover, through analysing differentially expressed genes related to the epididymis in both mouse and pig models, we successfully identified potential marker genes associated with sperm development and maturation for each species studied. (4) Conclusions: This research presented a comprehensive single-cell landscape analysis of both testicular and epididymal tissues, shedding light on the intricate processes involved in spermatogenesis and sperm maturation, specifically within mouse and pig models.

Germ cells do not progress through spermatogenesis in the infertile zebrafish testis

Vertebrate spermatogonial stem cells maintain sperm production over the lifetime of an animal but fertility declines with age. While morphological studies have greatly informed our understanding of typical spermatogenesis, the molecular and cellular mechanisms underlying spermatogenesis are not yet understood, particularly with respect to the onset of fertility. We used single-cell RNA sequencing to generate a developmental atlas of the zebrafish testis. Using 5 timepoints across the adult life of a zebrafish, we described cellular profiles in the testis during and after fertility. While all germ cell stages of spermatogenesis are detected in testes from fertile adult zebrafish, testes from older infertile males only contained spermatogonia and a reduced population of spermatocytes. These remaining germ cells are transcriptionally distinct from fertile spermatogonia. Immune cells including macrophages and lymphocytes drastically increase in abundance in infertile testes. Our developmental atlas reveals the cellular changes as the testis ages and defines a molecular roadmap for the regulation of male fertility.

Macrophage-Related Testicular Inflammation in Individuals with Idiopathic Non-Obstructive Azoospermia: A Single-Cell Analysis

Male infertility is a global issue that seriously affects reproductive health. This study aimed to understand the underlying causes of idiopathic non-obstructive azoospermia (iNOA), which is a type of male infertility with unknown origins that accounts for 10-15% of cases. By using single-cell analysis techniques, we aimed to uncover the mechanisms of iNOA and gain insight into the cellular and molecular changes in the testicular environment. In this study, we performed bioinformatics analysis using scRNA-seq and microarray data obtained from the GEO database. The analysis included techniques such as pseudotime analysis, cell-cell communication, and hdWGCNA. Our study showed a significant difference between the iNOA and the normal groups, indicating a disorder in the spermatogenic microenvironment in iNOA. We observed a reduction in the proportion of Sertoli cells and blocked germ cell differentiation. Additionally, we found evidence of testicular inflammation related to macrophages and identified ODF2 and CABYR as potential biomarkers for iNOA.

Expression of scp3 and dazl reveals the meiotic characteristics of the olive flounder Paralichthys olivaceus†

Olive flounder Paralichthys olivaceus is an important cultured marine fish. We found that the meiosis marker scp3 and its intrinsic regulator dazl were mainly expressed in the gonads. During the ovarian differentiation, scp3 signal was detected first in pre-meiotic oogonia at 60-mm total length (TL) and then in primary oocytes at 80- and 100-mm TL, with a sharp increase in scp3 expression level observed at 80- and 100-mm TL. Dazl signal was detected in primordial germ cells at 30-mm TL and oogonia at 60-mm TL, but no significant change of expression was observed. During the testicular differentiation period, scp3 and dazl expression remained at low levels, and scp3 signal was weakly detected in spermatogonia at 80-mm TL, whereas dazl signal was not found. During the ovarian developmental stages, the highest expression levels of scp3 and dazl were detected at stages I and II, respectively, and strong signals of scp3 and dazl were detected in primary oocytes and oocytes at phases I and II. In the testis, the high expression of scp3 and dazl was detected at stages II-IV and II-III, respectively. Scp3 signal was weakly observed in pre-meiotic spermatogonia at stages I and II and strongly detected in primary spermatocytes at stages III-V. Dazl was detected in the nuclei of spermatogonia and spermatids at stages II-IV. Furthermore, scp3 expression in the ovary could be promoted by 17α-ethynylestradiol and tamoxifen, whereas dazl expression could be downregulated by tamoxifen.

Sex steroid profile during oocyte development and maturation in the intertidal worm Marphysa madrasi (Polychaeta: Eunicidae) from the east coast of India

Marphysa madrasi is a commercially valuable maturation diet in crustacean aquaculture. This study presents the first detailed investigation of oogenesis in the intertidal polychaete worm M. madrasi and reports the steroid profile during oocyte growth and development. Oogenesis is extraovarian type I, originating from coelomic epithelial cells, with four stages of development - primary growth, early vitellogenic, late vitellogenic, and maturation. The primary growth phase contains oogonial cells and previtellogenic oocyte clusters in the early, mid, and late stages of development form a dispersed ovary attached to blood vessels. The late previtellogenic oocytes detach from the ovary at the onset of vitellogenesis. The detached oocytes complete vitellogenesis and final maturation in the coelomic fluid as solitary free-floating cells without any connection with follicle cells. The worms display asynchronous reproduction with a heterogeneous population of developing oocytes. Steroid extracts from the polychaete homogenates in different stages of oogenesis were identified by HPLC and confirmed by LC-MS/MS. In M. madrasi, two vertebrate-type steroids, pregnenolone (P5) and 17α-hydroxyprogesterone (17-OHP) were detected and quantified. The P5 levels were low in immature worms but increased significantly by ∼ 8.3-fold in the previtellogenic stage and peaked during oocyte maturation. 17-OHP levels were low in immature worms but gradually increase as the oogenesis progress to the primary growth and early vitellogenic phase, with a significant increase (p < 0.001) during the late vitellogenic phase. Although an increase in the concentration of P5 and 17-OHP during vitellogenesis and maturation of oocytes points to a possible role in reproduction, the absence of other vertebrate-type steroids in the investigated polychaete signifies a plausible uptake of P5 and 17-OHP from the environment.

A Germline-Specific Regulator of Mitochondrial Fusion is Required for Maintenance and Differentiation of Germline Stem and Progenitor Cells

Maintenance and differentiation of germline stem and progenitor cells (GSPCs) is important for sexual reproduction. Here, the authors identify zebrafish pld6 as a novel germline-specific gene by cross-analyzing different RNA sequencing results, and find that pld6 knockout mutants develop exclusively into infertile males. In pld6 mutants, GSPCs fail to differentiate and undergo apoptosis, leading to masculinization and infertility. Mitochondrial fusion in pld6-depleted GSPCs is severely impaired, and the mutants exhibit defects in piRNA biogenesis and transposon suppression. Overall, this work uncovers zebrafish Pld6 as a novel germline-specific regulator of mitochondrial fusion, and highlights its essential role in the maintenance and differentiation of GSPCs as well as gonadal development and gametogenesis.

Comprehensive expression analysis for the core cell cycle regulators in the chicken embryo reveals novel tissue-specific synexpression groups and similarities and differences with expression in mouse, frog and zebrafish

The core cell cycle machinery is conserved from yeast to humans, and hence it is assumed that all vertebrates share the same set of players. Yet during vertebrate evolution, the genome was duplicated twice, followed by a further genome duplication in teleost fish. Thereafter, distinct genes were retained in different vertebrate lineages; some individual gene duplications also occurred. To which extent these diversifying tendencies were compensated by retaining the same expression patterns across homologous genes is not known. This study for the first time undertook a comprehensive expression analysis for the core cell cycle regulators in the chicken, focusing in on early neurula and pharyngula stages of development, with the latter representing the vertebrate phylotypic stage. We also compared our data with published data for the mouse, Xenopus and zebrafish, the other established vertebrate models. Our work shows that, while many genes are expressed widely, some are upregulated or specifically expressed in defined tissues of the chicken embryo, forming novel synexpression groups with markers for distinct developmental pathways. Moreover, we found that in the neural tube and in the somite, mRNAs of some of the genes investigated accumulate in a specific subcellular localisation, pointing at a novel link between the site of mRNA translation, cell cycle control and interkinetic nuclear movements. Finally, we show that expression patterns of orthologous genes may differ in the four vertebrate models. Thus, for any study investigating cell proliferation, cell differentiation, tissue regeneration, stem cell behaviour and cancer/cancer therapy, it has to be carefully examined which of the observed effects are due to the specific model organism used, and which can be generalised.

Cyp11a2 Is Essential for Oocyte Development and Spermatogonial Stem Cell Differentiation in Zebrafish

Cytochrome P45011A1, encoded by Cyp11a1, converts cholesterol to pregnenolone (P5), the first and rate-limiting step in steroidogenesis. In zebrafish, cyp11a1 is maternally expressed and cyp11a2 is considered the ortholog of Cyp11a1 in mammals. A recent study has shown that depletion of cyp11a2 resulted in steroidogenic deficiencies and the mutants developed into males with feminized secondary sexual characteristics. Here, we independently generated cyp11a2 mutants in zebrafish and showed that the mutants can develop into males and females in the juvenile stage, but finally into infertile males with defective mating behavior in the adult stage. In the developing ovaries, the cyp11a2 mutation led to stage I oocyte apoptosis and final sex reversal, which could be partially rescued by treatment with P5 but not estradiol. In the developing testes, depletion of cyp11a2 resulted in dysfunction of Sertoli cells and lack of functional Leydig cells. Spermatogonial stem cells (SSCs) in the mutant testes underwent active self-renewal but no differentiation, resulting in a high abundance of SSCs in the testis, as revealed by immunofluorescence staining with Nanos2 antibody. The high abundance and differentiation competence of SSCs in the mutant testes were verified by a novel testicular cell transplantation method developed in this study, by transplanting mutant testicular cells into germline-depleted wild-type (WT) fish. The transplanted mutant SSCs efficiently differentiated into functional spermatids in WT hosts. Overall, our study demonstrates the functional importance of cyp11a2 in early oogenesis and differentiation of SSCs.

Pou5f1 and Nanog Are Reliable Germ Cell-Specific Genes in Gonad of a Protogynous Hermaphroditic Fish, Orange-Spotted Grouper (Epinephelus coioides)

Pluripotency markers Pou5f1 and Nanog are core transcription factors regulating early embryonic development and maintaining the pluripotency and self-renewal of stem cells. Pou5f1 and Nanog also play important roles in germ cell development and gametogenesis. In this study, Pou5f1 (EcPou5f1) and Nanog (EcNanog) were cloned from orange-spotted grouper, Epinephelus coioides. The full-length cDNAs of EcPou5f1 and EcNanog were 2790 and 1820 bp, and encoded 475 and 432 amino acids, respectively. EcPou5f1 exhibited a specific expression in gonads, whereas EcNanog was expressed highly in gonads and weakly in some somatic tissues. In situ hybridization analyses showed that the mRNA signals of EcNanog and EcPou5f1 were exclusively restricted to germ cells in gonads. Likewise, immunohistofluorescence staining revealed that EcNanog protein was limited to germ cells. Moreover, both EcPou5f1 and EcNanog mRNAs were discovered to be co-localized with Vasa mRNA, a well-known germ cell maker, in male and female germ cells. These results implied that EcPou5f1 and EcNanog could be also regarded as reliable germ cell marker genes. Therefore, the findings of this study would pave the way for elucidating the mechanism whereby EcPou5f1 and EcNanog regulate germ cell development and gametogenesis in grouper fish, and even in other protogynous hermaphroditic species.

Isolation and Characterization of Highly Pure Type A Spermatogonia From Sterlet (Acipenser ruthenus) Using Flow-Cytometric Cell Sorting

Sturgeons are among the most ancient linages of actinopterygians. At present, many sturgeon species are critically endangered. Surrogate production could be used as an affordable and a time-efficient method for endangered sturgeons. Our study established a method for identifying and isolating type A spermatogonia from different developmental stages of testes using flow cytometric cell sorting (FCM). Flow cytometric analysis of a whole testicular cell suspension showed several well-distinguished cell populations formed according to different values of light scatter parameters. FCM of these different cell populations was performed directly on glass slides for further immunocytochemistry to identify germ cells. Results showed that the cell population in gate P1 on a flow cytometry plot (with high forward scatter and high side scatter parameter values) contains the highest amount of type A spermatogonia. The sorted cell populations were characterized by expression profiles of 10 germ cell specific genes. The result confirmed that setting up for the P1 gate could precisely sort type A spermatogonia in all tested testicular developmental stages. The P2 gate, which was with lower forward scatter and side scatter values mostly, contained type B spermatogonia at a later maturing stage. Moreover, expressions of plzf, dnd, boule, and kitr were significantly higher in type A spermatogonia than in later developed germ cells. In addition, plzf was firstly found as a reliable marker to identify type A spermatogonia, which filled the gap of identification of spermatogonial stem cells in sterlet. It is expected to increase the efficiency of germ stem cell culture and transplantation with plzf identification. Our study thus first addressed a phenotypic characterization of a pure type A spermatogonia population in sterlet. FCM strategy can improve the production of sturgeons with surrogate broodstock and further the analysis of the cellular and molecular mechanisms of sturgeon germ cell development.

Meiotic Chromosome Dynamics in Zebrafish

Recent studies in zebrafish have revealed key features of meiotic chromosome dynamics, including clustering of telomeres in the bouquet configuration, biogenesis of chromosome axis structures, and the assembly and disassembly of the synaptonemal complex that aligns homologs end-to-end. The telomere bouquet stage is especially pronounced in zebrafish meiosis and sub-telomeric regions play key roles in mediating pairing and homologous recombination. In this review, we discuss the temporal progression of these events in meiosis prophase I and highlight the roles of proteins associated with meiotic chromosome architecture in homologous recombination. Finally, we discuss the interplay between meiotic mutants and gonadal sex differentiation and future research directions to study meiosis in living cells, including cell culture.

Rbm46, a novel germ cell-specific factor, modulates meiotic progression and spermatogenesis

It has been suggested that many novel RNA-binding proteins (RBPs) are required for gametogenesis, but the necessity of few of these proteins has been functionally verified. Here, we identified one RBP, Rbm46, and investigated its expression pattern and role in zebrafish reproduction. We found that rbm46 is maternally provided and specifically expressed in the germ cells of gonadal tissues using in situ hybridization, reverse transcription-PCR, and quantitative real-time polymerase chain reaction (qRT-PCR). Two independent rbm46 mutant zebrafish lines were generated via the transcription activator-like effector nuclease technique. Specific disruption of rbm46 resulted in masculinization and infertility in the mutants. Although the spermatogonia appeared grossly normal in the mutants, spermatogenesis was impaired, and meiosis events were not observed. The introduction of a tp53M214K mutation could not rescue the female-to-male sex-reversal phenotype, indicating that rbm46 acts independently of the p53-dependent apoptotic pathway. RNA sequencing and qRT-PCR subsequently indicated that Rbm46 might be involved in the posttranscriptional regulation of functional genes essential for germ cell development, such as nanos3, dazl, and sycp3, during gametogenesis. Together, our results reveal for the first time the crucial role of rbm46 in regulating germ cell development in vivo through promotion of germ cell progression through meiosis prophase I.

Knockout of myoc Provides Evidence for the Role of Myocilin in Zebrafish Sex Determination Associated with Wnt Signalling Downregulation

Myocilin is a secreted glycoprotein with a poorly understood biological function and it is mainly known as the first glaucoma gene. To explore the normal role of this protein in vivo we developed a myoc knockout (KO) zebrafish line using CRISPR/Cas9 genome editing. This line carries a homozygous variant (c.236_239delinsAAAGGGGAAGGGGA) that is predicted to result in a loss-of-function of the protein because of a premature termination codon p.(V75EfsX60) that resulted in a significant reduction of myoc mRNA levels. Immunohistochemistry showed the presence of myocilin in wild-type embryonic (96 h post-fertilization) anterior segment eye structures and caudal muscles. The protein was also detected in different adult ocular and non-ocular tissues. No gross macroscopic or microscopic alterations were identified in the KO zebrafish, but, remarkably, we observed absence of females among the adult KO animals and apoptosis in the immature juvenile gonad (28 dpf) of these animals, which is characteristic of male development. Transcriptomic analysis showed that adult KO males overexpressed key genes involved in male sex determination and presented differentially expressed Wnt signalling genes. These results show that myocilin is required for ovary differentiation in zebrafish and provides in vivo support for the role of myocilin as a Wnt signalling pathway modulator. In summary, this myoc KO zebrafish line can be useful to investigate the elusive function of this protein, and it provides evidence for the unexpected function of myocilin as a key factor in zebrafish sex determination.

Stress responses of testicular development, inflammatory and apoptotic activities in male zebrafish (Danio rerio) under starvation

Food deprivation is a severe stress across multiple fields and challenged to organismal development and immune system. Here, adult male zebrafish were used to investigate the starvation stress on organismal development, spermatogenesis, testicular inflammation and apoptosis. Results showed that the biological indexes, blood parameters, and RNA/DNA ratio in testis dramatically decreased after 1-3 weeks of starvation. The testicular architecture was impaired and the spermatogenesis was retarded with increased proportions of spermatogonia and spermatocytes, and decreased proportion of spermatozoa in the starved fish. The mRNA expressions of amh and sycp3 were downregulated, the retinoic acid content increased at later stage of starvation through the transcriptional regulation of aldh1a2 and cyp26a1. Besides, the immune response was elevated with upregulated mRNA and protein expressions of TNF-α, IL-6, and IL-1β, which indicated the inflammation of opportunistic risk in testis. The apoptotic activity was stimulated, accompanied by differentially upregulated expressions of baxa, casp9, casp3, casp2, and decreased ratio of Bcl-2/Bax in the attenuate testis. Taken together, our findings revealed that the stress responses of testicular development, inflammatory and apoptotic activities in male zebrafish under starvation and pointed out the susceptibility of fish gonad to food fluctuation.

Regulation of spermatogenesis and reproductive capacity by Igf3 in tilapia

A novel insulin-like growth factor (igf3), which is exclusively expressed in the gonads, has been widely identified in fish species. Recent studies have indicated that Igf3 regulates spermatogonia proliferation and differentiation in zebrafish; however, detailed information on the role of this Igf needs further in vivo investigation. Here, using Nile tilapia (Oreochromis niloticus) as an animal model, we report that igf3 is required for spermatogenesis and reproduction. Knockout of igf3 by CRISPR/Cas9 severely inhibited spermatogonial proliferation and differentiation at 90 days after hatching, the time critical for meiosis initiation, and resulted in less spermatocytes in the mutants. Although spermatogenesis continued to occur later, more spermatocytes and less spermatids were observed in the igf3-/- testes when compared with wild type of testes at adults, indicating that Igf3 regulates spermatocyte to spermatid transition. Importantly, a significantly increased occurrence of apoptosis in spermatids was observed after loss of Igf3. Therefore, igf3-/- males were subfertile with drastically reduced semen volume and sperm count. Conversely, the overexpression of Igf3 in XY tilapia enhanced spermatogenesis leading to more spermatids and sperm count. Transcriptomic analysis revealed that the absence of Igf3 resulted in dysregulation of many genes involved in cell cycle, meiosis and pluripotency regulators that are critical for spermatogenesis. In addition, in vitro gonadal culture with 17α-methyltetosterone (MT) and 11-ketotestosterone (11-KT) administration and in vivo knockout of cyp11c1 demonstrated that igf3 expression is regulated by androgens, suggesting that Igf3 acts downstream of androgens in fish spermatogenesis. Notably, the igf3 knockout did not affect body growth, indicating that this Igf specifically functions in reproduction. Taken together, our data provide genetic evidence for fish igf3 in the regulation of reproductive capacity by controlling spermatogenesis.

setd2 knockout zebrafish is viable and fertile: differential and developmental stress-related requirements for Setd2 and histone H3K36 trimethylation in different vertebrate animals

Setd2 is the only enzyme that catalyzes histone H3 lysine 36 trimethylation (H3K36me3) on virtually all actively transcribed protein-coding genes, and this mechanism is evolutionarily conserved from yeast to human. Despite this widespread and conserved activity, Setd2 and H3K36me3 are dispensable for normal growth of yeast but are absolutely required for mammalian embryogenesis, such as oocyte maturation and embryonic vasculogenesis in mice, raising a question of how the functional requirements of Setd2 in specific developmental stages have emerged through evolution. Here, we explored this issue by studying the essentiality and function of Setd2 in zebrafish. Surprisingly, the setd2-null zebrafish are viable and fertile. They show Mendelian birth ratio and normal embryogenesis without vascular defect as seen in mice; however, they have a small body size phenotype attributed to insufficient energy metabolism and protein synthesis, which is reversable in a nutrition-dependent manner. Unlike the sterile Setd2-null mice, the setd2-null zebrafish can produce functional sperms and oocytes. Nonetheless, related to the requirement of maternal Setd2 for oocyte maturation in mice, the second generation of setd2-null zebrafish that carry no maternal setd2 show decreased survival rate and a developmental delay at maternal-to-zygotic transition. Taken together, these results indicate that, while the phenotypes of the setd2-null zebrafish and mice are apparently different, they are matched in parallel as the underlying mechanisms are evolutionarily conserved. Thus, the differential requirements of Setd2 may reflect distinct viability thresholds that associate with intrinsic and/or extrinsic stresses experienced by the organism through development, and these epigenetic regulatory mechanisms may serve as a reserved source supporting the evolution of life from simplicity to complexity.

Establishment of novel monoclonal antibodies for identification of type A spermatogonia in teleosts†

We recently established a germ cell transplantation system in salmonids. Donor germ cells transplanted into the body cavity of recipient embryos migrate toward and are incorporated into the recipient gonad, where they undergo gametogenesis. Among the various types of testicular germ cells, only type A spermatogonia (A-SG) can be incorporated into the recipient gonads. Enriching for A-SG is therefore important for improving the efficiency of germ cell transplantation. To enrich for A-SG, an antibody against a cell surface marker is a convenient and powerful approach used in mammals; however, little is known about cell surface markers for A-SG in fish. To that end, we have produced novel monoclonal antibodies (mAbs) against cell-surface molecules of rainbow trout (Oncorhynchus mykiss) A-SG. We inoculated mice with living A-SG isolated from pvasa-GFP transgenic rainbow trout using GFP-dependent flow cytometry. By fusing lymph node cells of the inoculated mice with myeloma cells, we generated 576 hybridomas. To identify hybridomas that produce mAbs capable of labeling A-SG preferentially and effectively, we screened them using cell ELISA, fluorescence microscopy, and flow cytometry. We thereby identified two mAbs that can label A-SG. By using flow cytometry with these two antibodies, we could enrich for A-SG with transplantability to recipient gonads from amongst total testicular cells. Furthermore, one of these mAbs could also label zebrafish (Danio rerio) spermatogonia. Thus, we expect these monoclonal antibodies to be powerful tools for germ cell biology and biotechnology.

Tributyltin impaired spermatogenesis and reproductive behavior in male zebrafish

Tributyltin (TBT) was reported to affect sexual behavior and gametogenesis in fish. However, the modes of action involved are largely unclear. In order to elucidate the toxicological mechanisms of TBT in reproduction, zebrafish (Danio rerio) males were exposed to TBT at concentrations of 100 and 500 ng/L for 28 days. After exposure, the sperm count of the treated fish was sharply decreased though the testis weight and gonadosomatic index remained unchanged. Moreover, reduced number of spermatogonia and spermatozoa and increased spermatocytes were observed in TBT-treated fish by histological observation and PCNA-immunostaining. Increased number of apoptotic-positive spermatocytes was also present in TBT-treated fish, indicating an enhanced apoptosis in these cells. Consistent to decreased number of spermatogonia, down-regulated expressions of genes responsible for germ cell proliferation (cyclind1 and pcna) were observed in TBT-treated fish. In contrast, TBT elevated the expressions of genes involved in meiotic entry and maintenance (aldhla2, sycp3 and dmc1) while suppressed the mRNA level of gene responsible for terminus of meiotic entry (cyp26a1), in agreement with arrested meiosis and reduced sperm count. Furthermore, TBT significantly elevated the ratios of bax/bcl-2 and tnfrsf1a/tnfrsf1b in testis, which are markers for intrinsic- and extrinsic-apoptotic pathways, consistent with the enhanced TUNEL positive signals in spermatocytes. Moreover, TBT also significantly affected the parameter of reproductive behaviors in treated fish (reflected by decreased frequency of meeting, visits and time spent in spawning area). Consistently, the expressions of genes responsible for the modulation of reproductive behaviors in brain (such as cyp19a1b, kiss2, gnrh3 and ompb) were significantly down-regulated in treated-fish. Interestingly, disrupted reproductive behaviors of untreated female fish were also observed in the present study. The present study indicated that TBT might affect the reproduction of zebrafish male by disrupting the spermatogenesis and reproductive behavior of the fish.

Spermatogonial Stem Cells in Fish: Characterization, Isolation, Enrichment, and Recent Advances of In Vitro Culture Systems

Spermatogenesis is a continuous and dynamic developmental process, in which a single diploid spermatogonial stem cell (SSC) proliferates and differentiates to form a mature spermatozoon. Herein, we summarize the accumulated knowledge of SSCs and their distribution in the testes of teleosts. We also reviewed the primary endocrine and paracrine influence on spermatogonium self-renewal vs. differentiation in fish. To provide insight into techniques and research related to SSCs, we review available protocols and advances in enriching undifferentiated spermatogonia based on their unique physiochemical and biochemical properties, such as size, density, and differential expression of specific surface markers. We summarize in vitro germ cell culture conditions developed to maintain proliferation and survival of spermatogonia in selected fish species. In traditional culture systems, sera and feeder cells were considered to be essential for SSC self-renewal, in contrast to recently developed systems with well-defined media and growth factors to induce either SSC self-renewal or differentiation in long-term cultures. The establishment of a germ cell culture contributes to efficient SSC propagation in rare, endangered, or commercially cultured fish species for use in biotechnological manipulation, such as cryopreservation and transplantation. Finally, we discuss organ culture and three-dimensional models for in vitro investigation of fish spermatogenesis.

The progestin norethindrone alters growth, reproductive histology and gene expression in zebrafish (Danio rerio)

The aim of this study was to assess the long-term effects of synthetic progestin norethindrone (NET) on the growth, reproductive histology, and transcriptional expression profiles of genes associated with the hypothalamic-pituitary-gonadal (HPG) axis and germ cells in adult zebrafish. Adult zebrafish were exposed to 7, 84 and 810 ng/L NET for 90 days. The results showed that exposure to 810 ng/L NET caused a significant decrease in growth of females and males. The ovary weight and GSI was significantly reduced by NET at concentrations of 84 or 810 ng/L, which came along with the delay of ovary maturation in females. However, NET at all treatments resulted in acceleration of sperm maturation in males. In the ovaries of females, a strong inhibition of cyp19a1a gene was observed following exposure to NET at 810 ng/L. Similarly, NET at the highest treatment led to a significant down-regulation of cyp17, cyp19a1a, vasa, nanos1, dazl and dmc1 genes in the testes of males. Taken together, the overall results demonstrated that NET could impact growth and gonadal maturation, with significant alterations of transcriptional expression genes along HPG axis and germ cells.

Transcriptome profiling of laser-captured germ cells and functional characterization of zbtb40 during 17alpha-methyltestosterone-induced spermatogenesis in orange-spotted grouper (Epinephelus coioides)

BACKGROUND

Spermatogenesis is an intricate process regulated by a finely organized network. The orange-spotted grouper (Epinephelus coioides) is a protogynous hermaphroditic fish, but the regulatory mechanism of its spermatogenesis is not well-understood. In the present study, transcriptome sequencing of the male germ cells isolated from orange-spotted grouper was performed to explore the molecular mechanism underlying spermatogenesis.

RESULTS

In this study, the orange-spotted grouper was induced to change sex from female to male by 17alpha-methyltestosterone (MT) implantation. During the spermatogenesis, male germ cells (spermatogonia, spermatocytes, spermatids, and spermatozoa) were isolated by laser capture microdissection. Transcriptomic analysis for the isolated cells was performed. A total of 244,984,338 clean reads were generated from four cDNA libraries. Real-time PCR results of 13 genes related to sex differentiation and hormone metabolism indicated that transcriptome data are reliable. RNA-seq data showed that the female-related genes and genes involved in hormone metabolism were highly expressed in spermatogonia and spermatozoa, suggesting that these genes participate in the spermatogenesis. Interestingly, the expression of zbtb family genes showed significantly changes in the RNA-seq data, and their expression patterns were further examined during spermatogenesis. The analysis of cellular localization of Eczbtb40 and the co-localization of Eczbtb40 and Eccyp17a1 in different gonadal stages suggested that Eczbtb40 might interact with Eccyp17a1 during spermatogenesis.

CONCLUSIONS

Our study, for the first time, investigated the transcriptome of the male germ cells from orange-spotted grouper, and identified functional genes, GO terms, and KEGG pathways involved in spermatogenesis. Furthermore, Eczbtb40 was first characterized and its role during spermatogenesis was predicted. These data will contribute to future studies on the molecular mechanism of spermatogenesis in teleosts.

The Function of Pre-mRNA Alternative Splicing in Mammal Spermatogenesis

Alternative pre-mRNA splicing plays important roles in co-transcriptional and post-transcriptional regulation of gene expression functioned during many developmental processes, such as spermatogenesis. The studies focusing on alternative splicing on spermatogenesis supported the notion that the development of testis is regulated by a higher level of alternative splicing than other tissues. Here, we aim to review the mechanisms underlying alternative splicing, particularly the splicing variants functioned in the process of spermatogenesis and the male infertility. There are five points regarding the alternative splicing including ⅰ) a brief introduction of alternative pre-mRNA splicing; ⅱ) the alternative splicing events in spermatogenesis-associated genes enriched in different stages of spermatogenesis; ⅲ) the mechanisms of alternative splicing regulation, such as splicing factors and m⁶A demethylation; ⅳ) the splice site recognition and alternative splicing, including the production and degradation of abnormal transcripts caused by gene variations and nonsense-mediated mRNA decay, respectively; ⅴ) abnormal alternative splicing correlated with male infertility. Taking together, this review highlights the impacts of alternative splicing and splicing variants in mammal spermatogenesis and provides new insights of the potential application of the alternative splicing into the therapy of male infertility.

Heat Shock Factor 5 Is Essential for Spermatogenesis in Zebrafish

Heat shock factors (Hsfs) are transcription factors that regulate responses to heat shock and other environmental stimuli. Four heat shock factors (Hsf1-4) have been characterized from vertebrates to date. In addition to stress response, they also play important roles in development and gametogenesis. Here, we study the fifth member of heat shock factor family, Hsf5, using zebrafish as a model organism. Mutant hsf5^-/- males, generated by CRISPR/Cas9 technique, were infertile with drastically reduced sperm count, increased sperm head size, and abnormal tail architecture, whereas females remained fertile. We show that Hsf5 is required for progression through meiotic prophase 1 during spermatogenesis as suggested by the accumulation of cells in the leptotene and zygotene-pachytene stages and increased apoptosis in post-meiotic cells. hsf5^-/- mutants show gonadal misregulation of a substantial number of genes with roles in cell cycle, apoptosis, protein modifications, and signal transduction, indicating an important role of Hsf5 in early stages of spermatogenesis.

Molecular Cloning and Characterization of SYCP3 and TSEG2 Genes in the Testicles of Sexually Mature and Immature Yak

Testis-specific genes play an essential part in the centromere union during meiosis in male germ cells, spermatogenesis, and in fertility. Previously, there was no research report available on the expression pattern of SYCP3 and TSEG2 genes in different ages of yaks. Therefore, the current research compared the expression profiling of SYCP3 and TSEG2 genes in testes of yaks. The expression pattern of SYCP3 and TSEG2 mRNA was investigated using qPCR, semi-quantitative PCR, western blot, immunohistochemistry, and molecular bioinformatics. Our findings displayed that SYCP3 and TSEG2 genes were prominently expressed in the testicles of yaks as compared to other organs. On the other hand, the protein encoded by yak SYCP3 contains Cor1/Xlr/Xmr conserved regions, while the protein encoded by yak TSEG2 contains synaptonemal complex central element protein 3. Additionally, multiple alignments sequences indicated that proteins encoded by Datong yak SYCP3 and TSEG2 were highly conserved among mammals. Moreover, western blot analysis specified that the molecular mass of SYCP3 protein was 34-kDa and TSEG2 protein 90-kDa in the yak. Furthermore, the results of immunohistochemistry also revealed the prominent expression of these proteins in the testis of mature yaks, which indicated that SYCP3 and TSEG2 might be essential for spermatogenesis, induction of central element assembly, and homologous recombination.

Comparison of PLZF Gene Expression between Pluripotent Stem Cells and Testicular Germ Cells

Objective

Spermatogonial stem cells (SSCs), as unipotent stem cells, are responsible for the production of sperm throughout the male's life. Zinc finger and BTB domain containing 16 (ZBTB16/PLZF) genes provide various functions in the cell development, signaling pathway, growth regulatory and differentiation. Here, we aimed to investigate expression of the PLZF germ cell gene marker in testis, SSCs, pluripotent embryonic stem cells (ES cells) and ES-like cells of mouse testis.

Materials and Methods

In this experimental study, we examined the expression of the PLZF germ cell marker in the testis section and testicular cell culture of neonate and adult mice by immunohistochemistry (IMH), immunocytochemistry (ICC) and Fluidigm Real-Time polymerase chain reaction (PCR).

Results

IMH data indicated that the PLZF protein was localized in the neonate testis cells of the tubules center as well as the basal compartment of adult testis seminiferous tubules. Counting PLZF IMH-positive cells in the sections of seminiferous tubules of adult and neonate testis revealed significant expression of positive cells in adult testis compared to the neonate (P<0.05). Under in vitro conditions, isolated SSC colonies were strongly ICC-positive for the PLZF germ cell marker, while ES cells and ES-like cells were negative for PLZF. Fluidigm Real-Time-PCR analysis demonstrated a significant expression of the PLZF germ cell gene in the neonate and adult SSCs, compared to ES cells and ES-like cells (P<0.05).

Conclusion

These results indicate that PLZF is a specific transcription factor of testicular germ cell proliferation, but it is downregulated in pluripotent germ cells. This can be supportive for the analysis of germ cells development both in vitro and in vivo.

Ferredoxin 1b Deficiency Leads to Testis Disorganization, Impaired Spermatogenesis, and Feminization in Zebrafish

The roles of steroids in zebrafish sex differentiation, gonadal development, and function of the adult gonad are poorly understood. Herein, we used ferredoxin 1b (fdx1b) mutant zebrafish to explore such processes. Fdx1b is an essential electron-providing cofactor to mitochondrial steroidogenic enzymes, which are crucial for glucocorticoid and androgen production in vertebrates. Fdx1b-/- zebrafish mutants develop into viable adults in which concentrations of androgens and cortisol are significantly reduced. Adult fdx1b-/- mutant zebrafish display predominantly female secondary sex characteristics but may possess either ovaries or testes, confirming that androgen signaling is dispensable for testicular differentiation in this species, as previously demonstrated in androgen receptor mutant zebrafish. Adult male fdx1b-/- mutant zebrafish exhibit reduced characteristic breeding behaviors and impaired sperm production, resulting in infertility in standard breeding scenarios. However, eggs collected from wild-type females can be fertilized by the sperm of fdx1b-/- mutant males by in vitro fertilization. The testes of fdx1b-/- mutant males are disorganized and lack defined seminiferous tubule structure. Expression of several promale and spermatogenic genes is decreased in the testes of fdx1b-/- mutant males, including promale transcription factor sox9a and spermatogenic genes igf3 and insl3. This study establishes an androgen- and cortisol-deficient fdx1b zebrafish mutant as a model for understanding the effects of steroid deficiency on sex development and reproductive function. This model will be particularly useful for further investigation of the roles of steroids in spermatogenesis, gonadal development, and regulation of reproductive behavior, thus enabling further elucidation of the physiological consequences of endocrine disruption in vertebrates.

Differential Regulation of TLE3 in Sertoli Cells of the Testes during Postnatal Development

Spermatogenesis is a process by which haploid cells differentiate from germ cells in the seminiferous tubules of the testes. TLE3, a transcriptional co-regulator that interacts with DNA-binding factors, plays a role in the development of somatic cells. However, no studies have shown its role during germ cell development in the testes. Here, we examined TLE3 expression in the testes during spermatogenesis. TLE3 was highly expressed in mouse testes and was dynamically regulated in different cell types of the seminiferous tubules, spermatogonia, spermatids, and Sertoli cells, but not in the spermatocytes. Interestingly, TLE3 was not detected in Sertoli cells on postnatal day 7 (P7) but was expressed from P10 onward. The microarray analysis showed that the expression of numerous genes changed upon TLE3 knockdown in a Sertoli cell line TM4. These include 1597 up-regulated genes and 1452 down-regulated genes in TLE3-knockdown TM4 cells. Ingenuity Pathway Analysis (IPA) showed that three factors were up-regulated and two genes were down-regulated upon TLE3 knockdown in TM4 cells. The abnormal expression of the three factors is associated with cellular malfunctions such as abnormal differentiation and Sertoli cell formation. Thus, TLE3 is differentially expressed in Sertoli cells and plays a crucial role in regulating cell-specific genes involved in the differentiation and formation of Sertoli cells during testicular development.

Characterization and localization of cyclin B3 transcript in both oocyte and spermatocyte of the rainbow trout (Oncorhynchus mykiss)

B-type cyclins are regulatory subunits with distinct roles in the cell cycle. To date, at least three subtypes of B-type cyclins (B1, B2, and B3) have been identified in vertebrates. Previously, we reported the characterization and expression profiles of cyclin B1 and B2 during gametogenesis in the rainbow trout (Oncorhynchus mykiss). In this paper, we isolated another subtype of cyclin B, cyclin B3 (CB3), from a cDNA library of the rainbow trout oocyte. The full-length CB3 cDNA (2,093 bp) has an open reading frame (1,248 bp) that encodes a protein of 416 amino acid residues. The CB3 transcript was widely distributed in all the examined tissues, namely, eye, gill, spleen, brain, heart, kidney, stomach, skin, muscle, and, especially, gonad. Northern blot analysis indicated only one form of the CB3 transcript in the testis and ovary. In situ hybridization revealed that, in contrast to cyclin B1 and B2 transcripts, CB3 transcripts were localized in the oocytes, spermatocytes, and spermatogonia. These findings strongly suggest that CB3 plays a role not only as a mitotic cyclin in spermatogonial proliferation during early spermatogenesis but also during meiotic maturation of the spermatocyte and oocyte in the rainbow trout.

Gonadal transcriptome analysis of the common carp, Cyprinus carpio: Identification of differentially expressed genes and SSRs

Common carp (Cyprinus carpio) is a world-wide freshwater fish of eutrophic waters. C. carpio, have various reproductive traits, including early sexual maturity, that may make them excellent, large, realistic, aquaculture model species. In the present work, de novo assembly of gonadal (testicular and ovarian) transcriptomes from juvenile common carp was performed to identify genes involved in gonadal development. A total of 81,757 and 43,257 transcripts with average lengths of 769 and 856 bp, were obtained from the immature testicular and ovarian transcriptomes, respectively. About 84,367 unigenes were constructed after removing redundancy involving representation of transcripts in both gonadal transcriptomes. Gene ontology (39,171 unigenes), clusters of orthologous group's analysis (6651 unigenes) and Kyoto encyclopedia of genes, and genomes automatic annotation server analysis (4783 unigenes) were performed to identify potential genes along with their functions. Furthermore, 18,342 (testis) and 8693 (ovary) simple sequence repeats were identified. About 298 differentially expressed genes were identified, of which 171 and 127 genes were up-regulated in testis and ovary, respectively. Quantitative real-time reverse transcription PCR was performed to validate differential expression of selected genes in testis and ovary. Nearly 809 genes related to reproduction were identified, sex-wise expression pattern of genes related to steroid synthesis, endocrine regulation, germ cell maintenance and others factors related to gonadal differentiation was observed, and expression analysis of nanos, ad4bp/sf-1, and gdf9 was performed. The present study identified certain important genes/factors involved in the gonadal development of C. carpio which may provide insights into the understanding of sex-differentiation and gonadal development processes.

Isolation and molecular characterization of spermatogonia from male Sprague-Dawley rats exposed in utero and postnatally to dibutyl phthalate or acrylamide

The increased incidence of testicular disorders in young men and the possible influence of environmental chemicals, such as dibutyl phthalate (DBP) and acrylamide (AA), requires experimental models for identifying modes of action. Most published reproductive toxicologic studies use RNA samples from the total testis to evaluate testicular gene expression; however, analyses of isolated cell types could provide a more specific tool. Among testicular germ cells, spermatogonia are critical since they represent the onset of spermatogenesis. This study aimed, (1) to establish a technique for spermatogonia isolation; (2) to apply this isolation technique to verify possible gene expression alterations (Pou5f1, Kitlg, Mki-67, Bak1 and Spry4) in prepubertal post-natal day, (PND24) and pubertal (PND45) testes after in utero and postnatal exposure to DBP or AA. The technique was efficient for isolation of a majority of spermatogonia. In utero DBP exposure led to reduced litter body weight at birth, reduced anogenital distance of male pups on PND4, and increased frequency of male nipple retention on PND14 compared to controls. DBP-exposed relative testes weights were reduced only at PND24 compared to control but they did not differ at PND45. DBP-exposed animals showed reduced expression levels of Pou5f1 and Mki67 on PND24, and reduced expression of Pou5f1 and Spry4 on PND45. AA exposure reduced expression of Pou5f1, Mki67, and Spry4 at PND45 although not significantly. Our results suggest that DBP acts by reducing cell proliferation and impairing differentiation in prepubertal and pubertal testes.

Duration of spermatogenesis and identification of spermatogonial stem cell markers in a Neotropical catfish, Jundiá (Rhamdia quelen)

Spermatogenesis is a process driven by stem cell, where germ cell cycle is under the control of a specific genotype species. Considering that Jundiá (Rhamdia quelen) is a Neotropical catfish with great economical importance and useful experimental model, little information is available on basic aspects of its reproductive biology, especially on spermatogenesis. As a result, this study aimed to characterize the male germ cells, estimate the duration of spermatogenesis and evaluate the expression of selected stem cell genes in Jundiá testis. Similar to other fish species, our results showed a remarkable decrease of germ cell nuclear volume during Jundiá spermatogenesis, particularly from type A undifferentiated to late type B spermatogonia and from diplotene to late spermatids. Using a S-phase marker, bromodeoxyuridine (BrdU), the combined duration of meiotic and spermiogenic phases in this species was estimated in approximately 7 days. This is considered very short when compared to mammals, where spermatogenesis last from 30 to 74 days. Selected stem cell genes were partially sequenced and characterized in Jundiá testis. Expression analysis showed higher plzf and pou5f3 mRNA levels in the cell fractions enriched by type A undifferentiated spermatogonia. These results were further confirmed by in situ hybridization that showed strong signal of plzf and pou5f3 mRNA in type A undifferentiated spermatogonia. Altogether, these information will expand our knowledge of the reproductive biology of this species, contributing to improve its production and management, and also for biotechnological applications, such as germ cell transplantation.

Cyclin Cyc2p is required for micronuclear bouquet formation in Tetrahymena thermophila

Meiotic bouquet formation (known as crescent formation in Tetrahymena thermophila) is indispensable for homologous pairing and recombination, but the regulatory mechanism of bouquet formation remains largely unknown. As a conjugation specific cyclin gene, CYC2 knockout mutants failed to form an elongated crescent structure and aborted meiosis progress in T. thermophila. γ-H2A.X staining revealed fewer micronuclear DNA double-strand breaks (DSBs) in cyc2Δ cells than in wild-type cells. Furthermore, cyc2Δ cells still failed to form a crescent structure even though DSBs were induced by exogenous agents, indicating that a lack of DSBs was not completely responsible for failure to enter the crescent stage. Tubulin staining showed that impaired perinuclear microtubule structure may contribute to the blockage in micronuclear elongation. At the same time, expression of microtubule-associated kinesin genes, KIN11 and KIN141, was significantly downregulated in cyc2Δ cells. Moreover, micronuclear specific accumulation of heterochromatin marker trimethylated H3K23 abnormally increased in the cyc2Δ mutants. Together, these results show that cyclin Cyc2p is required for micronuclear bouquet formation via controlling microtubule-directed nuclear elongation in Tetrahymena.

Long-term exposure of xenoestrogens with environmental relevant concentrations disrupted spermatogenesis of zebrafish through altering sex hormone balance, stimulating germ cell proliferation, meiosis and enhancing apoptosis

Environmental estrogens are capable of interfering with the spermatogenesis and fertility of fish. However in natural waters, these chemicals are more likely to occur as a combination rather than a single stressor. Whether and how the mixture of xenoestrogens with environmental relevant concentrations may affect fish spermatogenesis remains largely unknown. In this study, male zebrafish adults were administered to 17alpha-ethinylestradiol (EE2) and a mixture of xenoestrogens (Mix (E2, EE2, DES, 4-t-OP, 4-NP and BPA)), with the estrogenic potency equivalent to EE2. After a 60-day exposures, elevated mRNA levels of vitellogenin 1 (vtg1) and estrogen receptor 1 (esr1) in the liver of fish in both treated groups were observed. Moreover, the plasma level of E2 declined significantly in the Mix group and the ratio of 11-KT/E2 was significantly elevated in both treated groups. Consistently, the mRNA level of P450 side-chain cleavage (scc) in the EE2 group and ovarian type aromatase (cyp19a1a) in the Mix group was significantly suppressed. In addition, decreased gonadosomatic index and sperm count in the fish of Mix group were present. Furthermore, increased number of the proliferating germ cells (such as spermatogonia and spermatocytes) was observed in the fish of both groups, suggesting a stimulated germ cell proliferation and meiosis. Accordingly, both exposures significantly up-regulated the mRNA levels of genes in mitosis (cyclinb1) and meiosis (cyp26a1 in EE2 group, aldh1a2, cyp26a1, sycp3 and spo11 in Mix). In addition, decreased number of spermatozoa and increased number of TUNEL-positive signals were present in the testis of fish in the Mix group, indicating an enhanced apoptosis. Further analyses demonstrated the significant elevated expressions of tnfrsf1a and the ratio of tnfrsf1a/tnfrsf1b in the Mix group, suggesting an elevated apoptosis in the testis of fish in the Mix group via extrinsic pathway. The present study greatly extends our understanding of the underlying mechanisms of the reproductive toxicity of xenoestrogens on fish.

Identification of a Novel Zebrafish Mutant Line that Develops Testicular Germ Cell Tumors

Testicular tumors are the most common solid malignant tumors in men 20-35 years of age. Although most of testicular tumors are curable, current treatments still fail in 15%-20% of patients. However, insufficient understanding of the molecular basis and lack of animal models limit development of more effective treatments. This study reports the identification of a novel zebrafish mutant line, ns1402, which develops testicular germ cell tumors (TGCTs). While both male and female ns1402 mutants were fertile at young age, male ns1402 mutants became infertile as early as 9 months of age. This infertility was associated with progressive loss of mature sperm. Failure of spermatogenesis was, at least in part, explained by progressive loss of mature Leydig cells, a source of testosterone that is essential for spermatogenesis. Interestingly, TGCTs in ns1402 mutants contained a large number of Sertoli cells and gene expression profiles of Sertoli cells were altered before loss of mature Leydig cells. This suggests that changes in Sertoli cell properties happened first, followed by loss of mature Leydig cells and failure of spermatogenesis. Taken together, this study emphasizes the importance of cell-cell interactions and cell signaling in the testis for spermatogenesis and tissue homeostasis.

Gonocyte transformation in a congenitally cryptorchid rat is normal and may be similar to the situation reported in human acquired cryptorchidism

BACKGROUND

In congenital undescended testis (UDT) in humans, thermal insult damages early germ cell development during mini-puberty (3-6months) causing increased risk of both cancer and infertility. In rodents however, UDT causes infertility but not cancer. In the TS rat with congenital UDT we hypothesized that early germ cell development would be normal as UDT only becomes manifest at 3-4weeks (and the germ cells only become sensitive to thermal injury) after minipuberty is complete at 1week.

METHODS

Normal testis and potential UDT from unilateral cryptorchid TS rats were collected at week 1 and 4 and processed into paraffin sections labeled for Sertoli cells (AMH), early germ cells (MVH) and spermatogonial stem cells (PLZF). Confocal microscopic images and Fiji Image J were used to count cells in testicular tubules with paired T-test statistical analysis.

RESULTS

Total germ cells/tubule, basement membrane-bound germ cells/tubule, and Sertoli cells/tubule were unchanged between normally descending and future UDT at 1-4weeks old (P>0.05) Total germ cells/tubule and spermatogonial stem cells/tubule increased dramatically between weeks 1 and 4.

CONCLUSION

Rat gonocyte transformation is normal in both normally descending and future UDT. This suggests that congenitally cryptorchid rats may not develop testicular cancer because gonocytes (the putative origin of malignant degeneration) normally transform into spermatogonial stem cells before UDT occurs and the risk of thermal injury develops. This suggests the TS rat may be a good model for acquired UDT in human where the abnormal testicular position develops after gonocyte transformation is completed in the first year.

Tributyltin impaired reproductive success in female zebrafish through disrupting oogenesis, reproductive behaviors and serotonin synthesis

Tributyltin (TBT), an organotin acting as aromatase (Cyp19a1) inhibitor, has been found to disrupt gametogenesis and reproductive behaviors in several fish species. However, few studies addressing the mechanisms underlying the impaired gametogenesis and reproduction have been reported. In this study, female adults of zebrafish (Danio rerio) were continuously exposed to two nominal concentrations of TBT (100 and 500 ng/L, actual concentrations: 90.8 ± 1.3 ng/L and 470.3 ± 2.7 ng/L, respectively) for 28 days. After exposures, TBT decreased the total egg number, reduced the hatchability and elevated the mortality of the larvae. Decreased gonadosomatic index (GSI) and altered percentages of follicles in different developmental stages (increased early-stage follicles and reduced mid/late-stage follicles) were also observed in the ovary of TBT-treated fish. TBT also lowered the plasma level of 17β-estradiol and suppressed the expressions of cyp19a1a in the ovary. In treated fish, up-regulated expressions of aldhla2, sycp3 and dmc1 were present in the ovary, indicating an enhanced level of meiosis. The mRNA level of vtg1 was dramatically suppressed in the liver of TBT-treated fish, suggesting an insufficient synthesis of Vtg protein, consistent with the decreased percentage of mid/late-stage follicles in the ovaries. Moreover, TBT significantly suppressed the reproductive behaviors of the female fish (duration of both sexes simultaneously in spawning area, the frequency of meeting and the visit in spawning area) and down-regulated the mRNA levels of genes involved in the regulation of reproductive behaviors (cyp19a1b, gnrh-3 and kiss 2) in the brain. In addition, TBT significantly suppressed the expressions of serotonin-related genes, such as tph2 (encoding serotonin synthase), pet1 (marker of serotonin neuron) and kiss 1 (the modulator of serotonin synthesis), suggesting that TBT might disrupt the non-reproductive behaviors of zebrafish. The present study demonstrated that TBT may impair the reproductive success of zebrafish females probably through disrupting oogenesis, disturbing reproductive behaviors and altering serotonin synthesis. The present study greatly extends our understanding on the reproductive toxicity of TBT on fish.

Deletion of Spata2 by CRISPR/Cas9n causes increased inhibin alpha expression and attenuated fertility in male mice

As somatic cells in the testis seminiferous tubule, Sertoli cells provide the medium for spermatogenesis. One of the important functions of Sertoli cells is synthesizing and secreting cell factors to affect the production of sperm; however, much of those molecular regulation mechanisms remain unknown. Here, we confirm the localization of protein SPATA2 (spermatogenesis-associated protein 2), which had previously been shown to be highly expressed in Sertoli cells of the adult mouse testis. To further conduct a functional study, we generated SPATA2 global knockout mice via use of the CRISPR/Cas9n gene editing technology. The 120-day-old knockout mice testes showed almost a 40% decrease in size and weight and variations in the histomorphology of the seminiferous epithelium, with a 40% decrease in sperm count. Further examination revealed that the proliferation of germ cells in the seminiferous tubules was attenuated by 28%. In addition, we found that SPATA2 deletion led to an approximately 70% increase in the inhibin alpha-subunit mRNA and protein level in the testes compared to that of wild-type mice. Our data revealed the impact of SPATA2 on male fertility and suggested that SPATA2 ensures the normal secretory function of Sertoli cells.

Diethylstilbestrol arrested spermatogenesis and somatic growth in the juveniles of yellow catfish (Pelteobagrus fulvidraco), a fish with sexual dimorphic growth

In fish, spermatogenesis and somatic growth are mainly regulated by hypothalamic-pituitary-gonadal (HPG) and hypothalamic-pituitary-somatic (HPS) axes, respectively. Xenoestrogens have been reported to impair spermatogenesis in some fishes, and arrest somatic growth in some others, whereas, whether xenoestrogens are capable of disrupting spermatogenesis and somatic growth simultaneously in fish that exhibits sexual dimorphic growth is little known, and the underlying mechanisms remain poorly understood. In this study, male juveniles of yellow catfish (Pelteobagrus fulvidraco), which exhibits a sexual dimorphic growth that favors males, were exposed to diethylstilbestrol (DES) for 28 days. After exposure, DES significantly disrupted the spermatogenesis (decreased gonadal-somatic index (GSI) and germ cell number) and arrested the somatic growth (declined body weight) of the catfish juveniles. Gene expression and plasma steroid analyses demonstrated the suppressed mRNA levels of genes in HPG axis (gnrh-II, fshβ, and lhβ in the brain and dmrt1, sf1, fshr, cyp17a1, cyp19a1a, and cyp11b2 in the testis) and decreased 17β-estrodial (E2) and 11-ketotestosterone (11-KT) levels in plasma. Further analysis revealed the arrested germ cell proliferation (cyclin d1), meiosis (dmc1, sycp3), and enhanced apoptosis (decreased bcl-2 and elevated bax/bcl-2 ratio) in the testis. Besides, DES also suppressed the mRNA levels of genes in HPS axis (ghrh, gh, and prl in the brain and ghr, igf1, igf2a, and igf2b in the liver). The suppressed HPG and HPS axes were thus supposed to disturb spermatogenesis and arrest somatic growth in yellow catfish. The present study greatly extended our understanding on the mechanisms underlying the toxicity of DES on spermatogenesis and somatic growth of fish.

The protective effects of selenium-enriched spirulina on the reproductive system of male zebrafish (Danio rerio) exposed to beta-cypermethrin

Beta-cypermethrin (beta-CYP), which is widely used for the control of indoor and field pests, is a highly lipophilic insecticide with environmental estrogenic effects.

Distinct and Cooperative Roles of amh and dmrt1 in Self-Renewal and Differentiation of Male Germ Cells in Zebrafish

Spermatogenesis is a fundamental process in male reproductive biology and depends on precise balance between self-renewal and differentiation of male germ cells. However, the regulative factors for controlling the balance are poorly understood. In this study, we examined the roles of amh and dmrt1 in male germ cell development by generating their mutants with Crispr/Cas9 technology in zebrafish. Amh mutant zebrafish displayed a female-biased sex ratio, and both male and female amh mutants developed hypertrophic gonads due to uncontrolled proliferation and impaired differentiation of germ cells. A large number of proliferating spermatogonium-like cells were observed within testicular lobules of the amh-mutated testes, and they were demonstrated to be both Vasa- and PH3-positive. Moreover, the average number of Sycp3- and Vasa-positive cells in the amh mutants was significantly lower than in wild-type testes, suggesting a severely impaired differentiation of male germ cells. Conversely, all the dmrt1-mutated testes displayed severe testicular developmental defects and gradual loss of all Vasa-positive germ cells by inhibiting their self-renewal and inducing apoptosis. In addition, several germ cell and Sertoli cell marker genes were significantly downregulated, whereas a prominent increase of Insl3-positive Leydig cells was revealed by immunohistochemical analysis in the disorganized dmrt1-mutated testes. Our data suggest that amh might act as a guardian to control the balance between proliferation and differentiation of male germ cells, whereas dmrt1 might be required for the maintenance, self-renewal, and differentiation of male germ cells. Significantly, this study unravels novel functions of amh gene in fish.

Diethylstilbestrol impaired oogenesis of yellow catfish juveniles through disrupting hypothalamic-pituitary-gonadal axis and germ cell development

Diethylstilbestrol (DES), a non-steroidal estrogen, has been found to cause altered germ cell development and disordered ovarian development in fish females. However, the mechanisms that might be involved are poorly understood. In this study, female juveniles of yellow catfish (Pelteobagrus fulvidraco) (120 days post-hatching) were exposed to two doses (10 and 100 ng l^-1 ) of DES for 28 days. After the endpoint of exposure, decreased ovary weight and gonadosomatic index, as well as various ovarian impairments were observed in response to DES. Besides, DES elevated the mRNA levels of vitellogenin 1 (vtg 1) and estrogen receptor 1 (esr 1) in liver and decreased 17β-estradiol level in plasma. Correspondingly, suppressed mRNA levels of the key genes in the hypothalamic-pituitary-gonadal axis (such as cyp19a1b, gnrh-II, fshβ and lhβ in brain and fshr, lhr and cyp19a1a in ovary) after DES exposure were also observed. The declined level of plasma 17β-estradiol and altered gene expressions of genes in the hypothalamic-pituitary-gonadal axis were thus supposed to be closely related to the disrupted oogenesis in DES-treated fish. Analyses further demonstrated that, higher concentration of DES elevated the expression ratio of bax/bcl-2, indicating the enhanced apoptosis occurred in ovary. Moreover, DES upregulated the expressions of genes involved in proliferation (cyclin d1 and pcna), meiotic entry (cyp26a1 and scp3) and meiotic maintenance (dmc1), resulting in arrested oogenesis in catfish. The present study greatly extended our understanding on the mechanisms underlying of reproductive toxicity of DES on fish oogenesis.

Unraveling transcriptome dynamics in human spermatogenesis

Spermatogenesis is a dynamic developmental process that includes stem cell proliferation and differentiation, meiotic cell divisions and extreme chromatin condensation. Although studied in mice, the molecular control of human spermatogenesis is largely unknown. Here, we developed a protocol that enables next-generation sequencing of RNA obtained from pools of 500 individually laser-capture microdissected cells of specific germ cell subtypes from fixed human testis samples. Transcriptomic analyses of these successive germ cell subtypes reveals dynamic transcription of over 4000 genes during human spermatogenesis. At the same time, many of the genes encoding for well-established meiotic and post-meiotic proteins are already present in the pre-meiotic phase. Furthermore, we found significant cell type-specific expression of post-transcriptional regulators, including expression of 110 RNA-binding proteins and 137 long non-coding RNAs, most of them previously not linked to spermatogenesis. Together, these data suggest that the transcriptome of precursor cells already contains the genes necessary for cellular differentiation and that timely translation controlled by post-transcriptional regulators is crucial for normal development. These established transcriptomes provide a reference catalog for further detailed studies on human spermatogenesis and spermatogenic failure.

Highlighted Article: Using laser capture microscopy, a comprehensive transcriptomic dataset of well-defined and distinct germ cell subtypes based on morphology and localization in the human testis is generated.

Diethylstilbestrol, flutamide and their combination impaired the spermatogenesis of male adult zebrafish through disrupting HPG axis, meiosis and apoptosis

Both diethylstilbestrol (DES, an environmental estrogen) and flutamide (FLU, an anti-androgen) are found to impair spermatogenesis by disrupting hypothalamic-pituitary-gonadal (HPG) axis and altering androgen levels through different mechanisms/modes of action in fish with poorly understood underlying mechanisms. Furthermore, it is not known whether and how a combined exposure of DES and FLU has a stronger effect than the compounds alone. In this study, male zebrafish adults were exposed to DES, FLU and their combination (DES+FLU) for 30days, and their effects on histological structure and sperm count in testis, androgen level in plasma, as well as the mRNA levels of genes involved in HPG axis, meiotic regulation and apoptosis were analyzed. After exposure, DES and FLU disrupted spermatogenesis in zebrafish, and their combination resulted in even more severe impairment, indicating the inhibitory roles of these chemicals on spermatogenesis and their additive effects on zebrafish. The different regulation of vtg1 expression in the liver in response to DES and FLU further confirmed the different modes of action of these drugs. Gene expression and plasma steroid level analyses demonstrated the suppressed mRNA levels of the key genes (such as gnrh3, fshβ and lhβ in brain and dmrt1, sf1, cyp17a1 and cyp11b2 in testis) in HPG axis and decreased 11-ketotestosterone (11-KT) levels in plasma. The declined level of 11-KT was thus supposed to be closely related to the down-regulation of cyp26a1 (encoding the catabolic enzyme of retinoic acid) and suppression of genes involved in meiotic regulation (nanos1, dmc1 and sycp3). In fish exposed to DES and DES+FLU, enhanced apoptosis (elevated bax/bcl-2 expression ratio) was also observed. The suppression of meiotic regulation in response to all the exposures and enhanced apoptosis in response to DES were thus supposed to result in the spermatogenic impairment in zebrafish. The present study greatly extends our understanding on the mechanisms underlying of reproductive toxicity of environment estrogens and anti-androgens in fish.

Scp3 expression in relation to the ovarian differentiation in the protogynous hermaphroditic ricefield eel Monopterus albus

Synaptonemal complex protein 3 (Scp3), which is encoded by scp3, is a meiotic marker commonly used to trace the timing of gonadal differentiation in vertebrates. In the present study, the ricefield eel scp3 cDNA was cloned, and a fragment encoding amino acids 49 to 244 was overexpressed. The recombinant Scp3 polypeptide was purified and used to generate a rabbit anti-Scp3 polyclonal antiserum. In adult ricefield eels, scp3 mRNA was predominantly detected in the gonads and faintly detected in discrete brain areas. In the gonads, Scp3 immunoreactivities were shown to be localized to the germ cells, including meiotic primary growth oocytes, spermatocytes, and pre-meiotic spermatogonia. During early ovarian differentiation, immunoreactive Scp3 was not detected in the gonads of ricefield eels at 6 days post-hatching (dph) but was found to be abundantly localized in the cytoplasm of some oogonia at 7 dph, coinciding with the appearance of the ovarian cavity and ovarian differentiation. At 14 dph, strong Scp3 immunostaining was detected on one side of the nucleus with a distinct polarity in some germ cells, presumably at the leptotene stage. Consistent with these results, the expression of scp3 mRNA was faintly detected in the gonads of ricefield eels at 6 dph, increased at 8 dph, and then remained relatively high thereafter. Taken together, these results suggest that the appearance of immunoreactive Scp3 in oogonia could be a marker for early ovarian differentiation in ricefield eels. The translocation of the Scp3 protein from the cytoplasm to the nucleus in the oogonium of ricefield eels appears to be a controlled process that warrants further study.