Cyp17a1 is Required for Female Sex Determination and Male Fertility by Regulating Sex Steroid Biosynthesis in Fish

dmrt1 Is Responsible for Androgen-Induced Masculinization in Nile Tilapia

17α-Methyltestosterone (MT) is a widely used androgen for all-male fish production in aquaculture. However, the molecular mechanism underlying MT-induced masculinization remains unclear. In this study, we aim to identify the key gene responsible for MT-induced masculinization using the Nile tilapia (Oreochromis niloticus) amhy, dmrt1, and gsdf mutants, which exhibit male-to-female sex reversal. Nile tilapia fry from these three mutant lines were treated with 50 μg/g MT from 5 to 30 days after hatching (dah). The results showed that amhy and gsdf mutants, but not dmrt1 mutants, were masculinized by the MT treatment. Gonadal transcriptome analysis revealed that genes involved in steroidogenesis and germ cell development in MT-treated dmrt1 mutants exhibited a similar expression pattern to that of the wild type (WT) XX. In addition, the dmrt1 mutants cannot be masculinized by co-treatment with MT and the aromatase inhibitor fadrozole. The MT treatment completely blocked early steroidogenic enzyme (Star2, Cyp17a2, and Cyp19a1a) expression independent of amhy, gsdf, and dmrt1. A luciferase analysis showed that MT directly suppressed basal and Sf-1-activated cyp19a1a promoter activity through ara and arb in cultured HEK293 cells. Furthermore, MT treatment inhibited germ cell proliferation in amhy and gsdf mutants but not in dmrt1 mutants. Consistently, dmrt1 expression was induced in MT-treated WT XX, -amhy, and -gsdf mutants. Taken together, these results suggest that dmrt1 is indispensable for MT-induced masculinization in Nile tilapia and that MT functions by inhibiting early steroid synthesis and activating dmrt1 to promote testis development.

Assessing reproductive effects and epigenetic responses in Austrolebias charrua exposed to Roundup Transorb®: Insights from miRNA profiling and molecular interaction analysis

This study examines the effects of Roundup Transorb® (RDT) exposure on reproductive functions and ovarian miRNA expression in Austrolebias charrua. Exposure to RDT (at 0.065 or 5 mg. L-1 for 96 h) significantly disrupts fertility, evidenced by changes in fertilization rates and egg diameter. Profiling of ovarian miRNAs identified a total 205 miRNAs in A. charrua. Among these, three miRNAs were upregulated (miR-10b-5p, miR-132-3p, miR-100-5p), while ten miRNAs were downregulated (miR-499-5p, miR-375, miR-205-5p, miR-206-3p, miR-203a-3p, miR-133b-3p, miR-203b-5p, miR-184, miR-133a-3p, miR-2188-5p) compared to non-exposed fish. This study reveals that differentially expressed miRNAs are linked to molecular pathways such as steroid hormone biosynthesis, lipid and carbohydrate metabolism, bioenergetics, and antioxidant defense. It also analyzes molecular interactions between miRNAs and target genes during RDT exposure in annual killifish, providing insights into biomarkers in ecotoxicology. Moreover, it provides scope for developing environmental health assessment models based on epigenomic endpoints, supporting the protection of biodiversity and ecosystem services through the quantification of stress responses in living organisms exposed to pesticides.

Decoding the fish genome opens a new era in important trait research and molecular breeding in China

Aquaculture represents the fastest-growing global food production sector, as it has become an essential component of the global food supply. China has the world's largest aquaculture industry in terms of production volume. However, the sustainable development of fish culture is hindered by several concerns, including germplasm degradation and disease outbreaks. The practice of genomic breeding, which relies heavily on genome information and genotypephenotype relationships, has significant potential for increasing the efficiency of aquaculture production. In 2014, the completion of the genome sequencing and annotation of the Chinese tongue sole signified the beginning of the fish genomics era in China. Since then, domestic researchers have made dramatic progress in functional genomic studies. To date, the genomes of more than 60 species of fish in China have been assembled and annotated. Based on these reference genomes, evolutionary, comparative, and functional genomic studies have revolutionized our understanding of a wide range of biologically and economically important traits of fishes, including growth and development, sex determination, disease resistance, metamorphosis, and pigmentation. Furthermore, genomic tools and breeding techniques such as SNP arrays, genomic selection, and genome editing have greatly accelerated genetic improvement through the incorporation of functional genomic information into breeding activities. This review aims to summarize the current status, advances, and perspectives of the genome resources, genomic study of important traits, and genomic breeding techniques of fish in China. The review will provide aquaculture researchers, fish breeders, and farmers with updated information concerning fish genomic research and breeding technology. The summary will help to promote the genetic improvement of production traits and thus will support the sustainable development of fish aquaculture.

Star1 gene mutation reveals the essentiality of 11-ketotestosterone and glucocorticoids for male fertility in Nile Tilapia (Oreochromis niloticus)

Steroidogenic acute regulatory protein (Star) plays an essential role in the biosynthesis of corticosteroids and sex steroids by mediating the transport of cholesterol from the outer to the inner membrane of mitochondria. Two duplicated Star genes, namely star1 and star2, have been identified in non-mammalian vertebrates. To investigate the roles of star genes in fish steriodogenesis, we generated two mutation lines of star1-/- and star1-/-/star2-/- in Nile tilapia (Oreochromis niloticus). Previous studies revealed that deficiency of star2 gene caused delayed spermatogenesis, sperm apoptosis and sterility in male tilapia. Our present data revealed that mutation of star genes impaired male fertility. Disordered seminiferous lobules and spermatic duct obstruction were found in the testis of both types of mutants. Moreover, significant decline in semen volume, sperm abnormality and impaired fertility were also detected in star1-/- and star1-/-/star2-/- males. In star1-/- male fish, lipid accumulation, up-regulation of steroidogenic enzymes, and significant decline of androgens were found. Additionally, hyperplasic interrenal cells, elevated steroidogenic gene expression level and decline of serum glucocorticoids were detected in star1 mutants. Intriguingly, either 11-KT or cortisol supplementation successfully rescued the impaired fertility of the star1-/- mutants. Taken together, these results further indicate that Star1 might play critical roles in the production of both 11-KT and glucocorticoids, which are indispensable for the maintenance of male fertility in fish.

Hypogonadotropic hypogonadism in male tilapia lacking a functional rln3b gene

Relaxin 3 is a neuropeptide that plays a crucial role in reproductive functions of mammals. Previous studies have confirmed that rln3a plays an important role in the male reproduction of tilapia. To further understand the significance of its paralogous gene rln3b in male fertility, we generated a homozygous mutant line of rln3b in Nile tilapia. Our findings indicated that rln3b mutation delayed spermatogenesis and led to abnormal testes structure. Knocking out rln3b gene resulted in a decrease in sperm count, sperm motility and male fish fertility. TUNEL detection revealed a small amount of apoptosis in the testes of rln3b-/- male fish at 390 days after hatching (dah). RT-qPCR analysis demonstrated that mutation of rln3b gene caused a significant downregulation of steroid synthesis-related genes such as cyp17a1, cyp11b2, germ cell marker gene, Vasa, and gonadal somatic cell marker genes of amh and amhr2. Furthermore, we found a significant down-regulation of hypothalamic-pituitary-gonadal (HPG) axis-related genes, while a significantly up-regulation of the dopamine synthetase gene in the rln3b-/- male fish. Taken together, our data strongly suggested that Rln3b played a crucial role in the fertility of XY tilapia by regulating HPG axis genes.

How Per- and Poly-Fluoroalkyl Substances Affect Gamete Viability and Fertilization Capability: Insights from the Literature

There has been emerging research linking per- and poly-fluoroalkyl substances (PFAS) to gamete viability and fertility. PFAS, prevalent in the environment and water supplies, undergo slow degradation due to their C-F bond and a long half-life (2.3-8.5 years). In females, PFAS inhibit the hypothalamic-pituitary-gonadal (HPG) axis, reducing follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels, leading to the inhibition of androgen and estradiol production. PFAS have been found to cause detrimental effects on egg quality through impairing folliculogenesis. In males, PFAS can impair sperm motility and morphology: two fundamental qualities of successful fertilization. PFAS exposure has been proven to inhibit testosterone production, sperm capacitation, and acrosomal reaction. After fertilization, the results of PFAS exposure to embryos have also been investigated, showing reduced development to the blastocyst stage. The aim of this review is to report the main findings in the literature on the impact of PFAS exposure to gamete competency and fertilization capability by highlighting key studies on both male and female fertility. We report that there is significant evidence demonstrating the negative impacts on fertility after PFAS exposure. At high doses, these environmentally abundant and widespread compounds can significantly affect human fertility.

Comparative transcriptomic analysis of the different developmental stages of ovary in the cuttlefish Sepia pharaonis

The cuttlefish, Sepia pharaonis, is characterized by rapid growth and strong disease resistance, making it an important commercially farmed cephalopod species in the southeastern coastal regions of China. However, in the reproductive process of S. pharaonis, there are challenges such as a low output of eggs, poor quality, and low survival rates of newly hatched juveniles. Therefore, there is an urgent need to study the molecular mechanisms underlying ovarian development in this species. In this study, we conducted the first transcriptomic analysis of the ovary at four developmental stages: the undeveloped stage, developing stage, nearly-ripe stage, and ripe stage, and compared the transcriptomics among these four stages using Illumina sequencing technology. The total numbers of clean reads of the four stages ranged from 40,890,772 to 52,055,714 reads. A total of 136,829 DEGs were obtained, GC base ratios of raw data were between 38.44 and 44.59%, and the number of uniquely mapped reads spanned from 88.08 to 95.90%. The Pearson correlation coefficient demonstrated a strong correlation among different samples within the same group, PCA and Anosim analysis also revealed that the grouping of these four stages was feasible, and each stage could be distinguished from the others. GO enrichment analysis demonstrated that ovarian follicle growth, sex differentiation, and transforming growth factor beta receptor, played a foreshadowing role at the early ovarian development stage, and the terms of small molecule metabolic process, peptide metabolic process, and catalytic activity were prominent at the mature stage. Meanwhile, KEGG analysis showed that the early ovarian development of S. pharaonis was mainly associated with the cell cycle, DNA replication, and carbon metabolism, while the mid-late ovarian development was involved with the signal transduction, endocrine system, and reproduction pathway. RT-qPCR further confirmed the consistent expression patterns of genes such as 17β-HSD, GH, VGS, NFR, and NYR in the ovaries of S. pharaonis, exhibiting elevated levels of expression during the maturation stage. Conversely, ER and OM exhibited high expression levels during the early stages of ovarian development. These transcriptomic data provide insights into the molecular mechanisms of S. pharaonis ovarian development. The findings of this study will contribute to improving the reproduction and development of cuttlefish and enriching the bioinformatics knowledge of cephalopods.

Tilapia, a good model for studying reproductive endocrinology

The Nile tilapia (Oreochromis niloticus), with a system of XX/XY sex determination, is a worldwide farmed fish with a shorter sexual maturation time than that of most cultured fish. Tilapia show a spawning cycle of approximately 14 days and can be artificially propagated in the laboratory all year round to obtain genetically all female (XX) and all male (XY) fry. Its genome sequence has been opened, and a perfect gene editing platform has been established. With a moderate body size, it is convenient for taking enough blood to measure hormone level. In recent years, using tilapia as animal model, we have confirmed that estrogen is crucial for female development because 1) mutation of star2, cyp17a1 or cyp19a1a (encoding aromatase, the key enzyme for estrogen synthesis) results in sex reversal (SR) due to estrogen deficiency in XX tilapia, while mutation of star1, cyp11a1, cyp17a2, cyp19a1b or cyp11c1 affects fertility due to abnormal androgen, cortisol and DHP levels in XY tilapia; 2) when the estrogen receptors (esr2a/esr2b) are mutated, the sex is reversed from female to male, while when the androgen receptors are mutated, the sex cannot be reversed; 3) the differentiated ovary can be transdifferentiated into functional testis by inhibition of estrogen synthesis, and the differentiated testis can be transdifferentiated into ovary by simultaneous addition of exogenous estrogen and androgen synthase inhibitor; 4) loss of male pathway genes amhy, dmrt1, gsdf causes SR with upregulation of cyp19a1a in XY tilapia. Disruption of estrogen synthesis rescues the male to female SR of amhy and gsdf but not dmrt1 mutants; 5) mutation of female pathway genes foxl2 and sf-1 causes SR with downregulation of cyp19a1a in XX tilapia; 6) the germ cell SR of foxl3 mutants fails to be rescued by estrogen treatment, indicating that estrogen determines female germ cell fate through foxl3. This review also summarized the effects of deficiency of other steroid hormones, such as androgen, DHP and cortisol, on fish reproduction. Overall, these studies demonstrate that tilapia is an excellent animal model for studying reproductive endocrinology of fish.

CircEpha5 regulates the synthesis and secretion of androgen in mouse preantral follicles by targeting miR-758-5p

Circular RNAs are involved in the pathogenesis of various diseases, although its expression pattern and role in polycystic ovary syndrome (PCOS), characterised by hyperandrogenism, are not very clear. This article assessed the circRNAs expression profile in the ovaries of PCOS mice by circRNAs high-throughput sequencing and explored the role of circEpha5 in hyperandrogenism. The results showed that the overexpression of circEpha5 in mouse preantral follicles could increase the expression of Cyp17a1, an androgen synthesis-related gene, which resulted in a higher serum level of testosterone. Dual-luciferase reporter gene studies identified miR-758-5p as a direct target of circEpha5. Consequently, miR-758-5p expression was downregulated upon circEpha5 overexpression. Ectopically expressed miR-758-5p reversed the stimulation effects of circEpha5 on steroidogenesis-related gene expression and testosterone release. Therefore, circEpha5 could sponge miR-758-5p to regulate the expression of Cyp17a1, thereby promoting the synthesis and secretion of androgen in the preantral follicles. This work is contributed to the understanding of the pathogenesis of hyperandrogenemia and lays the foundation for the development of therapeutic targets of PCOS hyperandrogenism.

Insulin-like Androgenic Gland Hormone Induced Sex Reversal and Molecular Pathways in Macrobrachium nipponense: Insights into Reproduction, Growth, and Sex Differentiation

This study investigated the potential to use double-stranded RNA insulin-like androgenic gland hormone (dsIAG) to induce sex reversal in Macrobrachium nipponense and identified the molecular mechanisms underlying crustacean reproduction and sex differentiation. The study aimed to determine whether dsIAG could induce sex reversal in PL30-male M. nipponense during a critical period. The sex-related genes were selected by performing the gonadal transcriptome analysis of normal male (dsM), normal female (dsFM), neo-female sex-reversed individuals (dsRM), and unreversed males (dsNRM). After six injections, the experiment finally resulted in a 20% production of dsRM. Histologically, dsRM ovaries developed slower than dsFM, but dsNRM spermathecae developed normally. A total of 1718, 1069, and 255 differentially expressed genes were identified through transcriptome sequencing of the gonads in three comparison groups, revealing crucial genes related to reproduction and sex differentiation, such as GnRHR, VGR, SG, and LWS. Principal Component Analysis (PCA) also distinguished dsM and dsRM very well. In addition, this study predicted that the eyestalks and the "phototransduction-fly" photoperiodic pathways of M. nipponense could play an important role in sex reversal. The enrichment of related pathways and growth traits in dsNRM were combined to establish that IAG played a significant role in reproduction, growth regulation, and metabolism. Finally, complete sex reversal may depend on specific stimuli at critical periods. Overall, this study provides valuable findings for the IAG regulation of sex differentiation, reproduction, and growth of M. nipponense in establishing a monoculture.

Effect of long-term hypoxia on the reproductive systems of female and male yellow catfish (Pelteobagrus fulvidraco)

This study investigated the effects of different levels of hypoxia on the reproductive system of yellow catfish. Yellow catfish (Pelteobagrus fulvidraco) were exposed to three dissolved oxygen concentration levels: normoxia (6.5 ± 0.2 mg/L), moderate hypoxia (MH, 3.8 ± 0.3 mg/L) and severe hypoxia (SH, 1.9 ± 0.2 mg/L) for 30 days. The gonadosomatic index of males, not females, significantly decreased in the SH group. In the SH group, for the females, the ratio of vitellogenic follicles significantly decreased, whereas the number of atretic follicles significantly increased. In male fish, a significantly reduced number of spermatozoa was observed in both the MH and SH groups. Elevated apoptosis levels in the testes and ovaries were observed only in the SH group. Serum 17β-estradiol and vitellogenin levels in females and testosterone levels in males significantly decreased in the SH group. The concentration of 11-ketotestosterone in males significantly decreased in both the MH and SH groups. In female fish, dysregulated expression of the hypothalamic-pituitary-gonadal (HPG) axis, steroidogenesis genes, and hepatic genes related to vitellogenesis were observed only in the SH group. However, in male fish, moderate hypoxia altered the expression of HPG genes, including gnrh1, lhcgr, and amh. Moreover, the MH group significantly altered the expression of steroidogenesis genes like star, 17β-hsd, and cyp17a1. The results of this study suggest that severe hypoxia can cause reproductive defects in female and male yellow catfish. Moreover, the reproductive system of male yellow catfish is more sensitive to moderate hypoxia than that of female catfish. Our findings contribute to our understanding of the response of the teleost reproductive system to long-term hypoxia.

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

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

Gonadal transcriptomes reveal sex-biased expression genes associated with sex determination and differentiation in red-tail catfish (Hemibagrus wyckioides)

BACKGROUND

Red-tail catfish (Hemibagrus wyckioides) is an important commercially farmed catfish in southern China. Males of red-tail catfish grow faster than females, suggesting that all-male catfish will produce more significant economic benefits in aquaculture practice. However, little research has been reported on sex determination and gonadal development in red-tail catfish.

RESULTS

In this study, we performed the first transcriptomic analysis of male and female gonads at four developmental stages at 10, 18, 30, and 48 days post hatching (dph) using RNA-seq technology. A total of 23,588 genes were screened in 24 sequenced samples, of which 28, 213, 636, and 1381 differentially expressed genes (DEGs) were detected at four developmental stages, respectively. Seven candidate genes of sex determination and differentiation were further identified. Real-time quantitative PCR (RT-qPCR) further confirmed that anti-Mullerian hormone (amh), growth differentiation factor 6a (gdf6a), testis-specific gene antigen 10 (tsga10), and cytochrome P450 family 17 subfamily A (cyp17a) were highly expressed mainly in the male, while cytochrome P450 family 19 subfamily A polypeptide 1b (cyp19a1b), forkhead box L2 (foxl2), and hydroxysteroid 17-beta dehydrogenase 1 (hsd17b1) were highly expressed in the female. The KEGG pathway enrichment data showed that these identified DEGs were mainly involved in steroid hormone biosynthesis and TGF-β signaling pathways.

CONCLUSIONS

Based on RNA-seq data of gonads at the early developmental stages, seven DEGs shared by the four developmental stages were identified, among which amh and gdf6a may be the male-biased expression genes, while foxl2, cyp19a1b and hsd17b1 may be the female-biased expression genes in red-tail catfish. Our study will provide crucial genetic information for the research on sex control in red-tail catfish, as well as for exploring the evolutionary processes of sex determination mechanisms in fish.

Rxrs and their partner receptor genes inducing masculinization plausibly mediated by endocrine disruption in Paralichthys olivaceus

Retinoid X receptors (RXRs) can form homo- or heterodimers with orphan receptors involved in multiple intertwined signaling pathways. However, there is limited study on the formation of sex phenotypes and the regulation of steroidogenesis by RXRs in fish. Here, in Paralichthys olivaceus, we first indicated that PPARγ::RXRα was predictably a transcription factor for steroidogenesis genes, and Foxl2 and Dmrt1 were also transcription factors for rxrs and their partner receptor genes. When the flounder fry were exposed to LG100268 (LG, RXRs agonist, 50 mg/kg diet), the percentage of males increased from 50% to 71.4%. Before histological differentiation of the flounder ovary (3 cm TL) and testis (6 cm TL), the transcripts of rar β and rar γ (P < 0.05) were activated, and the steroidogenesis gene Hsd3b1 was down-regulated (P < 0.05). The ratios of testosterone (T)/17β-estradiol (E2) were all greatly increased (P < 0.05), and the ratio of 11-ketotestosterone (11-KT)/E2 was elevated at 3 cm TL. Moreover, LG was used to treat the cultured gonads in vitro (10 μM) and the fish with intraperitoneal injection in vivo (12 mg/kg body weight), respectively. LG was able to up-regulate rxr γ, rar γ, and ppar δ, and Hsd3b1 was significantly up-regulated (P < 0.05). The ratios of 11-KT/E2 in the culture medium and in the ovaries of the fish were decreased. Furthermore, the recombinant flounder Foxl2 protein was able to significantly down-regulate ppar γ (P < 0.05) and tr β (P < 0.01) in the ovaries in vitro, and the result of the Dmrt1 in the testes was opposite to that of the Foxl2, probably indicating a feedback loop between RXRs' partner receptors and Foxl2/Dmrt1. These findings introduce for the first time the mode of action of RXRs on the flounder steroidogenesis and provide important data to learn the potential function of RXRs in fish sex differentiation and the potential role of RXRs in aquatic animals in the presence of water pollutants.

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.

Multi-omics analysis reveals that iron deficiency impairs spermatogenesis by gut-hormone synthesis axis

Considering that research has mainly focussed on how excessive iron supplementation leads to reproductive cytotoxicity, there is a lack of in-depth research on reproductive system disorders caused by iron deficiency. To gain a better understanding of the effects of iron deficiency on the reproductive system, especially spermatogenesis, we first constructed a mouse model of iron deficiency. We employed multi-omic analysis, including transcriptomics, metabolomics, and microbiomics, to comprehensively dissect the impact of iron deficiency on spermatogenesis. Moreover, we verified our findings in detail using western blot, immunofluorescence, immunohistochemistry, qRT-PCR and other techniques. Microbiomic analysis revealed altered gut microbiota in iron-deficient mice, and functional predictive analysis showed that gut microbiota can regulate spermatogenesis. The transcriptomic data indicated that iron deficiency directly alters expression of meiosis-related genes. Transcriptome data also revealed that iron deficiency indirectly regulates spermatogenesis by affecting hormone synthesis, findings confirmed by metabolomic data, western blot and immunofluorescence. Interestingly, competing endogenous RNA networks also play a vital role in regulating spermatogenesis after iron deficiency. Taken together, the data elucidate that iron deficiency impairs spermatogenesis and increases the risk of male infertility by affecting hormone synthesis and promoting gut microbiota imbalance.

Identification of genes related to sexual differentiation and sterility in embryonic gonads of Mule ducks by transcriptome analysis

The key genes of avian gonadal development are of great significance for sex determination. Transcriptome sequencing analysis of Mule duck gonad as potential sterile model is expected to screen candidate genes related to avian gonad development. In this study, the embryonic gonadal tissues of Mule ducks, Jinding ducks, and Muscovy ducks were collected and identified. Six sample groups including female Mule duck (A), male Mule duck (B), female Jinding duck (C), male Jinding duck (D), female Muscovy duck (E), and male Muscovy duck (F) were subjected to RNA sequencing analysis. A total of 9,471 differential genes (DEGs) and 691 protein-protein interaction pairs were obtained. Totally, 12 genes (Dmrt1, Amh, Sox9, Tex14, Trim71, Slc26a8, Spam1, Tdrp, Tsga10, Boc, Cxcl14, and Hsd17b3) were identified to be specifically related to duck testicular development, and 11 genes (Hsd17b1, Cyp19a1, Cyp17a1, Hhipl2, Tdrp, Uts2r, Cdon, Axin2, Nxph1, Brinp2, and Brinp3) were specifically related to duck ovarian development. Seven genes (Stra8, Dmc1, Terb1, Tex14, Tsga10, Spam1, and Plcd4) were screened to be specifically involved in the female sterility of Mule ducks; eight genes (Gtsf1, Nalcn, Tat, Slc26a8, Kmo, Plcd4, Aldh4a1, and Hgd) were specifically involved in male sterility; and five genes (Terb1, Stra8, Tex14 Tsga10 and Spam1) were involved in both female and male sterility. This study provides an insight into the differential development between male and female gonads of ducks and the sterility mechanism of Mule ducks through function, pathway, and protein interaction analyses. Our findings provide theoretical basis for the further research on sex determination and differentiation of birds and the sterility of Mule ducks.

Augmentation of progestin signaling rescues testis organization and spermatogenesis in zebrafish with the depletion of androgen signaling

Disruption of androgen signaling is known to cause testicular malformation and defective spermatogenesis in zebrafish. However, knockout of cyp17a1, a key enzyme responsible for the androgen synthesis, in ar-/- male zebrafish paradoxically causes testicular hypertrophy and enhanced spermatogenesis. Because Cyp17a1 plays key roles in hydroxylation of pregnenolone and progesterone (P4), and converts 17α-hydroxypregnenolone to dehydroepiandrosterone and 17α-hydroxyprogesterone to androstenedione, we hypothesize that the unexpected phenotype in cyp17a1-/-;androgen receptor (ar)-/- zebrafish may be mediated through an augmentation of progestin/nuclear progestin receptor (nPgr) signaling. In support of this hypothesis, we show that knockout of cyp17a1 leads to accumulation of 17α,20β-dihydroxy-4-pregnen-3-one (DHP) and P4. Further, administration of progestin, a synthetic DHP mimetic, is sufficient to rescue testicular development and spermatogenesis in ar-/- zebrafish, whereas knockout of npgr abolishes the rescue effect of cyp17a1-/- in the cyp17a1-/-;ar-/- double mutant. Analyses of the transcriptomes among the mutants with defective testicular organization and spermatogenesis (ar-/-, ar-/-;npgr-/- and cyp17a-/-;ar-/-;npgr-/-), those with normal phenotype (control and cyp17a1-/-), and rescued phenotype (cyp17a1-/-;ar-/-) reveal a common link between a downregulated expression of insl3 and its related downstream genes in cyp17a-/-;ar-/-;npgr-/- zebrafish. Taken together, our data suggest that genetic or pharmacological augmentation of the progestin/nPgr pathway is sufficient to restore testis organization and spermatogenesis in zebrafish with the depletion of androgen signaling.

Cyp17a2 is involved in testicular development and fertility in male Nile tilapia, Oreochromis niloticus

BACKGROUND

Steroid hormones play an essential role in many reproductive processes of vertebrates. Previous studies revealed that teleost-specific Cyp17a2 (cytochrome P450 family 17 subfamily a 2) might be required for the production of cortisol in the head-kidney and 17α,20β-dihydroxy-4-pregnen-3-one (DHP) in ovary during oocyte maturation. However, the role of Cyp17a2 in male reproduction remains to be largely unknown. The aim of this study was to explore the essentiality of cyp17a2 gene in male steroidogenesis, spermatogenesis, and male fertility.

METHODS

A homozygous mutation line of cyp17a2 gene was constructed in tilapia by CRISPR/Cas9 gene editing technology. The expression level of germ cell and meiosis-related genes and steroidogenic enzymes were detected by qRT-PCR, IHC, and Western blotting. EIA and LC-MS/MS assays were used to measure the steroid production levels. And sperm quality was examined by Sperm Quality Analyzer software.

RESULTS

In this study, cyp17a2 gene mutation resulted in the significant decline of serum DHP and cortisol levels. On the contrary, significant increases in intermediate products of cortisol and DHP were found in cyp17a2-/- male fish. The deficiency of cyp17a2 led to the arrest of meiotic initiation in male fish revealing as the reduction of the expression of germ cell-related genes (vasa, piwil, oct4) and meiosis-related genes (spo11 and sycp3) by 90 dah. Afterwards, spermatogenesis was gradually recovered with the development of testis in cyp17a2-/- males, but it showed a lower sperm motility and reduced fertility compared to cyp17a2+/+ XY fish. Deletion of cyp17a2 led to the abnormal upregulation of steroidogenic enzymes for cortisol production in the head-kidney. Moreover, unaltered serum androgens and estrogens, as well as unchanged related steroidogenic enzymes were found in the testis of cyp17a2-/- male fish.

CONCLUSION

This study proved that, for the fist time, Cyp17a2 is indispensable for cortisol and DHP production, and cyp17a2 deficiency associated curtailed meiotic initiation and subfertility suggesting the essentiality of DHP and cortisol in the male fertility of fish.