A Deep Learning Model for Accurate Diagnosis of Infection Using Antibody Repertoires.

The adaptive immune receptor repertoire consists of the entire set of an individual's BCRs and TCRs and is believed to contain a record of prior immune responses and the potential for future immunity. Analyses of TCR repertoires via deep learning (DL) methods have successfully diagnosed cancers and infectious diseases, including coronavirus disease 2019. However, few studies have used DL to analyze BCR repertoires. In this study, we collected IgG H chain Ab repertoires from 276 healthy control subjects and 326 patients with various infections. We then extracted a comprehensive feature set consisting of 10 subsets of repertoire-level features and 160 sequence-level features and tested whether these features can distinguish between infected individuals and healthy control subjects. Finally, we developed an ensemble DL model, namely, DL method for infection diagnosis (https://github.com/chenyuan0510/DeepID), and used this model to differentiate between the infected and healthy individuals. Four subsets of repertoire-level features and four sequence-level features were selected because of their excellent predictive performance. The DL method for infection diagnosis outperformed traditional machine learning methods in distinguishing between healthy and infected samples (area under the curve = 0.9883) and achieved a multiclassification accuracy of 0.9104. We also observed differences between the healthy and infected groups in V genes usage, clonal expansion, the complexity of reads within clone, the physical properties in the α region, and the local flexibility of the CDR3 amino acid sequence. Our results suggest that the Ab repertoire is a promising biomarker for the diagnosis of various infections.

Inhibition of oocyte maturation by nitric oxide synthase 1 (NOS1) in zebrafish.

It is well-documented that nitric oxide (NO) is an important regulator of oocyte maturation in mammals. Conversely, the function of NO during oocyte maturation has received little attention in nonmammalian vertebrates. NO is produced from L-arginine through the action of the enzyme NO synthase (NOS). Herein, we examined the expression, hormonal regulation, and involvement of NOS in meiotic signaling in zebrafish oocyte maturation. Three types of nos genes, nos1, nos2a, and nos2b, have been identified in zebrafish. We found that the expression of nos1 was highest in the ovary among the three nos genes, with maximal expression in full-grown (FG)-stage follicles during folliculogenesis. In addition, the concentration of NO was reduced during oocyte maturation and this corresponded with the decreased expression of nos1 in the follicular cell layers, suggesting that NOS1-derived NO may be one of the inhibitors of oocyte maturation in zebrafish. This is the first description of nos1 involvement in oocyte maturation in vertebrates. Moreover, the NO donor SNAP (S-nitroso-l-acetyl penicillamine) partially attenuates human chorionic gonadotropin (hCG)- and 17,20ß-P-induced GVBD (germinal vesicle breakdown), perhaps by increasing cGMP levels during oocyte maturation. Finally, our results showed that SNAP and the cGMP analog 8-Br-cGMP inhibited hCG-induced mitogen-activated protein kinase (MAPK) activation, further indicating that NO and cGMP block oocyte maturation in zebrafish.

New insights into the role of mTORC1 in male fertility in zebrafish.

Mechanistic target of rapamycin complex 1 (mTORC1) plays crucial roles in male fertility. In mammals, deregulation of mTORC1 led to disordered spermatogonia proliferation and spermatogenesis, which eventually caused infertility in males. However, its roles in male fertility of non-mammalian species remain unclarified. In the present study, it was found that treatment of rapamycin, an mTORC1 inhibitor, resulted in infertility with decreased milt production and sperm motility in zebrafish. However, it is surprising to find that spermatogenesis was normal in these fish. All types of germ cells were found and the proliferation of spermatogonia and spermatocyte were normal. These results suggested that maturation of sperm may be impaired in males treated with rapamycin. Increased apoptosis was found surrounding the lumen containing spermatozoa, implicating a loss of Sertoli cells in testes treated with rapamycin. Moreover, LH/hCG mediated up-regulation of steroidogenic genes was abolished. The expression of npr and ar induced by LH/hCG was also blocked, which further suppressed the signaling of progestin and androgen. Collectively, mTORC1 maintains male fertility via different mechanisms in fish and mammals. mTORC1 is dispensable for spermatogenesis in zebrafish, but possibly supports the maintenance of Sertoli cells and mediates the signaling of hormones, which are crucial for sperm maturation.

Fertility impairment with defective spermatogenesis and steroidogenesis in male zebrafish lacking androgen receptor.

The pivotal role of androgen receptor (AR) in regulating male fertility has attracted much research attention in the past two decades. Previous studies have shown that total AR knockout would lead to incomplete spermatogenesis and lowered serum testosterone levels in mice, resulting in azoospermia and infertility. However, the precise physiological role of ar in controlling fertility of male fish is still poorly understood. In this study, we have established an ar knockout zebrafish line by transcription activator-like effectors nucleases. Homozygous ar mutant male fish with smaller testis size were found to be infertile when tested by natural mating. Intriguingly, a small amount of mature spermatozoa was observed in the ar mutant fish. These mature spermatozoa could fertilize healthy oocytes, albeit with a lower fertilization rate, by in vitro fertilization. Moreover, the expression levels of most steroidogenic genes in the testes were significantly elevated in the ar mutants. In contrast, the levels of estradiol and 11-ketotestosterone (11-KT) were significantly decreased in the ar mutants, indicating that steroidogenesis was defective in the mutants. Furthermore, the protein level of LHß in the serum decreased markedly in the ar mutants when compared with wild-type fish, probably due to the positive feedback from the diminished steroid hormone levels.

Molecular mechanism of feedback regulation of 17ß-estradiol on two kiss genes in the protogynous orange-spotted grouper (Epinephelus coioides).

Kisspeptins are considered critical regulators in the hypothalamic-pituitary-gonadal axis because they can stimulate secretion of Gonadotropin-releasing hormone in mammals, and may also mediate the feedback regulation of sex steroids in the hypothalamus. Two kiss1 paralogues (kiss1 and kiss2) were identified in teleosts, hinting at their increased complexity of signaling for sex-steroid feedback regulation. In the present study, molecular pathways by which 17ß-estradiol (E2 ) exerted feedback regulation on two kiss genes, via three types of estrogen receptors, were investigated in the protogynous orange-spotted grouper (Epinephelus coioides). kiss2 expression in the brain significantly increased in ovariectomized orange-spotted groupers, while E2 replacement in ovariectomized fish reversed these changes to levels in the sham-surgery group; conversely, kiss1 expression did not change. Dual-label in situ hybridization showed that kiss1 and kiss2 neurons express erα, erß1, and erß2, indicating that E2 may directly regulate kiss1 and kiss2. Indeed, E2 treatment of transiently transfected HEK293T cells decreased the activity of both kiss promoters in the presence of erß1 and erß2 rather than erα. Further deletion and site-directed mutagenesis of the kiss promoters indicated that kiss1 is regulated by E2 via an estrogen-responsive element (ERE)-dependent, classical pathway utilized by Erß1, as well as via an Activator protein 1 (Ap1)-dependent, non-classical pathway utilized by Erß2. kiss2 was also differently regulated by E2 through the Creb transcription factor, utilized by Erß1 as well as a half-ERE-dependent, classical pathway utilized by Erß2. Taken together, multiple signaling pathways in orange-spotted grouper are clearly involved in the feedback regulation of E2 on kiss genes via different estrogen receptors.

The multilevel extensive diversity across the cynomolgus macaque captured by ultra-deep adaptive immune receptor repertoire sequencing.

The extent to which AIRRs differ among and within individuals remains elusive. Via ultra-deep repertoire sequencing of 22 and 25 tissues in three cynomolgus macaques, respectively, we identified 84 and 114 novel IGHV and TRBV alleles, confirming 72 (85.71%) and 100 (87.72%) of them. The heterogeneous V gene usage patterns were influenced, in turn, by genetics, isotype (for BCRs only), tissue group, and tissue. A higher proportion of intragroup shared clones in the intestinal tissues than those in other tissues suggests a close intra-intestinal adaptive immunity network. Significantly higher mutation burdens in the public clones and the inter-tissue shared IgM and IgD clones indicate that they might target the shared antigens. This study reveals the extensive heterogeneity of the AIRRs at various levels and has broad fundamental and clinical implications. The data generated here will serve as an invaluable resource for future studies on adaptive immunity in health and diseases.

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,20ß-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.

Dual UMIs and Dual Barcodes With Minimal PCR Amplification Removes Artifacts and Acquires Accurate Antibody Repertoire.

Antibody repertoire sequencing (Rep-seq) has been widely used to reveal repertoire dynamics and to interrogate antibodies of interest at single nucleotide-level resolution. However, polymerase chain reaction (PCR) amplification introduces extensive artifacts including chimeras and nucleotide errors, leading to false discovery of antibodies and incorrect assessment of somatic hypermutations (SHMs) which subsequently mislead downstream investigations. Here, a novel approach named DUMPArts, which improves the accuracy of antibody repertoires by labeling each sample with dual barcodes and each molecule with dual unique molecular identifiers (UMIs) via minimal PCR amplification to remove artifacts, is developed. Tested by ultra-deep Rep-seq data, DUMPArts removed inter-sample chimeras, which cause artifactual shared clones and constitute approximately 15% of reads in the library, as well as intra-sample chimeras with erroneous SHMs and constituting approximately 20% of the reads, and corrected base errors and amplification biases by consensus building. The removal of these artifacts will provide an accurate assessment of antibody repertoires and benefit related studies, especially mAb discovery and antibody-guided vaccine design.

Antibody upstream sequence diversity and its biological implications revealed by repertoire sequencing.

The sequence upstream of the antibody variable region (antibody upstream sequence [AUS]) consists of a 5' untranslated region (5' UTR) and a preceding leader region. The sequence variations in AUS affect antibody engineering and PCR based antibody quantification and may also be implicated in mRNA transcription and translation. However, the diversity of AUSs remains elusive. Using 5' rapid amplification of cDNA ends and high-throughput antibody repertoire sequencing technique, we acquired full-length AUSs for human, rhesus macaque, cynomolgus macaque, mouse, and rat. We designed a bioinformatics pipeline and identified 3307 unique AUSs, corresponding to 3026 and 1457 unique sequences for 5' UTR and leader region, respectively. Comparative analysis indicated that 928 (63.69%) leader sequences are novel relative to those recorded in the international ImMunoGeneTics information system. Evolutionarily, leader sequences are more conserved than 5' UTR and seem to coevolve with their downstream V genes. Besides, single-nucleotide polymorphisms are position dependent for leader regions and may contribute to the functional reversal of the downstream V genes. Finally, the AUGs in AUSs were found to have little impact on gene expression. Taken together, our findings can facilitate primer design for capturing antibodies efficiently and provide a valuable resource for antibody engineering and molecule-level antibody studies.

RAPID: A Rep-Seq Dataset Analysis Platform With an Integrated Antibody Database.

The antibody repertoire is a critical component of the adaptive immune system and is believed to reflect an individual's immune history and current immune status. Delineating the antibody repertoire has advanced our understanding of humoral immunity, facilitated antibody discovery, and showed great potential for improving the diagnosis and treatment of disease. However, no tool to date has effectively integrated big Rep-seq data and prior knowledge of functional antibodies to elucidate the remarkably diverse antibody repertoire. We developed a Rep-seq dataset Analysis Platform with an Integrated antibody Database (RAPID; https://rapid.zzhlab.org/), a free and web-based tool that allows researchers to process and analyse Rep-seq datasets. RAPID consolidates 521 WHO-recognized therapeutic antibodies, 88,059 antigen- or disease-specific antibodies, and 306 million clones extracted from 2,449 human IGH Rep-seq datasets generated from individuals with 29 different health conditions. RAPID also integrates a standardized Rep-seq dataset analysis pipeline to enable users to upload and analyse their datasets. In the process, users can also select set of existing repertoires for comparison. RAPID automatically annotates clones based on integrated therapeutic and known antibodies, and users can easily query antibodies or repertoires based on sequence or optional keywords. With its powerful analysis functions and rich set of antibody and antibody repertoire information, RAPID will benefit researchers in adaptive immune studies.

Interaction of nuclear ERs and GPER in vitellogenesis in zebrafish.

Estrogens exert their biological functions through the estrogen receptors (ERs). In zebrafish, three nuclear estrogen receptors (nERs) named ERα, ERß1 and ERß2 and one membrane-bound G protein-coupled estrogen receptor (GPER) are identified. Vitellogenin (Vtg) is predominantly expressed in liver and strongly response to the stimulation of estrogen. It has been proposed that all three nERs are functionally involved in vitellogenesis and ERα may act as the major mediator in teleost. However, the role of GPER and its interaction with nERs in this process are not yet defined in teleost species. In the present study, we provide genetic evidence for the functional significance of ERα that the expression of Vtg genes (vtg1, vtg2, vtg3) and their response to estradiol stimulation were significantly decreased in esr1 mutant zebrafish. Activation of ERß1 and ERß2 induced Vtg expression through ERα. Moreover, the involvement of GPER in vitellogenesis and its interaction with nERs in zebrafish were firstly proposed in this work. Activation of GPER induced Vtg genes expression while inhibition of GPER significantly attenuated the estrogenic effect on Vtg. Both treatments altered the expression levels of nERs, suggesting GPER acts interactively with nERs. Collectively, the involvement of both nERs and GPER in regulation of vitellogenesis is demonstrated. ERα is the central factor, acting interactively with ERß1, ERß2 and GPER, and GPER regulates vitellogenesis directly and interactively with nERs.

Fertility Enhancement but Premature Ovarian Failure in esr1-Deficient Female Zebrafish.

It is well established that estrogens regulate female reproduction through estrogen receptors (ERs) in the ovary. However, the precise physiological role of estrogen/ER signaling in reproduction processes remains poorly defined in zebrafish. In this study, we successfully generated an ERα (esr1) mutant line in zebrafish via transcription activator-like effectors nucleases (TALENs). It was found in the mutant females that the fertility was enhanced and the ovarian histology was normal at 90 days post-fertilization (dpf). However, the number of fertile females decreased with age. By 180 dpf, esr1 mutant females were infertile with degenerated ovaries, while the age-matched wild-type females were still fertile. Additionally, few large vitellogenic granules can be found in full grown (FG) follicles at 90 dpf and the expression of vtg genes were down-regulated at both 90 and 180 dpf in esr1 mutant zebrafish. Moreover, steroidogenesis pathway and mTOR signaling pathway were over-activated at 90 dpf, but declined prematurely in esr1 mutant zebrafish by 180 dpf. Collectively, the present study provides evidence that esr1 is fundamental for ovarian maintenance in zebrafish.

Ovulation is associated with the LH-dependent induction of pla2g4aa in zebrafish.

The effects of the preovulatory luteinizing hormone (LH) surge on the ovulatory process are mediated by prostaglandins (PGs), the synthesis of which involves prostaglandin synthetase and cytosolic phospholipase A2 (cPLA2). In our previous study, we systematically investigated the function of prostaglandin endoperoxide synthase (ptgs) genes on ovulation in zebrafish. However, the role of cPLA2 in ovulation was not determined in zebrafish. In this study, we investigated the function of cpla2α in PGs production and ovulation in periovulatory follicles. Our data showed that the expression of pla2g4aa increased during zebrafish folliculogenesis and the follicular layer was the primary region with expression of pla2g4aa. In addition, the expression of pla2g4aa was regulated by LH in vitro and in vivo. Furthermore, injection of AACOCF3, a specific inhibitor of cPLA2, significantly reduced ovarian PGs level and blocked hCG-induced ovulation. Collectively, these findings suggest that pla2g4aa is related to the ovulation process in zebrafish.

Estrogen directly stimulates LHb expression at the pituitary level during puberty in female zebrafish.

The LHb expression is up-regulated during puberty in female zebrafish. However, the molecular mechanism underlying how LHb expression is regulated during puberty remains largely unknown. In this study, we found that the mRNA expression levels of lhb, fshb and cyp19a1b were up-regulated along with the puberty onset in zebrafish. Among the three nuclear estrogen receptors (nERs), the esr2b is the only type whose expression is significantly up-regulated during puberty onset in the pituitary. However, in situ hybridization results revealed that lhb mRNA was colocalized with esr1 and esr2a but not esr2b. Exposure to estradiol (E2) significantly stimulates LHb expression in both wild-type and kiss1-/-;kiss2-/-;gnrh3-/- triple knockout pubertal zebrafish. Moreover, exposure of cultured pituitary cells to E2 increased the LHb expression, indicating that the estrogenic effect on LHb expression could be acted at the pituitary level. Finally, we cloned and analyzed the promoter of lhb by luciferase assay. Our results indicated that the E2 responsive regions of lhb promoter for ERα and ERß2 are identical, suggesting that ERα and ERß2 could bind to the same half ERE region of the promoter of lhb, exhibiting a classical ERE-dependent pathway. In summary, we demonstrate that E2 could directly act on the pituitary level to stimulate LHb transcription during puberty in zebrafish.

New Insights Into the Role of Estrogens in Male Fertility Based on Findings in Aromatase-Deficient Zebrafish.

It has been demonstrated that estrogens are indispensable for male fertility in mammals. Aromatase (encoded by CYP19) catalyzes the final step of estradiol biosynthesis. However, less is known about the role of aromatase in male fertility in nonmammalian species. Fish aromatase is encoded by two separate genes: the gonad-specific cyp19a1a and the brain-specific cyp19a1b. In a recent study, we used transcription activatorlike effector nucleases to systematically generate cyp19a1a and cyp19a1b mutant lines and a cyp19a1a;cyp19a1b double-mutant line in zebrafish and demonstrated that cyp19a1a was indispensable for sex differentiation. In this study, we focused on male fertility in these aromatase-deficient zebrafish. Our results showed that all aromatase-deficient male fish had normal fertility even at 1 year after fertilization. Interestingly, we observed more spermatozoa in the cyp19a1a and double-mutant males than in the wild-type and cyp19a1b mutant males. The whole-body androgen levels, follicle-stimulating hormone ß and luteinizing hormone ß protein levels in the pituitary, and transcript levels of genes known to be involved in spermatogenesis and steroidogenesis in the testes were significantly higher in the cyp19a1a mutant and aromatase double-mutant males than in the wild-type and cyp19a1b mutant males. These results might explain why more spermatozoa were observed in these fish. Collectively, our findings indicate that estrogens are not needed to achieve and maintain normal fertility in male zebrafish. This finding challenges the traditional view that estrogens are indispensable for male fertility.

Targeted Disruption of Aromatase Reveals Dual Functions of cyp19a1a During Sex Differentiation in Zebrafish.

Aromatase (encoded by the cyp19a1a and cyp19a1b genes) plays a central role in sex differentiation in fish, but its precise roles during sex differentiation are still largely unknown. Here, we systematically generated cyp19a1a and cyp19a1b mutant lines as well as a cyp19a1a;cyp19a1b double mutant line in zebrafish using transcription activatorlike effector nucleases. Our results showed that cyp19a1a mutants and cyp19a1a;cyp19a1b double mutants, but not cyp19a1b mutants, had impaired sex differentiation, and all cyp19a1a mutants and cyp19a1a;cyp19a1b double mutants were males. During sex differentiation, the ovary-like gonads were not observed and the male sex differentiation program was delayed in the cyp19a1a-null fish, and these phenotypes could be partially rescued by 17ß-estradiol treatment. Gene expression analysis indicated that male and female sex differentiation-related genes were significantly decreased in the cyp19a1a mutant. Collectively, our results revealed dual functions of the cyp19a1a gene during sex differentiation: cyp19a1a is not only indispensable for female sex differentiation but also required for male sex differentiation.

Genetic Evidence for Multifactorial Control of the Reproductive Axis in Zebrafish.

It is generally believed that kisspeptin and gonadotropin-releasing hormone (GnRH) are required for reproduction in vertebrates. In this study, we generated gnrh3-null zebrafish and found that gnrh3 mutation did not impair gonad development and reproductive capacity. Moreover, zebrafish triple knockout mutant lacking gnrh3 and the 2 kiss1s genes undergo normal puberty and gonad maturation. The expression of follicle-stimulating hormone beta (fshß) and luteinizing hormone beta (lhß) was not significantly altered whereas the expression of neuropeptide Y (npy), tachykinin 3 (tac3), and secretogranin-II (sgII) was significantly increased in the triple knockout mutant, suggesting that compensation mechanisms exist to stimulate the reproductive axis in the absence of kiss and gnrh. Our results challenge the prevailing view that GnRH is indispensable for reproduction across species. These data provide genetic evidence that different mechanisms have evolved for the neuroendocrine control of reproduction between mammals and fish: pulsatile release of GnRH to the portal system is the final gateway to stimulate the reproductive axis in mammals, whereas multiple factors act in parallel with GnRH to stimulate the reproductive axis in certain fish species.

LH signaling induced ptgs2a expression is required for ovulation in zebrafish.

It is well known that ovulation is induced by luteinizing hormone (LH) surge. However, the down-stream factors that mediating LH surge induced ovulation are less clear. The cyclooxygenases (also known as PTGS) as key enzymes for prostaglandins synthesis appear to be important for ovulation in mammals, but their functional roles and molecular mechanism in regulation of fish ovulation are largely unexplored. In this study, we have systematically investigated the expression, regulation and functional roles of cox genes during zebrafish ovulation. Three types of cox genes including ptgs1, ptgs2a and ptgs2b have been identified in zebrafish. The ptgs2a was dominantly expressed in the ovary with a maximal level at the maturation stage of the follicles. In addition, the ptgs2a expression is up-regulated by LH signaling in vitro and in vivo. Moreover, co-injection of a selective Ptgs2 inhibitor and non-selective Ptgs inhibitor with hCG could significantly block the stimulatory effect of hCG induced ovulation in vivo. Collectively, our findings indicate that LH signaling induced ptgs2a expression is required for ovulation in zebrafish.

Spexin Suppress Food Intake in Zebrafish: Evidence from Gene Knockout Study.

Spexin1 (SPX1) is a newly discovered neuropeptide in vertebrates. Its biological function remains to be elucidated. In this study, we have generated the zebrafish spx1 -/- mutant lines using transcription activator-like effector nucleases. Phenotypes of the spx1 -/- mutant zebrafish were analyzed in order to understand the effects on reproduction and food intake. The reproductive capability is not impaired in spx1 mutant zebrafish. However, we found that the spx1 -/- mutant fish had a higher food intake than the wild type (WT) fish. Real-time PCR revealed that the expression level of agouti-relate protein 1 (AgRP1), a significant appetite stimulant, was significantly higher in spx1 -/- mutant fish after feeding. Intracranial administration of SPX1 could also reduce the mRNA expression of the AgRP1. These data suggest that SPX1 might decrease the food intake by down regulating the expression level of agrp1. Furthermore, spx1 -/- mutant fish exhibited higher glucose, triacylglycerol and cholesterol in the serum than WT fish. However, the hyperphagia did not lead to a higher growth rate or body fat percentage. Taken together, our study suggests that SPX1 may serve as a satiety signal molecular by suppressing the AgRP1 in the brain.

Molecular identification of StAR and 3ßHSD1 and characterization in response to GnIH stimulation in protogynous hermaphroditic grouper (Epinephelus coioides).

Gonadal steroids are critical factors in reproduction and sex reverse process. StAR (steroidogenic acute regulatory protein), transferring the cholesterol from the outer mitochondrial membrane to the inner membrane, is the rate-limiting factor of steroidogenesis. 3ßHSD (3ß-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase), converting Δ5-steroids into Δ4-steroids, is an important oxidoreductase in steroidogenesis. In the present study, StAR and 3ßHSD1 were cloned and characterized from protogynous orange-spotted grouper. StAR cDNA contains an 861bp open reading frame (ORF), encoding a predicted protein of 286 amino acids, and the ORF of 3ßHSD1 was 1125bp, encoding a predicted protein of 374 amino acids. The transcript of StAR was mainly expressed in gonad, while 3ßHSD1 mRNA was predominantly detected in brain and gonad. In the previous study, we found the expression of GnIH mRNA level in male, as well as in 17 alpha-methyltestosterone (MT)-induced male fish was significantly higher than in female fish, this indicating that GnIH/GnIHR signaling might be involved in the regulation of sex reversal and male maintenance. In order to figure out the function of GnIH in steroidogenesis, the expression of StAR and 3ßHSD1 regulated by GnIH was examined. In vitro study showed that treatment of cultured ovary fragments with gGnIH peptides significantly stimulated the expression of StAR and 3ßHSD1. In addition, the mRNA levels of StAR and 3ßHSD1 were significantly increased after intraperitoneal injection (i.p.) with gGnIH peptides. Moreover, during MT-induced sex change from female to male, the levels of StAR mRNA significantly increased by 5.2, 24.8 and 353.5 folds, and that of 3ßHSD1 mRNA by 3.5, 32.5 and 55.4 folds at the 2nd, 4th and 6th week after MT implantation, respectively. Collectively, our results indicate that GnIH may be involved in the regulation of sex reversal or male maintenance by stimulating the expression of StAR and 3ßHSD1 in protogynous grouper.