Regulation of steroidogenic acute regulatory protein and luteinizing hormone receptor messenger ribonucleic acid in hen granulosa cells

Investigations of the function of AMH in granulosa cells in hens

Anti-mullerian hormone (AMH) plays a crucial role in follicle regulation in mammals by preventing premature primordial follicle activation and restricting follicle development through reduction of FSH sensitivity and inhibition of FSH-induced increase of steroidogenic enzymes. AMH is produced by granulosa cells from growing follicles and expression declines at the time of selection in both mammalian and avian species. The role of AMH in chicken granulosa cells remains unclear, as research is complicated because mammalian AMH is not bioactive in chickens and there is a lack of commercially available chicken AMH. In the current experiments, we used RNA interference to study the role of AMH on markers of follicle development in the presence and absence of FSH. Cultured chicken granulosa cells from 3-5 mm follicles and 6-8 mm follicles, the growing pool from which follicle selection is thought to occur, were used. Transfection with an AMH-specific siRNA significantly reduced AMH mRNA expression in granulosa cells from 3-5 mm and 6-8 mm follicles. Genes of interest were only measured in granulosa cells of 3-5 mm follicles due to low expression of AMH mRNA at the 6-8 mm follicle stage. Knockdown of AMH mRNA did not affect markers of follicle development (follicle stimulating hormone receptor, FSHR; steroidogenic acute regulatory protein, STAR; cytochrome P450 family 11 subfamily A member 1, CYP11A1; bone morphogenetic protein receptor type 2, BMPR2) or FSH responsiveness in granulosa cells from 3-5 mm follicles, indicating that AMH does not regulate follicle development directly by affecting markers of steroidogenesis, FSHR or BMPR2 at this follicle stage in chickens.

Effect of quercetin on granulosa cells development from hierarchical follicles in chicken

1. The bioflavonoid quercetin is a biologically active component, but its functional regulation of granulosa cells (GCs) during chicken follicular development is little studied. To investigate the effect of quercetin on follicular development in laying hens, an in vitro study was conducted on granulosa cells from hierarchical follicles treated with quercetin.2. The effect of quercetin on cell activity, proliferation and apoptosis of granulosa cells was detected by CCK-8, EdU and apoptosis assays. The effect on progesterone secretion from granulosa cells was investigated by enzyme-linked immunosorbent assay (ELISA). Expression of proliferating cell nuclear antigen (PCNA) mRNA and oestrogen receptors (ERs), as well as the expression of steroid acute regulatory protein (StAR), cytochrome P450 cholesterol side chain cleavage enzyme (P450scc) and 3β-hydroxysteroid dehydrogenase (3β-HSD) mRNA during progesterone synthesis, were measured by real-time quantitative polymerase chain reaction (RT-qPCR). PCNA, StAR and CYP11A1 protein expression levels were detected using Western blotting (WB).3. The results showed that treatment with quercetin in granulosa cells significantly enhanced cell vitality and proliferation, reduced apoptosis and promoted the expression of gene and protein levels of PCNA. The levels of progesterone secretion increased significantly following quercetin treatment, as did the expression levels of StAR and CYP11A1 using the Western Blot (WB) method.4. The mRNA expression levels of ERα were significantly upregulated in the 100 ng/ml and 1000 ng/ml quercetin-treated groups, while there was no significant difference in expression levels of ERβ mRNA.

Effect of IGF1 and FSH on the function of granulosa cells from prehierarchal follicles in chickens†

Insulin-like growth factor 1 (IGF1) is an essential regulator of mammalian follicle development and synergizes with follicle-stimulating hormone (FSH) to amplify its effects. In avian preovulatory follicles, IGF1 increases the expression of genes involved in steroidogenesis and progesterone and inhibin A production. The role of IGF1 in prehierarchal follicles has not been well studied in chickens. The aim of this study was to investigate the role of IGF1 in granulosa cells from prehierarchal follicles and to determine whether IGF1 and FSH synergize to promote follicle development. Granulosa cells of 3-5 and 6-8 mm prehierarchal follicles were cultured with IGF1 (0, 10, 100 ng/mL) in the presence or absence of FSH (0, 10 ng/mL). Cell proliferation, expression of genes important in follicle development (FSHR, IGF1R, AMH, STAR, CYP11A1, INHA, and INHBA), and progesterone production were evaluated following treatment. IGF1 treatment alone significantly increased STAR, CYP11A1, and INHBA mRNA expression and cell proliferation in granulosa cells of 6-8 mm follicles. IGF1 and FSH synergized to increase STAR mRNA expression in 6-8 mm follicles. IGF1 and FSH co-treatment were necessary to increase INHA mRNA expression in 6-8 mm follicles. Although IGF1 significantly increased the expression of genes involved in steroidogenesis, progesterone production in granulosa cells of 6-8 mm follicles was not affected. IGF1 did not affect AMH mRNA expression, although FSH significantly decreased AMH expression in granulosa cells of 3-5 mm follicles. These results suggest that IGF1 may act with FSH to promote follicle selection at the prehierarchal follicle stage.

Effects of quercetin on granulosa cells from prehierarchical follicles by modulating MAPK signaling pathway in chicken

Quercetin (Que), widely found in a huge variety of plants, plays important roles in ovarian function. However, to data, there have been no reports about Que regulating granulosa cells (GCs) in prehierarchical follicles in chicken. Herein, GCs from follicles diameter from 4 to 8 mm in chicken were treated by Que in vitro culture to investigate how Que exerts its effect on follicular development. GCs treated by Que in concentrations of 10, 100, and 1,000 ng/mL were tested for cell proliferation and progesterone secretion. Eight cDNA libraries were constructed from GCs (4 samples per group) to explore transcriptome expression changes. The role of the MAPK/ERK signaling pathway was validated in this process. Treatment with 100 and 1,000 ng/mL levels of Que significantly promoted cell proliferation and progesterone secretion (P < 0.05). RNA-seq analysis data showed that 402 and 263 differentially expressed genes (DEGs) were up- and down-regulated, respectively. Functional enrichment analysis that the pathways related to follicular development included biosynthesis of amino acids, MAPK signaling pathway, and calcium signaling pathway. Notably, the function exerted in GCs of the different levels of Que was associated with the suppression of the MAPK pathway. In conclusion, our results proved that low levels of Que could promote MAPK signaling pathway, but high levels of Que inhibit MAPK signaling pathway in GCs from the prehierarchical follicles, promote cell proliferation and progesterone secretion, and benefit follicle selection.

Efficacy of Immunization against a Novel Synthetic 13-Amino Acid Betaglycan-Binding Peptide Sequence of Inhibin α Subunit on Promoting Fertility in Female Rats

Inhibins suppress the FSH production in pituitary gonadotrope cells by robustly antagonizing activin signaling by competitively binding to activin type II receptors (ACTR II). The binding of inhibin A to ACTR II requires the presence of its co-receptor, namely, betaglycan. In humans, the critical binding site for betaglycan to inhibin A was identified on the inhibin α subunit. Through conservation analysis, we found that a core 13-amino-acid peptide sequence <VRTTSDGGYSFKY> within the betaglycan-binding epitope on human inhibin α subunit is highly conserved across species. Based on the tandem sequence of such a conserved 13-amino-acid betaglycan-binding epitope (INHα13AA-T), we developed a novel inhibin vaccine and tested its efficacy in promoting female fertility using the female rat as a model. Compared with placebo-immunized controls, INHα13AA-T immunization induced a marked (p < 0.05) antibody generation, enhanced (p < 0.05) ovarian follicle development, and increased ovulation rate and litter sizes. Mechanistically, INHα13AA-T immunization promoted (p < 0.05) pituitary Fshb transcription and increased (p < 0.05) serum FSH and 17β-estradiol concentrations. In summary, active immunization against INHα13AA-T potently increased FSH levels, ovarian follicle development, ovulation rate and litter sizes, thus causing super-fertility in females. Therefore, immunization against INHα13AA is a promising alternative to the conventional approach of multiple ovulation and super-fertility in mammals.

Exposure to Fluoride From in Utero to Puberty Alters Gonadal Structure and Steroid Hormone Expression in Offspring Rats

The reproductive toxicity of fluoride has been proven by a large number of studies. While the underlying mechanism of reproductive toxicity during pregnancy is still unclear. Hence, in this study, we investigated the effects of fluoride exposure on ovarian and testicular steroid hormone synthesis in young and adult rat offspring. We established a model of fluoride-exposed rat pups from in utero to puberty to explore the mechanisms of fluoride impacts on reproductive toxicity in the offspring. The results showed that NaF exposure did not affect the 3 weeks of age offspring. Whereas the body weight in both sexes significantly decreased, and the ovarian and testicular tissue structures were damaged at 11 weeks of age. In females, the total number of secondary follicles and mature follicles were significantly reduced after NaF exposure. Moreover, estradiol (E2) and follicle-stimulating hormone (FSH) levels in the females were significantly reduced in the 100 mg/L NaF exposure group. In males, the sperm viability and testosterone (T) were significantly decreased in the NaF exposure groups. Additionally, during steroidogenesis in ovaries and testes, fluoride remarkably decreased the expression levels of genes and proteins, including acute regulatory protein (StAR), 3β-hydroxysteroid dehydrogenase (3β-HSD), cytochrome P450 17a-hydroxylase (CYP17A1), and cholesterol side-chain cleavage enzyme (CYP11A1), while the mRNA levels of 17β-hydroxysteroid dehydrogenase (17β-HSD) decreased only in the testes. These results indicated that fluoride exposure disrupted the steroid hormone balance by changing several important steroidogenic-related genes associated with the development of the gonads, and damage the normal structure of the gonads in rat offspring.

miR-27b-3p inhibits estrogen secretion of goose granulosa cells by targeting CYP1B1 through the AMPK signaling pathway

Although miR-27b-3p has been evidenced to regulate the proliferation, apoptosis, and differentiation of a variety of mammalian cell types, its actions and mechanisms on ovarian cell steroidogenesis remains largely unknown in both mammalian and avian species. In this study, we aimed to determine the expression profiles of miR-27b-3p in granulosa cell layers during goose ovarian follicle development and to reveal its actions on estrogen (E₂) secretion of goose granulosa cells as well as the underlying regulatory mechanisms. It was observed that miR-27b-3p was ubiquitously expressed throughout follicle development but exhibited much higher levels in hierarchical- than in prehierarchical follicles. In cultured granulosa cells from the fourth through second largest preovulatory (F4-F2) follicles of goose, up- and downregulation of miR-27b-3p by using its mimic and inhibitor significantly decreased and increased E₂ secretion, respectively. Meanwhile, the mRNA levels of STAR and CYP19A1 were significantly reduced while those of CYP11A1 and 3βHSD were elevated in the mimic-transfected granulosa cells. By comparison, downregulation of miR-27b-3p enhanced the mRNA levels of STAR but had no significant effects on those of CYP19A1, CYP11A1, and 3βHSD. Results from bioinformatic prediction and luciferase reporter assay demonstrated that CYP1B1 was a downstream target of miR-27b-3p. Although the siRNA-mediated downregulation of CYP1B1 did not significantly change E₂ secretion by goose granulosa cells, it reduced the mRNA levels of STAR and CYP19A1 as well as those of LKB1 and AMPKα, which are involved in the AMPK signaling pathway. Taken together, these data suggest that miR-27b-3p plays an inhibitory role in E₂ secretion by goose F4-F2 granulosa cells, at least in part, by targeting CYP1B1 through the AMPK signaling pathway.

Transcriptomic analysis of ovarian follicles uncovers the crucial genes relevant to follicle selection and preovulatory hierarchy in hens

Follicle selection and preovulatory hierarchy of hen ovaries were important stages of follicle development and crucially determining egg-laying performance. The selected follicles with a higher expression level of follicle-stimulating hormone receptor (FSHR) mRNA that facilitates response to FSH, and rapidly develops into preovulatory follicles with distinctive characteristics of granulosa cells (GCs) proliferation and differentiation. Identification of the key genes involved in these developmental events is helpful for elucidation of the molecular mechanism underlying egg-laying traits in chicken and other domestic fowl. Herein, the comparative transcriptomic analysis of ovarian prehierarchical follicles before selection (BSF), follicles at selection stage (ASF), and hierarchical follicles (HF) were implemented in the Jilin Black chicken (JB) and Lohmann Brown layer (LB) with the divergences in their egg-laying performance by RNA-sequencing. The results showed that nine deferentially expressed genes (DEGs), including STMN4, FABP3, ROBO2, RSPO4, and DMRT1 were revealed between follicles BSF and ASF; and seventeen DEGs, such as SLC6A15, SLITRK3, PRKG2 and TMC3 were mined between ASF and HF. These two group DEGs being co-expressed between BSF and ASF, and between ASF and HF were compared and substantiated in the JB and LB layers, respectively. Furthermore, 10 signaling pathways, such as cAMP signaling, PPAR signaling pathway, AMPK(Adenosine 5'-monophosphate (AMP)-activated protein kinase) pathway, and estrogen signaling pathway were also identified. Moreover, the roles of two representative candidates ROBO2 and PRKG2 genes presented as downregulated mRNA expression pattern in the transcriptomic profiles were further verified in vitro. The results demonstrated that downregulation of ROBO2 or PRKG2 significantly increased the expression levels of FSHR mRNA and protein with the boosted expression of CCND1, STAR, and BCL-2, whereas remarkably inhibited the expression of Caspase-3, consequently, brought about the decrease of GC apoptosis in the ovarian follicles, but increase of GC proliferation and differentiation serving as the hallmarks for follicle selection. It indicated that ROBO2 and PRKG2 may play indispensable roles in follicle selection and preovulatory hierarchy of hen ovaries separately. Our findings provided a comparative transcriptomic evidence for clarifying the molecular mechanism of the follicle development underlying egg-laying traits in chicken.

cAMP signaling in ovarian physiology in teleosts: A review

Ovarian function in teleosts, like in other vertebrates, is regulated by two distinct gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH). Gonadotropin effects are mediated by membrane-bound G protein-coupled receptors localized on the surface of follicle cells. Gonadotropin receptor activation results in increased intracellular cAMP, the most important second cellular signaling molecule. FSH stimulation induces the production of 17β-estradiol in the cells of growing follicles to promote vitellogenesis in oocytes. In contrast, in response to LH, fully grown post-vitellogenic follicles gain the ability to synthesize maturation-inducing steroids, which induce meiotic resumption and ovulation. All these events were induced downstream of cAMP. In this review, we summarize studies addressing the role of the cAMP pathway in gonadotropin-induced processes in teleost ovarian follicles. Furthermore, we discuss future problems concerning cAMP signaling in relation to teleost ovarian function and the differences and similarities in the gonadotropin-induced cAMP signaling pathways between mammals and teleosts.

Compared to Fishmeal, Dietary Soybean Meal Improves the Reproductive Performance of Female Yellow Catfish (Pelteobagrus fulvidraco) Broodstock

To investigate the effects of different dietary protein sources on the reproductive performance of female broodstock, yellow catfish (Pelteobagrus fulvidraco) were fed with three experimental diets using fishmeal (FM), soybean meal (SBM), and rapeseed meal (RSM) as main protein sources, respectively. Females (initial weight: 64.56 ± 0.45 g) were distributed into 9 net cages for feeding trial. Results indicated that 30% dietary SBM improved the reproductive performance for higher gonadosomatic index (GSI), relative fecundity, total egg production, egg diameter, and hatching rate. In addition, SBM and RSM diets resulted in higher estradiol (E2), vitellogenin (VTG), luteinizing hormones (LH), and lower follicle-stimulating hormone (FSH) and testosterone (T) in plasma (P < 0.05) of female broodstock. Dietary SBM and RSM also resulted in lower mesenteric fat index (MFI), plasma total cholesterol (TC), plasma total bilirubin (T-Bil) contents, and gonadal cortisol concentrations, while dietary SBM downregulated the transcription levels of steroidogenesis-related proteins by negative feedback (P < 0.05). The results demonstrated that dietary SBM and RSM could promote sex steroid hormone and VTG biosynthesis and showed hypocholesterolemic effects. Besides, 30% dietary SBM inclusion could improve the reproductive performance of female yellow catfish broodstock.

Corticosterone stage-dependently inhibits progesterone production presumably via impeding the cAMP-StAR cascade in granulosa cells of chicken preovulatory follicles

Stress can suppress reproduction capacity in either wild or domestic animals, but the exact mechanism behind it, especially in terms of steroidogenesis, remains under-investigated so far. Considering the important roles of progesterone in avian breeding, we investigated the modulation of corticosterone on progesterone production in cultured granulosa cells of chicken follicles at different developmental stages. Using enzyme immunoassays, our study showed that corticosterone could only inhibit progesterone synthesis in granulosa cells from F5-6, F4, and F3 follicles, but not F2 and F1 follicles. Coincidentally, both quantitative real-time PCR and western blotting revealed that corticosterone could downregulate steroidogenic acute regulatory protein (StAR) expression, suggesting the importance of StAR in corticosterone-related actions. Using the dual-luciferase reporter system, we found that corticosterone can potentially enhance, rather than inhibit, the activity of StAR promoter. Of note, combining high-throughput transcriptomic analysis and quantitative real-time PCR, phosphodiesterase 10A (PDE10A), protein kinase cAMP-dependent type II regulatory subunit alpha (PRKAR2A) and cAMP responsive element modulator (CREM) were identified to exhibit the differential expression patterns consistent with cAMP blocking in granulosa cells from F5-6, F4, and F3, but not F2 and F1 follicles. Afterward, the expression profiles of these genes in granulosa cells of distinct developmental-stage follicles were examined by quantitative real-time PCR, in which all of them expressed correspondingly with progesterone levels of granulosa cells during development. Collectively, these findings indicate that corticosterone can stage-dependently inhibit progesterone production in granulosa cells of chicken preovulatory follicles, through impeding cAMP-induced StAR activity presumptively.

miR-10a-5p inhibits chicken granulosa cells proliferation and Progesterone(P4) synthesis by targeting MAPRE1 to suppress CDK2

The proliferation and steroid hormone synthesis of granulosa cells (GCs) are essential for ovarian follicle growth and ovulation, which are necessary to support the normal function of the follicle. Numerous studies suggest that miRNAs play key roles in this process. In this study, we report a novel role for miR-10a-5p that inhibits ovarian GCs proliferation and progesterone (P4) synthesis in chicken. Specifically, we found that miR-10a-5p significantly decreased the P4 secretion by quantitative real-time PCR (qRT-PCR), enzyme-linked immunosorbent assay (ELISA), and western blot. Moreover, we observed that miR-10a-5p can inhibit the proliferation of chicken GCs through the investigation of cell proliferation gene expression, cell counting kit 8 (CCK-8), cell cycle progression, and 5-ethynyl-2'-deoxyuridine (EdU) assay. Then we screened a target gene MAPRE1 of miR-10a-5p, which can promote P4 synthesis and proliferation of GCs. To explore how miR-10a-5p affects cell cycle by MAPRE1, we investigated the interaction between MAPRE1 and cyclin-dependent kinase 2 (CDK2) by Co-Immunoprecipitation (Co-IP), and then we found that MAPRE1 can form a complex with CDK2. In addition, miR-10a-5p was found to inhibit CDK2 expression by repressing the expression of MAPRE1. Overall, our results indicate that miR-10a-5p regulates the proliferation and P4 synthesis of chicken GCs by targeting MAPRE1 to suppress CDK2.

The Diverse Roles of 17β-Estradiol in Non-Gonadal Tissues and Its Consequential Impact on Reproduction in Laying and Broiler Breeder Hens

Estradiol-17β (E2) has long been studied as the primary estrogen involved in sexual maturation of hens. Due to the oviparous nature of avian species, ovarian production of E2 has been indicated as the key steroid responsible for activating the formation of the eggshell and internal egg components in hens. This involves the integration and coordination between ovarian follicular development, liver metabolism and bone physiology to produce the follicle, yolk and albumen, and shell, respectively. However, the ability of E2 to be synthesized by non-gonadal tissues such as the skin, heart, muscle, liver, brain, adipose tissue, pancreas, and adrenal glands demonstrates the capability of this hormone to influence a variety of physiological processes. Thus, in this review, we intend to re-establish the role of E2 within these tissues and identify direct and indirect integration between the control of reproduction, metabolism, and bone physiology. Specifically, the sources of E2 and its activity in these tissues via the estrogen receptors (ERα, ERβ, GPR30) is described. This is followed by an update on the role of E2 during sexual differentiation of the embryo and maturation of the hen. We then also consider the implications of the recent discovery of additional E2 elevations during an extended laying cycle. Next, the specific roles of E2 in yolk formation and skeletal development are outlined. Finally, the consequences of altered E2 production in mature hens and the associated disorders are discussed. While these areas of study have been previously independently considered, this comprehensive review intends to highlight the critical roles played by E2 to alter and coordinate physiological processes in preparation for the laying cycle.

Effects of active immunization against a 13-amino acid receptor-binding epitope of FSHβ on fertility regulation in female mice

Follicle-stimulating hormone (FSH) is crucial for ovarian folliculogenesis and thus essential for female fertility. Here, we developed a novel FSH vaccine based on the tandem of a 13-amino acid receptor-binding epitope of FSHβ (FSHβ13AA-T) and used a mouse model to test its efficacy in female fertility regulation. Compared to placebo-immunized controls, FSHβ13AA-T vaccination: induced a marked (P < 0.05) antibody generation; reduced (P < 0.05) serum concentrations of FSH, inhibin B and 17β-estradiol; disrupted (P < 0.05) normal estrous cyclicity; delayed (P = 0.08) establishment of pregnancy; blocked (P < 0.05) folliculogenesis; and reduced (P < 0.05) litter size. Mechanistically, FSH vaccination reduced (P < 0.05) ovarian estrogen production by decreasing Lhcgr, Cyp19a1 and HSD3β1 expression, and suppressed ovarian follicular development by decreasing ovarian Fshr, Inhα, Foxo3a, Bmp15 and Cdh1 expression. Overall, vaccination of female mice with FSHβ13AA-T substantially disrupted FSH-dependent ovarian steroidogenesis and folliculogenesis, and caused subfertility. Therefore, vaccines based on FSHβ13AA-T have potential as anti-fertility/contraceptive agents in females.

Characterization of Chicken α2A-Adrenoceptor: Molecular Cloning, Functional Analysis, and Its Involvement in Ovarian Follicular Development

Adrenoceptors are suggested to mediate the functions of norepinephrine (NE) and epinephrine (EPI) in the central nervous system (CNS) and peripheral tissues in vertebrates. Compared to mammals, the functionality and expression of adrenoceptors have not been well characterized in birds. Here, we reported the structure, expression, and functionality of chicken functional α_2A-adrenoceptor, named ADRA2A. The cloned chicken ADRA2A cDNA is 1335 bp in length, encoding the receptor with 444 amino acids (a.a.), which shows high amino acid sequence identity (63.4%) with its corresponding ortholog in humans. Using cell-based luciferase reporter assays and Western blot, we demonstrated that the ADRA2A could be activated by both NE and EPI through multiple signaling pathways, including MAPK/ERK signaling cascade. In addition, the mRNA expression of ADRA2A is found to be expressed abundantly in adult chicken tissues including thyroid, lung, ovary and adipose from the reported RNA-Seq data sets. Moreover, the mRNA expression of ADRA2A is also found to be highly expressed in the granulosa cells of 6–8 mm and F5 chicken ovarian follicles, which thus supports that ADRA2A signaling may play a role in ovarian follicular growth and differentiation. Taken together, our data provide the first proof that the α_2A-adrenoceptor is functional in birds involving avian ovarian follicular development.

Exploring the expression and preliminary function of chicken regulator of G protein signalling 3 (RGS3) gene in follicular development

1. The following study explored the expression and preliminary function of RGS3. The spatial and temporal expression patterns of the RGS3 gene were analysed in the ovarian stroma of Shendan No. 6 Green shell hens and Hy-line Brown hens at four time points (6, 28, 40 and 52 weeks old), as well as in various organs and follicles of Hy-line Brown hens.2. Based on the genomic and protein sequences of RGS3 in NCBI database, phylogenetic trees were constructed using MEGA-X. The protein interaction network was analysed using STRING. According to the results of protein-protein interaction network and pathways, the mRNA expression levels of RGS3 and three interaction proteins were explored by qRT-PCR in vitro.3. Spatio-temporal expression data revealed that RGS3 mRNA was expressed in all the organs tested, being highest in the hypothalamus. In different follicles, RGS3 mRNA was highly expressed in post-ovulatory follicles, followed by ovarian stroma and large white follicles. The expression levels of RGS3 mRNA in the ovarian stroma were significantly higher in Shendan No. 6 Green shell hens than that in the Hy-line Brown hens at all egg-laying stages.4. The phylogenetic tree results showed that ducks, geese and chickens had higher homology based on the genomic and protein sequence of RGS3. Moreover, chicken RGS3 interacted with GSK3B, RAF1 and BRAF based on STRING prediction. In vitro follicle stimulating hormone (FSH) treatment showed that mRNA expression levels of RGS3 and those of its predicted interacting proteins BRAF and GSK3B decreased with increasing FSH concentration. The results suggested that RGS3 responds to FSH and may play an important role in the regulation follicular development in chicken.

Morphological Characteristics and Transcriptome Landscapes of Chicken Follicles during Selective Development

Ovarian follicle selection largely depends on the transition of granulosa cells from an undifferentiated to a fully differentiated state, which is accompanied by morphological and functional changes in follicles. The processes and transcriptional regulation of follicles during follicle selection are unclear; we thus used follicles from the prehierarchal to the hierarchal stage to investigate histology, reproductive endocrinology, and transcription. The morphology of follicles changed markedly during follicle selection. The numbers of large white, small yellow, and large yellow follicles (LWF, SYF, and LYF, respectively) were 11.83 ± 2.79, 6.83 ± 2.23, and 1.00, respectively, per ovary. LYF showed thicker granulosa cell layers than those of other prehierarchal follicles. Progesterone concentrations were significantly higher in LYF than that in LWF and SYF. In total, 16,823 genes were positively expressed in LWF, SYF, and LYF. Among follicle types, 1,290 differentially expressed genes were enriched regarding cell differentiation, blood vessel morphogenesis, and response to steroid hormones. Candidate genes associated with follicle selection participated in the Wnt signaling pathway, steroid hormone biosynthesis, and the TGF-β signaling pathway. We produced insights into crucial morphological characteristics of transcriptional regulation in follicle development. Our results provide an important basis for revealing the mechanism of follicle selection and potential impact on the poultry industry.

The opposite effects of VGLL1 and VGLL4 genes on granulosa cell proliferation and apoptosis of hen ovarian prehierarchical follicles

Transcription cofactors Vestigial like family (VGLL) members consisting of four homologs (VGLL1-4) are associated with cell growth and metastasis in mammals, among which VGLL1 gene has been documented to possess tumorigenic functions in various types of tumor, and VGLL4 acts as a new tumor suppressor; likewise several studies indicated that they potentially play a role in the regulation of ovary growth and function. However, the biological effects of chicken VGLL1 and VGLL4 on the proliferation, apoptosis, and steroidogenesis of the granulosa cells (GCs) during ovarian follicle development remain unknown now. This study found that VGLL1 and VGLL4 genes present divergent expression patterns of the transcripts in the GCs of various sized prehierarchical follicles (PFs) before follicle selection. Specific small interfering RNA (siRNA) was employed to elucidate the exact roles of VGLL1 and VGLL4 in regulating the PF development of the hen ovary. The results demonstrated that the mRNA expression levels of the steroidogenic-related enzyme steroidogenic acute regulatory protein (STAR) gene and the cell proliferation-related factors B-cell lymphoma-2 (BCL2), and cyclin D1 (CCND1) genes were significantly down-regulated in the cells with VGLL1 silence but remarkably up-regulated in the cells lacking VGLL4. Whereas the expression level of the cell apoptosis biomarker caspase-3 (CASP3) transcript was noticeably enhanced in the GCs without VGLL1 but significantly decreased in the GCs deprived of VGLL4. Further results showed that the siRNA-mediated silence of VGLL1 caused a significant increase in apoptosis with a reduction in the proliferation of GCs. Nevertheless, knockdown of VGLL4 resulted in a remarkable decrement in apoptosis but a memorable augment in proliferation of the GCs. Taken together, this study proved that VGLL1 promotes cell proliferation and steroidogenesis but inhibits apoptosis. In contrast, VGLL4 stimulates GC apoptosis while suppressing the GC proliferation and steroidogenesis in the hen ovarian follicles. We conluded that VGLL1 and VGLL4 affect oppositely the ovarian prehierarchical follicle development by the different regulatory manner in the GC proliferation and apoptosis of chicken ovary.

Transcriptome comparative analysis of ovarian follicles reveals the key genes and signaling pathways implicated in hen egg production

Background

Ovarian follicle development plays an important role in determination of poultry egg production. The follicles at the various developmental stages possess their own distinct molecular genetic characteristics and have different biological roles in chicken ovary development and function. In the each stage, several genes of follicle-specific expression and biological pathways are involved in the vary-sized follicular development and physiological events. Identification of the pivotal genes and signaling pathways that control the follicular development is helpful for understanding their exact regulatory functions and molecular mechanisms underlying egg-laying traits of laying hens.

Results

The comparative mRNA transcriptomic analysis of ovarian follicles at three key developmental stages including slow growing white follicles (GWF), small yellow follicles (SYF) of recruitment into the hierarchy, and differentiated large yellow follicles (LYF), was accomplished in the layers with lower and higher egg production. Totally, 137, 447, and 229 of up-regulated differentially expressed genes (DEGs), and 99, 97, and 157 of down-regulated DEGs in the GWF, SYF and LYF follicles, including VIPR1, VIPR2, ADRB2, and HSD17B1 were identified, respectively. Moreover, NDUFAB1 and GABRA1 genes, two most promising candidates potentially associated with egg-laying performance were screened out from the 13 co-expressed DEGs in the GWF, SYF and LYF samples. We further investigated the biological effects of NDUFAB1 and GABRA1 on ovarian follicular development and found that NDUFAB1 promotes follicle development by stimulating granulosa cell (GC) proliferation and decreasing cell apoptosis, increases the expression of CCND1 and BCL-2 but attenuates the expression of caspase-3, and facilitates steroidogenesis by enhancing the expression of STAR and CYP11A1. In contrast, GABRA1 inhibits GC proliferation and stimulates cell apoptosis, decreases the expression of CCND1, BCL-2, STAR, and CYP11A1 but elevates the expression of caspase-3. Furthermore, the three crucial signaling pathways such as PPAR signaling pathway, cAMP signaling pathway and neuroactive ligand-receptor interaction were significantly enriched, which may play essential roles in ovarian follicle growth, differentiation, follicle selection, and maturation.

Conclusions

The current study provided new molecular data for insight into the regulatory mechanism underlying ovarian follicle development associated with egg production in chicken.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08213-w.

Tri-ortho-cresyl phosphate exposure leads to low egg production and poor eggshell quality via disrupting follicular development and shell gland function in laying hens

Tri-ortho-cresyl phosphate (TOCP) has been used commercially as a plasticizer and a flame retardant, which has been reported to cause multiple toxicities in humans and other animals. However, the effect of TOCP on female reproductive system is still unclear. The aim of this investigation was to evaluate the reproductive toxicity of TOCP in female avian and investigate its molecular mechanism. In the current study, 50 adult hens were given a single oral dose of TOCP (750 mg/kg). Egg laid by the hens were harvested and counted. Egg quality is assessed by determining the shell strength and thickness. Samples of ovary, shell gland, and serum were collected on day 0, 2, 7, and 21 after the administration. The morphological and pathological changes in tissues were examined. Cell death, follicular development, and steroidogenesis were determined to assess the toxicity of TOCP on laying hens. The results showed that egg production, egg weight, and eggshell strength significantly decreased after TOCP exposure. The calcium levels in serum and eggshell decreased and the expression levels of the eggshell formation-related genes calbindin-D28k (CaBP-D28k) and carbonic anhydrase 2 (CA2) were downregulated. The inhibitory effects of TOCP on follicular development and steroidogenesis were observed with changes in the levels of the related proteins such as forkhead box O1 (FoxO1) and mothers against decapentaplegic homolog 2/3 (Smad2/3). Cell death was identified, which might lead to follicular development disorder. Taken together, TOCP reduced the quantity and quality of the eggs laid by the hens through disrupting follicular development, steroidogenesis, and shell gland function.

Ad Libitum Feeding in Broiler Breeder Hens Alters the Transcriptome of Granulosa Cells of Pre-Hierarchal Follicles

Intense selective breeding of chickens has resulted in suboptimal egg production in broiler breeder hens. This reproductive phenotype is exacerbated by ad libitum feeding, which leads to excessive and disorganized follicular growth. One strategy used to improve broiler breeder hens' reproductive efficiency is restricted feeding. In this study, we sought to identify transcriptional changes, which translate the level of dietary intake into increased follicle selection. Broiler breeder hens (n = 16 per group) were raised according to commercial guidelines until 28 weeks of age and then randomly assigned to an ad libitum diet (FF) or continued on a restricted diet (RF) for 6 weeks. Following dietary treatment, FF hens (n = 2) with excessive follicle selection and RF hens (n = 3) with normal follicle selection were selected for RNA-sequencing. Transcriptomes of granulosa cells from 6-8-mm follicles were sequenced to identify transcriptional differences in the follicle population from which selection was made for the preovulatory stage. Differential expression analysis identified several genes known to play a role in follicle development (CYP11A1, STAR, INHA, and INHBB) that are upregulated in FF hens. These changes in gene expression suggest earlier granulosa cell differentiation and steroidogenic competency in the granulosa layer from FF hens.

The functions of Patchouli and Elsholtzia in the repair of hen follicular granular cells after heat stress

The objective of this experimental study was to examine the effects of the Chinese herbal medicines Patchouli and Elsholtzia on the follicular granulosa cells of hens undergoing heat stress conditions. In the current investigation, hen follicular granulosa cells were isolated from the prehierarchical follicles of layer hens and then cultured in-vitro. The cells were randomly divided into the 6 groups. Following the completion of this study's experiments using different heat stress and medicinal treatments, the cell activities of each group were measured using an MTT method. The levels of the heat shock protein 70 (HSP70) were detected using ELISA. The expressions of the steroidogenic acute regulatory protein (StAR) mRNA; cytochrome P450 family 11, subfamily A, member 1 (CYP11A1) mRNA; proliferating cell nuclear antigen (PCNA) mRNA; and the follicle stimulating hormone receptor (FSHR) were detected using the real-time quantitative polymerase chain reactions. The concentration levels of estrogen and progesterone in the cell supernatant of each group were measured using ELISA. The results showed that cell activity had significantly decreased following the heat stress treatments at 43℃, 44℃, and 45℃ (P < 0.01), respectively. Meanwhile, cell activities observed in Patchouli and Elsholtzia were found to be much better than those of heat stress group (P < 0.05). In addition, the expression levels of HSP70 in the follicular granulosa cells of Patchouli and Elsholtzia groups were lower than those of heat stress group. Patchouli and Elsholtzia can maintain expressions of the receptor at 43℃. This study determined that the estrogen and progesterone in the supernatant fluid of Patchouli and Elsholtzia were higher than those observed in heat stress. Therefore, the results obtained in this study indicated that the Patchouli and Elsholtzia treatments administered prior the heat stress experiments had successfully protected the follicular granulosa cells from heat damages while maintaining the normal secretory functions of the granulosa cells.

Transcriptome Analysis During Follicle Development in Turkey Hens With Low and High Egg Production

Low and high egg producing hens exhibit gene expression differences related to ovarian steroidogenesis. High egg producing hens display increased expression of genes involved in progesterone and estradiol production, in the granulosa layer of the largest follicle (F1G) and small white follicles (SWF), respectively, whereas low egg producing hens display increased expression of genes related to progesterone and androgen production in the granulosa (F5G) and theca interna layer (F5I) of the fifth largest follicle, respectively. Transcriptome analysis was performed on F1G, F5G, F5I, and SWF samples from low and high egg producing hens to identify novel regulators of ovarian steroidogenesis. In total, 12,221 differentially expressed genes (DEGs) were identified between low and high egg producing hens across the four cell types examined. Pathway analysis implied differential regulation of the hypothalamo-pituitary-thyroid (HPT) axis, particularly thyroid hormone transporters and thyroid hormone receptors, and of estradiol signaling in low and high egg producing hens. The HPT axis showed up-regulation in high egg producing hens in less mature follicles but up-regulation in low egg producing hens in more mature follicles. Estradiol signaling exclusively exhibited up-regulation in high egg producing hens. Treatment of SWF cells from low and high egg producing hens with thyroid hormone in vitro decreased estradiol production in cells from high egg producing hens to the levels seen in cells from low egg producing hens, whereas thyroid hormone treatment did not impact estradiol production in cells from low egg producing hens. Transcriptome analysis of the major cell types involved in steroidogenesis inferred the involvement of the HPT axis and estradiol signaling in the regulation of differential steroid hormone production seen among hens with different egg production levels.

Effect of anti-müllerian hormone on the development and selection of ovarian follicle in hens

To elucidate the role of anti-müllerian hormone (AMH) in regulating the development of ovarian follicles in laying hens, the expressions of follicle-stimulating hormone receptor (FSHR), AMH receptor type 2 (AMHR2), steroidogenic-related genes steroidogenic acute regulatory protein (STAR), cytochrome P450 side-chain cleavage (CYP11A1), and 3β-hydroxysteroid dehydrogenase (HSD3B1) genes were measured from different sized follicles and granulosa cells. The results showed that the expressions of FSHR and AMHR2 genes were higher in small follicles and decreased after follicular selection. Oppositely, the expressions of STAR, CYP11A1, and HSD3B1 were significantly increased after follicular selection. It indicated that AMHR2 might mediate AMH suppression in the stimulating effects of follicle-stimulating hormone (FSH) on steroidogenic-related genes expression. To make sure the effects of AMH in this process, a total of 40 hens were treated (negative control, sham operation, 150 ng AMH/d or 300 ng AMH/d) for 25 d. We analyzed ovarian morphology, progesterone concentration in blood plasma, and the expressions of steroidogenic genes in ovaries and follicles. The AMH300 group had significantly lower weight of ovary and hierarchical follicles. Egg weight and ovary weight in AMH150 group were higher than those of sham operation and AMH300 groups, so did hierarchical follicles weight. The steroidogenic genes expressions showed an increase in ovarian tissue and the largest follicle of AMH150 and AMH300 groups. However, progesterone level in the blood was reduced by AMH injection with different concentrations. To further verify the above results, granulosa cells from 6 to 8 mm follicles were cultured with AMH (0, 5, 10, 20, 40, or 80 ng/mL). The results revealed that excessive AMH (80 ng/mL) exerted an inhibitory effect on progesterone synthesis and the expressions of STAR, CYP11A1, and HSD3B1. However, these genes expressions showed a significant increase in 20 ng/mL AMH-treated group. In summary, AMH inhibited the development of prehierarchical follicles in laying hens. The effects of AMH treatment with different concentrations on follicle development showed the follicle was selected by changing FSH responsiveness of prehierarchical follicles.

Nitrophenols are negative modulators of steroidogenesis in preovulatory follicles of the hen (Gallus domesticus) ovary: An in vitro and in vivo study

This study assessed the effects of 4-nitrophenol (PNP) and 3-methyl-4-nitrophenol (PNMC) on steroidogenesis in the granulosa layers (GLs) and theca layers (TLs) of chicken preovulatory follicles in vitro and in vivo. In the in vitro experiment, three of the largest yellow preovulatory follicles (F3 < F2 < F1) were exposed to PNP or PNMC (10^-8-10^-4 M), ovine luteinising hormone (oLH; 10 ng/mL), and combinations of oLH and PNP or PNMC (10^-6 M). In the in vivo experiment, laying hens were treated for 6 days with PNP or PNMC (10 mg/kg). In vitro experiments revealed that PNP and PNMC decreased basal and oLH-stimulated P4 secretion from the GL as well as T and E2 secretion from the TLs of F3-F1 follicles. Treatment of laying hens with nitrophenols lowered plasma concentrations of luteinising hormone and all three steroids. The reduction of steroid secretion was associated with decrease in LHR, HSD3B1 and CYP19A1 mRNA expression in the GL and/or TLs of the preovulatory follicles, both in vitro and in vivo. Moreover, PNP decreased HSD3B protein expression in the GL of F2 follicles in vitro and in vivo, while PNMC diminished its expression in the GL of F1 follicles in vivo. In vitro, nitrophenols did not affect CYP19A1 protein expression; however, nitrophenols inhibited its expression in the TLs of F3 and F2 follicles in vivo. The results obtained clearly demonstrate that nitrophenols are negative modulators of steroidogenesis in chicken preovulatory follicles and, in consequence, may not only impair ovulation process, but also affect function of the hypothalamic-pituitary-ovarian axis.

Should I Lay or Should I Grow: Photoperiodic Versus Metabolic Cues in Chickens

While photoperiod has been generally accepted as the primary if not the exclusive cue to stimulate reproduction in photoperiodic breeders such as the laying hen, current knowledge suggests that metabolism, and/or body composition can also play an influential role to control the hypothalamic-pituitary gonadal (HPG)-axis. This review thus intends to first describe how photoperiodic and metabolic cues can impact the HPG axis, then explore and propose potential common pathways and mechanisms through which both cues could be integrated. Photostimulation refers to a perceived increase in day-length resulting in the stimulation of the HPG. While photoreceptors are present in the retina of the eye and the pineal gland, it is the deep brain photoreceptors (DBPs) located in the hypothalamus that have been identified as the potential mediators of photostimulation, including melanopsin (OPN4), neuropsin (OPN5), and vertebrate-ancient opsin (VA-Opsin). Here, we present the current state of knowledge surrounding these DBPs, along with their individual and relative importance and, their possible downstream mechanisms of action to initiate the activation of the HPG axis. On the metabolic side, specific attention is placed on the hypothalamic integration of appetite control with the stimulatory (Gonadotropin Releasing Hormone; GnRH) and inhibitory (Gonadotropin Inhibitory Hormone; GnIH) neuropeptides involved in the control of the HPG axis. Specifically, the impact of orexigenic peptides agouti-related peptide (AgRP), and neuropeptide Y (NPY), as well as the anorexigenic peptides pro-opiomelanocortin (POMC), and cocaine-and amphetamine regulated transcript (CART) is reviewed. Furthermore, beyond hypothalamic control, several metabolic factors involved in the control of body weight and composition are also presented as possible modulators of reproduction at all three levels of the HPG axis. These include peroxisome proliferator-activated receptor gamma (PPAR-γ) for its impact in liver metabolism during the switch from growth to reproduction, adiponectin as a potential modulator of ovarian development and follicular maturation, as well as growth hormone (GH), and leptin (LEP).

The effect of total flavonoids of Epimedium on granulosa cell development in laying hens

To investigate the impact of total flavonoids of Epimedium (TFE) on the development of follicles of laying hens, 3 types of follicles including primary, prehierarchical, and preovulatory follicles were selected to obtain the follicular granulosa cells cultured in vitro. First, extraction of TFE was conducted by alcohol-soluble and ultrasonic methods. The effects of TFE on activity and proliferation of follicular granulosa cells were detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and measuring the expression of proliferating cell nuclear antigen mRNA through real-time quantitative polymerase chain reaction, and the expression of the follicle-stimulating hormone receptor, luteinizing hormone receptor, steroidogenic acute regulatory protein, and cytochrome P450 family 11 subfamily A member 1 mRNA was detected to study the functions of TFE affecting the differentiation and hormone secretion by granulosa cells. The results showed that TFE significantly improved the proliferation of 3 types of granulosa cells and promoted the differentiation of granulosa cells and accelerated the conversion of primary follicles to prehierarchical follicles. Total flavonoids of Epimedium played an important role in promoting progesterone secretion by prehierarchical and preovulatory granulosa cells. The results indicated that TFE could promote proliferation and differentiation of follicular granulosa cells and improve hormone secretion and follicle development, which provided reference data for TFE used as a feed additive or safe Chinese veterinary medicine to promote the laying rate.

Characterization of gene expression in the hypothalamo-pituitary-gonadal axis during the preovulatory surge in the turkey hen

A preovulatory surge (PS) of luteinizing hormone (LH) and progesterone triggers follicle ovulation, which is the first step of egg production and is orchestrated by the hypothalamo-pituitary-gonadal (HPG) axis. In the HPG axis, hypothalamic peptides, gonadotropin releasing hormone, and gonadotropin inhibitory hormone, control the production of follicle stimulating hormone and LH by the pituitary, which subsequently regulate ovarian production of estradiol and progesterone, respectively. The goal of this study was to characterize the HPG axis function of average egg producing hens by assessing plasma hormone profiles and hypothalamic, pituitary, and follicle gene expression outside and during the PS (n = 3 per group). Results were analyzed by a one-way ANOVA using the mixed models procedure of SAS. Plasma estradiol was not affected by the PS (P > 0.05), but plasma progesterone levels increased 8-fold during the PS when compared to basal progesterone levels (P < 0.05). HPG axis gene expression related to ovulation stimulation (e.g., GNRH, GNRHR, and LHB) was down-regulated during the PS; whereas gene expression related to follicle development (e.g., FSHB) was up-regulated during the PS. Additionally, in the hypothalamus and pituitary, estradiol receptor expression was up-regulated during the PS, whereas progesterone receptor expression was down-regulated during the PS. In the follicle cells, gene expression pertaining to progesterone (e.g., STAR), androgen (e.g., HSD17B1), and estradiol (e.g., CYP19A1) production was up-regulated during the PS. Prior to this study, the HPG axis had yet to be characterized during the PS in the turkey hen. This study showed that the PS significantly impacted gene expression in the hypothalamus, pituitary, and ovarian follicles. These results provide a foundation for further research into the regulation of ovulation and egg production in turkey hens.

Transcriptome analysis to unravel the gene expression profile of ovarian follicular development in Magang goose

Magang geese exhibit a unique characteristic of follicular development, with eight largest orderly arranged pre-ovulatory follicles in the abdominal cavity. However, little is known about the mechanisms underlying this follicular development. This study aimed to compare gene expression profiles of granulosa cells (GCs) at different stages of follicular development and provide comprehensive insights into follicle selection and the mechanisms underlying the well-defined follicle hierarchy in Magang geese. GCs of large white follicles (LWFs), small yellow follicles (SYFs), F8, F4, and F1 were used for RNA-seq analysis; 374, 1117, 791, and 593 genes were differentially expressed in stages LWFs to SYFs, SYFs to F8, F8 to F4, and F4 to F1, respectively, suggesting that these genes contribute to follicle selection and development. Reliability of sequencing data was verified through qPCR analysis of 24 genes. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathways revealed a complex mechanism that remodels the extracellular matrix and turnover of extracellular matrix components in follicular development and ovulation and involves multiple pathway, such as focal adhesion, adherens junction, and extracellular matrix–receptor interaction. Some unique characteristics were observed during the different follicular development stages. For instance, some differentially expressed genes were enriched in progesterone-mediated oocyte maturation and steroid biosynthesis from stage SYFs to F8, whereas others were enriched in actin cytoskeleton regulation and vascular smooth muscle contraction from stage F4 to F1. These findings enhance our current understanding of GC function and ovarian follicles during the key stages of follicular development.

Nitrophenols suppress steroidogenesis in prehierarchical chicken ovarian follicles by targeting STAR, HSD3B1, and CYP19A1 and downregulating LH and estrogen receptor expression

To assess the effects of 4-nitrophenol (PNP) and 3-methyl-4-nitrophenol (PNMC) on steroidogenesis in the chicken ovary, white (WF, 1-4 mm) and yellowish (YF, 4-8 mm) prehierarchical follicles were incubated in a medium supplemented with PNP or PNMC (10^-8-10^-4 M), ovine LH (oLH; 10 ng/mL), and combinations of oLH with PNP or PNMC (10^-6 M). Testosterone (T) and estradiol (E2) concentrations in media and mRNA expression for steroidogenic proteins (STAR, HSD3B1, and CYP19A1), and LH receptors (LHR), estrogen receptor α (ESR1) and β (ESR2) in follicles were determined by RIA and real-time qPCR, respectively. PNP and PNMC decreased T and E2 secretion by the WF and YF, and oLH-stimulated T secretion from these follicles. PNP decreased basal STAR and HSD3B1 mRNA levels both in the WF and YF, and CYP19A1 mRNAs in the WF. PNP reduced oLH-affected mRNA expression of these genes in the YF. PNMC inhibited basal STAR, HSD3B1, and CYP19A1 mRNA expression in the WF, but not in the YF. PNMC reduced oLH-stimulated STAR and CYP19A1 expression in the YF and WF, respectively. PNP decreased basal mRNA expression of LHR, ESR1, and ESR2 in the WF, but it increased ESR1 and ESR2 mRNA levels in the YF. PNMC reduced both basal and oLH-affected LHR, ESR1, and ESR2 mRNA expression in the WF; however, it did not influence expression of these genes in the YF. We suggest that nitrophenols by influencing sex steroid synthesis and transcription of LH and estrogen receptors in prehierarchical ovarian follicles may impair their development and selection to the preovulatory hierarchy.

Genistein increases progesterone secretion by elevating related enzymes in chicken granulosa cells

Genistein, a biologically active isoflavone, exists in many soy products. It is well known that genistein binds to both oestrogen receptor alpha (ERα) and oestrogen receptor beta (ERβ), but it has a higher affinity to ERβ. Genistein can also bind to the G protein-coupled receptor 30 (GPR30, also known as G protein-coupled oestrogen receptor 1 or GPER). Furthermore, weak oestrogenic activity has been found in genistein, but the mechanism of action remains unknown. The aim of this study was to investigate the in vitro effects of genistein on the secretion of progesterone (P4) and oestradiol (E2) in chicken granulosa cells harvested from follicles, as well as the mRNA expression of ERs in these cells. In addition, we examined the expression of key enzymes including steroidogenic acute regulatory protein (StAR), cytochrome P450 side-chain cleavage (P450scc), and 3β-hydroxysteroid dehydrogenase (3β-HSD) in the process of P4 synthesis. The results showed that genistein did not affect the viability of granulosa cells, nor was the proliferating cell nuclear antigen (PCNA) protein changed. Among the 1-, 10-, 100-, and 1,000-nM concentrations tested, treatment with 1 nM genistein for 48 h significantly increased P4 but did not affect E2 secretion. Real-time PCR results showed that the ERβ gene expression in granulosa cells was markedly upregulated by 1 nM genistein treatment for 48 h, but there was no significant difference in ERα and GPR30 expression. Genistein also increased the gene expression of StAR, P450scc and 3β-HSD in the cultured granulosa cells. These results indicate that genistein acts directly on chicken granulosa cells to increase P4 production by upregulating the gene expression of key enzymes through binding in ERβ. It may exert positive effects on the reproduction of late-laying hens and act as an effective and safe feed additive for animals.

Transcriptomic Diversification of Granulosa Cells during Follicular Development in Chicken

Granulosa cells play important roles in ovarian follicular development. To better understand the molecular mechanisms involved in this physiological process in chicken, high-throughput transcriptome analyses were performed to study the expression profiles of granulosa cells harvested from 6 mm white follicles, F5 follicles and F1 follicles. The analyses elucidated a clear tendency of granulosa cells in shifting its expression profile from proliferation to differentiation during follicular development. Transcripts down-regulated during this process were mainly associated with cell division, cell cycle and DNA replication while the up-regulated transcripts were related to ribosomal function, lipid metabolism and protein synthesis. Our study for the first time provides the complete gene expression profiles along follicular development supporting the active involvement of many genes characterized in cell signaling (AMH, Inhibins, Activins, BMPs) and transcription factors (SMAD3, SMAD5, ID1, ID2, ID3). Their temporal expression profiles support the notion of continual cross-talk between granulosa cells and its neighboring cells and shed light on the mechanisms behind avian follicular selection and pave the way to the better understanding of reproductive efficiency.

Dynamic expression and functional analysis of circRNA in granulosa cells during follicular development in chicken

Background

Circular RNA (circRNA) is a type of noncoding RNA involved in a variety of biological processes, especially in post-transcriptional regulation. The granulosa cells of follicles play a determining role in ovarian development. However, the function of circRNA in chicken follicles is unclear. To better understand the molecular mechanism underlying follicular development and granulosa cell function, we performed a strategy of second-generation sequencing and linear RNA depletion for granulosa cells from small yellow follicles (SYF, 5–8 mm), the smallest hierarchal follicles (F6, 9–12 mm), and the largest hierarchal follicles (F1, ~ 40 mm).

Results

We predicted a total of 11,642 circRNAs that distributed on almost all chromosomes. The majority of the splice lengths of circRNAs were 200–500 nt and mainly produced from intron and CDS regions. During follicle growth, differentially expressed (DE) circRNAs showed dynamic changes which were tissue- and stage-specific. The host genes of DE circRNAs were functionally enriched in GTPase activity and several pathways involved in reproduction. Moreover, bioinformatic prediction analysis for circRalGPS2 demonstrated that circRNAs from the same genes may share common miRNA to act as a sponge. The predicted target genes were enriched in various biological processes including cognition, cell communication, and regulation of signaling, and several pathways related to reproduction such as tight junction, oocyte meiosis, progesterone-mediated oocyte maturation, and GnRH signaling.

Conclusions

This study provides a starting point for further experimental investigations into chicken circRNAs and casts a light on the understanding of follicle development.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5462-2) contains supplementary material, which is available to authorized users.

Expression dynamics of gonadotropin-releasing hormone-I and its mutual regulation with luteinizing hormone in chicken ovary and follicles

Gonadotropin-releasing hormone-I (GnRH-I) has been identified in the ovaries of vertebrate species, and this decapeptide is a key regulator of reproductive functions. However, its biological action and regulatory mechanism in the chicken ovary remain to be characterized. In this study, the expression of GnRH-I gene in chicken hypothalamus and ovaries at different developmental stages and different sizes of follicles was investigated, and the effect of GnRH-I mRNA on chicken follicular cells was analyzed in vitro. The results showed that the expression of GnRH-I was dramatically decreased in the hen ovary compared to that in the hypothalamus after sexual maturation. In the mature ovarian follicles, GnRH-I mRNA levels were significantly higher in theca cells than that in granulosa cells. Overexpression of GnRH-I decreased the expression of luteinizing hormone receptor (LHR) mRNA in theca cells from preovulatory follicles but had no effect on granulosa cells. Treatment of theca cells with different concentrations of luteinizing hormone (LH) significantly increased GnRH-I mRNA expression at low doses (50 ng/ml) but significantly decreased it at higher doses (200 ng/ml). Furthermore, GnRH-I inhibited LH-induced LHR expression at the lower dose of LH (50 ng/ml). These findings provide strong evidence indicating that GnRH-I is an important regulator in the chicken ovary.

Implication of SLIT3-ROBO1/ROBO2 in granulosa cell proliferation, differentiation and follicle selection in the prehierarchical follicles of hen ovary

The SLIT/ROBO pathway has been implicated in prehierarchical follicular development of hen ovary by an intrafollicular autocrine and/or paracrine fashion. SLIT3, one of the key components of the SLIT/ROBO family, serves as a ligand that potentially interacts with the four receptors, ROBO1, ROBO2, ROBO3 and ROBO4. But the exact roles and regulatory mechanism of SLIT3 in chicken ovarian follicle development remain largely unclear. The present study was conducted to investigate the potential roles and molecular regulation of SLIT3 in granulosa cell (GC) proliferation, differentiation and follicle selection within the prehierarchical follicles of hen ovary. We found that SLIT3 interacts physically with the four ROBO receptors, but the expression of the ROBO1 and ROBO2 genes are more susceptible to the regulation of SLIT3 ligand than that of the ROBO3 and ROBO4 genes. Moreover, the siRNA-mediated knockdown of SLIT3 in the follicular GCs leads to a significant increase in cell proliferation. Conversely, overexpression of SLIT3 results in a remarkable reduction in GC proliferation. Furthermore, the overexpressed SLIT3 has notably decreased the mRNA and protein expression levels of follicle-stimulating hormone (FSHR), growth and differentiation factor 9 (GDF9), steroidogenic acute regulatory protein (STAR) and cytochrome P450 11A1 (CYP11A1) in the GCs. These results indicated that SLIT3 may play an inhibitory effect on GC proliferation, differentiation and follicle selection, and these suppressive actions of SLIT3 in the GC proliferation can be prohibited by the siRNA-mediated knockdown of ROBO1 and ROBO2 receptors. The current data provide a basis for further investigation of molecular mechanisms of SLIT3-ROBO1/2 pathway in controlling the prehierarchical follicle development of the hen ovary.

Comparison of growth characteristics of in vitro cultured granulosa cells from geese follicles at different developmental stages

Granulosa cells (GCs) are essential components of follicles and are involved in regulating the process of follicles development. However, comparative studies on GCs isolated from different staged follicles have not been conducted in goose. The aim of the present study was to identify the growth characteristics of goose GCs from pre-hierarchical (6–10 mm) and hierarchical (F4–F2, F1) follicles. Our results showed that the three cohorts of cells had different tolerance to collagenase and had noticeable morphological differences. The F1 granulosa layers were fully digested by 0.1% collagenase, while higher concentration (0.3%) was used for both F4–F2 and pre-hierarchical granulosa layers. In the state of suspension, the diameter of F1 individual cell was larger than the other two cohorts. However, after adhering to the culture plate, cells of F1 just had changes in the diameter accompanied by small bright spots, while both pre-hierarchical and F4–F2 GCs proliferated rapidly with spreading and irregularly shaped voids. Furthermore, all attached cells could be stained by the follicle-stimulating hormone receptor antibody. Analyses of both growth curve and the mRNA expression profiles of genes related to cellular proliferation, apoptosis, and steroidogenesis suggested that three cohorts of in vitro cultured GCs had different physiological viability and functions. Taken together, the present study not only revealed differences of the growth characteristics among three cohorts of goose GCs from pre-hierarchical, F4–F2 and F1 follicles, but also optimized the in vitro culture system of geese different staged GCs.

Effects of nonglycosylated and glycosylated prolactin on basal and gonadotropin-stimulated steroidogenesis in chicken ovarian follicles

In galliformes, the circulating isoform of prolactin (PRL) significantly changes during different reproductive states. However, the role of the major isoform (glycosylated PRL [G-PRL]) in ovarian steroidogenesis is unknown. The present study aimed to compare the effects of nonglycosylated (NG-) and G-PRL on basal and gonadotropin-stimulated estradiol (E₂) and progesterone (P₄) production in granulosa cells or follicular walls of chicken of different size class follicles. In the initial experiment, granulosa cells of preovulatory F3-F1 and prehierarchical 6- to 8-mm follicles were incubated for 24 h with different concentrations of NG- or G-PRL (0, 1, 10, 100, or 1,000 ng/mL). In the subsequent experiments, these categorized granulosa cells and follicular walls of prehierarchical 4-6, 2-4, and <2-mm follicles were incubated for 24 h in the absence and presence of 10-ng/mL FSH or LH, or in combination with different concentrations of NG- or G-PRL (10, 100, or 1,000 ng/mL). We observed that lower levels of NG-PRL induced (P < 0.05) E₂ and P₄ secretion in granulosa cells of either preovulatory or prehierarchical follicles, but at higher levels, this effect was reduced. In contrast, G-PRL promoted (P < 0.05) basal E₂ and P₄ secretion in preovulatory granulosa cells but was inhibitory (P < 0.05) in prehierarchical granulosa cells. Results obtained by real-time quantitative PCR (qPCR) demonstrated that these effects were mediated through modulation of the expression of StAR, CYP11A1, CYP19A1, and 3β-HSD. Furthermore, G-PRL was less potent than NG-PRL in inhibiting FSH- or LH-stimulated E₂ and P₄ production in granulosa cells of preovulatory follicles, whereas NG-PRL enhanced (P < 0.05) but G-PRL reduced (P < 0.05) FSH-induced P₄ production in those of prehierarchical follicles. In follicular walls from each group of prehierarchical 4-6, 2-4, and <2-mm follicles, NG- and G-PRL had both stimulatory and inhibitory influences on the actions of FSH on E₂ and P₄ secretion, but both suppressed (P < 0.05) LH-induced E₂ and P₄ secretion except for the synergistic effects of LH and G-PRL on P₄ secretion by follicular walls of the follicles of 4-6 mm. Taken together, these results suggest that both NG- and G-PRL are biologically active in regulating basal and gonadotropin-stimulated E₂ and P₄ production in chicken ovarian follicles. However, their effects are different depending on the concentration, the type of gonadotropin (FSH or LH), and the stage of follicle development.

Comparative proteomic analysis of pituitary glands from Huoyan geese between pre-laying and laying periods using an iTRAQ-based approach

In this study, we performed a comprehensive evaluation of the proteomic profile of the pituitary gland of the Huoyan goose during the laying period compared to the pre-laying period using an iTRAQ-based approach. Protein samples were prepared from pituitary gland tissues of nine pre-laying period and nine laying period geese. Then the protein samples from three randomly selected geese within each period were pooled in equal amounts to generate one biological sample pool. We identified 684 differentially expressed proteins, including 418 up-regulated and 266 down-regulated proteins. GO annotation and KEGG pathway analyses of these proteins were conducted. Some of these proteins were found to be associated with hormone and neurotransmitter secretion and transport, neuropeptide signalling and GnRH signalling pathways, among others. Subsequently, the modification of the abundance of three proteins (prolactin, chromogranin-A and ITPR3) was verified using western blotting. Our results will provide a new source for mining genes and gene products related to the egg-laying performance of Huoyan geese, and may provide important information for the conservation and utilization of local goose breeds.

Regulatory Mechanisms Underlying the Expression of Prolactin Receptor in Chicken Granulosa Cells

Prolactin (PRL) has both pro- and anti-gonadal roles in the regulation of avian ovarian functions through its interaction with the receptor (PRLR). However, neither the pattern of expression of PRLR nor its regulatory mechanisms during follicle development have been clearly defined. The objective of the present study was to investigate mechanisms of PRLR expression in chicken granulosa cells. Levels of PRLR transcript were highest in the stroma and walls of follicles < 2 mm in diameter and progressively declined with the maturation of follicles. In preovulatory follicles, PRLR was expressed at higher levels in granulosa than theca layers. FSH exerted the greatest stimulatory effect on PRLR and StAR expression in cultured granulosa cells of the 6–8 mm follicles but this effect declined as follicles matured to F1. In contrast, LH did not alter the expression of PRLR in granulosa cells of all follicular classes but increased levels of StAR in F2 and F1 granulosa cells. Both non-glycosylated- (NG-) and glycosylated- (G-) PRL upregulated basal PRLR expression in granulosa cells of the 6–8 mm, F3 or F1 follicles but had little effect in F2 follicles. Furthermore, FSH-stimulated PRLR expression was reduced by the addition of either isoform of PRL especially in F2 granulosa cells. These results indicate that PRLR is differentially distributed and regulated by FSH or PRL variants independently or in combination in the follicular hierarchy. By using activators and inhibitors, we further demonstrated that multiple signaling pathways, including PKA, PKC, PI3K, mTOR and AMPK, are not only directly involved in, but they can also converge to modulate ERK2 activity to regulate FSH-mediated PRLR and StAR expression in undifferentiated granulosa cells. These data provide new insights into the regulatory mechanisms controlling the expression of PRLR in granulosa cells.

Effects of PCB 126 and PCB 153 on secretion of steroid hormones and mRNA expression of steroidogenic genes (STAR, HSD3B, CYP19A1) and estrogen receptors (ERα, ERβ) in prehierarchical chicken ovarian follicles

The objective of this study was to assess the in vitro effects of dioxin-like PCB 126 and non-dioxin-like PCB 153 on basal and ovine LH (oLH)-stimulated testosterone (T) and estradiol (E2) secretion and expression of steroidogenic genes (STAR, HSD3B and CYP19A1) and estrogen receptors α (ERα) and β (ERβ) in white (WF) and yellowish (YF) prehierarchical follicles of the hen ovary. Steroid concentrations in a medium and gene expression in follicles following 6h of exposition were determined by RIA and real-time qPCR, respectively. Both PCBs increased basal and oLH-stimulated T secretion by the WF follicles. PCB 126 reduced basal E2 secretion by the WF follicles. PCB 153 elevated but PCB 126 reduced oLH-stimulated E2 secretion by the prehierarchical follicles. PCB 126 increased basal STAR and HSD3B and reduced CYP19A1 mRNA expression in these follicles. PCB 153 increased basal expression of STAR and HSD3B in YF follicles, but diminished HSD3B mRNA levels in the WF. The studied PCBs had an opposite effect on basal and oLH-stimulated CYP19A1 mRNA expression in prehierarchical follicles. Both PCBs modulated basal and inhibited oLH-stimulated ERα and ERβ gene expression in the prehierarchical follicles. In conclusion, data of the current study demonstrate the congener-specific effects of PCBs on sex steroid secretion by prehierarchical follicles of the chicken ovary, which are at least partly related to STAR, HSD3B and CYP19A1 gene expression. It is suggested that PCBs, by influencing follicular steroidogenesis and expression of estrogen receptors, may impair development and selection of yellowish follicles to the preovulatory hierarchy.

Effects and mechanisms of waterborne copper exposure influencing ovary development and related hormones secretion in yellow catfish Pelteobagrus fulvidraco

The present study was conducted to determine the effects and mechanism of waterborne copper (Cu) exposure influencing ovary development and related hormones secretion in yellow catfish Pelteobagrus fulvidraco. To this end, two experiments were conducted. In Exp. 1, the partial cDNA sequences of three steroidogenesis-related genes (androgen receptor (ar), steroidogenic factor 1 (sf-1) and steroidogenic acute regulatory protein (star)) were firstly characterized from P. fulvidraco. The predicted amino acid sequences for the P. fulvidraco ar, sf-1 and star contained the main structural features characteristic in other species. In Exp. 2, P. fulvidraco were exposed to three waterborne Cu concentrations (control, 30μg/l and 60μg/l, respectively) for 56days. Sampling occurred on day 28 and day 56, respectively. On day 28, the levels of serum sex-steroid hormones (FSH and LH) and the mRNA levels of steroidogenesis-related genes (3β-hsd, cyp11a1, cyp17, cyp19a, sf-1 and star) were significantly increased in ovary of P. fulvidraco exposed to 30μg Cu/l. The immunohistochemical analysis showed the positive reaction of ER, VTG and aromatase in low dose exposure group. These indicated that in low dose and relative short-term exposure, Cu was beneficial. In contrast, 60μg Cu/l exposure significantly reduced the levels of serum FSH, LH, E2 and P, and the mRNA levels of ovarian 20β-hsd, cyp19a and erα in P. fulvidraco. On day 56, waterborne Cu concentration exposure reduced the levels of serum gonadotropins and sex hormones, and down-regulated the mRNA levels of steroidogenesis-related genes, indicating long-term Cu exposure had toxic effect on the secretion of sex-steroid hormone in P. fulvidraco. For the first time, our study cloned cDNA sequences of ar, sf-1 and star in P. fulvidraco, and demonstrated the effects and mechanism of waterborne Cu exposure influencing hormones secretion and synthesis in dose- and time-dependent manner in P. fulvidraco, which will help to understand the Cu-induced reproductive toxicity at both protein and transcriptional levels in fish.

Effects of Steroid Hormone in Avian Follicles

The aim of the present study was to examine the effects of testosterone (T) and estradiol-17β (E₂) on the production of progesterone (P₄) by granulosa cells, and of the E₂ on the production of P₄ and T by theca internal cells. In the first experiment, granulosa cells isolated from the largest (F₁) and third largest (F₃) preovulatory follicle were incubated for 4 h in short-term culture system, P₄ production by granulosa cells of both F₁ and F₃ was increased in a dose-dependent manner by ovine luteinizing hormone (oLH), but not T or E₂. In the second experiment, F₁ and F₃ granulosa cells cultured for 48 h in the developed monolayer culture system were recultured for an additional 48 h with increasing doses of various physiological active substances existing in the ovary, including T and E₂. Basal P₄ production for 48 h during 48 to 96 h of the cultured was about nine fold greater by F₁ granulosa cells than by F₃ granulosa cells. In substances examined oLH, chicken vasoactive intestinal polypeptide (cVIP) and T, but not E₂, stimulated in a dose-dependent manner P₄ production in both F₁ and F₃ granulosa cells. In addition, when the time course of P₄ production by F₁ granulosa cells in response to oLH, cVIP, T and E₂ was examined for 48 h during 48 to 96 h of culture, although E₂ had no effect on P₄ production by granulosa cells of F₁ during the period from 48 to 96 h of culture, P₄ production with oLH was found to be increased at 4 h of the culture, with a maximal 9.14 fold level at 6 h. By contrast, P₄ production with cVIP and T increased significantly (p<0.05) from 8 and 12 h of the culture, respectively, with maximal 6.50 fold response at 12 h and 6, 48 fold responses at 36 h. Furthermore, when F₁ granulosa cells were precultured with E₂ for various times before 4 h culture with oLH at 96 h of culture, the increase in P₄ production in response to oLH with a dose-related manner was only found at a pretreatment time of more than 12 h. In the third experiment, theca internal cells of F₁, F₂ and the largest third to fifth preovulatory follicles (F_3-5) were incubated for 4 h in short-term culture system with increasing doses of E₂. The production of P₄ and T by theca internal cells were increased with the addition of E₂ of 10⁻⁶ M. These increases were greater in smaller follicles. These results indicate that, in granulosa cells of the hen, T may have a direct stimulatory action in the long term on P₄ production, and on E₂ in long-term action which may enhance the sensitivity to LH for P₄ production, and thus, in theca internal cells, E₂ in short term action may stimulate the production of P₄ and T.

Growth Differentiation Factor-8 Decreases StAR Expression Through ALK5-Mediated Smad3 and ERK1/2 Signaling Pathways in Luteinized Human Granulosa Cells

Growth differentiation factor-8 (GDF-8) has been recently shown to be expressed in human granulosa cells, and the mature form of GDF-8 protein can be detected in the follicular fluid. However, the biological function and significance of this growth factor in the human ovary remains to be determined. Here, we investigated the effects of GDF-8 on steroidogenic enzyme expression and the potential mechanisms of action in luteinized human granulosa cells. We demonstrated that treatment with GDF-8 did not affect the mRNA levels of P450 side-chain cleavage enzyme and 3β-hydroxysteroid dehydrogenase, whereas it significantly down-regulated steroidogenic acute regulatory protein (StAR) expression and decreased progesterone production. The suppressive effect of GDF-8 on StAR expression was abolished by the inhibition of the TGF-β type I receptor. In addition, treatment with GDF-8 activated both Smad2/3 and ERK1/2 signaling pathways. Furthermore, knockdown of activin receptor-like kinase 5 reversed the effects of GDF-8 on Smad2/3 phosphorylation and StAR expression. The inhibition of Smad3 or ERK1/2 signaling pathways attenuated the GDF-8-induced down-regulation of StAR and production of progesterone. Interestingly, the concentrations of GDF-8 were negatively correlated with those of progesterone in human follicular fluid. These results indicate a novel autocrine function of GDF-8 to down-regulate StAR expression and decrease progesterone production in luteinized human granulosa cells, most likely through activin receptor-like kinase 5-mediated Smad3 and ERK1/2 signaling pathways. Our findings suggest that granulosa cells might play a critical role in the regulation of progesterone production to prevent premature luteinization during the final stage of folliculogenesis.

Ovarian follicle selection and granulosa cell differentiation

The reproductive strategy for avian species that produce a sequence (or clutch) of eggs is dependent upon the maintenance of a small cohort of viable, undifferentiated (prehierarchal) follicles. It is from this cohort that a single follicle is selected on an approximate daily basis to initiate rapid growth and final differentiation before ovulation. This review describes a working model in which follicles within this prehierarchal cohort are maintained in an undifferentiated state by inhibitory cell signaling until the time of selection. Ultimately, follicle selection represents a process in which a single undifferentiated follicle per day is predicted to escape such inhibitory mechanisms to begin rapid growth and final maturation before ovulation. Several processes initiated within the granulosa cell layer at selection are dependent upon G protein-coupled receptors signaling via cyclic adenosine monophosphate (cAMP), and several critical processes are described herein. Finally, reference is made to several practical outcomes that can result from understanding the process of selection, including applications within the poultry industry. Proximal factors and processes that mediate follicle selection can either extend or decrease the length of the laying sequence, and thus directly influence overall egg production. In particular, any aberration that results in the selection of more than one follicle per day will result in decreased egg production. More generally, in wild birds these processes are modified by prevailing environmental conditions and by social interactions to influence clutch size. The elucidation of cellular processes that regulate follicle selection can assist in the development of assisted reproductive technologies for application in threatened and endangered avian species.

Transcriptome profiling identifies differentially expressed genes in Huoyan goose ovaries between the laying period and ceased period

The Huoyan goose is famous for its high egg-laying performance and is listed as a nationally protected domestic animal by the Chinese government. To elucidate the key regulatory genes involved in Huoyan goose egg laying, RNA from ovarian tissue during the ceased and laying periods was sequenced using the Illumina HiSeq 2000 sequencing platform. More than 12 million reads were produced in ceased and laying libraries that included 11,896,423 and 12,534,799 clean reads, respectively. More than 20% of the reads were matched to the reference genome, and 23% of the reads were matched to reference genes. Genes with a false discovery rate (FDR) ≤0.001 and log₂ratio ≧1 or ≤−1 were characterized as differentially expressed, and 344 up-regulated and 344 down-regulated genes were classified into functional categories. Twelve genes that are mainly involved in pathways for reproduction regulation, such as steroid hormone biosynthesis, GnRH signaling pathways, oocyte meiosis, progesterone-mediated oocyte maturation, steroid biosynthesis, calcium signaling pathways, and G-protein coupled receptor signaling pathway were selected for validation by a quantitative real-time polymerase chain reaction (qRT-PCR) analysis, the qRT-PCR results are consistent with the general expression patterns of those genes from the Illumina sequencing. These data provide comprehensive gene expression information at the transcriptional level that might increase our understanding of the Huoyan goose's reproductive biology.