CircRNAs involved in the red light of effect on follicle selection in pigeons

Red light (RL) can enhance egg production in poultry. CircRNAs play a crucial role by serving as transcriptional regulators. However, their role in influencing follicle development in White King pigeons remains unexplored. In this study, 54 paired White King pigeons were chosen and divided into RL and white light (WL) groups, each with 3 subgroups. The egg production of paired pigeons in each replicate was recorded for 45 d, and the characteristics of follicle development were monitored during the laying interval (LI). The granulosa cell layer from follicles of the second-largest follicle (F2) was collected, and high-throughput sequencing was performed to elucidate the molecular mechanism of follicle development in pigeons. The study confirmed that RL enhances egg production in pigeons. Additionally, under RL, the F2 follicle was selected, while under WL, small follicles were kept on the third day (LI3). A total of 5,510 circRNAs were identified across all samples, revealing differentially expressed circRNAs (DECs) in various comparisons: 627 in RF1 vs. WF1, 900 in RF2 vs. WF2, 606 in RF1 vs. RF2, and 937 in WF1 vs. WF2. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that host genes of DECs were enriched in pathways like steroid hormone biosynthesis, oocyte meiosis, GnRH signaling pathway, and apoptosis pathway. Moreover, circRNA_5497, circRNA_2016, and circRNA_3328 were common DECs across 4 groups, sharing miRNA binding sites with follicle selection-associated genes. In conclusion, our findings suggest that RL promotes egg production by stimulating follicle selection during LI, offering insights into the regulatory mechanisms of circRNAs in follicle selection under RL. This knowledge can help enhance the reproductive performance of pigeons.

Chicken ovarian follicular atresia: interaction network at organic, cellular, and molecular levels

Most of follicles undergo a degenerative process called follicular atresia. This process directly affects the egg production of laying hens and is regulated by external and internal factors. External factors primarily include nutrition and environmental factors. In follicular atresia, internal factors are predominantly regulated at 3 levels; organic, cellular and molecular levels. At the organic level, the hypothalamic-pituitary-ovary (HPO) axis plays an essential role in controlling follicular development. At the cellular level, gonadotropins and cytokines, as well as estrogens, bind to their receptors and activate different signaling pathways, thereby suppressing follicular atresia. By contrast, oxidative stress induces follicular atresia by increasing ROS levels. At the molecular level, granulosa cell (GC) apoptosis is not the only factor triggering follicular atresia. Autophagy is also known to give rise to atresia. Epigenetics also plays a pivotal role in regulating gene expression in processes that seem to be related to follicular atresia, such as apoptosis, autophagy, proliferation, and steroidogenesis. Among these processes, the miRNA regulation mechanism is well-studied. The current review focuses on factors that regulate follicular atresia at organic, cellular and molecular levels and evaluates the interaction network among these levels. Additionally, this review summarizes atretic follicle characteristics, in vitro modeling methods, and factors preventing follicular atresia in laying hens.

NR5A1 and NR5A2 regulate follicle development in chicken (Gallus gallus) by altering proliferation, apoptosis, and steroid hormone synthesis of granulosa cells

Chicken ovarian follicle development is regulated by complex and dynamic gene expression. Nuclear receptor 5A1 and 5A2 (NR5A1 and NR5A2, respectively) are key genes that regulate steroid hormone production and gonadal development in mammals; however, studies on follicular development in the chicken ovary are scarce. In this study, we investigated the functions of NR5A1 and NR5A2 on follicle development in chickens. The results showed that the expression of NR5A1 and NR5A2 was significantly higher in small yellow follicles and F5. Furthermore, the expression of NR5A1 and NR5A2 was significantly higher in follicular tissues of peak-laying hens (30 wk) than in follicular tissues of late-laying hens (60 wk), with high expression abundance in granulosa cells (GC). The overexpression of NR5A1 and NR5A2 significantly promoted proliferation and inhibited apoptosis of cultured GC; upregulated STAR, CYP11A1, and CYP19A1 expression and estradiol (E2) and progesterone (P4) synthesis in GC from preovulatory follicles (po-GC); and increased STAR, CYP11A1, and CYP19A1 promoter activities. In addition, follicle-stimulating hormone treatment significantly upregulated NR5A1 and NR5A2 expression in po-GC and significantly promoted FSHR, CYP11A1, and HSD3B1 expression in GC from pre-hierarchical follicles and po-GC. The core promoter region of NR5A1 was identified at the -1,095- to -483-bp and -2,054- to -1,536-bp regions from the translation start site (+1), and the core promoter region of NR5A2 was at -998 to -489 bp. Two single nucleotide polymorphisms (SNP) were identified in the core promoter region of the NR5A1 gene, which differed between high- and low-yielding chicken groups. Our study suggested that NR5A1 and NR5A2 promoted chicken follicle development by promoting GC proliferation and E2 and P4 hormone synthesis and inhibiting apoptosis. Moreover, we identified the promoter core region or functional site that regulates NR5A1 and NR5A2 expression.

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.

MFN2 regulates progesterone biosynthesis and proliferation of granulosa cells during follicle selection in hens

Follicle selection in hens refers to a biological process that only one small yellow follicle (SYF) is selected daily or near-daily for following hierarchical development (from F5/F6 to F1) until ovulation. MFN2 is a kind of GTPases located on the mitochondrial outer membrane, which plays a crucial role in mitochondrial fusion. This study aimed to elucidate the role of MFN2 in proliferation and progesterone biosynthesis of granulosa cells (GCs) during follicle selection in hens. The results showed that GCs began to produce progesterone (P4) after follicle selection, accompanied with changes from multi-layer with flat cells to single layer with cubic cells. MFN2 was detected in GCs of follicles from SYF to F1. After follicle selection, the expression level of MFN2 in GCs upregulated significantly, accompanied with increases in P4 biosynthesis, ATP production, mitochondrial DNA (mtDNA) copy numbers of granulosa cells. FSH (80 ng/mL) facilitated the effects of P4 biosynthesis and secretion, ATP production, mtDNA copy numbers, cell proliferation and the MFN2 transcription of granulosa cells from F5 (F5G) in vitro. However, FSH treatment did not promote P4 secretion in granulosa cells from SYF (SYFG) in vitro. Meanwhile, we observed that change fold of MFN2 transcription, ATP production, mtDNA copy numbers and cell proliferation rate in F5G after treatment with FSH were greater than those in SYFG. Furthermore, expression levels of MFN2 protein and messenger RNA in F5G were significantly higher than those in SYFG after treatment with FSH. P4 biosynthesis, ATP production, mtDNA copy numbers as well as cell proliferation reduced significantly in F5G with MFN2 knockdown. Oppositely, P4 biosynthesis, ATP production, mtDNA copy numbers and cell proliferation increased significantly in SYFG after the overexpression of MFN2. Our results suggest that the upregulation of MFN2 may be involved in the initiation of P4 biosynthesis, and promotion of GCs proliferation during follicle selection.

microRNA transcriptome analysis of granulosa cells predicts that the Notch and insulin pathways affect follicular development in chickens

MicroRNAs (miRNAs) have been documented to play critical roles in chicken reproduction. Granulosa cell (GC) development of the follicle is closely related to hierarchical follicle ordering, making it an important factor in determining laying performance. Thus, it is meaningful to mine follicular development-related miRNAs. To identify regulatory miRNAs and the biological mechanisms by which they control follicular development, we conducted small RNA sequencing of GCs isolated from prehierarchical follicles named small yellow follicle (SYFG), the smallest hierarchical follicle (F6G), and the largest hierarchical follicle (F1G). A total of 99, 196, and 110 differentially expressed miRNAs (DEMs) were identified in SYFG.vs.F6G, SYFG.vs.F1G, and F6G.vs.F1G, respectively. Of these, 22 miRNAs, including miR-223, miR-103a, miR-449c-3p, and miR-203a, were ubiquitously identified as DEMs in three stages. Target gene prediction suggested that these miRNAs are associated with the MAPK, TGF-β, and Wnt signaling pathways, which are all associated with follicular development. The Notch and insulin signaling pathways were commonly enriched in all three comparisons. RT-qPCR analysis further indicated that the expression levels of PSEN2, which encodes an essential factor regulating Notch and insulin signaling, was significantly changed in SYFG, F6G, and F1G. The current study provides basic data and offers a new foundation for further exploration of the roles of miRNAs in follicular development in chickens.

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.

FGF12 regulates cell cycle gene expression and promotes follicular granulosa cell proliferation through ERK phosphorylation in geese

The granulosa cells play an important role in the fate of follicular development or atresia in poultry. Fibroblast growth factor 12 (FGF12) is downregulated in atretic follicles and may be involved in regulating granulosa cell survival in previous studies, but its molecular mechanism remains unclear. In this study, FGF12 overexpression and knockdown models of goose granulosa cells were constructed to investigate its function. The downstream expression of the cell cycle pathway was analyzed by qPCR. Granulosa cell proliferative activity and apoptosis were detected by CCK8 and TUNEL. Protein phosphorylation levels of ERK and AKT were measured using Western blotting to analyze the key pathway of FGF12 regulation of granulosa cell proliferation. ERK protein phosphorylation inhibitor was added for further verification. After overexpression of FGF12, cell proliferation activity was increased, the expressions of cell cycle pathway genes CCND1, CCNA2, MAD2, and CHK1 were upregulated, the apoptosis of granulosa cell was decreased, and Caspase 3 gene and protein expression were downregulated. After the knockdown of FGF12, cell proliferation activity decreased, the expression of downstream genes in the cell cycle pathway was downregulated, the apoptosis of granulosa cells was increased, and the Bcl-2 gene and protein were downregulated. Overexpression of FGF12 promoted the synthesis of P4 and upregulates the expression of the STAR gene. Overexpression of FGF12 promoted ERK protein phosphorylation but did not affect AKT phosphorylation. The addition of ERK phosphorylation inhibitors resulted in the elimination of the increase in cell proliferative activity caused by FGF12 overexpression. In conclusion, FGF12 could promote proliferation and inhibit apoptosis of goose granulosa cells by increasing ERK phosphorylation.

Response of the hen ovary to eCG treatment: Insight into morphology and expression of genes related to steroidogenesis and vitellogenesis

The present study aimed to examine the effect of equine chorionic gonadotropin (eCG) treatment on the chicken ovarian folliculogenesis and steroidogenesis. The expression of vitellogenesis-related genes in the liver was also investigated. Laying hens were injected with 75 I.U./kg of body weight/0.2 mL of eCG, once a day for 7 successive days. On day 7 of the experiment hens, including control hens which were receiving vehicle, were euthanized. The liver and ovarian follicles were harvested. Blood was collected daily through the whole experiment. The eCG treatment resulted in the cessation of egg laying after 3 or 4 days. The eCG-treated hens had heavier ovaries with a higher number of yellowish and yellow follicles arranged in a non-hierarchical way in contrast to ovaries of control hens. Moreover, these birds had elevated plasma estradiol (E₂) and testosterone (T) concentrations. The molar ratios of E₂:progesterone (P4) and T:P4 were increased in chickens injected with eCG. Real-time polymerase chain reaction revealed changes in mRNA abundances of steroidogenesis-associated genes (StAR, CYP11A1, HSD3β, and CYP19A1) in ovarian follicles: white, yellowish, small yellow, and the largest yellow preovulatory (F3-F1) as well as VTG2, apoVLDL II, and gonadotropin receptors in the liver. In general, the abundances of gene transcripts were higher in eCG-treated hens than in control hens. Western blot analyses showed an elevated abundance of aromatase protein in the prehierarchical and small yellow follicles of eCG-treated hens. Unexpectedly, there was presence of both FSHR and LHCGR mRNA in the liver and the level of expression was shifted in eCG-treated hens. In summary, eCG treatment leads to disruption of the ovarian hierarchy with accompanying changes in circulating steroids and ovarian steroidogenesis.

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.

Phosphoproteomic analysis on ovarian follicles reveals the involvement of LSD1 phosphorylation in Chicken follicle selection

BACKGROUND

Follicle selection in chickens refers to the process of selecting one follicle from a group of small yellow follicles (SY, 6-8 mm in diameter) for development into 12-15 mm hierarchal follicles (usually F6 follicles), which is controlled by sex hormones including follicle-stimulating factor (FSH), estrogen and progesterone. Follicle selection is a critical process impacting egg production in chicken, therefore, is the focus of many studies. Phosphorylation is important for the proper function of proteins, thus, needs to be analyzed by proteomic level.

RESULT

In this study, we compared the phosphoproteomes of SY and F6 follicles in laying hens and identified 2,386 phosphoproteins and 5,940 phosphosites, of which 4,235 sites of 1,963 phosphoproteins were quantified. From SY to F6 follicles, 190 phosphorylation sites of 149 proteins changed significantly, among which the phosphorylation level of lysine demethylase 1 A (LSD1) at the conserved 54^th serine (LSD1Ser54p) was significantly upregulated in F6 follicles compared to SY follicles (p < 0.05); however, the expression of chicken LSD1 were not significantly different on both mRNA and protein levels. LSD1Ser54p is mainly located in the nucleus of both SY and F6 follicles, and was higher in F6 follicles than that of SY follicles revealed by both immunofluorescence and Western blotting. LSD1Ser54p level increased after treatment with 5 ng/mL and 10 ng/mL of FSH in the theca cells and the granulosa cells of pre-hierarchal follicles, and with 50 ng/mL in granulosa cells of hierarchal follicles. In the theca cells of hierarchal follicles, estrogen stimulated the level of LSD1Ser54p in a dosage-dependent manner, and in granulosa cells of pre-hierarchal follicles, 10 ng/mL of estrogen increased LSD1Ser54p expression. Treatment with 50 ng/mL of progesterone increased LSD1Ser54p expression in theca cells of pre-hierarchal follicles, and with 10 to 100 ng/ml enhanced LSD1Ser54p expression in the granulosa cells of hierarchal follicles.

CONCLUSION

The expression dynamics of LSD1Ser54p in follicles from SY to F6 and its regulation by sex hormones suggest that it is involved in chicken follicle selection.

The adiponectin receptor agonist, AdipoRon, promotes reproductive hormone secretion and gonadal development via the hypothalamic-pituitary-gonadal axis in chickens

Adiponectin is a key hormone secreted by fat tissues that has multiple biological functions, including regulating the energy balance and reproductive system by binding to its receptors AdipoR1 and AdipoR2. This study investigated the correlation between the levels of adiponectin and reproductive hormones in the hypothalamic-pituitary-ovarian (HPO) axis of laying hens at 4 different developmental stages (15, 20, 30, and 68 wk) and explored the effects of AdipoRon (an activator of adiponectin receptors) on the hypothalamic-pituitary-gonadal (HPG) axis and follicle and testicular Leydig cells in vitro and in vivo. The results demonstrated that the adiponectin level was significantly correlated with that of reproductive hormones in the HPO axis (e.g., GnRH, FSH, LH, and E2) in laying hens at 4 different ages. Moreover, AdipoRon could promote the expression of AdipoR1 and AdipoR2 and the secretion of reproductive hormones in the HPG axis, including GnRH, FSH, LH, P4, and T. AdipoRon could also upregulate the expression of genes related to follicular steroidogenesis (STAR, CYP19A1, CYP17A1, and CYP11A1), hepatic lipid synthesis (OVR, MTP), follicular lipid uptake (PPAR-g), and follicular angiogenesis (VEGFA1, VEGFA2, VEGFR1, ANGPT1, ANGPT2, TEK) in the oviposition period, and all of these findings were consistent with the results obtained from in vitro experiments after the transfection of small white follicles (SWFs) with AdipoRon. Furthermore, the results suggest that AdipoRon increases the diameter of testicular seminiferous tubules, the number of spermatogenic cells and sperm production in vivo and enhances the expression of AdipoR1, AdipoR2 and steroid hormones in vitro. Collectively, the findings suggest that AdipoRon could facilitate the expression and secretion of reproductive hormones in the HPG axis by activating its receptors and then improve the growth and development of follicles and testes in chickens.

Integrated ONT Full-Length Transcriptome and Metabolism Reveal the Mechanism Affecting Ovulation in Muscovy Duck (Cairina moschata)

Ovulation is a complicated physiological process that is regulated by a multitude of different pathways. In comparison to mammalian studies, there are few reports of ovulation in Muscovy ducks, and the molecular mechanism of ovarian development remained unclear. In order to identify candidate genes and metabolites related to Muscovy duck follicular ovulation, the study combined Oxford Nanopore Technologies (ONT) full-length transcriptome and metabolomics to analyze the differences in gene expression and metabolite accumulation in the ovaries between pre-ovulation (PO) and consecutive ovulation (CO) Muscovy ducks. 83 differentially accumulated metabolites (DAMs) were identified using metabolomics analysis, 33 of which are related to lipids. Combined with data from previous transcriptomic analyses found that DEGs and DAMs were particularly enriched in processes including the regulation of glycerophospholipid metabolism pathway, arachidonic acid metabolic pathway and the steroid biosynthetic pathway. In summary, the novel potential mechanisms that affect ovulation in Muscovy ducks may be related to lipid metabolism, and the findings provide new insights into the mechanisms of ovulation in waterfowl and will contribute to a better understanding of changes in the waterfowl ovarian development regulatory network.

Protective Effect of Follicle-Stimulating Hormone on DNA Damage of Chicken Follicular Granulosa Cells by Inhibiting CHK2/p53

The increase in follicular atresia and the decrease in the fecundity of laying hens occur with the aging process. Therefore, the key measure for maintaining high laying performance is to alleviate follicular atresia in the aging poultry. Follicle-stimulating hormone (FSH), as an important pituitary hormone to promote follicle development and maturation, plays an important role in preventing reproductive aging in diverse animals. In this study, the physiological state of the prehierarchical small white follicles (SWFs) and atretic SWFs (ASWFs) were compared, followed by an exploration of the possible capacity of FSH to delay ASWFs’ progression in the hens. The results showed that the DNA damage within follicles increased with aging, along with Golgi complex disintegration, cell cycle arrest, increased apoptosis and autophagy in the ASWFs. Subsequently, the ACNU-induced follicular atresia model was established to evaluate the enhancing capacity of FSH on increasing cell proliferation and attenuating apoptosis in ASWFs. FSH inhibited DNA damage and promoted DNA repair by regulating the CHK2/p53 pathway. Furthermore, FSH inhibited CHK2/p53, thus, suppressing the disintegration of the Golgi complex, cell cycle arrest, and increased autophagy in the atretic follicles. Moreover, these effects from FSH treatment in ACNU-induced granulosa cells were similar to the treatment by a DNA repair agent AV-153. These results indicate that FSH protects aging-resulted DNA damage in granulosa cells by inhibiting CHK2/p53 in chicken prehierarchical follicles.

CircRNA expression in chicken granulosa cells illuminated with red light

Red light (RL) can improve egg production in Jinghai Yellow hens. Circular RNAs (circRNAs) are novel, non-coding RNAs, but the molecular mechanism underlying circRNA function during follicular development in hens under monochromatic light has not been established. Herein, we compared expression profiles of granulosa cells (GCs) from small yellow follicles (SYFs) from hens under RL and white light (WL). A total of 2,468 circRNAs were identified, of which 22 were differentially expressed (DE) in the RL and WL groups. DE circRNA host genes were enriched in ovarian steroidogenesis, and MAPK and PI3K-Akt signaling pathways. Furthermore, DE circRNA_0320 and circRNA_0185 interacted with miR-143-3p, which targets the follicle-stimulating hormone receptor and is essential for GC differentiation and follicle development. These findings will facilitate further analysis of the molecular mechanism leading to GC development in hens raised under monochromatic light, which could lead to increased egg production.

Transcriptome Analysis Reveals miR-302a-3p Affects Granulosa Cell Proliferation by Targeting DRD1 in Chickens

Egg production is an important economic trait in laying chickens as higher yields bring higher profits. Small yellow follicle (SYFL) development is a key determinant of chicken reproductive performance; however, the majority of SYFLs are not selected during the process of chicken reproduction and thus, atresia occurs. Although there have been numerous omic studies focused on egg production, the molecular mechanisms involved are still not well-understood. In this study, we used high-throughput technology to analyze the differences between the SYFL mRNA transcriptomes of high– (H) and low–egg-yielding (L) Taihang layer hens, with the aim of identifying the potential candidate genes involved in controlling the rate of egg production. We constructed six cDNA libraries, three from H and three from L Taihang hens and then performed high-throughput sequencing. Comparison of the H and L groups showed 415 differentially expressed genes (DEGs). In the high-yield group, 226 were upregulated and 189 were downregulated. Differentially enriched biological functions and processes were identified using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) database analysis. Ten of the candidate DEGs we identified (DRD1, MC5R, PCK1, CTSA, TGFBR3, AGO4, SLIT2, RGS1, SCNN1B, and ZP3) have been identified in previous studies as being involved in the development of small yellow follicles. DRD1 was significantly enriched in the gap junction pathway, which is an important pathway in chicken granulosa cells (GCs) to pass nutrition to an oocyte. Homology analysis showed that DRD1 was highly conserved in numerous species, indicating that it may be a productive target for improving egg production. Evidence from bioinformatics analysis revealed that gga-miR-302a-3p putatively targets the 3′UTR region of DRD1. We then identified the functions of gga-miR-302a-3p in follicular granulosa cell proliferation by targeting DRD1. RT-qPCR analysis showed that DRD1 and miR-302a-3p expression were inversely related in the SYLs of high and low egg-yielding chickens. Luciferase assays showed that miR-302a-3p targets the 3′UTR of DRD1, and overexpression of miR-302a-3p significantly inhibits the expression of DRD1 in chicken GCs (p < 0.01). Functional experiments revealed that by targeting DRD1, miR-302a-3p acts as an inhibitor of GC proliferation. Taken together, we concluded that miR-302a-3p affects chicken GC proliferation by targeting DRD1. Our data expanded the knowledge base of genes whose functions are important in egg production and the molecular mechanisms of high-yield egg production in chicken small yellow follicles.

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.

Proteomic Analysis Identifies Potential Markers for Chicken Primary Follicle Development

Simple Summary

Our study presents a comprehensive approach elaborating the mechanism of primary follicle development in the chicken. The identified differentially expressed proteins of small and developing primary follicles (SPFs and DPFs) could be used as potential markers in chicken primary follicle development. The DEPs have their functional involvement in different processes including glycolysis, pyruvate metabolism, amino acid synthesis, and oocyte meiosis. The Anxa2, Pdia3, and Capzb have a connotation in primary follicle development. These findings were validated by real-time quantitative PCR and provided a basis for the exploration of DEPs as suitable makers related to the primary follicle development in chicken.

Abstract

Follicles’ development in chicken imparts a major impact on egg production. To enhance the egg-laying efficiency, comprehensive knowledge of different phases of follicular development is a prerequisite. Therefore, we used the tandem mass tag (TMT) based proteomic approach to find the genes involved in the primary follicular development of chicken. The primary follicles were divided into two groups—small primary follicles (81–150 μm) and developed primary follicles (300–500 μm). Differential expression analysis (fold change > 1.2, p-value < 0.05) revealed a total of 70 differentially expressed proteins (DEPs), of which 38 were upregulated and 32 were downregulated. Gene ontology (GO) enrichment analysis disclosed that DEPs were intricate with cellular protein localization, the establishment of protein localization, and nucleoside phosphate-binding activities. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment pathway indicated the involvement of DEPs in different metabolic pathways such as glycolysis, pyruvate metabolism, galactose metabolism, and fructose and mannose metabolism. The current proteomic analysis suggested suitable markers such as Anxa2, Pdia3, and Capzb, which may serve as a potential role for primary follicle development. The present study provides the first insight into the proteome dynamics of primary follicle development and would play a potential role for further studies in chicken to improve egg productivity.

Histomorphology and gene expression profiles during early ovarian folliculogenesis in duck and goose

In contrast to the later stages of follicle development, little is known about the characteristics and mechanisms associated with early folliculogenesis in avian species. The objectives of the present study were to examine and compare the histomorphological and molecular changes of primordial, primary, and secondary follicles from duck and goose ovaries during the first 6 post-hatching week. Morphological analysis showed that the length and width of both duck and goose ovaries increased steadily during weeks 1 to 5 but increased acutely at week 6, whereas a greater increment was observed in the ovarian length of ducks than that of geese during weeks 4 to 5. Furthermore, smaller diameters of the 3 categories of follicles were observed in ducks than those in geese at the first appearance, but they reached a similar size at week 6. More importantly, secondary follicles were found in the ovaries of ducks 1 wk earlier than in those of geese. These results indicated a more rapid growth rate for ovarian follicles in ducks than in geese during early post-hatching development. At the molecular level, it was found that the mRNAs encoding follicle stimulating hormone receptor (FSHR), anti-Müllerian hormone (AMH), B-cell leukemia/lymphoma 2, and cysteine-dependent aspartate specific protease 3 (CASPASE3) were ubiquitously expressed in all ovarian follicles of ducks and geese with different expression profiles in each follicular category during the first 6 post-hatching week. Notably, transcript levels of FSHR, AMH, and CASPASE3 changed differently between ducks and geese during weeks 5 to 6, which was postulated to be one of the mechanisms inducing more rapid growth of ovarian follicles in ducks rather than in geese. In conclusion, our results revealed, for the first time, differences in early folliculogenesis, including the rate of growth of each follicular category and the timing of transition of primary to secondary follicles, between ducks and geese, and these differences could result from different expression profiles of FSHR, AMH, and CASPASE3 during early post-hatching development.

Effect of eCG treatment on gene expression of selected matrix metalloproteinases (MMP-2, MMP-7, MMP-9, MMP-10, and MMP-13) and the tissue inhibitors of metalloproteinases (TIMP-2 and TIMP-3) in the chicken ovary

Several metalloproteinases (MMPs) are present and functional in the chicken ovary and regulate the extracellular matrix (ECM) during follicle development, ovulation, atresia, and regression. The regulation of the abundance of MMPs in avian ovarian follicles, however, is largely unknown. The aim of the present study was to examine effects of equine chorionic gonadotropin (eCG) on abundance of selected MMPs and relevant tissue inhibitors of MMPs (TIMPs) in the hen ovary. The MMP-2 and MMP-9 activity was also determined. Results indicated there were effects of eCG on abundances of MMP-2, MMP-7, MMP-9, MMP-10, MMP-13, TIMP-2, and TIMP-3 mRNA transcript and/or protein relative abundances in white, yellowish, small yellow, and the largest yellow preovulatory (F3-F1) ovarian follicles. The response to eCG depended on the stage of follicle development, layer of follicular wall, and the type of MMPs or TIMPs affected by eCG. Furthermore, there was a pause in egg laying when eCG was administered and there were morphological changes in the ovary following eCG treatment that were associated with alterations in MMP-2 and MMP-9 activity. In general, the results indicate that eCG, which has primarily follicle stimulating hormone (FSH)-like bioactivities, is a negative regulator of MMP abundance and activity in the largest yellow preovulatory follicles. Results from the present study indicate the gonadotropins, especially FSH, by the regulation of transcription, translation, and/or activity of proteins of the MMP system have effects on the mechanisms that underlie ECM remodeling and cell function throughout ovarian follicle development in the chicken ovary.

Effects of Osthole on Progesterone Secretion in Chicken Preovulatory Follicles Granulosa Cells

Simple Summary

Progesterone produced by granulosa cells regulates the diverse reproductive events in poultry. Osthole is a natural compound extracted from Cnidium. In this study, we confirmed Osthole up-regulated the progesterone secretion though elevating the expression of key proteins in the process of progesterone synthesis. These results indicate Osthole could be used in the pre-peak phase and (or) the peak phase to maximize the output of egg production in laying hens. Moreover, it provided a new idea that natural compounds may be the target library to screen the potential drugs used in poultry to increase the egg quality and yield.

Abstract

Osthole (Ost) is an active constituent of Cnidium monnieri (L.) Cusson which possesses anti-inflammatory and anti-oxidative properties. It also has estrogen-like activity and can stimulate corticosterone secretion. The present study was aimed to check the role of Ost on progesterone (P4) secretion in cultured granulosa cells obtained from hen preovulatory follicles. Different concentrations (5, 2.5, and 1.25 µg/mL) of Ost was added to granulosa cells for 6, 12, 18, and 24 h to investigate the level of progesterone secretions using enzyme linked immunosorbent assay (ELISA). The results showed that progesterone secretion was significantly increased in cells treated with Ost at 2.5 μg/mL. Also, qRT-PCR showed that mRNA expression of steroidogenic acute regulatory protein (StAR) was significantly up-regulated by Ost at 2.5 μg/mL concentration. Cytochrome P450 side-chain cleavage (P450scc) and 3β-hydroxysteroid dehydrogenase (3β-HSD) was significantly up-regulated by Ost. However, no significant differences were observed for the expression of proliferating cell nuclear antigen (PCNA). The protein expression of StAR, P450scc and 3β-HSD were significantly up-regulated by Ost treatment. The concentration of cyclic adenosine monophosphate (cAMP) and protein kinase A (PKA) in cell lysates showed no change with Ost treatment at 2.5 μg/mL by ELISA. An ROS kit showed non-significant difference in the level of reactive oxygen species (ROS). In conclusion, Ost treatment at a concentration of 2.5 μg/mL for 24 h had significantly up-regulated P4 secretion by elevating P450scc, 3β-HSD and StAR at both gene and protein level in granulosa cells obtained from hen preovulatory follicles.

Synergistic inhibition of csal1 and csal3 in granulosa cell proliferation and steroidogenesis of hen ovarian prehierarchical development†

SALL1 and SALL3 are transcription factors that play an essential role in regulating developmental processes and organogenesis in many species. However, the functional role of SALL1 and SALL3 in chicken prehierarchical follicle development is unknown. This study aimed to explore the potential role and mechanism of csal1 and csal3 in granulosa cell proliferation, differentiation, and follicle selection within the prehierarchical follicles of hen ovary. Our data demonstrated that the csal1 and csal3 transcriptions were highly expressed in granulosa cells of prehierarchical follicles, and their proteins were mainly localized in the cytoplasm of granulosa cells and oocytes as well as in the ovarian stroma and epithelium. It initially revealed that both csal1 and csal3 may be involved in chicken prehierarchical follicle development via a translocation mechanism. Furthermore, our results showed an abundance of CCND1, Bcat, StAR, CYP11A1, and FSHR mRNA in granulosa cells, and the proliferation levels of granulosa cells from the prehierarchical follicles were significantly increased by siRNA-mediated knockdown of csal1 or/and csal3. Conversely, the overexpression of csal1 or/and csal3 in the granulosa cells led to a remarkably decreased of them. Moreover, csal1 and csal3 together exert a much stronger effect on the regulation than any of csal1 or csal3. These results indicated that csal1 and csal3 play synergistic inhibitory roles on granulosa cell proliferation, differentiation, and steroidogenesis during prehierarchical follicle development in vitro. The current data provide a basis of molecular mechanisms of csal1 and csal3 in controlling the prehierarchical follicle development and growth of hen ovary in vivo.

Effects of RAC1 on Proliferation of Hen Ovarian Prehierarchical Follicle Granulosa Cells

Simple Summary

The growth and development of ovary follicles is an intricate, highly organized process involving many local intra-ovarian factors. Ras-related C3 botulinum toxin substrate1 (RAC1) is speculated to be associated with prehierarchical follicle development of hen ovaries. The current study initially revealed RAC1 mRNA to be expressed in varied-size follicles and stroma and its expression levels in the prehierarchical follicles of 1.0–3.9 mm, 6.0–6.9 mm and 7.0–8.0 mm in diameter were remarkably higher than the other groups. Moreover, RAC1 protein was mainly expressed in the oocytes and granulosa cells (GC), as well as in stromal tissues of the follicles. To understand the exact roles of the RAC1 gene in regulation of follicular GC proliferation and differentiation, siRNA interference and overexpression of the RAC1 gene were conducted. Our experiments demonstrated that the RAC1 gene can significantly promote the expression of mRNA and proteins of FSHR, CCND2, CYP11A1, PCNA and StAR genes in GC and directly elevate the proliferation of GC in vitro. These results indicated RAC1 played a crucial role in regulation of GC proliferation and differentiation and steroidogenesis during the development of prehierarchical follicles. This study provided a base for elucidating the molecular mechanisms underlying the biological effect of RAC1 on the hen ovary follicle growth and development.

Abstract

RAC1 belongs to the small G protein Rho subfamily and is implicated in regulating gene expression, cell proliferation and differentiation in mammals and humans; nevertheless, the function of RAC1 in growth and development of hen ovarian follicles is still unclear. This study sought to understand the biological effects of RAC1 on granulosa cell (GC) proliferation and differentiation of hen ovarian prehierarchical follicles. Firstly, our results showed expression levels of RAC1 mRNA in the follicles with diameters of 7.0–8.0 mm, 6.0–6.9 mm and 1.0–3.9 mm were greater than other follicles (p < 0.05). The RAC1 protein was mainly expressed in oocyte and its around GCs and stromal tissues of the prehierarchical follicles by immunohistochemistry. Further investigation revealed the RAC1 gene remarkably enhanced the mRNA and protein expression levels of FSHR (a marker of follicle selection), CCND2 (a marker of cell-cycle progression and GC differentiation), PCNA (a marker of GC proliferation), StAR and CYP11A1 (markers of GC differentiation and steroidogenesis) (p < 0.05). Furthermore, our data demonstrated siRNA interference of RAC1 significantly reduced GC proliferation (p < 0.05), while RAC1 gene overexpression enhanced GC proliferation in vitro (p < 0.05). Collectively, this study provided new evidence that the biological effects of RAC1 on GC proliferation, differentiation and steroidogenesis of chicken ovary follicles.

Enhancing effect of FSH on follicular development through yolk formation and deposition in the low-yield laying chickens

Healthy and efficient development of ovarian follicles largely determines poultry laying performance. In low-yield laying chickens, retarded follicle progression resulted in decreased prehierarchical follicles. In this study the extenuating effect of follicle-stimulating hormone (FSH) on delayed follicular development was investigated in the low-yield chickens. Results showed that FSH administration in vivo accelerated development of prehierarchical follicles, with increased expression of steroidogenic enzymes and follicular angiogenesis through elevating plasma levels of 17β-estradiol, progesterone, luteinizing hormone and the expression of vascular endothelial growth factor and its receptor as well as angiopoietins. Furthermore, treatment with FSH raised expression of lipid uptake and adipogenesis-related proteins and decreased tight junctions between granulosa cells. Meanwhile, the results of the in vivo studies were confirmed by the in vitro studies as FSH promoted development of the cultured prehierarchical follicles with increased angiogenesis, cell proliferation, steroid hormones synthesis and yolk deposition. These results indicated FSH enhanced follicular development in the low-yield laying chickens involving increased follicular angiogenesis.

Determination of the roles of GREM1 gene in granulosa cell proliferation and steroidogenesis of hen ovarian prehierarchical follicles

Gremlin genes are known members of the DAN family of bone morphogenetic protein (BMP) antagonists, but their functions and regulatory mechanisms in ovarian follicular development of chicken remain unknown. The current study was designed to investigate the mRNA expression patterns of gremlin1 gene (GREM1) and its protein location in the follicles sampled, and to explore the biological effect of GREM1 on the prehierarchical follicular development. This work revealed that chicken GREM1 mRNA exhibits a constant expression level across all the prehierarchical follicles (PFs) from 1-4 mm to 7-8 mm in diameter, and the preovulatory follicles (from F6 to F1) by using RT-qPCR (P > 0.05). The GREM1 protein is predominantly expressed in the oocytes and granulosa cells (GCs) of the PFs by immunohistochemistry. Furthermore, our data demonstrated that siRNA-mediated knockdown of GREM1 in the GCs resulted in a significant reduction in cell proliferation (P < 0.001); conversely, overexpression of GREM1 in the GCs led to a remarkable increase in cell proliferation (P < 0.001). Interestingly, the expression levels of proliferating cell nuclear antigen (PCNA) and cyclin D2 (CCND2) mRNA and proteins were notably increased when GREM1 expression was upregulated in the GCs (P < 0.01), however, the expression levels of CYP11A1 and StAR were markedly downregulated (P < 0.01). The current results showed that GREM1 gene plays a stimulatory role in GC proliferation during growth and development of the prehierarchical follicles in vitro but an inhibitory role in GC differentiation and steroidogenesis of the hen ovary follicles.

Melatonin ameliorates excessive PINK1/Parkin-mediated mitophagy by enhancing SIRT1 expression in granulosa cells of PCOS

Mitochondrial injury in granulosa cells is associated with the pathogenesis of polycystic ovary syndrome (PCOS). However, the protective effects of melatonin against mitochondrial injury in the granulosa cells of PCOS remain unclear. In this study, decreased mitochondrial membrane potential and mtDNA content, increased number of autophagosomes were found in the granulosa cells of PCOS patients and the dihydrotestosterone (DHT)-treated KGN cells, with decreased protein level of the autophagy substrate p62 and increased levels of the cellular autophagy markers Beclin 1 and LC3B-II, while the protein levels of PTEN-induced kinase-1 (PINK1) and Parkin were increased and the level of sirtuin 1 (SIRT1) was decreased. DHT-induced PCOS-like mice also showed enhanced mitophagy and decreased SIRT1 mRNA expression. Melatonin treatment significantly increased the protein level of SIRT1 and decreased the levels of PINK1/Parkin, whereas it ameliorated the mitochondrial dysfunction and PCOS phenotype in vitro and in vivo. However, when the KGN cells were treated with SIRT1 siRNA to knock down SIRT1 expression, melatonin treatment failed to repress the excessive mitophagy. In conclusion, melatonin protects against mitochondrial injury in granulosa cells of PCOS by enhancing SIRT1 expression to inhibit excessive PINK1/Parkin-mediated mitophagy.

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.

Dietary calcium deficiency suppresses follicle selection in laying ducks through mechanism involving cyclic adenosine monophosphate-mediated signaling pathway

Ovarian follicle selection is a natural biological process in the pre-ovulatory hierarchy in birds that drives growing follicles to be selected within the ovulatory cycle. Follicle selection in birds is strictly regulated, involving signaling pathways mediated by dietary nutrients, gonadotrophic hormones and paracrine factors. This study aimed to test the hypothesis that dietary Ca may participate in regulating follicle selection in laying ducks through activating the signaling pathway of cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA)/extracellular signal-regulated kinase (ERK), possibly mediated by gonadotrophic hormones. Female ducks at 22 weeks of age were initially fed one of two Ca-deficient diets (containing 1.8% or 0.38% Ca) or a Ca-adequate control diet (containing 3.6% Ca) for 67 days (depletion period), then all birds were fed the Ca-adequate diet for an additional 67 days (repletion period). Compared with the Ca-adequate control, ducks fed 0.38% Ca during the depletion period had significantly decreased (P < 0.05) numbers of hierarchical follicles and total ovarian weight, which were accompanied by reduced egg production. Plasma concentration of FSH was decreased by the diet containing 1.8% Ca but not by that containing 0.38%. The ovarian content of cAMP was increased with the two Ca-deficient diets, and phosphorylation of PKA and ERK1/2 was increased with 0.38% dietary Ca. Transcripts of ovarian estradiol receptor 2 and luteinizing hormone receptor (LHR) were reduced in the ducks fed the two Ca-deficient diets (P < 0.05), while those of the ovarian follicle stimulating hormone receptor (FSHR) were decreased in the ducks fed 0.38% Ca. The transcript abundance of ovary gap junction proteins, A1 and A4, was reduced with the Ca-deficient diets (P < 0.05). The down-regulation of gene expression of gap junction proteins and hormone receptors, the increased cAMP content and the suppressed hierarchical follicle numbers were reversed by repletion of dietary Ca. These results indicate that dietary Ca deficiency negatively affects follicle selection of laying ducks, independent of FSH, but probably by activating cAMP/PKA/ERK1/2 signaling pathway.

Single nucleotide polymorphism rs737028527 (G>A) affect miR-1b-3p biogenesis and effects on chicken egg-laying traits

The abundance of miR-1b-3p in the chicken ovary is greater after sexual maturation. In the present study there was assessment of whether a single nucleotine polymorphism (SNP) led to an alteration in expression of reproductive traits. The miR-1b-3p abundance was greatest in ovarian follicles The SNP site of rs737028527 (G > A), located in the 734 bp upstream region of pre-miR-1b-3p, was identified in three different chicken breeds. Results from an association analysis of chicken egg-laying traits indicated the SNP was associated with age at first egg production (AFE) and egg number at 32 and 48 weeks (E32, E48; P < 0.01). Hens with genotype AA had an earlier AFE and greater E32 and E48 than hens with other genotypes. The abundance of mature miR-1b-3p in the hens with the GG genotype was larger than those with the AA genotype (P < 0.01), and the luciferase activity of GG genotype promoter was also greater in birds with the AA than GG genotype (P < 0.05). There was inhibition of the production of the transcription factor bound by the specificity protein 1 (Sp1) as a result of the G-to-A mutation, and the luciferase activity of the GG, but not AA, genotype was markedly increased by Sp1. In conclusion, the SNP, rs737028527 (G> A), affected the abundance of mature miR-1b-3p by Sp1 and was associated with chicken egg-laying traits. Data from the present study allow for an increased understanding of the functions and regulation of miR-1b-3p in ovarian follicle development of hens.

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.

Reproductive management of poultry

Based on data from the UN's Food and Agricultural Organization, about 120 million metric tons of poultry meat were produced globally in 2016. In addition, about 82 million metric tons of eggs were produced. One of the bases for this production is the reproductive efficiency of today's poultry. This, in turn, is due to their inherent reproductive physiology, intensive genetic selection and advances in husbandry/management. The system of reproduction in males in largely similar to that in mammals except that there is no descent of testes. In females, there are marked differences with there being a single ovary and oviduct; the latter being the name of the differentiated entire Müllerian duct. Moreover, females produce eggs with a yolky oocyte surrounded by albumen, membranes and shell. Among the most successful reproductive management techniques are optimizing photoperiod, light intensity and nutrition. Widespread employment of these has allowed maximizing production. Laying hens can be re-cycled toward the end egg production. Other aspects of reproductive management in poultry include the following: artificial insemination (almost exclusively employed in turkeys) and approaches to reduce broodiness together with cage free (colony), conventional, enriched and free-range systems.

Expression of FOXL2 and RSPO1 in Hen Ovarian Follicles and Implication of Exogenous Leptin in Modulating Their mRNA Expression in In Vitro Cultured Granulosa Cells

In this study, using a laying hen model, we determined the expression of FOXL2 and RSPO1 in different central and peripheral tissue and ovarian follicles at different stages of development. At the same time, mRNA expression of both genes in granulosa and theca cells harvested from follicles at different stages of folliculogenesis was also evaluated. Finally, we assessed the effect of leptin treatment on expression of FOXL2 and RSPO1 in in vitro cultured granulosa cells harvested from 1-5 mm to F3-F1 follicles. Our RT-qPCR results revealed that a comparatively higher expression of FOXL2 and RSPO1 was observed in ovary, hypothalamus, and pituitary. Abundant mRNA expression of FOXL2 was observed in small prehierarchical follicles (1-1.9 and 2-2.9 mm follicles; p < 0.05), whereas mRNA expression of RSPO1 showed an increasing trend in large hierarchical follicles (F5-F1), and its abundant expression was observed in post-ovulatory follicles. FOXL2 mRNA expression was stable in granulosa cells harvested from 3-5 mm to F4 follicles, and exhibited a significantly higher expression in large hierarchical follicles. Conversely, relatively low mRNA expression of FOXL2 was observed in theca cells. RSPO1 mRNA expression was relatively lower in granulosa cells; however, theca cells exhibited a significantly higher mRNA expression of RSPO1 in F4 to F1 follicles. In the next experiment, we treated the in vitro cultured granulosa cells with different concentrations (1, 10, 100, and 1000 ng/mL) of exogenous leptin. Compared to the control group, a significant increase in the expression of FOXL2 was observed in groups treated with 1, 10, and 100 ng/mL leptin, whereas expression of RSPO1 was increased in all leptin-treated groups. When treated with 100 ng/mL leptin, FOXL2 and RSPO1 expression was upregulated in cultured granulosa cells harvested from both large hierarchical (F3-F1) and small prehierarchical follicles (1-5 mm). Based on these findings and evidence from mainstream literature, we envisage that FOXL2 and RSPO1 genes (in connection with hypothalamic-hypophysis axis) and leptin (via modulation of FOXL2 and RSPO1 expression) might have significant physiological roles, at least in part, in modulating the ovarian mechanisms, such as follicle development, selection, and steroidogenesis in laying hens.

Basic fibroblast growth factor promotes prehierarchical follicle growth and yolk deposition in the chicken

Basic fibroblast growth factor (bFGF) plays a pivotal role in prompting ovarian follicular development and angiogenesis as well as inhibiting atresia. In the chicken, high laying performance depends largely on efficient healthy development of ovarian follicles. Moreover, rapid growth of oocytes resulted from abundant yolk deposition via blood circulation and intra-ovarian interactions among somatic and germ cells. The major components of yolk mass consist of very low density lipoprotein (VLDL) and vitellogenin that are taken up by maturing oocytes via VLDL receptor (VLDLR)-mediated endocytosis from blood capillaries in the theca layer and gaps between granulosa cells. Here we used immunofluorescence, BrdU, TUNEL, Western bolt and RT-qPCR methods to investigate effects of bFGF on growth and yolk deposition of chicken prehierarchical follicles. Results showed that VLDLR was mainly expressed in the granulosa cells of the prehierarchical and preovulatory follicles, and its expression declined with follicle growth. Moreover, bFGF caused a dose-dependent promoting effect on growth of small white follicles and this effect was inhibited by SU5402 (an FGFR1 antagonist). Proliferation of follicular theca externa cells was accelerated by bFGF via FGFR1-AKT signaling, coupled with augmented angiogenesis and up-regulated p-ERK expression in granulosa cells. After combined inhibition of FGFR1 and PPARγ, we found that PPARγ could also suppress VLDLR expression in granulosa cells. These results indicate that bFGF facilitated growth and yolk deposition in chicken prehierarchical follicles through promoting proliferation and angiogenesis in theca layers, and also through down-regulating VLDLR expression in granulosa cells.

Growth differentiation factor 9 promotes follicle-stimulating hormone-induced progesterone production in chicken follicular granulosa cells

The function of oocyte-derived growth differentiation factor 9 (GDF9) in ovarian follicles has thus far been poorly defined in avian species compared with the defined function in mammals. Our aim here is to investigate the effects of GDF9 on steroidogenesis and on chicken ovarian granulosa cell (GC) mitosis. Primary GCs from both prehierarchical (6-8 mm in diameter, phGCs) and preovulatory follicles (F1-F5, poGCs) were cultured in the presence or absence of the GDF9 protein. The progesterone (P4) levels in the culture medium were then measured by radioimmunoassay (RIA), and the expression levels of steroidogenesis genes were detected by quantitative PCR. We found that GDF9 alone showed no significant effect on the P4 levels by regulating the expression of steroidogenesis genes, such as STAR, CYP11A1 and HSD3B. Further experiments indicated that GDF9 promoted follicle-stimulating hormone (FSH)-induced P4 production and STAR expression. GDF9 also rescued the FSH-induced decrease of FSH receptor (FSHR) expression but had no effect on the forskolin-induced P4, STAR and forskolin-inhibited FSHR expression levels, suggesting that GDF9 might achieve its regulatory role of P4 by enhancing FSHR and STAR expression. In addition, GDF9 also promoted GC cell cycle progression, regulated the gene transcription of related genes, potentiated DNA replication and inhibited apoptosis. Interestingly, these effects differed between the phGCs and the poGCs. To our knowledge, this is the first report that illustrates the function of GDF9 on chicken GCs and the effects on ovarian steroidogenesis. Our findings highlight the regulation of central oocytes on the surrounding granulosa cells and emphasize the interaction between paracrine signals and endocrine hormones on ovarian progesterone production; these findings contribute to the understanding of the development of avian ovarian follicles.

The Role of PTHLH in Ovarian Follicle Selection, Its Transcriptional Regulation and Genetic Effects on Egg Laying Traits in Hens

In hens, follicle selection is an important process affecting egg laying traits. This study investigated the role of parathyroid hormone-like hormone (PTHLH) in chicken follicle selection, its transcriptional regulation and genetic effects on egg laying traits. PTHLH and its receptor PTH1R were mainly expressed in follicles of 6–8 mm in diameter, exhibits differential expression pattern in the theca and granulosa cells of pre- and hierarchal follicles. PTHLH stimulates the proliferation of follicular granulosa and theca cells, the expression of StAR and CYP11A1 mRNA and the production of progesterone (P4) in pre-hierarchal follicles. Treatment with FSH increased PTHLH mRNA expression in pre-hierarchal follicular theca cells and hierarchal follicular granulosa cells. Two critical regions regulating chicken PTHLH transcription were revealed, each of which harbored a SNP: C>T (chr1: 72530014) for AP-1 and a SNP: A>G (chr1: 72531676). Hens with diplotype AC/GT were younger at first laying and laid more eggs at 32 weeks. The haplotype (G^-1827T^-165) with double mutations had the greatest promoter activity of chicken PTHLH transcription. Collectively, PTHLH plays an important role in chicken follicle selection by stimulating cell proliferation and steroidogenesis. Polymorphisms in chicken PTHLH promoter region are associated with egg laying traits by affecting the binding of transcription factor AP-1.

The Role of microRNAs in Ovarian Granulosa Cells in Health and Disease

The granulosa cell (GC) is a critical somatic component of the ovary. It is essential for follicle development by supporting the developing oocyte, proliferating and producing sex steroids and disparate growth factors. Knowledge of the GC's function in normal ovarian development and function, and reproductive disorders, such as polycystic ovary syndrome (PCOS) and premature ovarian failure (POF), is largely acquired through clinical studies and preclinical animal models. Recently, microRNAs have been recognized to play important regulatory roles in GC pathophysiology. Here, we examine the recent findings on the role of miRNAs in the GC, including four related signaling pathways (Transforming growth factor-β pathway, Follicle-stimulating hormones pathway, hormone-related miRNAs, Apoptosis-related pathways) and relevant diseases. Therefore, miRNAs appear to be important regulators of GC function in both physiological and pathological conditions. We suggest that targeting specific microRNAs is a potential therapeutic option for treating ovary-related diseases, such as PCOS, POF, and GCT.

Response of hen pre-recruitment ovarian follicles to follicle stimulating hormone, in vivo

In laying hens, pre-recruitment ovarian follicles (1-8 mm diameter) are arranged as a continuum of size and predicted maturity. Cyclic recruitment of a pre-recruitment follicle to the preovulatory stage begins, in part, by the ability of the granulosa cell (GC) layer to initiate responsiveness to follicle stimulating hormone- (FSH-) induced cyclic adenosine monophosphate. The objective of this study was to determine if increased circulating concentrations of FSH during the ovulatory cycle increase the number of recruited follicles, in a dose-dependent manner. Equine chorionic gonadotropin (eCG) was initially tested due to its FSH-like properties and long half-life. Laying hens were injected, i.m., with 0 or 100 IU eCG, and ovaries were collected 29 h later. Recruited follicles were initially identified based on incorporation of yellow yolk and a weight of 250-900 mg. Recruitment was subsequently confirmed by both incubating the GC layer for 3 h with recombinant human (rh) FSH to establish FSH-responsiveness and quantifying P450 side-chain cleavage enzyme (CYP11A1) mRNA. Additional hens were injected with 0, 30, 75, and 300 IU eCG to establish a dose-response. Because eCG exhibits some luteinizing hormone activity, FSH-induced recruitment was evaluated by injecting 0.1, 0.33, 0.66, 1 or 3.3 µg rhFSH. Ovaries were collected 29 h post-injection, and expression of CYP11A1 mRNA was quantitated in GCs from recruited and pre-recruitment follicles. One hundred IU eCG induced recruitment of 2-8 follicles compared to a single follicle in control hens. In contrast to pre-recruitment follicles, incubated GC from eCG-recruited follicles had initiated differentiation, indicated by increased CYP11A1 and rhFSH-induced STAR mRNA and progesterone. Equine CG and rhFSH each increased the number of recruited follicles in a dose-dependent manner. Further, CYP11A1 mRNA was significantly increased in GC layers from recruited, compared to non-recruited, follicles. We conclude that FSH-responsiveness within the GC layer of each pre-recruitment follicle increases with follicle size, and propose that this establishes the order of daily follicle recruitment.

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.

Analyzing the Transcriptome Profile of Human Cumulus Cells Related to Embryo Quality via RNA Sequencing

Selecting excellent oocytes is required to improve the outcomes of in vitro fertilization (IVF). Cumulus cells (CCs) are an integral part of the oocyte maturation process. Therefore, we sought to identify differentially expressed genes in CCs to assess oocyte quality and embryo development potential. We divided the participants' embryos into the high-quality embryo group and low-quality embryo group by the information including age, body mass index, and the levels of luteinizing hormone, follicle-stimulating hormone, estradiol, and progesterone. We analyzed a total of 7 CC samples after the quality control in RNA sequencing. We found that 2499 genes were unregulated and 5739 genes were downregulated in high-quality embryo group compared to the low-quality embryo group (Padj < 0.05). Interestingly, MSTN, CTGF, NDUFA1, VCAN, SCD5, and STAR were significantly associated with the quality of embryo. In accordance with the results of RNA sequencing, the association of the expression levels of MSTN, CTGF, NDUFA1, VCAN, SCD5, and STAR with the embryo quality was verified by quantitative reverse-transcription polymerase chain reaction (RT-qPCR) in 50 CC samples. Despite the small sample size and lack of validation in animal models, our study supports the fact that differential gene expression profile of human CCs, including MSTN, CTGF, NDUFA1, VCAN, SCD5, and STAR, can serve as potential indicator for embryo quality.

Inhibitory effect of SLIT2 on granulosa cell proliferation mediated by the CDC42-PAKs-ERK1/2 MAPK pathway in the prehierarchical follicles of the chicken ovary

The SLIT2 ligand and ROBO receptors of the SLIT/ROBO pathway are expressed in hen ovarian follicles and have been shown to play critical roles in ovary development, cell proliferation and apoptosis in mammals. However, the exact roles of SLIT2 and the molecular mechanisms of chicken follicle development remain poorly understood. Here, we discovered that high levels of SLIT2 suppress FSHR, GDF9, STAR and CYP11A1 mRNA and protein expression in granulosa cells (GCs) and cell proliferation (p < 0.01). However, these inhibitory effects can be abolished by the siRNA-mediated knockdown of the ROBO1 and ROBO2 receptors. Furthermore, the activity of CDC42, which is a key Rho GTPase in the SLIT/ROBO pathway, is regulated by the ligand SLIT2 because the intrinsic GTPase activation activity of CDC42 is activated or repressed by regulating SRGAP1 expression (p < 0.01). The effects of the SLIT2 overexpression on GC proliferation and phosphorylation of the B-RAF, RAF1 and ERK1/2 kinases were completely abrogated by knocking down endogenous PAK1 and partially abrogated by the knockdown of PAK2 and PAK3 in the GCs. Collectively, our findings indicate that SLIT2 suppresses GC proliferation, differentiation and follicle selection mainly by a mechanism involving ROBO1 and ROBO2 and that this suppression is mediated by the CDC42-PAKs-ERK1/2 MAPK signaling cascade in the prehierarchical follicles of the chicken ovary.

Interferon-γ acts as a regulator in the trade-off between phagocytosis and production performance in dwarf chickens

Background

Interferon-γ (IFN-γ) is critical for innate and adaptive immunity against viral and bacterial infections. IFN-γ reportedly affects the phagocytic ability of monocytes and macrophages as well as regulates pituitary function in humans and mice. The present study analyzed the impact of IFN-γ on monocyte and macrophage phagocytosis, production performance, and pituitary function in vivo and in vitro (in dwarf chickens). IFN-γ was injected into dwarf chickens through a vein, and then, the laying rate, average egg weight, and levels of follicle-stimulating hormone (FSH) and IFN-γ were measured in treatment and control groups. For the in vitro experiment, the pituitary tissues were supplemented with IFN-γ, and the mRNA expression levels of follicle-stimulating hormone beta subunit (FSH-β), interferon gamma receptor 1 (IFNGR1), and interferon gamma receptor 2 (IFNGR2) in the pituitary were assessed.

Results

Monocyte and macrophage phagocytosis product (PP) was decreased by IFN-γ treatment in a dose-dependent manner in vitro. In the in vivo experiment, the level of IFN-γ in the treatment group was higher than that in the control group at 7 d (P < 0.05), 14 d (P < 0.01), and 21 d (P < 0.01) post-injection. Compared with the control group, monocyte and macrophage PP was lower in the treatment group after injection (P < 0.01). The laying rate was higher in the treatment group than in the control group at 2 and 3 wk post-injection (P < 0.05). There was a significant difference between the treatment and control groups in the levels of FSH at 1, 3, 7, and 14 d post-injection (P < 0.01). In the in vitro experiment, increased mRNA expression levels of FSH-β, IFNGR1, and IFNGR2 were observed in the treatment group after stimulation with 100 U/mL IFN-γ for 24 h compared to those in the control group (P < 0.05).

Conclusions

IFN-γ inhibited the phagocytosis of monocytes and macrophages; up-regulated the mRNA expression levels of the FSH-β, IFNGR1, and IFNGR2; enhanced the secretion of FSH; and improved the laying rate. IFN-γ might be an important regulator in the trade-off between the immune effect and production performance in dwarf chickens.

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.

Characterization of NMB, GRP and their receptors (BRS3, NMBR and GRPR) in chickens

The two structurally and functionally related peptides, gastrin-releasing peptide (GRP) and neuromedin B (NMB) play critical roles in many physiological/pathological processes in mammals. However, the information regarding the expression and functionality of avian NMB, GRP and their receptors is limited. Here, we characterized cNMB, cGRP and their receptors (cNMBR, cGRPR and cBRS3) in chickens. Our results showed that: (1) cNMBR and cGRPR expressed in CHO cells could be potently activated by cNMB and cGRP, respectively, as monitored by cell-based luciferase reporter assays, indicating that cNMBR and cGRPR are cNMB- and cGRP-specific receptors; strikingly, BRS3 of chickens (/spotted gars), which is orthologous to mouse bombesin receptor subtype-3 (BRS3), could be potently activated by GRP and NMB, demonstrating that both peptides are the endogenous ligands for chicken (/spotted gar) BRS3; (2) quantitative real-time PCR (qPCR) revealed that cGRPR is widely expressed in chicken tissues with abundant expression in the ovary, pancreas, proventriculus, spinal cord and brain, whereas cNMB, cNMBR and cBRS3 are mainly expressed in the brain and testes; (3) interestingly, qPCR, Western blot and immunostaining revealed that cGRP is predominantly expressed in the anterior pituitary and mainly localized to LH-cells, suggesting that cGRP is likely a novel pituitary hormone in chickens. In summary, our data help to uncover the roles of GRP, NMB and their receptors in birds, and provide the first persuasive evidence from an evolutionary prospective that in vertebrates, GRP and NMB are the endogenous ligands for BRS3, an orphan receptor that has puzzled endocrinologists for more than two decades.

Transcriptome Analysis on Single Small Yellow Follicles Reveals That Wnt4 Is Involved in Chicken Follicle Selection

Ovarian follicle selection is an important process impacting the laying performance and fecundity of hens, and is regulated by follicle-stimulating hormone (FSH) through binding to its receptor [follicle-stimulating hormone receptor (FSHR)]. In laying hens, the small yellow follicle (6-8 mm in diameter) with the highest expression of FSHR will be recruited into the preovulatory hierarchy during ovarian follicle development. The study of molecular mechanism of chicken follicle selection is helpful for the identification of genes underlying egg-laying traits in chicken and other poultry species. Herein, the transcriptomes of chicken small yellow follicles differing in the mRNA expression of FSHR were compared, and a total of 17,993 genes were identified in 3 pairs of small yellow follicles. The Wnt signaling pathway was significantly enriched in the follicles with the greatest fold change in FSHR expression. In this pathway, the expression level of Wnt4 mRNA was significantly upregulated with a log₂(fold change) of 2.12. We further investigated the expression, function, and regulation of Wnt4 during chicken follicle selection and found that Wnt4 mRNA reached its peak in small yellow follicles; Wnt4 stimulated the proliferation of follicular granulosa cells (GCs), increased the expression of StAR and CYP11A1 mRNA in prehierarchical and hierarchical follicles, increased the expression of FSHR mRNA, and decreased the expression of anti-Müllerian hormone and OCLN mRNA. Treatment with FSH significantly increased Wnt4 expression in GCs. Moreover, Wnt4 facilitated the effects of FSH on the production of progesterone (P4) and the mRNA expression of steroidogenic enzyme genes in the GCs of hierarchical follicles, but inhibited the effects of FSH in the GCs of prehierarchical follicles. Collectively, these data suggest that Wnt4 plays an important role in chicken follicle selection by stimulating GC proliferation and steroidogenesis. This study provides a theoretical basis for improving the egg-laying performance of chicken and a reference for the elucidation of the molecular mechanism of follicular selection in mammals.