Epidermal growth factor (EGF) receptor ligands in the chicken ovary: I. Evidence for heparin-binding EGF-like growth factor (HB-EGF) as a potential oocyte-derived signal to control granulosa cell proliferation and HB-EGF and kit ligand expression

The Multiple Functions of HB-EGF in Female Reproduction and Related Cancer: Molecular Mechanisms and Targeting Strategies

Heparin-binding growth factor (HB-EGF) is a member of the epidermal growth factor (EGF) ligand family which has a crucial role in women's health. However, there is a lack of comprehensive review to summarize the significance of HB-EGF. Therefore, this work first described the expression patterns of HB-EGF in the endometrium and ovary of different species and gestational time. Then, the focus was on exploring how it promotes the successful implantation and regulates the process of decidualization and the function of ovarian granulosa cells as an intermediate molecule. Otherwise, we also focused on the clinical and prognostic significance of HB-EGF in female-related cancers (including ovarian cancer, cervical cancer, and endometrial cancer) and breast cancer. Lastly, the article also summarizes the current drugs targeting HB-EGF in the treatment of ovarian cancer and breast cancer. Overall, these studies found that the expression of HB-EGF in the endometrium is spatiotemporal and species-specific. And it mediates the dialogue between the blastocyst and endometrium, promoting synchronous development of the blastocyst and endometrium as an intermediate molecule. HB-EGF may serve as a potentially valuable prognostic clinical indicator in tumors. And the specific inhibitor of HB-EGF (CRM197) has a certain anti-tumor ability, which can exert synergistic anti-tumor effects with conventional chemotherapy drugs. However, it also suggests that more research is needed in the future to elucidate its specific mechanisms and to accommodate clinical studies with a larger sample size to clarify its clinical value.

CircRAB11A act as miR-24-5p sponge promotes proliferation and resists apoptosis of chicken granulosa cell via EGFR/ERK1/2 and RAB11A/ PI3K/AKT pathways

Circular RNAs (circRNAs) are a class of endogenous non-coding RNAs that have been implicated in mediating granulosa cell (GC) proliferation and apoptosis. CircRAB11A was found to have a significantly higher expression in normal follicles compared to atrophic follicles. In this study, we determined that the knockdown of circRAB11A resulted in the inhibition of proliferation and promotion of apoptosis in GCs of chicken. Moreover, circRAB11A was found to act as a sponge for miR-24-5p, both member RAS oncogene family (RAB11A) and epidermal growth factor receptor (EGFR) were revealed to be targets of miR-24-5p through a dual-luciferase reporter assay. RAB11A or EGFR promoted proliferation and suppressed apoptosis in GCs through the phosphatidylinositol-kinase (PI3K)/AKT or extracellular signal-regulated kinase (ERK)1/2 pathway. These findings suggest that circRAB11A may function as a competing endogenous RNA (ceRNA) by targeting the miR-24-5p/RAB11A and miR-24-5p/EGFR axes and activating the ERK1/2 and PI3K/AKT pathways, offering a potential avenue for exploring the mechanism of follicle development.

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.

Vitrified turkey ovarian tissue cultured and assessed through gene expression patterns: A potential screening tool

Biobanking of turkey ovarian tissue has the potential to play a crucial part in preserving female genetics. To date, ovarian tissue has only been vitrified using a standard protocol, with immediate analyses after warming, therefore, long-term cryoinjury is unknown. Long-term cryoinjury was investigated here by in-ovo culturing, fresh (non-vitrified), a purposefully suboptimal poor vitrification (PV), and the standard vitrified (StV) protocol. Assessments were performed via cellular morphological changes and mRNA gene expression differences, immediately (day 0) or after 2, 4, or 6 days of in-ovo culturing. On day 0, the mRNA levels of heat-shock protein A2 (HSPA2) were lowest in the fresh tissue, and increased 5-fold in the StV treatment, and 18-fold in the PV treatment. Whereas, by day 6, growth determining factor 9 (GDF9) mRNA levels within the fresh tissue were over 3-fold and 21-fold higher than StV and PV treatments, respectively. After 6 days of in-ovo culture the follicle density was highest in the fresh ovarian tissue (4701 ± 950 #/mm3), followed by the StV (1601 ± 300 #/mm3), with PV having the lowest density (172 ± 145 #/mm3). This shows that although the density of follicles was higher in StV versus PV, a considerable number (∼65 %) were lost compared to the fresh treatment. Additionally, the HSPA2 expression could be an early screening tool, whereas GDF9 expression could be a late screening tool, used to assess turkey ovarian tissue vitrification protocols. We conclude that the StV protocol should be further optimized to try and improve follicle numbers post-warming.

Regulation of Follicular Development in Chickens: WIF1 Modulates Granulosa Cell Proliferation and Progesterone Synthesis via Wnt/β-Catenin Signaling Pathway

Proliferation, apoptosis, and steroid hormone secretion by granulosa cells (GCs) and theca cells (TCs) are essential for maintaining the fate of chicken follicles. Our previous study showed that the Wnt inhibitor factor 1 (WIF1) plays a role in follicle selection. However, the significance of WIF1 in GC- and TC-associated follicular development was not explicitly investigated. This study found that WIF1 expression was strongly downregulated during follicle selection (p < 0.05) and was significantly higher in GCs than in TCs (p < 0.05). WIF1 inhibits proliferation and promotes apoptosis in GCs. Additionally, it promotes progesterone secretion in prehierarchal GCs (pre-GCs, 1.16 ± 0.05 ng/mg vs. 1.58 ng/mg ± 0.12, p < 0.05) and hierarchal GCs (hie-GCs, 395.00 ng/mg ± 34.73 vs. 527.77 ng/mg ± 27.19, p < 0.05) with the participation of the follicle-stimulating hormone (FSH). WIF1 affected canonical Wnt pathways and phosphorylated β-catenin expression in GCs. Furthermore, 604 upregulated differentially expressed genes (DEGs) and 360 downregulated DEGs in WIF1-overexpressed GCs were found through RNA-seq analysis (criteria: |log2⁡(FoldChange)| > 1 and p_adj < 0.05). Cytokine-cytokine receptor interaction and the steroid hormone biosynthesis pathway were identified. In addition, the transcript of estrogen receptor 2 (ESR2) increased significantly (log2⁡(FoldChange) = 1.27, p_adj < 0.05). Furthermore, we found that WIF1 regulated progesterone synthesis by upregulating ESR2 expression in GCs. Additionally, WIF1 suppressed proliferation and promoted apoptosis in TCs. Taken together, these results reveal that WIF1 stimulates follicle development by promoting GC differentiation and progesterone synthesis, which provides an insight into the molecular mechanism of follicle selection and egg-laying performance in poultry.

Growth factors and female reproduction in vertebrates

Female reproductive efficiency is influenced by the outcomes of various processes, including folliculogenesis, apoptosis, response to gonadotropin signaling, oocyte maturation, and ovulation. The role of hormones in regulating these processes and other reproductive activities has been well established. It is becoming increasingly evident that in addition to well-characterized hormones, growth factors play vital roles in regulating some of these reproductive activities. Growth factors and their receptors are widely distributed in vertebrate ovaries at different stages of ovarian development, indicating their involvement in intraovarian reproductive functions. In the ovary, cell surface receptors allow growth factors to regulate intraovarian reproductive activities. Understanding these actions in the reproductive axis would provide a tool to target growth factors and/or their receptors to yield desirable reproductive outcomes. These include enrichment of in vitro maturation and fertilization culture media, and management of infertility. This review discusses some widely characterized growth factors belonging to the TGF, EGF, IGF, FGF, and BDNF family of peptides and their role in female reproduction in vertebrates, with a focus on mammals.

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.

HB-EGF upregulates StAR expression and stimulates progesterone production through ERK1/2 signaling in human granulosa-lutein cells

Background

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) belongs to the epidermal growth factor (EGF) family of growth factors. HB-EGF and its receptors, epidermal growth factor receptor (EGFR) and HER4, are expressed in the human corpus luteum. HB-EGF has been shown to regulate luteal function by preventing cell apoptosis. Steroidogenesis is the primary function of the human corpus luteum. Steroidogenic acute regulatory protein (StAR) plays a critical role in steroidogenesis. StAR expression and progesterone (P4) production in human granulosa-lutein (hGL) cells have been shown to be upregulated by a ligand of EGFR, amphiregulin. However, whether HB-EGF can achieve the same effects remains unknown.

Methods

A steroidogenic human ovarian granulosa-like tumor cell line, KGN, and primary culture of hGL cells obtained from patients undergoing in vitro fertilization treatment were used as experimental models. The underlying molecular mechanisms mediating the effects of HB-EGF on StAR expression and P4 production were explored by a series of in vitro experiments.

Results

Western blot showed that EGFR, HER2, and HER4 were expressed in both KGN and hGL cells. Treatment with HB-EGF for 24 h induced StAR expression but did not affect the expression of steroidogenesis-related enzymes, P450 side chain cleavage enzyme, 3β-hydroxysteroid dehydrogenase, and aromatase. Using pharmacological inhibitors and a siRNA-mediated knockdown approach, we showed that EGFR, HER4, but not HER2, were required for HB-EGF-stimulated StAR expression and P4 production. In addition, HB-EGF-induced upregulations of StAR expression and P4 production were mediated by the activation of the ERK1/2 signaling pathway.

Conclusion

This study increases the understanding of the physiological role of HB-EGF in human luteal functions.

HDAC1 in the Ovarian Granulosa Cells of Tan Sheep Improves Cumulus Cell Expansion and Oocyte Maturation Independently of the EGF-like Growth Factors

Previous studies have shown that some of the histone deacetylases (HDACs) play diverse roles in the regulation of ovarian somatic cell development, oocyte maturation and early embryonic development in different species including sheep. This study aimed to clarify whether HDAC1 also played pivotal roles in regulating oocyte maturation in Tan sheep. The results showed that HDAC1 was expressed in the nuclei of both the granulosa cells and oocytes of the growing follicles in the Tan sheep's ovaries. However, the level of HDAC1 was unaffected by luteinizing hormone (LH) induction in cultured granulosa cells. Meanwhile, the specific inhibition of HDAC1 using pyroxamide did not induce significant changes in the expression levels of EGF-like growth factors in vitro, whereas both the cumulus expansion and oocyte maturation of the cultured cumulus oocyte complexes (COCs) were significantly inhibited by pyroxamide. Additionally, the numbers of histone acetylation sites (H4K5, H4K12, H3K14 and H3K9) in ovarian granulosa cells were significantly increased. In conclusion, a constant expression of HDAC1 in the growing follicles of Tan sheep may be pivotal for supporting oocyte growth and maturation, although its action may not be closely correlated with LH induction, nor does it directly affect the expression of the EGF-like factors. Our study implies that there may exist diverse functions of the respective HDACs in modulating female reproduction in sheep.

Stimulatory effects of TGFα in granulosa cells of bovine small antral follicles

Intraovarian growth factors play a vital role in influencing the fate of ovarian follicles. They affect proliferation and apoptosis of granulosa cells (GC) and can influence whether small antral follicles continue their growth or undergo atresia. Transforming growth factor-alpha (TGFα), an oocyte-derived growth factor, is thought to regulate granulosa cell function; yet its investigation has been largely overshadowed by emerging interest in TGF-beta superfamily members, such as bone morphogenetic proteins (BMP) and anti-Mullerian hormone (AMH). Here, effects of TGFα on bovine GC proliferation, intracellular signaling, and cytokine-induced apoptosis were evaluated. Briefly, all small antral follicles (3-5 mm) from slaughterhouse specimens of bovine ovary pairs were aspirated and the cells were plated in T25 flasks containing DMEM/F12 medium, 10% FBS, and antibiotic-antimycotic, and incubated at 37 °C in 5% CO2 for 3 to 4 d. Once confluent, the cells were sub-cultured for experiments (in 96-, 12-, or 6-well plates) in serum-free conditions (DMEM/F12 medium with ITS). Exposure of the bGC to TGFα (10 or 100 ng/mL) for 24 h stimulated cell proliferation compared to control (P < 0.05; n = 7 ovary pairs). Proliferation was accompanied by a concomitant increase in mitogen-activated protein kinase (MAPK) signaling within 2 h of treatment, as evidenced by phosphorylated ERK1/2 expression (P < 0.05, n = 3 ovary pairs). These effects were entirely negated, however, by the MAPK inhibitor, U0126 (10uM, P < 0.05). Additionally, prior exposure of the bGC to TGFα (100 ng/mL) failed to prevent Fas Ligand (100 ng/mL)-induced apoptosis, as measured by caspase 3/7 activity (P < 0.05, n = 7 ovary pairs). Collectively, the results indicate TGFα stimulates proliferation of bGC from small antral follicles via a MAPK/ERK-mediated mechanism, but this action alone fails to prevent apoptosis, suggesting that TGFα may be incapable of promoting their persistence in follicles during the process of follicular selection/dominance.

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.

Disruption of Epidermal Growth Factor Receptor but Not EGF Blocks Follicle Activation in Zebrafish Ovary

Folliculogenesis is controlled by intimate communications between oocytes and surrounding follicle cells. Epidermal growth factor (EGF/Egf) is an important paracrine/autocrine factor in vertebrate ovary, and it is well known for its stimulation of oocyte maturation. However, the role of EGF signaling through its receptor (EGFR/Egfr) in ovarian folliculogenesis is poorly understood, especially at early stages of follicle development. In this study, we created zebrafish mutants for Egf (egf−/−) and Egfr (egfra−/− and egfrb−/−) by CRISPR/Cas9 technique. Surprisingly, these mutants all survived well with little abnormality in growth and development. Spermatogenesis and folliculogenesis were both normal in egf−/− males and females. Their fecundity was comparable to that of the wildtype fish at 4 months post-fertilization (mpf); however, the fertilization rate of mutant eggs (egf−/−) decreased significantly at 7 mpf. Interestingly, disruption of egfra (egfra−/−) led to failed follicle activation with folliculogenesis being blocked at primary–secondary growth transition (PG-SG transition), leading to female infertility, whereas the mutant males remained fertile. The mutant ovary (egfra−/−) showed abnormal expression of a substantial number of genes involved in oxidative metabolism, gene transcription, cytomembrane transport, steroid hormone biosynthesis, and immune response. The stunted PG oocytes in egfra−/− ovary eventually underwent degeneration after 6 months followed by sex reversal to males with functional testes. No abnormal phenotypes were found in the mutant of truncated form of EGFR (egfrb). In summary, our data revealed critical roles for EGFR signaling in early folliculogenesis, especially at the PG-SG transition or follicle activation.

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.

Single-Cell RNA Sequencing Analysis of Chicken Anterior Pituitary: A Bird's-Eye View on Vertebrate Pituitary

It is well-established that anterior pituitary contains multiple endocrine cell populations, and each of them can secrete one/two hormone(s) to regulate vital physiological processes of vertebrates. However, the gene expression profiles of each pituitary cell population remains poorly characterized in most vertebrate groups. Here we analyzed the transcriptome of each cell population in adult chicken anterior pituitaries using single-cell RNA sequencing technology. The results showed that: (1) four out of five known endocrine cell clusters have been identified and designated as the lactotrophs, thyrotrophs, corticotrophs, and gonadotrophs, respectively. Somatotrophs were not analyzed in the current study. Each cell cluster can express at least one known endocrine hormone, and novel marker genes (e.g., CD24 and HSPB1 in lactotrophs, NPBWR2 and NDRG1 in corticotrophs; DIO2 and SOUL in thyrotrophs, C5H11ORF96 and HPGDS in gonadotrophs) are identified. Interestingly, gonadotrophs were shown to abundantly express five peptide hormones: FSH, LH, GRP, CART and RLN3; (2) four non-endocrine/secretory cell types, including endothelial cells (expressing IGFBP7 and CFD) and folliculo-stellate cells (FS-cells, expressing S100A6 and S100A10), were identified in chicken anterior pituitaries. Among them, FS-cells can express many growth factors, peptides (e.g., WNT5A, HBEGF, Activins, VEGFC, NPY, and BMP4), and progenitor/stem cell-associated genes (e.g., Notch signaling components, CDH1), implying that the FS-cell cluster may act as a paracrine/autocrine signaling center and enrich pituitary progenitor/stem cells; (3) sexually dimorphic expression of many genes were identified in most cell clusters, including gonadotrophs and lactotrophs. Taken together, our data provides a bird's-eye view on the diverse aspects of anterior pituitaries, including cell composition, heterogeneity, cell-to-cell communication, and gene expression profiles, which facilitates our comprehensive understanding of vertebrate pituitary biology.

Protegrin-1 Regulates Porcine Granulosa Cell Proliferation via the EGFR-ERK1/2/p38 Signaling Pathway in vitro

Antimicrobial peptides (AMPs) are traditionally known to be essential components in host defense via their broad activities against bacteria, fungi, viruses, and protozoa. Their immunomodulatory properties have also recently received considerable attention in mammalian somatic tissues of various species. However, little is known regarding the role of AMPs in the development and maturation of ovarian follicles. Protegrin-1 (PG-1) is an antimicrobial peptide which is known to have potent antimicrobial activity against both gram positive and negative bacteria. Here we report that the PG-1 is present in the porcine ovarian follicular fluid. Treatment of granulosa cell with PG-1 enhanced granulosa cell proliferation in a dose-dependent manner. This is accompanied by increased expression of cell-cycle progression-related genes such as cyclin D1(CCND1), cyclin D2 (CCND2), and cyclin B1(CCNB1). Additionally, Western blot analysis showed that PG-1 increased phosphorylated epidermal growth factor receptor (EGFR), and the phosphorylated-/total extracellular signal-regulated kinase (ERK)1/2 ratio. Pretreatment with either U0126, a specific ERK1/2 phosphorylation inhibitor, or EGFR kinase inhibitor, AG1478, blocked the PG-1 induced proliferation. Moreover, luciferase reporter assay revealed that ETS domain-containing protein-1 (Elk1) C/EBP homologous protein (CHOP), and the transcription activators downstream of the MAPK pathway, were activated by PG-1. These data collectively suggest that PG-1 may regulate pig granulosa cell proliferation via EGFR-MAPK pathway., Hence, our finding offers insights into the role of antimicrobial peptides on follicular development regulation.

Characterization of Four Orphan Receptors (GPR3, GPR6, GPR12 and GPR12L) in Chickens and Ducks and Regulation of GPR12 Expression in Ovarian Granulosa Cells by Progesterone

The three structurally related orphan G protein-coupled receptors, GRP3, GPR6, and GPR12, are reported to be constitutively active and likely involved in the regulation of many physiological/pathological processes, such as neuronal outgrowth and oocyte meiotic arrest in mammals. However, the information regarding these orphan receptors in nonmammalian vertebrates is extremely limited. Here, we reported the structure, constitutive activity, and tissue expression of these receptors in two representative avian models: chickens and ducks. The cloned duck GPR3 and duck/chicken GPR6 and GPR12 are intron-less and encode receptors that show high amino acid (a.a.) sequence identities (66–88%) with their respective mammalian orthologs. Interestingly, a novel GPR12-like receptor (named GPR12L) sharing 66% a.a. identity to that in vertebrates was reported in the present study. Using dual-luciferase reporter assay and Western blot, we demonstrated that GPR3, GPR6, GPR12, and GPR12L are constitutively active and capable of stimulating the cAMP/PKA signaling pathway without ligand stimulation in birds (and zebrafish), indicating their conserved signaling property across vertebrates. RNA-seq data/qRT-PCR assays revealed that GPR6 and GPR12L expression is mainly restricted to the chicken brain, while GPR12 is highly expressed in chicken ovarian granulosa cells (GCs) and oocytes of 6 mm growing follicles and its expression in cultured GCs is upregulated by progesterone. Taken together, our data reveal the structure, function, and expression of GPR3, GPR6, GPR12, and GPR12L in birds, thus providing the first piece of evidence that GPR12 expression is upregulated by gonadal steroid (i.e., progesterone) in vertebrates.

Transcriptomic analysis of granulosa cell populations proximal and distal to the germinal disc of chicken preovulatory follicles

Within the oocytes of chicken preovulatory follicles, the engulfed yolk constitutes 99% of the oocyte content, while the small germinal disc (GD) (which contains the nucleus and 99% ooplasm) occupies only less than 1%. Relative to the position of the GD, the single granulosa cell layer surrounding the oocyte can be sub-divided into two sub-populations: granulosa cells proximal (named Gp cells) and distal (Gd cells) to the GD. It was reported that Gp cells and Gd cells differ in their morphology, proliferative rate and steroidogenic capacity, however, the underlying mechanism controlling granulosa cell heterogeneity remains unclear. Here we analyzed the transcriptomes of Gd and Gp cells of preovulatory (F5 and F1) follicles in chicken ovaries. We found that: (1) genes associated with cell cycle and DNA replication (CDK1, CCNB3 etc.) have comparatively higher expression levels in Gp cells than in Gd cells, while genes associated with steroidogenesis (CYP51A1, DHCR24) are highly expressed in Gd cells, indicating that Gp cells are likely more mitotic and less steroidogenic than Gd cells; (2) genes associated with extracellular matrix remodeling, cell adhesion and sperm binding (ZP3, ZP2) are differentially expressed in Gp and Gd cells; (3) Furthermore, signaling molecules (WNT4/IHH) and receptors for NGF (NGFR), epidermal growth factor (EGFR), gonadotropins (FSHR/LHR) and prostaglandin (PTGER3) are abundantly but differentially expressed in Gp and Gd cells. Taken together, our data strongly supports the notion that Gp and Gd cells of preovulatory follicles differ in their proliferation rate, steroidogenic activity, ECM organization and sperm binding capacity, which are likely controlled by gonadotropins and local ovarian factors, such as GD-derived factors.

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.

Occludin expression and regulation in small follicles of the layer and broiler breeder hen

Synchronized yolk accumulation and follicle development are essential for egg production in oviparous species. In birds, yolk is incorporated into the oocyte by an avian specific yolk receptor (LR8), and it has been suggested that occludin (OCLN), a tight junction protein, mediates transfer of yolk material to the oocyte surface. OCLN may be a key regulator of yolk accumulation and follicle growth, however, the expression and regulation of OCLN in granulosa cells during various stages of follicle development is unknown. In the first experiment, we found that LR8 and OCLN mRNA were highest in small follicles within the ovary. In addition, OCLN decreased with increasing follicle size. OCLN mRNA was more abundant in the germinal disc region of the granulosa cell layer than the non-germinal disc region. In addition, we found epidermal growth factor (EGF) and activin B, decreased OCLN mRNA, while activin A increased OCLN. In the second experiment, restricted fed (RF) broiler breeder hens were randomly divided into two groups and one group remained on RF and the other was fed ad libitum (FF). OCLN expression in granulosa cells of 3-5mm follicles of FF hens was lower compared to RF hens and yolk weights were higher in the FF group, however, LR8 mRNA in small whole follicles (<3mm) did not differ between groups. In conclusion, the level of feed intake is related to or may directly regulate OCLN mRNA expression or may have an indirect effect through paracrine or autocrine factors in the ovary.

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.

Bone morphogenetic protein 15 may promote follicle selection in the hen

In the hen, optimal ovulation rate depends on selection of a single follicle into the pre-ovulatory hierarchy. Follicle selection is associated with increased oocyte growth and changes in gene expression in granulosa cells surrounding the oocyte, in preparation for ovulation. This study investigated the expression, function and regulation of bone morphogenetic protein-15 (BMP15) during follicle development in the hen. BMP15 mRNA expression was analyzed in the ooplasm and granulosa cells of 3mm follicles and was confirmed to be primarily in the ooplasm. BMP15 was detected by immunoblotting in 6 and 8mm follicles near the time of follicle selection. Expression of mRNA for BMP15 receptors (BMPR1B and BMPR2) in granulosa cells increased with follicle size, indicating that BMP15 may play an important role around follicle selection. The function of BMP15 was examined by culturing granulosa cells from 3-5mm and 6-8mm follicles with recombinant human BMP15 (rhBMP15). BMP15 increased expression of follicle stimulating hormone receptor (FSHR) mRNA and decreased anti-Müllerian hormone (AMH) mRNA and occludin (OCLN), factors associated with follicle maturation and growth in the hen. Hormonal regulation of BMP15 was assessed by whole follicle culture with estradiol (E2) which increased BMP15 mRNA expression. The distinct expression pattern of BMP15 and its receptors, coupled with the effects of BMP15 to increase FSHR mRNA and decrease AMH mRNA and OCLN mRNA and protein expression suggest that the oocyte may have a role in follicle selection in the chicken.

Chicken stem cell factor enhances primordial germ cell proliferation cooperatively with fibroblast growth factor 2

An in vitro culture system of chicken primordial germ cells (PGCs) has been recently developed, but the growth factor involved in the proliferation of PGCs is largely unknown. In the present study, we investigated the growth effects of chicken stem cell factor (chSCF) on the in vitro proliferation of chicken PGCs. We established two feeder cell lines (buffalo rat liver cells; BRL cells) that stably express the putative secreted form of chSCF (chSCF1-BRL) and membrane bound form of chSCF (chSCF2-BRL). Cultured PGC lines were incubated on chSCF1 or chSCF2-BRL feeder cells with fibroblast growth factor 2 (FGF2), and growth effects of each chSCF isoform were investigated. The in vitro proliferation rate of the PGCs cultured on chSCF2-BRL at 20 days of culture was more than threefold higher than those cultured on chSCF1-BRL cells and more than fivefold higher than those cultured on normal BRL cells. Thus, use of chSCF2-BRL feeder layer was effective for in vitro proliferation of chicken PGCs. However, the acceleration of PGC proliferation on chSCF2-BRL was not observed without FGF2, suggesting that chSCF2 would act as a proliferation co-factor of FGF2. We transferred the PGCs cultured on chSCF2-BRL cells to recipient embryos, generated germline chimeric chickens and assessed the germline competency of cultured PGCs by progeny test. Donor-derived progenies were obtained, and the frequency of germline transmission was 3.39%. The results of this study demonstrate that chSCF2 induces hyperproliferation of chicken PGCs retaining germline competency in vitro in cooperation with FGF2.

Promising Loci and Genes for Yolk and Ovary Weight in Chickens Revealed by a Genome-Wide Association Study

Because it serves as the cytoplasm of the oocyte and provides a large amount of reserves, the egg yolk has biological significance for developing embryos. The ovary and its hierarchy of follicles are the main reproductive organs responsible for yolk deposition in chickens. However, the genetic architecture underlying the yolk and ovarian follicle weights remains elusive. Here, we measured the yolk weight (YW) at 11 age points from onset of egg laying to 72 weeks of age and measured the follicle weight (FW) and ovary weight (OW) at 73 weeks as part of a comprehensive genome-wide association study (GWAS) in 1,534 F₂ hens derived from reciprocal crosses between White Leghorn (WL) and Dongxiang chickens (DX). For all ages, YWs exhibited moderate single nucleotide polymorphism (SNP)-based heritability estimates (0.25–0.38), while the estimates for FW (0.16) and OW (0.20) were relatively low. Independent univariate genome-wide screens for each trait identified 12, 3, and 31 novel significant associations with YW, FW, and OW, respectively. A list of candidate genes such as ZAR1, STARD13, ACER1b, ACSBG2, and DHRS12 were identified for having a plausible function in yolk and follicle development. These genes are important to the initiation of embryogenesis, lipid transport, lipoprotein synthesis, lipid droplet promotion, and steroid hormone metabolism, respectively. Our study provides for the first time a genome-wide association (GWA) analysis for follicle and ovary weight. Identification of the promising loci as well as potential candidate genes will greatly advance our understanding of the genetic basis underlying dynamic yolk weight and ovarian follicle development and has practical significance in breeding programs for the alteration of yolk weight at different age points.

Effect of epidermal growth factor (EGF) on the phosphorylation of mitogen-activated protein kinase (MAPK) in the bovine oviduct in vitro: Alteration by heat stress

Epidermal growth factor (EGF) has been shown to be involved in control of the oviductal microenvironment. To elucidate the potential mechanisms responsible for the detrimental effect of heat stress and to identify the relation with the endocrine status, the effects of EGF on the level of phosphorylated mitogen-activated-protein kinase (MAPK) and proliferation of bovine oviductal epithelial cells (OECs) exposed to different cyclic ovarian steroidal environments (luteal phase (LP), follicular phase (FP) and postovulatory phase (PO)) and temperatures (mild heat stress (40 C) and severe heat stress (43 C)) were investigated. Western blot was performed to evaluate phosphorylated MAPK, while proliferation was analyzed by MTT assay. Stimulation of OECs with EGF alone or with EGF in the PO and FP environments significantly increased the amount of phosphorylated MAPK, with MAPK 44 phosphorylation being highest during exposure to PO conditions. These effects were not observed in the LP. Heat treatment completely blocked effects of EGF on phosphorylated MAPK. Additionally, severe heat stress led to a significantly lower basal level of phosphorylated MAPK. PD98059 (MAPK inhibitor) completely abolished EGF-stimulated MAPK phosphorylation and OECs proliferation. Overall the results indicate that EGF has the potential to increase the amount of phosphorylated MAPK in OECs and therefore could be involved in regulation of the bovine oviductal microenvironment. However, these regulatory mechanisms may be compromised in the presence of heat stress (high ambient temperature), leading to low fertility rates and impaired embryo survival.

Expression and localisation of c-kit and KITL in the adult human ovary

BACKGROUND

The c-kit/kit ligand (KITL) signalling axis is an essential component of ovarian folliculogenesis in mammals, but little is known about expression and localisation of its key components in the ovaries of reproductive age women. This study aimed to characterise mRNA expression of c-kit and KITL isoforms and the localisation of c-kit and KITL proteins in adult human premenopausal ovaries.

METHODS

This study utilised granulosa cells obtained from the preovulatory follicles of women undergoing assisted reproduction, pieces of ovarian tissue obtained from premenopausal women undergoing gynaecological surgeries and archival paraffin-embedded premenopausal ovarian tissues. Methodology included PCR for gene expression and Western blot or immunohistochemistry for protein expression.

RESULTS

Both c-kit mRNA isoforms, known as GNNK+ and GNNK-, were detected in human ovarian cortex, while KITL protein isoforms (KITL1 and KITL2) were present in ovarian cortex and human granulosa cells. Immunohistochemistry showed expression of KITL and c-kit protein in multiple cell types within follicles throughout development, from primordial follicles to large antral follicles, in addition to atretic follicles. Oocytes of all follicle stages expressed c-kit protein exclusively. Interestingly, unlike animal models, expression of both proteins displayed a less cell-type specific distribution with immunostaining present in granulosa, theca and stromal cells, suggesting that autocrine signalling occurs within the human ovary.

CONCLUSION

The results of this study indicate that c-kit/KITL signalling also occurs in the human ovary, as established in various animal models, and may involve previously unknown autocrine signalling.

Salmonella Enteritidis infection slows steroidogenesis and impedes cell growth in hen granulosa cells

Infection by Salmonella Enteritidis (SE) causes decreased egg production in laying hens. Immunoresponse, steroidogenesis, and cell proliferation by chicken granulosa cells (cGCs) are of particular interest because these changes are involved in follicular growth, atresia, and ovulation. To elucidate the possible mechanisms underlying these changes, transcriptional alterations in cGCs at distinct stages of follicular maturity were studied. Luteinizing hormone (LH)-and follicle-stimulating hormone (FSH) were applied to the cGCs isolated from hierarchical and prehierarchical follicles, respectively, to imitate the effects of gonadotropin during in vitro SE infection. Results showed that the expression of Toll-like receptor 15 was dependent on the follicular maturity, with mature cells having a more significant and progressively stronger immunoresponse. Attenuated responses to LH and FSH as well as retardant steroidogenesis due to down-regulated LH receptor, FSH receptor, and the P450 side-chain cleavage system were observed and may have led to delayed hierarchical follicular growth. Deteriorated cell viability of prehierarchical follicles may occur, as the proliferation of stimulator heparin-binding epidermal growth factor was reduced significantly. Furthermore, the infection led to a higher probability of cGCs from the smaller follicles undergoing apoptosis than those from F1 follicles. Collectively, the data provide evidence of a tendency toward pathogen elimination in F1 follicles by induction of a strong immune response and cell apoptosis in smaller follicles to avoid bacterial transovarian infection. It is our speculation that slowed steroidogenesis and impeded follicular growth may play essential roles in decreased ovulation rate as well as further decreased egg production during SE infection.

Identification of the receptors for somatostatin (SST) and cortistatin (CST) in chickens and investigation of the roles of cSST28, cSST14, and cCST14 in inhibiting cGHRH1-27NH2-induced growth hormone secretion in cultured chicken pituitary cells

Somatostatin receptors (SSTRs) are proposed to mediate the actions of somatostatin (SST) and its related peptide, cortistatin (CST), in vertebrates. However, the identity, functionality, and tissue expression of these receptors remain largely unknown in most non-mammalian vertebrates including birds. In this study, five SSTRs (named cSSTR1, cSSTR2, cSSTR3, cSSTR4, cSSTR5) were cloned from chicken brain by RT-PCR. Using a pGL3-CRE-luciferase reporter system, we demonstrated that activation of each cSSTR expressed in CHO cells by cSST28, cSST14 and cCST14 treatment could inhibit forskolin-induced luciferase activity of CHO cells, indicating the functional coupling of all cSSTRs to Gi protein(s). Interestingly, cSSTR1-4 expressed in CHO cells could be activated by cSST28, cSST14 and cCST14 with high potencies, suggesting that they may function as the receptors common for these peptides. In contrast, cSSTR5 could be potently activated by cSST28 only, indicating that it is a cSST28-specific receptor. Using RT-PCR, wide expression of cSSTRs was detected in chicken tissues including pituitary. In accordance with their expression in pituitary, cSST28, cSST14, and cCST14 were demonstrated to inhibit basal and novel cGHRH1-27NH2-induced GH secretion in cultured chicken pituitary cells dose-dependently (0-10nM) by Western blot analysis, suggesting the involvement of cSSTR(s) common for these peptides in mediating their inhibitory actions. Collectively, our study establishes a molecular basis to elucidate the roles of SST/CST in birds and provide insights into the roles of SST/CST in vertebrates, such as their conserved actions on pituitary.

Human chorionic gonadotropin (hCG) induces MAPK3/1 phosphorylation in the zebrafish ovarian follicle cells independent of EGF/EGFR pathway

In mammals, human chorionic gonadotropin (hCG), a luteinizing hormone (LH) analogue, induces MAPK3/1 phosphorylation in the granulosa cells and this event is largely dependent on epidermal growth factor receptor (EGFR) activity. However, whether this mechanism also works in other vertebrates such as fish remains unknown. Here, we showed that treatment of cultured zebrafish ovarian follicle cells with hCG also resulted in MAPK3/1 phosphorylation without affecting the total protein level of MAPK3/1. The phosphorylation level peaked at 5 min and then declined to the basal level after 40 min of hCG treatment. Further experiment showed that H89 (a PKA inhibitor) could abolish hCG-stimulated MAPK3/1 phosphorylation, but had no effect on EGF-induced phosphorylation, suggesting a mediating role for cAMP/PKA in hCG activation of MAPK3/1. On the other hand, AG1478 (an EGFR inhibitor) completely blocked EGF-stimulated MAPK3/1 phosphorylation, but had no effect on the hCG-induced MAPK3/1 phosphorylation. These data indicate that similar to its action in mammals, hCG/LH also stimulated MAPK3/1 phosphorylation in the zebrafish ovarian follicle cells; however, unlike the situation in the mammalian ovary, the hCG-stimulated MAPK3/1 phosphorylation in cultured zebrafish ovarian follicle cells was independent of EGFR.

Molecular characterization of prolactin receptor (cPRLR) gene in chickens: gene structure, tissue expression, promoter analysis, and its interaction with chicken prolactin (cPRL) and prolactin-like protein (cPRL-L)

In this study, gene structure, tissue expression, and promoter usage of prolactin receptor (PRLR) and its interaction with prolactin (PRL) and the newly identified prolactin-like protein (PRL-L) were investigated in chickens. The results showed that (1) PRLR gene was found to consist of at least 25 exons by 5'-RACE and RT-PCR assays; (2) multiple PRLR 5'-UTR sequences different in exon composition were isolated from chicken liver or intestine by 5'-RACE and could be subdivided into type I and type II transcripts according to the first exon used (exon 1G or exon 1A); (3) PRLR Type I transcripts with exon 1G were detected to be predominantly expressed in adult kidney and small intestine by RT-PCR, implying their expression is likely controlled by a tissue-specific promoter (P1). By contrast, PRLR type II transcripts containing exon 1A are widely expressed in adult and embryonic tissues examined and their expression is controlled by a generic promoter (P2) near exon 1A, which was demonstrated to display promoter activities in cultured DF-1, HEK293 and LoVo cells by the dual-luciferase reporter assay; (4) Using a 5×STAT5-luciferase reporter system, cPRLR expressed in HepG2 cells was shown to be activated by recombinant cPRL and cPRL-L via interaction with PRLR membrane-proximal ligand-binding domain, suggesting that like cPRL, cPRL-L is also a functional ligand of cPRLR. Collectively, characterization of cPRLR gene helps to elucidate the roles of PRLR and its ligands in birds and provides insights into the regulatory mechanisms of PRLR expression conserved in birds and mammals.

Differential regulation of gonadotropin receptors (fshr and lhcgr) by epidermal growth factor (EGF) in the zebrafish ovary

Epidermal growth factor (egf) is expressed in the zebrafish oocyte whereas its receptor EGF receptor (egfr) is expressed in the somatic follicle layer, strongly suggesting a role for Egf in the intrafollicular paracrine communication that mediates an oocyte-to-follicle cell signaling pathway. However, the exact function of Egf in the follicle remains largely unknown. The present study aimed to explore the possible role of Egf in regulating gonadotropin receptors (fshr and lhcgr) in cultured zebrafish follicle cells. EGF down-regulated lhcgr expression dose-dependently in a biphasic manner with significant effect observed at 1.5 and 24 h. The effect was mediated via Egfr on the follicle cells. On the contrary, EGF also tended to decrease fshr expression at 1.5 h but it appeared to up-regulate fshr at 24 h. The EGF suppression of lhcgr expression was functionally relevant as pre-exposure to EGF reduced the follicle cell responsiveness to LH/hCG. We have recently reported that estradiol (E2) strongly stimulated lhcgr expression in the zebrafish ovary. In the current study, we further demonstrated that EGF and other EGF family members, heparin-binding EGF-like growth factor (HBEGF), transforming growth factor α (TGFα) and betacellulin (BTC), all reduced basal and E2-induced lhcgr expression. This study provides evidence for a potential paracrine role of Egf and its related peptides in the zebrafish follicle. The oocyte-derived EGF family ligands may actively control the process of follicle growth and maturation by differentially controlling the expression of fshr and lhcgr in the follicle cells in a paracrine manner.

Follicle selection in the avian ovary

Follicle development in the highly efficient laying hen is characterized by a well-organized follicular hierarchy. This is not the case in other chickens such as the broiler breeder hen that has excessive follicle development and lower reproductive efficiency. Although management practices can optimize egg production in less productive breeds of chickens, the factors that contribute to this difference are not known. Interactions between the oocyte and surrounding somatic cells are believed to be involved in promoting follicle selection. Anti-Müllerian hormone (AMH) has been shown to have a role in regulating rate of follicle development in mammals. In hens, the expression of AMH is restricted to the growing population of follicles and, similar to mammals, is markedly decreased at around the time of follicle selection. The oocyte factors, growth and differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15), have been identified in the hen, and their expression pattern has been characterized. Anti-Müllerian hormone expression in hens is decreased by a protein factor from the oocyte (not GDF9) and is also decreased by vitamin D. Associated with the decrease in AMH expression by vitamin D, follicle-stimulating hormone receptor mRNA is increased. These data suggest that information about AMH regulation may enhance our understanding of follicle selection, particularly in birds with aberrant follicle development.

The effects of epidermal growth factor (EGF) on the in vitro development of isolated goat secondary follicles and the relative mRNA expression of EGF, EGF-R, FSH-R and P450 aromatase in cultured follicles

The effects of varying concentrations of EGF were evaluated in terms of in vitro follicular development and the mRNA expression levels of EGF, EGF-R, FSH-R and P450 aromatase. After 6 days, the addition of 50 ng/mL of EGF to the culture medium increased the antrum formation rates in comparison to cultured control and after 18 days of culture produced oocytes with higher rates of meiosis resumption when compared to the other treatments (P<0.05). The daily follicular growth rates in presence of EGF (50 or 100) were increased in comparison to the cultured control (P<0.05). Treatment with EGF 50 stimulated the expression of EGF mRNA but reduced EGF-R mRNA expression and estradiol secretion as compared to the cultured control (P<0.05). After 18 days of culture, the mRNA levels for FSH-R and P450 aromatase were greater than those of the non-cultured controls (P<0.05). In conclusion, the effects of EGF treatment on the mRNA levels for EGF, EGF-R, FSH-R, and P450 aromatase varied according to the stage of follicle development.

Expression and regulation of Kit ligand in the ovary of the hen

The Kit system, composed of Kit ligand (KL) and its tyrosine kinase receptor, cKit, has been well characterized in mammals. Studies have shown that it is involved in signaling between the oocyte and somatic cells during the process of follicle maturation. We characterized KL mRNA expression during follicle maturation in the domestic hen, examined regulation of KL and a possible function of the Kit system. KL mRNA expression was assessed using quantitative PCR (n=4 replicates) in follicles of various sizes (1, 3, 5, 6-12 mm, F1). Expression of KL mRNA decreased significantly (p<0.01) with follicle development and was highest in <1 mm follicles, which contained the theca as well as granulosa layers, with high levels also found in the granulosa layer of 3 mm follicles and ovarian stroma. To study regulation of KL mRNA, granulosa cells from 6-8 mm follicles (n=4 replicates) were plated in M199 plus 0.1% BSA in the presence of various treatments including: oocyte conditioned medium (OCM), Vitamin D(3), FSH, estradiol, progesterone and testosterone. OCM caused a dose-related increase (p<0.05) in expression of KL mRNA; Vitamin D(3) increased and FSH decreased expression of KL mRNA. cKit was detected (at the expected size) in the theca layer of 3-5 mm follicles and in a lysate of whole <1mm follicles. Culture of granulosa cells in the presence of OCM resulted in a decrease of P4 secretion, an effect blocked by pre-incubation of OCM with cKit antibody. Although OCM caused a dose-related increase in E2 secretion from theca, this was not blocked by cKit antibody.

Characterization of glucagon-like peptide 1 receptor (GLP1R) gene in chickens: functional analysis, tissue distribution, and identification of its transcript variants

Glucagon-like peptide 1 (GLP1) receptor plays a critical role in mediating the biological actions of GLP1 in mammals and fish; however, the gene structure, expression, and functionality of GLP1 receptor (GLP1R) remain largely unknown in birds. In this study, the full-length cDNA of chicken GLP1R (cGLP1R) was first cloned from brain tissue by reverse transcription PCR. The putative cGLP1R is 459 amino acids in length and shares high amino acid sequence identity with that of human (79%), rat (80%), and Xenopus (75%). Using a pGL3-CRE luciferase reporter system, we found that cGLP1R expressed in Chinese hamster ovary cells could be potently activated by cGLP1 (EC(50), 0.11 nM) but not by other structurally related peptides, indicating that cGLP1R is a functional receptor specific to cGLP1. Interestingly, in addition to identification of the transcript encoding cGLP1R of 459 amino acids, eight transcript variants, which were generated by alternative mRNA splicing and predicted to encode either C-terminally or N-terminally truncated cGLP1Rs, were also identified from chicken brain or testis. In line with this finding, multiple cGLP1R transcripts were detected to be expressed in most chicken tissues examined, including pancreas, gastrointestinal tract, and various brain regions by reverse transcription PCR. Using the dual-luciferase reporter assay system, we further found that the 5'-flanking region of cGLP1R gene displays promoter activities in cultured HepG2 and HEK293 cells, suggesting that it may control cGLP1R gene transcription in chicken tissues, including nonpancreatic tissues. Taken together, the results from the present study establish a molecular basis to investigate the roles of GLP1 in chickens.

Novel signaling mechanisms in the ovary during oocyte maturation and ovulation

During the peri-ovulatory period, the gonadotropin LH triggers major changes in both the somatic and germ cell compartments of the ovarian follicle. The oocyte completes the meiotic cell cycle to become a fertilizable egg, and dramatic changes in gene expression and secretion take place in the somatic compartment of the follicle in preparation for follicular rupture and oocyte release. The concerted changes are regulated by activation of intracellular signaling pathways as well as paracrine and autocrine regulatory loops. This review will provide a summary of the current knowledge of the molecular events triggered by LH focusing mostly on the signaling pathways required for oocyte maturation.

Quantification of Transcriptome Responses of the Rumen Epithelium to Butyrate Infusion using RNA-seq Technology

Short-chain fatty acids (SCFAs), such as butyrate, produced by gut microorganisms, play a critical role in energy metabolism and physiology of ruminants as well as in human health. In this study, the temporal effect of elevated butyrate concentrations on the transcriptome of the rumen epithelium was quantified via serial biopsy sampling using RNA-seq technology. The mean number of genes transcribed in the rumen epithelial transcriptome was 17,323.63 ± 277.20 (±SD; N = 24) while the core transcriptome consisted of 15,025 genes. Collectively, 80 genes were identified as being significantly impacted by butyrate infusion across all time points sampled. Maximal transcriptional effect of butyrate on the rumen epithelium was observed at the 72-h infusion when the abundance of 58 genes was altered. The initial reaction of the rumen epithelium to elevated exogenous butyrate may represent a stress response as Gene Ontology (GO) terms identified were predominantly related to responses to bacteria and biotic stimuli. An algorithm for the reconstruction of accurate cellular networks (ARACNE) inferred regulatory gene networks with 113,738 direct interactions in the butyrate-epithelium interactome using a combined cutoff of an error tolerance (ɛ = 0.10) and a stringent P-value threshold of mutual information (5.0 × 10⁻¹¹). Several regulatory networks were controlled by transcription factors, such as CREBBP and TTF2, which were regulated by butyrate. Our findings provide insight into the regulation of butyrate transport and metabolism in the rumen epithelium, which will guide our future efforts in exploiting potential beneficial effect of butyrate in animal well-being and human health.

Identification of the receptors for prolactin-releasing peptide (PrRP) and Carassius RFamide peptide (C-RFa) in chickens

Prolactin-releasing peptide (PrRP) and its structurally related peptide, Carassius Arg-Phe-amide peptide (C-RFa), have been reported to play similar roles in regulating food intake and pituitary functions in vertebrates. However, the identity, functionality, and expression of the receptor(s) for PrRP and C-RFa remain largely unknown in nonmammalian vertebrates, including birds. In this study, three receptors homologous to mammalian PrRP receptor (PrRPR), named cPrRPR1, cPrRPR2, and cC-RFaR, respectively, were cloned from chicken brain by RT-PCR. Using a pGL3-NFAT-RE-luciferase reporter system, we demonstrated that cPrRPR1 and cPrRPR2 expressed in Chinese hamster ovarian cells could be activated by cPrRP₂₀ and cC-RFa₂₀ potently, whereas cC-RFaR could only be activated effectively by cC-RFa₂₀ (EC₅₀, 0.11 nM), indicating that cPrRPR1 and cPrRPR2 can function as common receptors for PrRP and C-RFa, whereas cC-RFaR is a receptor specific to C-RFa. Using a pGL3-CRE-luciferase reporter system, cPrRPR1, cPrRPR2, and cC-RFaR expressed in Chinese hamster ovarian cells were also shown to activate intracellular protein kinase A signaling pathway upon cC-RFa₂₀ treatment (100 nM). Moreover, RT-PCR assay revealed that cPrRPR1, cPrRPR2, and cC-RFaR were widely expressed in most adult chicken tissues examined, including various regions of brain. These findings, together with evidence of PrRP and C-RFa encoded by separate genes in chicken, Xenopus, and zebrafish, and the differential expression of PrRP and C-RFa genes in chicken tissues, strongly suggest that PrRP and C-RFa may play similar yet distinctive roles in nonmammalian vertebrates, including chicken, and their actions are mediated by common receptor(s) or a specific C-RFa receptor.

Characterization of chicken secretin (SCT) and secretin receptor (SCTR) genes: a novel secretin-like peptide (SCT-LP) and secretin encoded in a single gene

Secretin and the secretin receptor have been reported to play an important role in regulating pancreatic water and bicarbonate secretion in mammals; however, little is known about their expression, structure, and biological functions in non-mammalian vertebrates including birds. In this study, the full-length cDNAs encoding secretin and secretin receptor have first been cloned from duodenum of adult chickens. The putative chicken secretin receptor (cSCTR) is 449 amino acids in length and shares high sequence identity (58-63%) with its mammalian counterparts. Interestingly, chicken secretin cDNA encodes not only the secretin peptide (cSCT), but also a novel secretin-like peptide (cSCT-LP), which shares high amino acid identity with chicken (56%) and mammalian (48-52%) secretin. Using a pGL3-CRE-luciferase reporter system, we further demonstrated that both cSCT (EC(50): 0.31nM) and cSCT-LP (EC(50): 1.10nM), but not other structurally-related peptides, could potently activate cSCTR expressed in CHO cells, suggesting that both peptides may function as potential ligands for cSCTR. Using RT-PCR, the expression of secretin and secretin receptor in adult chicken tissues was also examined. Secretin was detected to be predominantly expressed in small intestine, while the mRNA expression of cSCTR was restricted to several tissues including gastrointestinal tract, liver, testis, pancreas and several brain regions. Collectively, results from present study not only established a molecular basis to elucidate the physiological roles of SCT, SCT-LP and SCTR in chickens, but also provide critical insights into structural and functional changes of secretin and its receptor during vertebrate evolution.

Steady-state level of epidermal growth factor (EGF) mRNA and effect of EGF on in vitro culture of caprine preantral follicles

Our aim was to verify the steady-state level of epidermal growth factor (EGF) mRNA in goat follicles at various developmental stages and to investigate the influence of EGF on the survival, antrum formation and growth of secondary follicles cultured for 6 days. Primordial, primary and secondary goat follicles and small and large antral follicles were obtained to quantify EGF mRNA by real-time reverse transcription with the polymerase chain reaction. The influence of EGF and the presence or absence of follicle-stimulating hormone (FSH) on the development of secondary follicles and on mRNA expression for EGF and FSH receptor (FSH-R) was determined after 6 days of culture. Survival, antrum formation and follicular diameter were evaluated every other day of culture. EGF mRNA levels in secondary follicles were significantly higher than those in primordial follicles, whereas in small and large antral follicles, EGF mRNA levels in cumulus-oocyte complexes (COCs) were significantly higher than in granulosa/theca cells. During culture, EGF in the presence or absence of FSH increased the follicular daily growth rate of secondary follicles when compared with that in enriched alpha minimal essential medium. FSH, EGF or both reduced EGF mRNA levels, whereas EGF reduced FSH-R mRNA levels after follicle culture for 6 days. Thus, EGF mRNA levels are higher in secondary follicles than in earlier stages, with both FSH and EGF promoting the growth of goat secondary follicles. EGF and/or FSH reduce EGF mRNA levels, whereas EGF decreases FSH-R mRNA levels, in cultured secondary follicles.

Spatial localization of EGF family ligands and receptors in the zebrafish ovarian follicle and their expression profiles during folliculogenesis

The roles of epidermal growth factor (EGF) family in the ovary have received increasing attention recently. Despite this, the production sites of EGF family members in the ovarian follicle still remain controversial. Using zebrafish as the model, the present study investigated spatial distribution of several EGF family ligands and receptors in the follicle as well as their temporal expression profiles during folliculogenesis. RT-PCR analysis on the somatic follicle layer and oocyte revealed that all EGF family ligands examined (egf, tgfa, btc and hbegf) were mostly or exclusively expressed in the oocyte. In contrast, their common receptor (egfr) was expressed exclusively in the follicle layer. By comparison, members of activin family showed an opposite pattern of distribution. Activin subunits (inhbaa and inhbb) were both expressed exclusively in the follicle layer whereas activin receptors and follistatin were abundantly present in the oocyte. During folliculogenesis, egf, tgfa and hbegf increased their expression together with egfr in the fast secondary growth phase. The developmental profiles of EGF family during embryogenesis appeared to argue for an important role for EGF family in folliculogenesis rather than embryogenesis as maternal molecules. The present study provided clear evidence for the existence of two paracrine pathways in the follicle, the oocyte-derived EGF family ligands and follicle cell-derived activins, which may mediate oocyte-to-follicle cell and follicle cell-to-oocyte communications, respectively. The functional relationship between these two signaling systems in the follicle is suggested by the observation that all four EGFR ligands examined significantly stimulated activin subunit expression in cultured follicle cells.

Intestinal phenotype in mice overexpressing a heparin-binding EGF-like growth factor transgene in enterocytes

PRIMARY OBJECTIVE

Heparin-binding EGF-like growth factor (HB-EGF) protects the intestine from damage in animals. Future clinical trials of HB-EGF may involve administration of repeated doses of HB-EGF. Since HB-EGF activates EGF receptors which have been implicated in tumor development, we examined the effects of HB-EGF overexpression in the intestine.

RESEARCH DESIGN

We generated transgenic (TG) mice in which the human HB-EGF gene is driven by the villin promoter to overexpress HB-EGF along the crypt-villous axis from the duodenum to the colon.

RESULTS

HB-EGF TG mice have increased enterocyte proliferation balanced by increased enterocyte apoptosis. Despite prolonged overexpression of HB-EGF, no evidence of intestinal hyperplasia or tumor formation occurs. Although HB-EGF TG mice have no significant phenotypic alterations under basal conditions, they have increased resistance to intestinal injury.

CONCLUSIONS

Prolonged intestinal HB-EGF overexpression results in no significant phenotypic alterations under basal conditions, but confers protection against intestinal injury.

A novel prolactin-like protein (PRL-L) gene in chickens and zebrafish: cloning and characterization of its tissue expression

In this study, a full-length cDNA encoding a prolactin-like protein (PRL-L) was cloned from chicken brain tissues using RT-PCR. This putative PRL-L precursor has 225 amino acids in length and shares 30-35% amino acid sequence identity with prolactin (PRL) of chicken, zebrafish, Xenopus, rat and human. Using RT-PCR, the mRNA expression of PRL-L in chicken tissues was further examined. Unlike the predominant expression of PRL in pituitary, PRL-L was found to be widely expressed in adult chicken extra-pituitary tissues with only minimal expression detected in pituitary. In day-7 chicken embryos, the expression of PRL-L, but not PRL, was also detected in all extra-pituitary tissues examined. In line with this finding, the 5'-flanking region of chicken PRL-L (cPRL-L) gene, but not PRL gene, displayed a strong promoter activity in cultured DF-1 cell (a chicken embryo fibroblast cell line), suggesting that the basal expression of PRL-L gene is controlled by a transcriptional regulatory mechanism different from that of PRL gene. As the same findings in chickens, PRL-like protein(s), which share high amino acid sequence (42-86%) identity with chicken PRL-L, was identified in several non-mammalian vertebrate species including zebra finch, tiger puffer, green puffer and zebrafish. RT-PCR assay demonstrated that zebrafish PRL-L, similar to chicken PRL-L, is expressed in extra-pituitary tissues including brain, gill, muscle, ovary and testis. Taken together, these findings strongly suggest that a novel PRL-like protein exists in some non-mammalian vertebrates and may play an important role in target tissues, such as extra-pituitary tissues of chickens and zebrafish.

A time-course study of gene responses of chicken granulosa cells to Salmonella Enteritidis infection

Consumption of eggs contaminated with Salmonella Enteritidis (SE) has been recognized as one of the important causes of human foodborne salmonellosis. Chicken granulosa cells (cGCs) comprise the last tissue layer surrounding the yolk in preovulatory follicles and are a preferred site for SE invasion. To understand the cGC response to SE infection, we conducted an in vitro time-course study to identify cGC transcriptional changes using chicken whole genome microarrays. The expression of 135 (4h postinfection) and 120 cGC genes (48 h postinfection) were altered (P<.01) compared to uninfected cells. Many of the altered genes were related to immune response, physiological processes, signal transduction, and transcription. Furthermore, we also found that the Jak-STAT pathway, which is essential in the regulation of cellular cytokines and growth factors, was highly active in this study. Among the genes identified by microarray, the mRNA levels of TLR15, IL-6, CXCLi1, CXCLi2, and K203 were shown to be upregulated by real-time RT-PCR (qRT-PCR). In contrast, the mRNA levels of RASD1 and HB-EGF decreased according to both microarray and qRT-PCR analyses. These results suggest that during the SE infection, cGCs recruit cells of the innate immune responses; the infection may also induce suppression of cGC cell proliferation, which alters follicular development and ovulation.

Characterization of the receptors for chicken GHRH and GHRH-related peptides: identification of a novel receptor for GHRH and the receptor for GHRH-LP (PRP)

Growth hormone-releasing hormone and its structurally related peptides, GHRH-like peptide (GHRH-LP) (also called PRP), peptide histidine-isoleucine (PHI), vasoactive intestinal polypeptide (VIP), and pituitary adenylate cyclase-activating polypeptide (PACAP), have been reported to play important physiological roles in pituitary and extrapituitary tissues of vertebrates; however, little is known about the identity of these GHRH-related peptide receptors in birds. In this study, 6 receptors for GHRH and GHRH-related peptides (cGHRHR(1), cGHRHR(2), cGHRH-LPR, cPAC(1), cVPAC(1), and cVPAC(2)) were cloned from chicken brain or pituitary, and their functionalities were examined in Chinese hamster ovary (CHO) cells using a pGL3-CRE-luciferase reporter system. Results showed that: (1) all receptors are G protein-coupled receptors functionally coupled to the intracellular PKA signaling pathway; (2) 2 GHRH receptors (cGHRHR(1) and cGHRHR(2)) were identified, and both receptors could be potently activated by cGHRH; (3) cGHRH-LP could activate its specific receptor cGHRH-LPR (cPRP-R), and it also activated cGHRHR(1) and cGHRHR(2); and (4) PACAP could potently activate its receptors cPAC(1), cVPAC(1) and cVPAC(2); however, cVPAC(1) and cVPAC(2) could also be effectively activated by cVIP and tPHI, indicating that they can serve as VIP receptors and potential PHI receptors. Using a reverse transcription polymerase chain reaction assay, we further examined the mRNA expression of these receptors in adult chicken tissues. The expressions of cGHRHR(1), cGHRHR(2), and cGHRH-LPR are restricted mainly to the pituitary and/or brain, whereas cPAC(1), cVPAC(1), and cVPAC(2) are expressed in most of the tissues examined. Collectively, our study identified the receptors for chicken GHRH and GHRH-related peptides, including a novel GHRH receptor (cGHRHR(2)), and established a basis to elucidate the roles of these peptides in target tissues.

Differential regulation of betacellulin and heparin-binding EGF-like growth factor in cultured zebrafish ovarian follicle cells by EGF family ligands

Recently the roles of epidermal growth factor (EGF) family ligands in vertebrate ovaries have received increasing attention, including betacellulin (BTC), amphiregulin (AR), heparin-binding EGF-like growth factor (HB-EGF), transforming growth factor alpha (TGFalpha), epiregulin, and EGF itself. In the zebrafish (Danio rerio), four members of EGF family have been identified by either molecular cloning or genome sequencing, which are EGF, TGFalpha, BTC, and HB-EGF. Although they are mostly expressed in the oocytes in the ovary, the present study demonstrated the expression of all the four EGF family ligands (egf, btc, tgfa, and hbegf) in cultured zebrafish follicle cells albeit at very low levels. Treatment of the cultured follicle cells with EGF, BTC, and HB-EGF demonstrated differential effects of these ligands on the expression of themselves. While the expression of egf was rather non-responsive to EGF, BTC, and HB-EGF, the expression of btc was consistently down-regulated by all the three molecules. In contrast, hbegf increased its expression in response to these molecules. These results suggest that there is an EGF signaling network in the zebrafish ovarian follicle, and the functionality of this network is self-regulated by its own members.