Effect of growth hormone on steroid content, proliferation and apoptosis in the chicken ovary during sexual maturation

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.

Untargeted Metabolomics Revealed Potential Biomarkers of Small Yellow Follicles of Chickens during Sexual Maturation

Sexual maturation provides economically important traits in poultry production. Research on the initiation mechanism of sexual maturity is of great significance for breeding high-yield laying hens. However, the underlying mechanisms are not fully clear. Here, one hundred and fifty Chahua No. 2 laying hens (the CH2 group, which has precocious puberty) and one hundred and fifty Wu Liang Shan black-bone laying hens (the WLS group, a late-maturing chicken breed) with similar weights and ages were randomly selected. ELISA was used to determine the secretion levels of luteinizing hormone (LH), estradiol (E2), and progesterone (P4) in 150-day-old serum and small yellow follicle (SYF) tissues. A histology examination, immunohistochemistry, and quantitative real-time PCR (qPCR) were used to explore the molecular mechanism of how some genes related to oxidative stress affect sexual maturation. The results showed that the secretion levels of LH, E2, and P4 in the CH2 group serum and SYF were higher than those in the WLS group. The results of the real-time PCR of all genes showed that the expression levels of cytochrome P450 family 11 subfamily A member 1, steroidogenic acute regulatory protein, follicle-stimulating hormone receptor, and cytochrome P450 family 19 subfamily A member 1 in the CH2 group were significantly higher than those in the WLS groups (p < 0.001). Untargeted metabolomics combined with multivariate statistical analysis was used to identify biomarkers of SYF tissues in the CH2 and WLS groups. A trajectory analysis of the principal component analysis (PCA) results showed that the samples within the group were clustered and that the samples were dispersed between the CH2 and the WLS groups, indicating that the results of the measured data were reliable and could be used for further research. Further analysis showed that a total of 319 metabolites in small yellow follicles of the CH2 and WLS groups were identified, among which 54 downregulated differential metabolites were identified. These 54 metabolites were found as potential CH2 biomarkers compared with WLS at 150 days, and the different expressions of L-arginine, L-prolinamide, (R)-4-hydroxymandelate, glutathione, and homovanillic acid were more significant. Twenty metabolic pathways were found when significantly differential metabolites were queried in the KEGG database. According to the impact values of the metabolic pathways, eighteen differential metabolites belonged to the mTOR signaling pathway, glutathione metabolism, ABC transporters, the cell ferroptosis pathway, and D-arginine and D-ornithine metabolism. Interestingly, we identified that the cell ferroptosis pathway played an important role in chicken follicle selection for the first time. The histology and immunohistochemistry of SYF showed that the number of granulosa cells increased in the CH2 groups and the expression levels of glutathione peroxidase 4, tumor protein p53, ribosomal protein S6 kinase, and sterol regulatory element binding protein 1 in the granulosa cell layer were upregulated in the CH2 group at the time of sexual maturation. Furthermore, we also speculated that the antioxidant system may play an indispensable role in regulating sexual maturity in chickens. Overall, our findings suggest differentially expressed metabolites and metabolic pathways between CH2 and WLS chickens, providing new insights into the initiation mechanism of sexual maturation.

RNA Sequencing of the Pituitary Gland and Association Analyses Reveal PRKG2 as a Candidate Gene for Growth and Carcass Traits in Chinese Ningdu Yellow Chickens

Growth and carcass traits are of great economic importance to the chicken industry. The candidate genes and mutations associated with growth and carcass traits can be utilized to improve chicken growth. Therefore, the identification of these genes and mutations is greatly importance. In this study, a total of 17 traits related to growth and carcass were measured in 399 Chinese Ningdu yellow chickens. RNA sequencing (RNA-seq) was performed to detect candidate genes using 12 pituitary gland samples (six per group), which exhibited extreme growth and carcass phenotypes: either a high live weight and carcass weight (H group) or a low live weight and carcass weight (L group). A differential expression analysis, utilizing RNA-seq, between the H and L groups identified 428 differentially expressed genes (DEGs), including 110 up-regulated genes and 318 down-regulated genes. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses of the identified genes showed a significant enrichment of 158 GO terms and two KEGG pathways, including response to stimulus and neuroactive ligand-receptor interaction, respectively. Furthermore, RNA-seq data, qRT–PCR, and quantitative trait transcript (QTT) analysis results suggest that the PRKG2 gene is an important candidate gene for growth and carcass traits of Chinese Ningdu yellow chickens. More specifically, association analyses of a single nucleotide polymorphism (SNP) in PRKG2 and growth and carcass traits showed that the SNP rs16400745 was significantly associated with 12 growth and carcass traits (P < 0.05), such as carcass weight (P = 9.68E-06), eviscerated weight (P = 3.04E-05), and semi-eviscerated weight (P = 2.14E-04). Collectively, these results provide novel insights into the genetic basis of growth in Chinese Ningdu yellow chickens and the SNP rs16400745 reported here could be incorporated into the selection programs involving this breed.

Transcriptome analyses of potential regulators of pre- and post-ovulatory follicles in the pigeon (Columba livia)

To identify the dominant genes controlling follicular maturation, ovulation and regression for pigeon, we used RNA-seq to explore the gene expression profiles of pre- and post-ovulatory follicles of pigeon. We obtained total of 4.73million (96% of the raw data) high-quality clean reads, which could be aligned with 20282 genes. Gene expression profile analysis identified 1461 differentially expressed genes (DEGs) between the pre- (P4) and post-ovulatory follicles (P5). Of these, 843 genes were upregulated, and 618 genes were down-regulated. Furthermore, many DEGs were significantly enriched in some pathways closely related to follicle maturation, ovulation and regression, such as ECM-receptor interaction, vascular smooth muscle contraction, progesterone-mediated oocyte maturation, phagosome. Importantly, the DGEs in ECM-receptor interaction pathway included COL1A1 , COL1A2 , COL4A1 , COL4A2 , ITGA11 , ITGB3 and SDC3 , in the progesterone-mediated oocyte maturation pathway involved CDK1 , CDC25A , CCNB3 , CDC20 and Plk1 , and in the vascular smooth muscle contraction covered CALD1 , KCNMA1 , KCNMB1 , CACNA1 , ACTA2 , MYH10 , MYL3 , MYL6 , MYL9 , closely related to promoting follicular maturation and ovulation in pre-ovulatory follicles. Moreover, it seems that the lysosomal cathepsin family has a decisive role in the regression of early stage of post-ovulatory follicle. Taken together, these data enrich the research of molecular mechanisms of pigeon follicular activities at the transcriptional level and provide novel insight of breeding-related physiology for birds.

Transcriptional regulation of CYP19A1 expression in chickens: ESR1, ESR2 and NR5A2 form a functional network

Aromatase, encoded by CYP19A1, is responsible for the conversion of androgen to estrogen, which plays a vital role in the development and function of the ovary and functions in many other physiological processes in both sexes. Instead of being expressed in ovarian granulosa cells, as in mammals, CYP19A1 is expressed in chickens in the theca cells of ovarian follicles, and the mechanism of CYP19A1 expression regulation remains unknown. Here, using immunofluorescence and western blotting assay, we first confirmed that CYP19A1 and FOXL2 (Forkheadbox L2) were coexpressed in pre-granulosa cells of female chicken embryonic gonads, while FOXL2 did not affect aromatase expression at embryonic stages. Second, our research showed that CYP19A1, ESR1 (estrogen receptor alpha), ESR2 (estrogen receptor beta) and NR5A2 (liver receptor homologue-1) were coexpressed in the theca cell layers of chicken small yellow follicles. There was cross-talk between CYP19A1 and candidate transcription factors (ESR1, ESR2 and NR5A2), which was identified by generating a reliable theca cell culture model. Using luciferase assays in theca cells and chicken embryonic fibroblast (DF-1) cells, the results suggested that ESR1 and NR5A2 had potential effects on CYP19A1 promoter activity in chickens. Overexpression of ESR1, ESR2 and NR5A2 in chicken embryonic fibroblast (DF-1) cells upregulated the protein expression of CYP19A1, mutually restricted each other and formed a potential regulatory network to coordinate the expression of CYP19A1. To conclude, our results indicated that FOXL2 cannot regulate the expression of CYP19A1 at chicken embryonic stages and after sexual maturity, ESR1, ESR2 and NR5A2 form a functional network to affect the expression of CYP19A1. These results laid a foundation for further research on the transcriptional regulation of chicken aromatase.

Regulation of ovarian function by growth hormone: Potential intervention of ovarian aging

Growth hormone (GH) is mainly secreted by eosinophils of anterior pituitary gland. GH plays an important role in regulating the growth and development of many tissues and cells, so it is used in the treatment of many diseases. In recent years, the regulation of GH on ovarian function has attracted much attention. GH has been applied in controlled ovarian hyperstimulation, particularly in the patients with advanced age, diminished ovarian reserve (DOR) and poor ovarian response (POR). GH can directly bind to the growth hormone receptor (GHR) on the ovary to promote the growth, maturation and ovulation of follicles, as well as to inhibit follicular atresia. GH so as to promote the occurrence of early follicles, enhance the sensitivity of follicles to gonadotropins, accelerate the maturation of oocyte nucleus, improve mitochondrial activity and the quality of oocytes through the insulin-like growth factor (IGF) system, which is an indirect regulation. The deep-seated effects of GH on human reproduction and ovarian aging need further basic research and clinical practice.

Dose-Effect of Zearalenone on the Localization and Expression of Growth Hormone, Growth Hormone Receptor, and Heat Shock Protein 70 in the Ovaries of Post-weaning Gilts

Zearalenone (ZEA) has an estrogen-like effect, which can injure the reproductive system of animals, causing infertility, and abortion in sows. However, the underlying mechanisms are still not clear. The objective of this study was to assess the effects of ZEA on the localization and expression of growth hormone (GH), growth hormone receptor (GHR), and heat shock protein 70 (Hsp70) in the ovaries of post-weaning gilts. Forty healthy post-weaning gilts were randomly provided one of four diets: normal basal diet supplemented with 0 (control), 0.5 (ZEA0.5), 1.0 (ZEA1.0), and 1.5 (ZEA1.5) mg ZEA/kg. Gilts were housed and fed individually for 35 days; the ovaries were collected after euthanasia for antioxidant index, relative mRNA and protein expression, and immunohistochemical analyses of GH, GHR, and Hsp70. The results revealed that the glutathione peroxidase and total superoxide dismutase levels decreased (p < 0.05), whereas the malondialdehyde level increased (p < 0.05) with increasing ZEA content. The localization pattern of GH, GHR, and Hsp70 in ZEA-treated gilts was the same as that in the control; however, the localization of yellow and brown immunoreactive substances of GH, GHR, and Hsp70 was stronger in the ZEA groups than in the control. The relative mRNA and protein expression of GHR and Hsp70 was the highest in the ZEA1.0 group (p < 0.05), whereas that of GH was the highest in the ZEA0.5 group (p < 0.05). The mRNA and protein expression of GH was lower in the ZEA1.5 group than in the control (p < 0.05). Hsp70 results showed adverse responses to increasing ZEA levels in gilt ovaries, suggesting that Hsp70 played an important role in alleviating ZEA-induced oxidative stress.

Effects of LPS on the Secretion of Gonadotrophin Hormones and Expression of Genes in the Hypothalamus-Pituitary-Ovary (HPG) Axis in Laying Yangzhou Geese

Simple Summary

Lipopolysaccharide (LPS), an endotoxin from E. coli, has been proven to impair follicle development and steroidogenesis, secretion of pituitary and hypothalamus reproductive hormones in mammals. However, the effects of LPS on the avian reproductive axis remain elusive. Pathogenic bacterial infection due to the particular mating behavior on the water containing pathogens was reported to decrease the laying rate and cause economic loss in goose production. In this study, we showed that LPS infection disturbed the plasma pituitary gonadotrophin hormone concentrations and the gene expression of the reproductive axis in Yangzhou geese. Notably, for the first time we proved that both the expression of gonadotrophin-releasing hormone (GnRH) and gonadotropin-inhibiting hormone (GnIH), two important reproductive genes from the hypothalamus, were altered after LPS treatment in birds. Our results can explain the decreased laying rate in goose after bacterial infection, and also provide new insights into reproductive dysfunction caused by LPS and the immune challenge in birds.

Abstract

Lipopolysaccharide (LPS) from gram-negative bacteria was found to be involved in the decrease in laying performance in goose flocks with high stocking density during summer months. LPS injection delayed the increase in the laying rate and altered hierarchical follicle morphology. While there is evidence that LPS exerts suppressive effects on goose reproduction, the time course effects of LPS on the hypothalamus-pituitary-ovary (HPG) axis remain elusive. In this study, we investigated the expression of genes in the HPG axis and the plasma gonadotrophin hormone concentrations in breeding geese at 0, 6, 12, 24, and 36 h after intravenous injection with LPS. The results showed that LPS treatment enhanced and suppressed expression of hypothalamic gonadotropin-inhibiting hormone (GnIH) and gonadotrophin-releasing hormone (GnRH) mRNA, respectively, and similar effects were observed on the mRNA expression of their receptors, GnIHR and GnRHR, in the pituitary. LPS treatment transiently increased follicle FSHβ mRNA expression at 12 h and exerted no significant effect on LHβ mRNA expression in the pituitary. Regardless of the expression of FSHβ and LHβ, plasma follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations were significantly increased during 24–36 h after LPS treatment. In the ovary, StAR and Cyp11a1 were mainly expressed in the granulosa layer (GL) of hierarchical follicles, while Cyp17a1 and Cyp19a1 were mainly expressed in white follicles (WFs) and yellowish follicles (YFs), and to a lesser extent in the theca layer (TL). After LPS treatment, the mRNA levels of Cyp11a1 in the GLs, Cyp17a1 in the WFs and TL, and Cyp19a1 in the WFs, YFs, and TL were significantly decreased. However, LPS treatment transiently upregulated StAR expression at 12 h. These results indicate that the exposure of laying geese to LPS may impair the HPG axis and disturb ovarian steroidogenesis. Our research provides new insights into reproductive dysfunction caused by LPS and the immune challenge in birds.

Novel Regulatory Factors in the Hypothalamic-Pituitary-Ovarian Axis of Hens at Four Developmental Stages

Ovarian follicular development is an extremely complex and precise process in which the hypothalamic-pituitary-ovarian (HPO) axis plays a crucial role. However, research on the regulatory factors of the HPO axis is sparse. In this study, transcriptomes of the tissues in the entire HPO axis at 15, 20, 30, and 68 w of age were analyzed. In total, 381, 622, and 1090 differentially expressed genes (DEGs) were found among the hypothalamus, pituitary, and ovary, respectively. In particular, the greatest number of DEGs (867) was identified from the comparison of ovary at 30 and 15 w, which might be related to ovarian development and function at high ovulation capacity. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses indicated that most of these DEGs in the significantly enriched biological process (BP) terms and pathways were primarily involved in tissue development and the regulation of reproductive hormone biosynthesis and secretion. The latter is highly related to the HPO axis. Therefore, a number of hub candidate genes strongly associated with the HPO axis in each tissue were filtered by analyzing the Protein-protein interaction (PPI) network and seven known reproductive hormone-associated key genes were obtained: PGR, HSD3B2, CYP17A1, CYP11A1, CYP21A2, STS, and CYP19A1, and 12 novel genes: ROCK2, TBP, GTF2H2, GTF2B, DHCR24, DHCR7, FDFT1, LSS, SQLE, MSMO1, CYP51A1, and PANK3. These will be utilized for further research into the function of the HPO axis. This study has highlighted the major role of the HPO axis in the reproduction of hens at the four developmental stages and explored the novel factors that might regulate reproduction, thus providing new insights into the function of the HPO axis on the reproductive system.

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

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

Gene Expression Profiling in Ovaries and Association Analyses Reveal HEP21 as a Candidate Gene for Sexual Maturity in Chickens

Simple Summary

Chicken meat and egg productions are essential for human beings. Sexual maturity is important for both egg production and meat flavor. It is necessary to elucidate the genetic mechanism of chicken sexual maturity. In current study, we used digital gene expression (DGE) RNA-sequencing analysis to investigate differential expression of genes in pre-pubertal and post-pubertal ovaries in two different sub-breeds of chicken with different onsets of sexual maturity. After the analysis of RNA-sequencing data, numerous differentially expressed genes were found in both comparisons (32 day old, early-sexual-maturity pre-laying hens (P-F-O1) vs. 103 day old early-sexual-maturity laying hens (P-F-O2), and 32 day old late-sexual-maturity pre-laying hens (L-F-O1) vs. 153 day old late-sexual-maturity pre-laying hens (L-F-O2)). With the bioinformatic analysis, hen egg protein 21 kDa (HEP21) was chosen as the candidate gene to conduct following experiment. The variations in HEP21 were screened and association analyses between rs315156783 and reproductive traits were investigated in fifth-generation Ningdu Yellow chickens from a closely bred population. These results demonstrated that HEP21 is a candidate gene for sexual maturity and ovary development in chickens. However, the underlying mechanism of how HEP21 regulates chicken sexual maturity needs further focused studies.

Abstract

The age of onset of sexual maturity is an important reproductive trait in chickens. In this study, we explored candidate genes associated with sexual maturity and ovary development in chickens. We performed DGE RNA-sequencing analyses of ovaries of pre-laying (P-F-O1, L-F-O1) and laying (P-F-O2, L-F-O2) hens of two sub-breeds of Ningdu Yellow chicken. A total of 3197 genes were identified in the two comparisons, and 966 and 1860 genes were detected exclusively in comparisons of P-F-O1 vs. P-F-O2 and L-F-O1 vs. L-F-O2, respectively. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed that genes involved in transmembrane signaling receptor activity, cell adhesion, developmental processes, the neuroactive ligand–receptor interaction pathway, and the calcium signaling pathway were enriched in both comparisons. Genes on these pathways, including growth hormone (GH), integrin subunit beta 3 (ITGB3), thyroid stimulating hormone subunit beta (TSHB), prolactin (PRL), and transforming growth factor beta 3 (TGFB3), play indispensable roles in sexual maturity. As a gene unique to poultry, hen egg protein 21 kDa (HEP21) was chosen as the candidate gene. Differential expression and association analyses were performed. RNA-seq data and qPCR showed that HEP21 was significantly differentially expressed in pre-pubertal and pubertal ovaries. A total of 23 variations were detected in HEP21. Association analyses of single nucleotide polymorphisms (SNPs) in HEP21 and reproductive traits showed that rs315156783 was significantly related to comb height at 84 and 91 days. These results indicate that HEP21 is a candidate gene for sexual maturity in chickens. Our results contribute to a more comprehensive understanding of sexual maturity and reproduction in chickens.

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.

Response of the chicken ovary to GH treatment during a pause in laying induced by fasting

This study was undertaken to examine the effect of GH treatment during a pause in laying on (1) ovarian follicle formation, growth (folliculogenesis), and atresia; (2) follicle cell proliferation and apoptosis; and (3) mRNA expression of selected yolk-specific proteins in the chicken liver. A pause in egg laying was induced by food deprivation for 5 d, followed by feeding every other day, and then feeding daily from day 10 onward. Birds were divided into 3 groups: control (n = 18) fed ad libitum, subjected to a pause in laying (n = 18), and subjected to a pause in laying and injected every day with 200 μg/kg BW of chicken GH (chGH; n = 18). The liver, ovarian stroma, and follicles were isolated from the hens of each group on days 6 (ovary regression), 13 (ovary recrudescence), and 17 or 20 (ovary rejuvenated) of the experiment. The results showed that injection of chGH during fasting (1) increased the number of follicles <1 mm and proliferating cell nuclear antigen (PCNA)-positive (proliferating) cells in these follicles; (2) attenuated the expression of PCNA and survivin mRNA in the white follicles and the activity of caspases 3, 8, and 9 in the stroma and white follicles; (3) intensified the atresia of yellow hierarchical follicles; and (4) deepened the effect of starvation on egg yolk gene expression concomitantly with considerably increased IGF-1 transcription levels in the liver (P < 0.05 to P < 0.001). Prolongation of chGH injections into the refeeding period did not exert pronounced effects on the examined parameters. In summary, the results provide evidence that GH promotes the formation and development of prehierarchical follicles in the hen ovary during a pause in laying by regulating cell proliferation and apoptosis. Alterations in cell proliferation- and apoptosis-related gene expression or enzyme activity in ovarian follicles as well as the expression of egg yolk proteins in the liver after chGH treatment strongly suggest that this hormone is involved in determining the rate of regression and rejuvenation of the chicken ovary during a pause in laying.

Trans-omics analyses revealed differences in hormonal and nutritional status between wild and cultured female Japanese eel (Anguilla japonica)

Long-term stock decline in the Japanese eel (Anguilla japonica) is a serious issue. To reduce natural resource utilization in Japan, artificial hormonal induction of maturation and fertilization in the Japanese eel has been intensively studied. Recent experiment on feminized (by feeding a commercial diet containing estradiol-17β for first half year) cultured female eels have shown ovulation problems, which is seldom observed in captured wild female eels. Therefore, the aim of this study is to try to investigate causes of ovulation problem frequently seen in cultured female eels by comparative trans-omics analyses. The omics data showed low growth hormone and luteinizing hormone transcription levels in the brain and low sex hormone–binding globulin transcription levels in the liver of the cultured female eels. In addition, it was found that high accumulation of glucose-6-phosphate and, maltose in the liver of the cultured female eel. It was also found that docosahexaenoic (DHA) acid, eicosapentaenoic acid (EPA) and arachidonic acid (ARA) ratios in cultured female eels were quite different from wild female eels. The data suggested that ovulation problem in cultured female eels was possibly resulted from prolonged intake of a high-carbohydrate diet and/or suboptimal DHA/EPA/ARA ratios in a diet.

Application of Growth Hormone in in vitro Fertilization

Growth hormone (GH) is a peptide hormone secreted mainly by the anterior part of the pituitary gland and plays a critical role in cell growth, development, and metabolism throughout the body. GH can not only directly influence human oocytes and cumulus cells but also indirectly improve oocyte quality through activating synthesis of insulin-like growth factor-I or promoting follicle-stimulating hormone-induced ovarian steroidogenesis. Since GH can regulate female and male infertility, it has been applied in the management of infertility for many years, especially in patients with poor ovarian response or poor prognosis. During ovarian stimulation, GH administration might improve the success rate of in vitro fertilization (IVF) probably through the beneficial effects of GH on oocyte quality as indicated by a higher number of mature oocytes and embryos arriving at the transfer stage and a higher fertility rate in GH-treated patients. However, there is still great controversy in the application of GH in IVF. While some researchers showed that pregnancy, implantation and live birth rates could be increased by ovarian pretreatment with GH, others did not support GH as an effective adjuvant for infertility treatment because the live birth rate was not increased. This study reviewed and summarized recent advancements and benefits in clinical application of GH, trying to reach a just unbiased conclusion regarding the effect of GH therapy in IVF.

Effect of growth hormone on steroid concentrations and mRNA expression of their receptor, and selected egg-specific protein genes in the chicken oviduct during pause in laying induced by fasting

This study was undertaken to examine the effect of growth hormone (GH) treatment during pause in laying on (1) the concentration of steroids in blood plasma and oviduct tissues, (2) the expression of mRNA of steroid receptors, and (3) the mRNA expression of selected egg-specific proteins in the chicken oviduct. A pause in egg laying was induced by food deprivation for 5 d, followed by feeding every other day, and then feeding daily from Day 10 onward. Birds were divided into three groups: control (n = 18) fed ad libitum, subjected to pause in laying (n = 18), and subjected to pause in laying and injected every day with 200 μg/kg BW of chicken GH (chGH; n = 18). The oviduct was isolated from hens of each group on Days 6 (when the oviduct was regressed), 13 (during oviduct recrudescence), and 17 or 20 (rejuvenated oviduct) of the experiment. Fasting caused a decrease in plasma concentrations of progesterone (P4), testosterone, and estradiol on Day 6 and a reduction in tissue concentrations of these steroids on Days 6 and 13. Fasting also caused an increased relative expression of estrogen receptor α and β (ERα, ERβ) and progesterone receptor (PR) in the magnum and shell gland on Day 6, increased ERα and PR in the magnum on Days 13 and 17 or 20, and increased androgen receptor (AR) mRNA in the magnum on Days 6 and 13 and in the shell gland on Day 13. A fasting-induced elevation in ovocalyxin-36 mRNA expression on Day 6 and a decrease in avidin mRNA on Days 6 and 13 and in ovocleidin-116 on Day 13 were also observed (P < 0.05 to P < 0.001). Administration of chGH abolished the fasting-induced decrease in the concentration of steroids in plasma and tissues. Furthermore, chGH enhanced the effect of fasting on mRNA expression of PR, ERα, and avidin in the magnum on Day 6, and ERα in the shell gland on Day 13. The gene expression of ovalbumin on Days 6 and 13, ovocalyxin-36 and ovocleidin-116 on Day 6 was decreased in chGH-treated chickens. In contrast, the expression of ovalbumin on Day 17 or 20 was increased (P < 0.05 to P < 0.001). The results obtained indicate that, by alterations in the concentration of steroid hormones and their receptor expression in the chicken oviduct, GH determines the rate of regression and rejuvenation of this organ during molting. Moreover, changes in the expression of selected egg proteins indicate that GH might be the regulator of the secretory activity of the hen oviduct.

Transcription of CYP19A1 is directly regulated by SF-1 in the theca cells of ovary follicles in chicken

Many studies have suggested the important role of estrogen in ovarian differentiation and development of vertebrates including chicken. Cytochrome P450 aromatase, encoded by CYP19A1, is a key enzyme in estrogen synthesis, but the mechanism of CYP19A1 regulation in chicken remains unknown. Here, we found that CYP19A1 was only expressed in the theca cell layers of chicken ovary follicles. Steroidogenic factor 1 (SF-1, also named as nuclear receptor subfamily 5 group A member 1, NR5A1), a potential regulators, was expressed in both the theca cell layers and granulosa cell layers. Forkheadbox L2 (FOXL2), another potential regulator, was only expressed in the granulosa cell layers. Using luciferase assays in vitro, we found that SF-1 could activate the promoter of CYP19A1 by binding to the nuclear receptor half-site (5'-TCAAGGTCA-3') from -280 to -271 base pairs. FOXL2 did not activate the promoter of chicken CYP19A1 gene in either 293T or DF-1 cells. Overexpression of SF-1 in DF-1 cells upregulated aromatase expression, but FOXL2 could not. Taken together, our results indicated that SF-1 activates CYP19A1 mRNA expression via a conserved binding site in chicken ovary, but FOXL2 may not affect the expression of CYP19A1.

Autocrine/paracrine proliferative effect of ovarian GH and IGF-I in chicken granulosa cell cultures

It is known that growth hormone (GH) and its receptor (GHR) are expressed in granulosa cells (GC) and thecal cells during the follicular development in the hen ovary, which suggests GH is involved in autocrine/paracrine actions in the female reproductive system. In this work, we show that the knockdown of local ovarian GH with a specific cGH siRNA in GC cultures significantly decreased both cGH mRNA expression and GH secretion to the media, and also reduced their proliferative rate. Thus, we analyzed the effect of ovarian GH and recombinant chicken GH (rcGH) on the proliferation of pre-hierarchical GCs in primary cultures. Incubation of GCs with either rcGH or conditioned media, containing predominantly a 15-kDa GH isoform, showed that both significantly increased proliferation as determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, proliferating cell nuclear antigen (PCNA) quantification and ((3)H)-thymidine incorporation ((3)H-T) assays in a dose response fashion. Both, locally produced GH and rcGH also induced the phosphorylation of Erk1/2 in GC cultures. Furthermore, GH increased IGF-I synthesis and its release into the GC culture incubation media. These results suggest that GH may act through local IGF-I to induce GC proliferation, since IGF-I immunoneutralization completely abolished the GH-induced proliferative effect. These data suggest that GH and IGF-I may play a role as autocrine/paracrine regulators during the follicular development in the hen ovary at the pre-hierarchical stage.

Growth Hormone Ameliorates the Radiotherapy-Induced Ovarian Follicular Loss in Rats: Impact on Oxidative Stress, Apoptosis and IGF-1/IGF-1R Axis

Radiotherapy is one of the standard cytotoxic therapies for cancer. However, it has a profound impact on ovarian function leading to premature ovarian failure and infertility. Since none of the currently available methods for fertility preservation guarantees future fertility, the need for an effective radioprotective agent is highly intensified. The present study investigated the mechanisms of the potential radioprotective effect of growth hormone (GH) on γ irradiation-induced ovarian failure and the impact of the insulin like growth factor 1 (IGF-1) in the underlying protection. Immature female Sprague-Dawley rats were either exposed to single whole body irradiation (3.2 Gy) and/or treated with GH (1 mg/kg s.c). Experimental γ-irradiation produced an array of ovarian dysfunction that was evident by assessment of hormonal changes, follicular development, proliferation marker (PCNA), oxidative stress as well as apoptotic markers. In addition, IGF-1/IGF-1R axis expression was assessed using real-time PCR and immunolocalization techniques. Furthermore, after full maturity, fertility assessment was performed. GH significantly enhanced follicular development and restored anti-Mullerian hormone serum level as compared with the irradiated group. In addition, GH significantly ameliorated the deleterious effects of irradiation on oxidative status, PCNA and apoptosis. Interestingly, GH was shown to enhance the ovarian IGF-1 at transcription and translation levels, a property that contributes significantly to its radioprotective effect. Finally, GH regained the fertility that was lost following irradiation. In conclusion, GH showed a radioprotective effect and rescued the ovarian reserve through increasing local IGF-1 level and counteracting the oxidative stress-mediated apoptosis.

Growth hormone production and role in the reproductive system of female chicken

The expression and role of growth hormone (GH) in the reproductive system of mammals is rather well established. In birds the limited information thus far available suggests that GH is an endocrine or paracrine/autocrine regulator of ovarian and oviductal functions too. GH and its receptors are expressed in all compartments of the ovary and oviduct and change accordingly to physiological state. The intra-ovarian role of GH likely includes the regulation of steroidogenesis, cell proliferation and apoptosis, the modulation of LH action and the synthesis of IGFs (insulin-like growth factors). In the oviduct, GH is also involved in the regulation of oviduct-specific protein expression. The present study provides a review of current knowledge on the presence and action of GH in the female reproduction, in which it is likely that act in endocrine, autocrine or paracrine mechanisms.

Growth hormone and reproduction: a review of endocrine and autocrine/paracrine interactions

The somatotropic axis, consisting of growth hormone (GH), hepatic insulin-like growth factor I (IGF-I), and assorted releasing factors, regulates growth and body composition. Axiomatically, since optimal body composition enhances reproductive function, general somatic actions of GH modulate reproductive function. A growing body of evidence supports the hypothesis that GH also modulates reproduction directly, exerting both gonadotropin-dependent and gonadotropin-independent actions in both males and females. Moreover, recent studies indicate GH produced within reproductive tissues differs from pituitary GH in terms of secretion and action. Accordingly, GH is increasingly used as a fertility adjunct in males and females, both humans and nonhumans. This review reconsiders reproductive actions of GH in vertebrates in respect to these new conceptual developments.

Extrapituitary growth hormone in the chicken reproductive system

Increasing evidence shows that growth hormone (GH) expression is not limited to the pituitary, as it can be produced in many other tissues. It is known that growth hormone (GH) plays a role in the control of reproductive tract development. Acting as an endocrine, paracrine and/or autocrine regulator, GH influences proliferation, differentiation and function of reproductive tissues. In this review we substantiate the local expression of GH mRNA and GH protein, as well as the GH receptor (GHR) in both male and female reproductive tract, mainly in the chicken. Locally expressed GH was found to be heterogeneous, with a 17 kDa variant being predominant. GH secretagogues, such as GHRH and TRH co-localize with GH expression in the chicken testis and induce GH release. In the ovarian follicular granulosa cells, GH and GHR are co-expressed and stimulate progesterone production, which was neutralized by a specific GH antibody. Both testicular and follicular cells in primary cultures were able to synthesize and release GH to the culture medium. We also characterized GH and GH mRNA expression in the hen's oviduct and showed that it had 99.6% sequence identity with pituitary GH. Data suggest local reproductive GH may have important autocrine/paracrine effects.

Localization of apoptotic and proliferating cells and mRNA expression of caspases and Bcl-2 in gonads of chicken embryos

The aim of the present study was to analyze participation of apoptosis and proliferation in gonadal development in the chicken embryo by: (1) localization of apoptotic (TUNEL) and proliferating (PCNA immunoassay) cells in male and female gonads and (2) examination of mRNA expression (RT-PCR) of caspase-3, caspase-6 and Bcl-2 in the ovary and testis during the second half of embryogenesis and in newly hatched chickens. Apoptotic cells were found in gonads of both sexes. At E18 the percentage of apoptotic cells (the apoptotic index, AI) in the ovarian medulla and the testis was lower (p<0.05) than in the ovarian cortex. In the ovarian medulla, the AI at E18 was lower (p<0.05) than on E12. In the testis, the AI was significantly lower (p<0.05) at E18 than at E15 and 1D. The percentage of proliferating cells (the proliferation index: PI) within the ovary significantly increased from E15 to 1D in the cortex, while proliferating cells in the medulla were detected only at E15. In the testis, the PI gradually increased from E12 to 1D. The mRNA expression of caspase-3 and -6 as well as Bcl-2 was detected in male and female gonads at days 12 (E12), 15 (E15) and 18 (E18) of embryogenesis and the day after hatching (1D). The expression of all analyzed genes on E12 was significantly higher (p<0.05) in female than in male gonads. This difference was also observed at E15 and E18, but only for the caspase-6. The results obtained showed tissue- and sex-dependent differences in the number of apoptotic and proliferating cells as well as mRNA expression of caspase-3, -6 and Bcl-2 genes in the gonads of chicken embryos. Significant increase in the number of proliferating cells in the ovarian cortex and lack of these cells in the ovarian medulla (stages E12, E18, 1D) simultaneous with decrease in the intensity of apoptosis only in the medulla indicates that proliferation is the dominant process involved in the cortical development, which constitutes the majority of the functional structure of the fully developed ovary. No pronounced changes in the expression of apoptosis-related genes found during embryogenesis suggest that they cannot be considered as important indicators of gonad development. The molecular mechanisms of the regulation of balance between apoptosis and proliferation in developing avian gonads need to be further investigated.

Chicken oviduct-the target tissue for growth hormone action: effect on cell proliferation and apoptosis and on the gene expression of some oviduct-specific proteins

The aim of this study was to examine the in vivo effect of growth hormone (GH) on cell proliferation and apoptosis and on the gene expression of selected proteins in the chicken oviduct before sexual maturity (first oviposition). Ten-week-old Hy-Line Brown chickens were injected three times a week with 200 μg · kg^-1 body weight of recombinant chicken GH (cGH) until 16 weeks of age. Control hens received 0.9 % NaCl with 0.05 % bovine serum albumin as a vehicle. Treatment with cGH increased (P < 0.05) oviduct weight at 16 weeks of age, i.e. 1–2 weeks before onset of egg laying. The highest number of proliferating (determined by proliferating cell nuclear antigen [PCNA] immunocytochemistry) and apoptotic (determined by TUNEL assay) cells in the oviduct was found in the mucosal epithelium, and the lowest in the stroma. Administration of cGH did not increase (P > 0.05) the number of PCNA-positive cells but it decreased (P < 0.01) the number of TUNEL-positive cells, thus increasing the proliferating-to-apoptotic cell ratio in the oviduct. Gene expression (determined by real-time polymerase chain reaction) of apoptosis-related caspase-2 in the magnum and caspase-3 in the magnum and isthmus and their activity (determined by fluorometric assay) in the magnum were attenuated (P < 0.05) in cGH-treated hens. The gene expression of the magnum-specific ovalbumin and the shell-gland-specific ovocalyxins 32 and 36 was increased (P < 0.05) in cGH-treated chickens. In contrast, the expression of Bcl-2 and of caspases 8 and 9 was not affected by cGH in any of the oviductal segments. The results suggest that GH, via the orchestration of apoptosis and expression of some oviduct-specific proteins, participates in the development and activity of the chicken oviduct prior to the onset of egg laying.

The role of thyroid hormones in regulation of chicken ovarian steroidogenesis

In all vertebrates, including birds, the normal development of the ovary and ovarian follicles is under the regulatory influence of hormones produced by the reproductive axis. In recent years, it has become clear that in birds an adequate level of thyroid hormones (THs), i.e. thyroxine (T4) and triiodothyronine (T3), in blood circulation is of primary importance for normal female reproductive functions. In avian species, characterized by seasonal reproduction, THs are involved in the photoperiodic regulation of reproduction acting at the mediobasal hypothalamus. In domestic fowl, where the seasonality of reproduction has been eliminated, the role of THs in ovarian function is not fully elucidated. Recent studies have revealed that ovarian follicles of the laying hen express mRNAs of TH nuclear receptors (TRα and TRβ0) as well as integrin (αVβ3) plasma membrane receptors, indicating genomic and nongenomic action of THs in the chicken ovary. In vivo experiments carried out on laying hens have showed that the bolus injection of T3 decreases levels of luteinizing hormone (LH) and estradiol (E2) in blood, and a hyperthyroid state evoked by administration of T3 for few days diminishes LH, E2 and progesterone (P4) levels, reduces the weight of the ovary, induces atresia of preovulatory follicles and eventually causes stoppage of egg laying. In vitro studies have demonstrated that T3 decreases E2 secretion from white nonhierarchical follicles and the theca layer of yellow preovulatory follicles, while on the other hand, it elevates P4 production from the granulosa layer of these follicles. These effects have been associated with steroidogenic enzyme expression and cyclic AMP synthesis. This review summarizes the current knowledge concerning the role of THs in regulation of steroidogenesis in chicken ovarian follicles.

Gonads directly regulate growth in teleosts

In general, there is a relationship between growth and reproduction, and gonads are known to be important organs for growth, but direct evidence for their role is lacking. Here, using a fish model, we report direct evidence that gonads are endocrine organs equal to the pituitary in controlling body growth. Gonadal loss of function, gain of function, and rescue of growth were investigated in tilapia. Gonadectomy experiments were carried out in juvenile males and females. Gonadectomy significantly retarded growth compared with controls; however, this retardation was rescued by the implantation of extirpated gonads. Because gonads express growth hormone, it is possible that gonads control body growth through the secretion of growth hormone and/or other endocrine factors. We propose that gonads are integral players in the dynamic regulation of growth in teleosts.

Local expression and distribution of growth hormone and growth hormone receptor in the chicken ovary: effects of GH on steroidogenesis in cultured follicular granulosa cells

Preovulatory follicular development (PFD) is mainly regulated by gonadotropins (FSH, LH) and steroids, although other intraovarian factors are also involved. We analyzed the local expression of growth hormone (GH) in the hen ovary and the role that this hormone may play on the regulation of steroidogenesis in granulosa cells (GCs). Ovarian follicles from sexually mature hens were studied at different developmental stages. Both GH mRNA (by in situ hybridization) and protein (by immunohistochemistry) were expressed mainly in the GCs, and to a lesser extent in the theca cells of the follicular wall. Sequence of a GH cDNA 690-bp fragment obtained from the follicular wall was identical to that obtained from the pituitary. The growth hormone receptor (GHR) mRNA was also expressed in the follicles. Nine GH variants were observed by SDS-PAGE and Western blotting, but the main isoform showed a MW of 17 kDa, at all developmental stages. Addition of GH (0.1, 1, 10 nM) stimulated the synthesis of progesterone (P4) in primary GCs cultures in a dose-dependent manner (1.5, 2.9, 5.4 times, respectively). GH also stimulated the expression of cholesterol side-chain cleavage enzyme (cytochrome P450scc) mRNA, a rate-limiting enzyme during P4 synthesis (2.9, 4.6, 4.9 times, respectively), whereas the synthesis of 3β-hydroxysteroid dehydrogenase (3β-HSD) mRNA (a constitutive enzyme) was not changed. Both GH and GHR were co-expressed in GCs cultures. The locally expressed GH present in concentrated (4×, 6×, 8×) conditioned media obtained from ovarian GC cultures stimulated P4 production (1.2, 2.2, 4.4 times, respectively) in additional fresh cultured GCs, and this effect disappeared when the conditioned media were treated with antiserum against GH. These data suggest that locally produced GH may modulate follicular development through autocrine/paracrine effects in the chicken ovary.

Comparison of Sex Steroid Concentration in Blood Plasma and Ovarian Follicles of White Leghorn and Greenleg Partridge Laying Hens

The study was performed to compare plasma and ovarian levels of progesterone (P4) and estradiol (E2) with laying rate in two different breeds of egg-type chickens, i.e. White Leghorn (WL) and Greenleg Partridge (GP). Thirty-five-week-old WL (line H22; n = 8) and GP (line Z11; n = 8) hens were used in the experiment. Blood samples were collected from hens at the time of C1 oviposition (i.e. 0.5 h before C2 ovulation), then at 20, 16, 12, 8, 4, 2 h before C3 ovulation, and at the time of predicted C3 ovulation (i.e. just after C2 oviposition). On the following day, six birds of each breed were decapitated 2 h before ovulation on the next day after the last blood collection. A stroma, small (SWF; 1-4 mm), medium (MWF; 4-6 mm) and large (LWF; 6-8 mm) white prehierarchical follicles, and yellow hierarchical (F6-F1; 8-36 mm) ovarian follicles were isolated. P4 and E2 levels in blood plasma and ovarian follicles were determined radioimmunologically. The average rate of lay in WL hens was significantly higher than in GP hens (P<0.05). The highest concentrations of P4 and E2 were found 4 h before ovulation in both WL and GP hens. In WL hens the levels of P4 at the time of oviposition and at 4 and 2 h before ovulation were significantly higher in comparison with GP hens (P<0.05). On the other hand, higher E2 concentrations were found in GP hens at the time of oviposition and 12, 8 and 4 h before ovulation (P<0.05). In LWF and hierarchical follicles of WL hens the level of P4 was significantly lower than in GP hens (P<0.05). With respect to E2, a reverse relationship was observed in LWF and F6-F4 follicles. In conclusion, the results obtained indicate that in egg-type layers the profiles of plasma and ovarian sex steroids depend on their genotype. The significant differences in sex steroid levels in blood and ovarian follicles of the WL and GP breeds may contribute to explain the endocrinological factors that determined their laying performance and productivity.