Identification of novel candidate genes for follicle selection in the broiler breeder ovary

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

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

Chicken ovarian follicles morphology and growth differentiation factor 9 gene expression in chicken ovarian follicles: review

Ovary follicular development is a progressive system from the beginning of small cortical follicles to the ovulation of hierarchical follicles. The review was conducted to provide information on the indigenous chickens commonly used for egg production, chicken ovarian follicles morphology and expression of growth differentiation factor 9 (GDF9) gene in ovarian follicles and its relationship with egg production. The research databases used in the study include google scholar, Science Direct, PubMed, JSTOR and Cambridge Core. Google, Yahoo and Baidu search engines were used to search the information. In this study, the papers selected for use were original research articles and reviews to ensure that the information used was from research results. Besides, only recent English papers, 2010-2021, were used. The keywords used to search for articles were chicken ovarian follicles, ovarian morphology and GDF9 gene expression. The documents showed that pre-hierarchical follicles include many small and large white follicles, which are about 2-5mm in diameter and 5 to 6 small yellow follicles (SYF) that are about 5-10mm in diameter. Preovulatory follicles are about five to six in number and above 10mm in diameter, with the sizes from F6 to F1, with F1 as the largest follicle. Further, the studies revealed that GDF9 gene mRNA is expressed in the highest concentration in small yellow follicles and other studies reported that the expression of GDF9 gene has been found in follicles of the primary to preovulatory stages in chickens. This review concludes that the GDF9 gene expression is mainly throughout follicular growth and it stimulates the proliferation of pre-hierarchical granulosa cells. The increased egg production in chickens depends on progressive developmental stages and the growth of ovarian follicles.

Comparison of body size and reproductive hormones in high- and low-yielding Wulong geese

Wulong geese are renowned for their egg-laying and reproductive abilities. This work investigated the potential of using body size traits in the selection and breeding of high-yielding Wulong geese. A total of forty 479day-old female geese (high-yielding geese, n = 20; low-yielding geese, n = 20) were selected to evaluate the relationship between body weight, body size trait indicators, serum reproductive hormones, and biochemical indicators. The results showed that serum estradiol (E2), glucose (GLU), and triglyceride (TG) concentrations, together with pubic spacing and abdominal circumference were significantly higher in high-yielding geese (P < 0.01), whereas the opposite was true for neck circumference, neck length, and tibial circumference. In addition, the serum testosterone (T) concentration and body weight were higher in high-yielding geese (P < 0.05). Neck circumference and neck length were negatively correlated with E2 and TG (P < 0.01); while pubic spacing and abdominal circumference were positively correlated with E2, GLU, and TG (P < 0.01), the highest correlation coefficient was 0.777 between TG and pubic spacing; T was also strongly associated with neck circumference (P < 0.01). In conclusion, high-yielding Wulong geese can be selected through neck circumference, neck length, pubic spacing, and abdominal circumference.

Long noncoding RNAs profiling in ovary during laying and nesting in Muscovy ducks (Cairina moschata)

There are recent reports of the important functions of long noncoding RNAs (lncRNAs) in female reproductive and ovarian development. Studies in which there was characterization of lncRNAs in the ovaries of laying compared with nesting poultry, however, are limited. In this study, RNA libraries were constructed by obtaining sequencing data of ovarian tissues from laying and nesting Muscovy ducks. In the ovarian tissues of Muscovy ducks, a total of 334 differentially abundant mRNA transcripts (DEGs) and 36 differentially abundant lncRNA transcripts were identified in the nesting period, when compared with during the laying period. These results were subsequently validated by qRT-PCR using nine randomly-selected lncRNAs and six randomly-selected DAMTs. Furthermore, the cis- and trans-regulatory target genes of differentially abundant lncRNA transcripts were identified, and lncRNA-gene interaction networks of 34 differentially abundant lncRNAs and 263 DEGs were constructed. A total of 7601 lncRNAs neighboring 10,542 protein-coding genes were identified and found to be enriched in the Wnt signaling pathway and oocyte meiosis pathways associated with follicular development. Overall, only 11 cis-targets and 57 mRNA-mRNA except trans-targets were involved in the lncRNA-gene interaction networks. Based on the interaction networks, nine DEGs were trans-regulated by differentially abundant lncRNAs and 20 differentially abundant lncRNAs were hypothesized to have important functions in the regulation of broodiness in Muscovy ducks. In this study, a predicted interaction network of differentially abundant lncRNAs and DEGs in Muscovy ducks was constructed for the first time leading to an enhanced understanding of lncRNA and gene interactions regulating broodiness.

The relationship between the mTOR signaling pathway and ovarian aging in peak-phase and late-phase laying hens

The molecular mechanisms underlying reproductive aging in avian species are poorly understood. Previous studies have shown the importance of mechanistic target of rapamycin (mTOR) signaling pathway in aging. In this study, we investigated the relationship between the mTOR signaling pathway and ovarian aging in the peak phase and late phase of egg production in laying hens. The egg production rate and egg quality were tracked for 5 consecutive weeks in 30-week-old and 70-week-old Dawu Jinfeng hens (N = 30/group). During the peak phase (week 35) and late phase (week 75), antioxidant and immune indicators were detected by enzyme-linked immunosorbent assay, and mTOR signaling-related genes (CLIP-170, GRB10, LIPIN-1, ATG1, 4E-BP1, S6K, PKC, RHO, and SGK1) were detected in the follicles by quantitative reverse transcription-PCR technology. The protein expression of key genes (mTOR, PKC, 4EBP1) was evaluated by Western blot analysis. The egg production rate and the antioxidant indexes superoxide dismutase and glutathione peroxidase and the levels of total antioxidant capacity and immunoglobulins (IgM and IgG) were significantly higher at week 35 than those at week 75 (P < 0.01), while malondialdehyde levels were significantly lower (P < 0.01). At week 75, there were fewer follicles in the different stages of development than were detected at week 35. The number of white follicles (large and small) and primary follicles were significantly higher at week 75 than those detected at week 35 (P < 0.01). The mRNA expression of avTOR, CLIP-170, GRB10, LIPIN-1, 4E-BP1, S6K, RHO, and SGK genes in small white follicles (SWF), large white follicles (LWF), F3, F1, and ovary at week 75 was lower than that in the hens at week 35 (P < 0.05). The mRNA expression in small yellow follicle (SYF) was significantly higher than that at week 35 (P < 0.05), while the mRNA expression of ULK1 in SWF, LWF, F3, F1, and ovary at week 75 was higher than that of hens at week 35 (P＜0.01), and SYF was lower (P < 0.05). Treatment of chicken granulosa cells with the mTOR agonist MHY1485 significantly enhanced granulocyte proliferation (P < 0.01) and inhibited apoptosis (P < 0.01) and significantly increased avTOR, S6K, 4E-BP1, and PKC gene expression (P < 0.01). The protein expression levels of mTOR, S6K, p-mTOR, and p-S6K were consistent with mRNA expression levels. The mTOR activity is age-specific, and a compensatory enhancement of the mTOR signaling cascade can regulate ovarian follicular development in aged laying hens.

Endocrine and genetic factors affecting egg laying performance in chickens: a review

1. Egg-laying performance reflects the overall reproductive performance of breeding hens. The genetic traits for egg-laying performance have low or medium heritability, and, depending on the period involved, usually ranges from 0.16 to 0.64. Egg-laying in chickens is regulated by a combination of environmental, endocrine and genetic factors. 2. The main endocrine factors that regulate egg-laying are gonadotropin-releasing hormone (GnRH), prolactin (PRL), follicle-stimulating hormone (FSH) and luteinising hormone (LH). 3. In the last three decades, many studies have explored this aspect at a molecular genetic level. Recent studies identified 31 reproductive hormone-based candidate genes that were significantly associated with egg-laying performance. With the development of genome-sequencing technology, 64 new candidate genes and 108 single nucleotide polymorphisms (SNPs) related to egg-laying performance have been found using genome-wide association studies (GWAS), providing novel insights into the molecular genetic mechanisms governing egg production. At the same time, microRNAs that regulate genes responsible for egg-laying in chickens were reviewed. 4. Research on endocrinological and genetic factors affecting egg-laying performance will greatly improve the reproductive performance of chickens and promote the protection, development, and utilisation of poultry. This review summarises studies on the endocrine and genetic factors of egg-laying performance in chickens from 1972 to 2019.

An eQTL in the cystathionine beta synthase gene is linked to osteoporosis in laying hens

BACKGROUND

Skeletal damage is a challenge for laying hens because the physiological adaptations required for egg laying make them susceptible to osteoporosis. Previously, we showed that genetic factors explain 40% of the variation in end of lay bone quality and we detected a quantitative trait locus (QTL) of large effect on chicken chromosome 1. The aim of this study was to combine data from the commercial founder White Leghorn population and the F2 mapping population to fine-map this QTL and understand its function in terms of gene expression and physiology.

RESULTS

Several single nucleotide polymorphisms on chromosome 1 between 104 and 110 Mb (galGal6) had highly significant associations with tibial breaking strength. The alternative genotypes of markers of large effect that flanked the region had tibial breaking strengths of 200.4 vs. 218.1 Newton (P < 0.002) and, in a subsequent founder generation, the higher breaking strength genotype was again associated with higher breaking strength. In a subsequent generation, cortical bone density and volume were increased in individuals with the better bone genotype but with significantly reduced medullary bone quality. The effects on cortical bone density were confirmed in a further generation and was accompanied by increased mineral maturity of the cortical bone as measured by infrared spectrometry and there was evidence of better collagen cross-linking in the cortical bone. Comparing the transcriptome of the tibia from individuals with good or poor bone quality genotypes indicated four differentially-expressed genes at the locus, one gene, cystathionine beta synthase (CBS), having a nine-fold higher expression in the genotype for low bone quality. The mechanism was cis-acting and although there was an amino-acid difference in the CBS protein between the genotypes, there was no difference in the activity of the enzyme. Plasma homocysteine concentration, the substrate of CBS, was higher in the poor bone quality genotype.

CONCLUSIONS

Validated markers that predict bone strength have been defined for selective breeding and a gene was identified that may suggest alternative ways to improve bone health in addition to genetic selection. The identification of how genetic variants affect different aspects of bone turnover shows potential for translational medicine.

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

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

Novel Polymorphisms in RAPGEF6 Gene Associated with Egg-Laying Rate in Chinese Jing Hong Chicken using Genome-Wide SNP Scan

The improvement of egg production is of vital importance in the chicken industry to maintain optimum output throughout the laying period. Because of the elongation of the egg-laying cycle, a drop in egg-laying rates in the late laying period has provoked great concern in the poultry industry. In this study, we calculated the egg-laying rate at weeks 61–69 (60 days) of Jing Hong chickens parent generation as the phenotype, and the genotype were detected by the chicken 600K Affymetrix Axiom High Density (HD) Single Nucleotide Polymorphisms (SNP)-array. The Genome-Wide Association Study (GWAS) result showed that the egg production trait is significantly associated with five SNPs (AX-75745366, AX-75745380, AX-75745340, AX-75745388, and AX-75745341), which are in the rap guanine nucleotide exchange factor 6 (RAPGEF6) gene on chicken chromosome 13. A total of 1676 Chinese commercial Jing Hong laying hens—including two populations, P1 population (858 hens) and P2 population (818 hens)—were genotyped using the Polymerase Chain Reaction-Restriction Fragments Length Polymorphisms (PCR-RFLP) method for the association analysis of egg-laying rates for the verification of the GWAS results. Genotypic and allelic frequencies of five SNPs were inconsistent with Hardy–Weinberg equilibrium, and the average population genetics parameters considering all the SNP values; i.e., gene homozygosity (Ho), gene heterozygosity (He), the effective number of alleles (Ne), and the polymorphism information content (PIC) were 0.75, 0.25, 1.40, and 0.20 in P1; 0.71, 0.29, 1.46, and 0.24 in P2; and 0.73, 0.27, 1.43, and 0.22 in P1 + P2 populations, respectively. The association analysis results revealed that out of the five polymorphisms, three of them (AX-75745366, AX-75745340, and AX-75745341; Patent applying No: 201810428916.5) had highly significant effects on egg-laying rates according to the GWAS results. Population-specific association analyses also showed similar significant association effects with this trait. Four haplotypes (AAGG, AAAG, AGGG, and AGAG) were inferred based on significant loci (AX-75745340 and AX-75745341) and also showed significant associations with the egg-laying rate, where haplotype AAGG had the highest egg-laying rate, with the exception of the egg-laying rate in P1 population, followed by other haplotypes. Furthermore, genotypes TT, AA, and GG showed the highest egg-laying rate compared to the corresponding genotypes at AX-75745366, AX-75745340, and AX-75745341 SNP loci in P1+P2, respectively. A similar result was found in the population-specific analysis except for the P1 population, in which TC genotype showed the highest egg-laying rate. No significant association was found in the egg-laying rate during the 60 days laying period for the SNPs (AX-75745380 and AX-75745388) in any group of population (p ≥ 0.05). Collectively, we report for the first time that 3 SNPs in the RAPGEF6 gene were significantly associated with the egg-laying rate during the later stage of egg production, which could be used as the potential candidate molecular genetic markers that would be able to facilitate in the selection and improvement of egg production traits through chicken breeding.

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

Background

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

Results

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

Conclusions

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

Electronic supplementary material

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

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

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

Whole genome sequence analysis to detect signatures of positive selection for high fecundity in sheep

Ovulation rate and prolificacy are the most important reproductive traits that have major impact on the efficiency of lamb meat production. Here, we compared the whole genomes of the Romanov sheep, known as one of the high prolific breeds, and four other sheep breeds namely Assaf, Awassi, Cambridge and British du cher, to identify genetic mechanisms underlying prolificacy in sheep. Selection signature analysis revealed 637 and 477 protein-coding genes under positive selection from F_ST and nucleotide diversity (Pi) statistics, respectively. Further analysis showed that several candidate genes including LEPR, PDGFRL and KLF5 genes are involved in sheep prolificacy. The identified candidate genes in the selected regions are novel and provide new insights into the genetic mechanisms underlying prolificacy in sheep and can be useful in sheep breeding programmes to develop improved breeds for high reproductive efficiency.

Gastrointestinal distribution of chicken gastrin-cholecystokinin family transcript expression and response to short-term nutritive state

The related peptide hormones cholecystokinin (CCK) and gastrin are conserved throughout vertebrate clades and implicated in energy homeostasis. CCK is generally accepted as a satiety hormone in poultry, but the role of gastrin remains poorly studied. Functional dissection of these ligands is required to characterise the molecular control of growth & satiety in the domestic chicken, for which there is an increasingly pressing mandate. There are limited descriptions of physiological distributions for the two genes in birds, and these are mostly reliant on immunohistochemistry which can prove problematic due to the shared structure of the targets. Therefore, we have defined the tissue distributions of CCK and gastrin in the chicken, focussing on the gastrointestinal tract, by using transcript-dependent techniques to improve reliability by increasing specificity. Though considerably more highly expressed in the brain, gastrointestinal CCK transcripts were dispersed throughout the small intestine and particularly around the proximal ileum. Gastrin expression was strictly limited to the gastric antrum region of the intestinal tract, albeit very highly expressed. We demonstrate that CCK mRNA expression does not respond as expected for a short-term satiety hormone, and that the short-term response of gastrin expression is paradoxical compared to its role in mammals. These results partially corroborate previous peptide distribution studies and initiate exploration of the nutrient-responsive roles of these hormones in avian energy balance.

Genetic Architecture and Candidate Genes Identified for Follicle Number in Chicken

Follicular development has a major impact on reproductive performance. Most previous researchers focused on molecular mechanisms of follicular development. The genetic architecture underlying the number of follicle, however, has yet not to be thoroughly defined in chicken. Here we report a genome-wide association study for the genetic architecture determining the numbers of follicles in a large F₂ resource population. The results showed heritability were low to moderate (0.05-0.28) for number of pre-ovulatory follicles (POF), small yellow follicles (SYF) and atresia follicles (AF). The highly significant SNPs associated with SYF were mainly located on GGA17 and GGA28. Only four significant SNPs were identified for POF on GGA1. The variance partitioned across chromosomes and chromosome lengths had a linear relationship for SYF (R² = 0.58). The enriched genes created by the closest correspondent significant SNPs were found to be involved in biological pathways related to cell proliferation, cell cycle and cell survival. Two promising candidate genes, AMH and RGS3, were suggested to be prognostic biomarkers for SYF. In conclusion, this study offers the first evidence of genetic variance and positional candidate genes which influence the number of SYF in chicken. These identified informative SNPs may facilitate selection for an improved reproductive performance of laying hens.

Melatonin Does Not Affect Progesterone Basal Secretion but Suppresses the Luteinizing Hormone Receptor Expression in Granulosa Cells of the Japanese Quail

The aim of this study was to evaluate the potential effect of melatonin on progesterone production by granulosa cells of the Japanese quail. For in vitro experiments, granulosa cells were isolated from pre-ovulatory follicles (F1–F3) when the F1 follicles were predicted to be either immature or mature (at 3–6 or 18–21 h after oviposition, respectively). Granulosa cells were cultured for 12 hwithor without melatonin concentration gradients of 0.0001–100 µg/mL, thereby averting luteinizing hormone (LH) stimulation. The concentration of progesterone in culture medium was measured using an enzyme immunoassay. The expression of melatonin receptor subtypes in granulosa cells from F1 follicles was detected by reverse transcription-PCR. The LH receptor (LHCGR) mRNA level in cultured granulosa cells of the F1 follicles was analyzed using quantitative real-time PCR. Six quails were used in each of four groups for in vivo experiments. Eachgroup received intraperitoneal injection of melatonin (0.67 mg/kg body weight) or mock-vehicle at 3 or 18 h after oviposition, respectively. The birds were decapitated to collect serum 3 hlater (at 6 or 21 h after oviposition, respectively). The serum progesterone level was also measured using an enzyme immunoassay. We observed that melatonin receptor subtypes (Mel-1a, 1b, and 1c) were expressed in the granulosa cells of the F1 follicles of the Japanese quail. Melatonin suppresses the LHCGR mRNA expression in granulosa cells of F1 follicles but does not affect the basal secretion of progesterone in cultured granulosa cells of the F1–F3 follicles. In addition, melatonin treatment has no influence on the serum progesterone concentration at 6 h post-oviposition, but suppresses progesterone level 21 h after oviposition in the Japanese quail.

Novel Polymorphisms of Adrenergic, Alpha-1B-, Receptor and Peroxisome Proliferator-activated Receptor Gamma, Coactivator 1 Beta Genes and Their Association with Egg Production Traits in Local Chinese Dagu Hens

Adrenergic, alpha-1B-, receptor (ADRA1B) and peroxisome proliferator-activated receptor gamma, coactivator 1 beta (PPARGC1B) genes are involved in regulation of hen ovarian development. In this study, these two genes were investigated as possible molecular markers associated with hen-housed egg production, egg weight (EW) and body weight in Chinese Dagu hens. Samples were analyzed using the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) technique, followed by sequencing analysis. Two novel single nucleotide polymorphisms (SNPs) were identified within the candidate genes. Among them, an A/G transition at base position 1915 in exon 2 of ADRA1B gene and a T/C mutation at base position 6146 in the 3′-untranslated region (UTR) of PPARGC1B gene were found to be polymorphic and named SNP A1915G and T6146C, respectively. The SNP A1915G (ADRA1B) leads to a non-synonymous substitution (aspartic acid 489-to-glycine). The 360 birds from the Dagu population were divided into genotypes AA and AG, allele A was found to be present at a higher frequency. Furthermore, the AG genotype correlated with significantly higher hen-housed egg production (HHEP) at 30, 43, 57, and 66 wks of age and with a higher EW at 30 and 43 wks (p<0.05). For the SNP T6146C (PPARGC1B), the hens were typed into TT and TC genotypes, with the T allele shown to be dominant. The TC genotype was also markedly correlated with higher HHEP at 57 and 66 wks of age and EW at 30 and 43 wks (p<0.05). Moreover, four haplotypes were reconstructed based on these two SNPs, with the AGTC haplotype found to be associated with the highest HHEP at 30 to 66 wks of age and with higher EW at 30 and 43 wks (p<0.05). Collectively, the two SNPs identified in this study might be used as potential genetic molecular markers favorable in the improvement of egg productivity in chicken breeding.

Association of novel polymorphisms of forkhead box L2 and growth differentiation factor-9 genes with egg production traits in local Chinese Dagu hens

Transcription factor forkhead box L2 (FOXL2) and growth differentiation factor-9 (GDF9) genes have critical roles in the regulation of hen ovarian development. In the present study, these genes were explored as possible molecular markers associated with BW, hen-housed egg production, and egg weight in Chinese Dagu hens. Samples were analyzed using the PCR-single strand conformation polymorphism (PCR-SSCP) technique followed by sequencing analysis, and two novel single nucleotide polymorphisms (SNPs) were identified within these candidate genes. Among them, an A/G transition at base position 238 in the coding region of the FOXL2 gene and a G/T transversion at base position 1609 in exon 2 of the GDF9 gene were found to be polymorphic and named SNPs A238G and G1609T, respectively. The SNP A238G (FOXL2) leads to a nonsynonymous substitution (isoleucine77-to-valine), and when the 360 Dagu hen samples were divided into genotypes AA and AB, allele A was found to be present at a higher frequency. Furthermore, the AA genotype correlated with significantly higher hen-housed egg production at 30, 43, 57, and 66 wk of age and with a higher egg weight at 43 wk (P<0.05). For the SNP G1609T (GDF9), the hens were typed into TT and TC genotypes, with the T allele shown to be dominant. The TC genotype was also markedly correlated with higher hen-housed egg production and a higher egg weight (P<0.05). Moreover, four haplotypes were reconstructed based on these two SNPs, with the AATC haplotype found to be correlated with the highest hen-housed egg production at 30 to 66 wk of age and with higher egg weights at 43 wk (P<0.05). Collectively, the two SNPs identified in this study might be used as possible genetic molecular markers to aid in the improvement of egg production traits in chicken breeding.

Identification and characterisation of alternative transcriptional variants of PDGFRL in two lines of commercial poultry

The platelet-derived growth factor (PDGF) family of genes and their receptors are involved in angiogenesis and steroid hormone production. A putative member of the family, platelet-derived growth factor receptor-like (PDGFRL), has been implicated in steroid-based feedback mechanisms within the chicken reproductive system. Three potential variants of PDGFRL were identified in the chicken, supported by in silico prediction and EST sequencing. The three potential transcripts have been further verified and the 5' terminal regions sequenced in this research. The sum of expression of all three transcripts in broiler breeders (the parents of broiler chickens) has been shown to be consistent with total expression of the gene. However, cumulative expression of the three transcripts in a range of tissues in egg layers was significantly short of total expression, indicating the existence of potential additional variants. Two additional variants were subsequently identified in egg layer cerebellum tissue and the 5' terminal regions sequenced. Sequence analysis of the three initial variants suggests that only one variant, which was the most abundant in broiler breeders and the majority of egg layer tissues, had a functional signal peptide. Although 5' RACE identified two additional transcripts in egg layers, the most likely protein translations indicated that these variants possessed no functional signal peptide, suggesting that, if they have a function, it is not a traditional one.

Digital gene-expression profiling analysis of the cholesterol-lowering effects of alfalfa saponin extract on laying hens

BACKGROUND

To prevent cardiovascular disease, people are advised to limit their intake of dietary cholesterol to less than 300 mg/day. Egg consumption has been seriously reduced because of the high levels of cholesterol. The purpose of the present study was to evaluate the cholesterol-lowering effects of alfalfa saponin extract (ASE) in yolk and the molecular mechanisms underlying these effects using digital gene-expression profiling analysis. Liver and ovary tissues were isolated from laying hens fed with ASE for RNA sequencing.

RESULTS

The cholesterol content of the yolks of eggs from hens fed 120 mg/kg ASE declined considerably on day 60. Other groups (60, 240, 480 mg/kg ASE group) also showed decreases, but they were not significant. Digital gene expression generated over nine million reads per sample, producing expression data for least 12,384 genes. Among these genes, 110 genes showed greater than normal expression in the liver and 107 genes showed greater than normal expression in the ovary. Cholesterol 7 alpha-hydroxylase (Cyp7a1) and apolipoprotein H (Apoh), which act in the synthesis of bile acid and cholesterol efflux, showed more expression in the livers of hens given dietary ASE supplementation. In the ovary, levels of very low density lipoprotein receptor (Vldlr), apolipoprotein B (Apob), apovitellenin 1 (ApovldlII) and vitellogenin (VtgI, VtgII and VtgIII) in ovary decreased with dietary ASE supplementation.

CONCLUSION

Transcriptome analysis revealed that the molecular mechanisms underlying the cholesterol-lowering effects of ASE were partially mediated by enhancement of cholesterol efflux in the liver and this reduced of cholesterol deposition in the ovary.

Hypothalamic agouti-related protein expression is affected by both acute and chronic experience of food restriction and re-feeding in chickens

The central melanocortin system is conserved across vertebrates. However, in birds, little is known about how energy balance influences orexigenic agouti-related protein (AGRP) and anorexigenic pro-opiomelanocortin (POMC) expression, despite the fact that commercial food restriction is critical to the efficient production of poultry meat. To enable contrasts to be made, in broiler-breeder chickens, between levels of food restriction, between birds with the same body weight but different feeding experience, and between birds moved from restricted feeding to ad lib. feeding for different periods, five groups of hens were established between 6 and 12 weeks of age with different combinations of food restriction and release from restriction. AGRP and neuropeptide Y expression in the basal hypothalamus was significantly increased by chronic restriction but only AGRP mRNA levels reflected recent feeding experience: hens at the same body weight that had recently been on ad lib. feeding showed lower expression than restricted birds. AGRP expression also distinguished between hens released from restriction to ad lib. feeding for different periods. By contrast, POMC and cocaine- and amphetamine-regulated transcript mRNA levels were not different. These results showed that AGRP mRNA not only reflected differences between a bird's weight and its potential weight or set point, but also discriminated between differing feeding histories of birds at the same body weight. Therefore, AGRP expression potentially provides an integrated measure of food intake experience and an objective tool to assess a bird's perception of satiety in feeding regimes for improved poultry welfare.

Decreased expression of the satiety signal receptor CCKAR is responsible for increased growth and body weight during the domestication of chickens

Animal domestication has resulted in changes in growth and size. It has been suggested that this may have involved selection for differences in appetite. Divergent growth between chickens selected for egg laying or meat production is one such example. The neurons expressing AGRP and POMC in the basal hypothalamus are important components of appetite regulation, as are the satiety feedback pathways that carry information from the intestine, including CCK and its receptor CCKAR (CCK1 receptor). Using 16 generations of a cross between a fast and a relatively slow growing strain of chicken has identified a region on chromosome 4 downstream of the CCKAR gene, which is responsible for up to a 19% difference in body weight at 12 wk of age. Animals possessing the high-growth haplotype at the locus have lower expression of mRNA and immunoreactive CCKAR in the brain, intestine, and exocrine organs, which is correlated with increased levels of orexigenic AGRP in the hypothalamus. Animals with the high-growth haplotype are resistant to the anorectic effect of exogenously administered CCK, suggesting that their satiety set point has been altered. Comparison with traditional breeds shows that the high-growth haplotype has been present in the founders of modern meat-type strains and may have been selected early in domestication. This is the first dissection of the physiological consequences of a genetic locus for a quantitative trait that alters appetite and gives us an insight into the domestication of animals. This will allow elucidation of how differences in appetite occur in birds and also mammals.

Orexin in the chicken hypothalamus: immunocytochemical localisation and comparison of mRNA concentrations during the day and night, and after chronic food restriction

In mammals Orexin-A and -B are neuropeptides involved in the hypothalamic regulation of diverse physiological functions including food intake and the sleep-wake cycle. This generalisation was investigated in meat-(broiler) and layer-type juvenile domestic chickens by immunocytochemical localisation of orexin A/B in the hypothalamus, and by measurements of hypothalamic hypocretin mRNA which encodes for orexin A/B after chronic food restriction, and during the sleep-wake cycle. Orexin immunoreactive fibres were observed throughout the hypothalamus with cell bodies in and around the paraventricular nucleus. No differences were observed in the pattern of immunoreactivity using anti- human orexin-A, or -B antisera. The amount of hypothalamic hypocretin mRNA in food -restricted broilers was higher than in broilers fed ad libitum, but the same as in layer- type hens fed ad libitum. Hypothalamic hypocretin mRNA was increased (P<0.01) in 12-week-old broilers fed 25% of their ad libitum intake between 6-12 weeks of age. No difference in hypothalamic hypocretin mRNA was seen in 12-week-old layer- type hens when they were awake (1-2h after lights on) or sleeping (1-2h after lights off). It is concluded that in the chicken, we could not find evidence that hypothalamic orexin plays a role in the sleep-wake cycle and it may be involved in aspects of energy balance.

Ovarian morphology and internal vis-à-vis non internal laying in relation to triacylglycerol, hormones and their receptors concentration around the age of sexual maturity in broiler breeder hens

1. Ovarian morphology, serum hormone concentrations of 17-β-estradiol, progesterone, testosterone, tri-iodothyronine (T3), thyroxine (T4) and triacylglycerol (TAG) were investigated at 23 and 26 weeks of age in broiler breeder hens provided with ad libitum access to feed. Progesterone, oestrogen-β, thyroid-α and -β receptor mRNAs were also quantified in the infundibulum at the same ages. 2. A large variation in the ovarian morphology was observed at 23 weeks of age including hens with undeveloped ovaries, non-laying hens with post ovulatory follicles (POF) and a predominance of non-laying hens without a POF. 3. Serum concentrations of triglyceride, 17-β-estradiol and progesterone at 23 weeks of age were lower in hens with an undeveloped ovary compared with other groups of hens, whereas testosterone, triiodothyronine and thyroxin were higher. 4. At 26 weeks of age, the average number of hierarchical yellow follicles in normal layers was 7.64 ± 0·41 whereas in internal layers, the follicular numbers were significantly greater at 8.66 ± 0·53. The higher follicular numbers in internal layers were associated with higher serum triglyceride and progesterone concentrations. 5. Oestrogen receptor-β and thyroid receptor-β mRNA was up regulated in the infundibulum of internal layers compared with normal laying hens at 26 weeks of age.