Expressed transcripts associated with high rates of egg production in chicken ovarian follicles

Pituitary whole transcriptome analysis reveals key genes regulating reproduction in Hy-Line Brown hens and the construction of their ceRNA molecular regulatory network

BACKGROUND

The development and egg-laying performance of hens are precisely regulated by hormones secreted by the pituitary. In this study, we performed comprehensive transcriptome sequencing of pituitary from Hy-Line Brown hens at 15, 20, 30 and 68 W of age. Through association analysis, we identified key genes and ceRNA regulatory networks related to pituitary development and egg production.

RESULTS

Based on the comprehensive transcriptome data, we identified 470 differentially expressed lncRNAs (DE-lncRNAs), 38 differentially expressed miRNAs (DE-miRNAs), and 2,449 differentially expressed mRNAs (DE-mRNAs). Time-series analysis pinpointed genes and signaling pathways that significantly influence pituitary hormone secretion at various stages. At 15 W, the high expression of GHRHR, NPY1R, and TSHR in the pituitary supports growth. At 20 and 30 W, elevated GNRHR expression sustains continuous egg production. In the late laying period, the expression of PRL may lead to a decline in egg production. Additionally, association analysis enabled the construction of a ceRNA regulatory network involving non-coding RNAs that regulate the development and reproduction of hens.

CONCLUSION

This study elucidated the comprehensive transcriptome expression profiles of the pituitary gland during the development and egg-laying processes in Hy-Line Brown hens and constructed the associated molecular regulatory networks. These findings lay the foundation for investigating the mechanisms by which non-coding RNAs regulate pituitary hormone secretion.

Melatonin alleviates endoplasmic reticulum stress to improve ovarian function by regulating the mTOR pathway in aged laying hens

Granular cell apoptosis is a key factor leading to follicular atresia and decreased laying rate in aged laying hens. Endoplasmic reticulum stress (ERS) induced cell apoptosis is a new type of apoptosis pathway. Previous studies have shown that the ERS pathway is involved in the regulation of follicular development and atresia, and can be regulated by mTOR. Melatonin (MEL) can protect the normal development of follicles, but the precise mechanism by which MEL regulates follicular development is not yet clear. So, we investigated the potential relationship between MEL and ERS and mTOR signaling pathway in vivo through intraperitoneal injection of MEL in aged laying hens. The results show that the laying rate, ovarian follicle number, plasma MEL, E2, LH, FSH concentrations, as well as the mRNA expression of mTOR signaling-associated genes TSC1, TSC2, mTOR, 4E-BP1, and S6K in old later-period chicken control (Old-CN) group was significantly decreased (P < 0.01). In contrast, the ERS-related of plasma and granular cell layer mRNA expression of Grp78, CHOP, and Caspase-3 was significantly increased (P < 0.01). While both of the effects were reversed by MEL. Then, aging granulosa cells were treated with MEL in vitro, followed by RNA seq analysis, and it was found that 259 and 322 genes were upregulated and downregulated. After performing GO enrichment analysis, it was found that DEGs significantly contribute to the biological processes including cell growth and apoptosis. Using pathway enrichment analysis, we found significant overrepresentation of cellular processes related to mTOR signaling and endoplasmic reticulum (ER) stress, involving genes such as GRB10, SGK1, PRKCA, RPS6KA2, RAF1, PIK3R3, FOXO1, DERL3, HMOX1, TLR7, VAMP7 and INSIG2. The obtained results of RT-PCR showed consistency with the RNA-Seq data. In summary, the underlined results revealed that MEL has significantly contributed to follicular development via activating the mTOR signaling pathway-related genes and alleviating ERS-related genes in laying hens. The current study provides a theoretical background for enhancing the egg-laying capability of hens and also providing a basis for elucidating the molecular mechanism of follicular selection.

RNA-seq identifies differentially expressed genes involved in csal1 overexpression in granulosa cells of prehierarchical follicles in Chinese Dagu hens

The transcription factor csal1 is an important molecule that plays a critical regulatory function in ovarian follicle development, as confirmed by our previous data. However, the candidate genes of csal1 and its regulatory mechanism remain poorly understood in the granulosa cells (GCs) of chicken prehierarchical follicles (PFs). Six transcriptomes of csal1 and empty vector were analyzed in Chinese Dagu hens by RNA sequencing. Six cDNA libraries were constructed, with more than 42 million clean reads and 16,779 unigenes. Of these 16,779 unigenes, 2,762 differentially expressed genes (DEGs) were found in GCs, including 1,605 upregulated and 1,157 downregulated unigenes. Fourteen genes, including BMP5, TACR2, AMH, PLAG1, MYOD1, BOP1, SIPA1, NOTCH1, BCL2L1, SOX9, ADGRA2, WNT5A, SLC7A11, and GATAD2B, were related to GC proliferation and differentiation, hormone production, ovarian follicular development, regulation of reproductive processes, and signaling pathways in the PFs. Further analysis demonstrated the DEGs in GCs of ovarian follicles were enriched in neuroactive ligand-receptor interaction, cell adhesion molecules, and pathways related to cytochrome P450, indicating a critical function for csal1 in the generation of egg-laying features by controlling ovarian follicle development. For the first time, the current study represents the transcriptome analysis with ectopic csal1 expression. These findings provide significant evidence for investigating the molecular mechanism by which csal1 controls PF development in the hen ovary.

Identification of nucleotide polymorphisms in the key promoter region of chicken annexins A2 gene associatied with egg laying traits

Annexin A2 (ANXA2) is a member of the A subfamily of a multifunctional calcium dependent membrane phospholipid binding protein family. The mRNA expression of ANXA2 is consistent with ovary function and egg laying in chickens. In this study, six nucleotide polymorphisms in the key promoter region of chicken ANXA2 gene (-2861 bp to -1394 bp), i.e.,: g.-2337 indel (GT), g.-2255 C > T, g. -2248 A > G, g.-2188 A > G, g.-2169 G > A, g.-2160 A > C, were identified. Their distributions in populations of Xinyang Brown, Recessive White Rock, Wenchang and Wenshang Barred chickens were analyzed. In the Recessive White Rock chicken population, CAA, CAG and TGG were three major haplotypes. Association analysis indicated that the individuals with diplotype TGG/TGG laid more eggs at 32 weeks, and the individual with diplotype CAG/TGG laid at the earlier age. Luciferase activity assay showed that mutation from C to T at -2255 increased trascriptional activity of chicken ANXA2, which is consistent with its effect on egg laying traits.

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

Background

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

Results

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

Conclusions

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

Supplementary Information

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

Transcriptome analysis of ovary tissues from low- and high-yielding Changshun green-shell laying hens

Background

Changshun green-shell laying hens are unique to Guizhou Province, China, and have high egg quality. Improving egg production performance has become an important breeding task, and in recent years, the development of high-throughput sequencing technology provides a fast and exact method for genetic selection. Therefore, we aimed to use this technology to analyze the differences between the ovarian mRNA transcriptome of low and high-yield Changshun green-shell layer hens, identify critical pathways and candidate genes involved in controlling the egg production rate, and provide basic data for layer breeding.

Results

The egg production rates of the low egg production group (LP) and the high egg production group (HP) were 68.00 ± 5.56 % and 93.67 ± 7.09 %, with significant differences between the groups (p < 0.01). Moreover, the egg weight, shell thickness, strength and layer weight of the LP were significantly greater than those of the HP (p < 0.05). More than 41 million clean reads per sample were obtained, and more than 90 % of the clean reads were mapped to the Gallus gallus genome. Further analysis identified 142 differentially expressed genes (DEGs), and among them, 55 were upregulated and 87 were downregulated in the ovaries. KEGG pathway enrichment analysis identified 9 significantly enriched pathways, with the neuroactive ligand-receptor interaction pathway being the most enriched. GO enrichment analysis indicated that the GO term transmembrane receptor protein tyrosine kinase activity, and the DEGs identified in this GO term, including PRLR, NRP1, IL15, BANK1, NTRK1, CCK, and HGF may be associated with crucial roles in the regulation of egg production.

Conclusions

The above-mentioned DEGs may be relevant for the molecular breeding of Changshun green-shell laying hens. Moreover, enrichment analysis indicated that the neuroactive ligand-receptor interaction pathway and receptor protein tyrosine kinases may play crucial roles in the regulation of ovarian function and egg production.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07688-x.

Effects of acute heat stress on protein expression and histone modification in the adrenal gland of male layer-type country chickens

The adrenal gland responds to heat stress by epinephrine and glucocorticoid release to alleviate the adverse effects. This study investigated the effect of acute heat stress on the protein profile and histone modification in the adrenal gland of layer-type country chickens. A total of 192 roosters were subject to acute heat stress and thereafter classified into a resistant or susceptible group according to body temperature change. The iTRAQ analysis identified 80 differentially expressed proteins, in which the resistant group had a higher level of somatostatin and hydroxy-δ-5-steroid dehydrogenase but a lower parathymosin expression in accordance with the change of serum glucocorticoid levels. Histone modification analysis identified 115 histone markers. The susceptible group had a higher level of tri-methylation of histone H3 lysine 27 (H3K27me3) and showed a positive crosstalk with K36me and K37me in the H3 tails. The differential changes of body temperature projected in physiological regulation at the hypothalamus-pituitary-adrenal axis suggest the genetic heterogeneity in basic metabolic rate and efficiency for heat dissipation to acclimate to thermal stress and maintain body temperature homeostasis. The alteration of adrenal H3K27me3 level was associated with the endocrine function of adrenal gland and may contribute to the thermotolerance of chickens.

Transcriptome analysis reveals differentially expressed genes associated with high rates of egg production in chicken hypothalamic-pituitary-ovarian axis

The hypothalamic-pituitary-ovarian (HPO) axis regulates the breeding process cycle of laying hens. However, the key regulatory genes of the HPO axis and pathways that drive chicken egg laying performance remain elusive. A total of 856 Chinese Luhua chicken was raised and the highest two hundred and the lowest two hundred chicken egg production were considered as high egg production (HEP) and low egg production (LEP) according to the total egg number at 300 days of age, respectively. RNA-seq sequencing (RNA-Seq) was conducted to explore the chicken transcriptome from the hypothalamus, pituitary gland and ovary tissue of 6 Chinese Luhua chicken with 3 high and low-rate egg production. In total, 76.09 Gb RNA-seq sequences were generated from 15 libraries with an average of 5.07 Gb for each library. Further analysis showed that 414, 356 and 10 differentially expressed genes (DEGs) were identified in pituitary gland, ovary and hypothalamus between HEP and LEP chickens, respectively. In pituitary gland, DEGs were involve in regulation of cellular glucose homeostasis, Ras protein signal transduction, negative regulation of hormone secretion. In Ovary DEGs were mainly involved in embryonic organ development, regulation of canonical Wnt signaling, response to peptide hormone. Our study identified DEGs that regulate mTOR signaling pathway, Jak-STAT signaling pathway, Tryptophan metabolism and PI3K-Akt signaling pathways at HPO-axis in laying hens. These important data contribute to improve our understanding of reproductive biology of chicken and isolating effective molecular markers that can be used for genetic selection in Chinese domestic Luhua chicken.

Characterization of the hypothalamo-pituitary-gonadal axis in low and high egg producing turkey hens

Variation in egg production exists in commercial turkey hens, with low egg producing hens (LEPH) costing more per egg produced than high egg producing hens (HEPH). Egg production correlates with ovulation frequency, which is governed by the hypothalamic-pituitary-gonadal (HPG) axis. Ovulation is stimulated by a preovulatory surge (PS) of progesterone and luteinizing hormone, triggered by gonadotropin releasing hormone release and inhibited by gonadotropin inhibiting hormone. Differences between LEPH and HEPH were characterized by determining HPG axis plasma hormone profiles and mRNA levels for key genes, both outside and inside of the PS (n = 3 per group). Data were analyzed with a 2-way ANOVA using the mixed models procedure of SAS. In the HPG axis, plasma progesterone levels were not affected by egg production level but were elevated during the PS. In contrast, plasma estradiol levels were higher in HEPH than in LEPH but were not associated with the PS. LEPH exhibited decreased gene expression associated with ovulation stimulation and increased gene expression associated with ovulation inhibition in the hypothalamus and pituitary. In ovarian follicle cells, LEPH displayed decreased gene expression associated with progesterone, androgen, and estradiol production in the F1 follicle granulosa cells, F5 theca interna cells, and small white follicle cells, respectively. Different degrees of stimulation and inhibition within all tissues of the HPG axis were noted between LEPH and HEPH turkey hens, with HEPH showing higher expression of genes related to ovulation and steroidogenesis.

Screening of differentially expressed immune-related genes from spleen of broilers fed with probiotic Bacillus cereus PAS38 based on suppression subtractive hybridization

The aim of this study was to construct the spleen differential genes library of broilers fed with probiotic Bacillus cereus PAS38 by suppression subtractive hybridization (SSH) and screen the immune-related genes. Sixty seven-day-old broilers were randomly divided into two groups. The control group was fed with basal diet, and the treated group was fed with basal diet containing Bacillus cereus PAS38 1×10⁶ CFU/g. Spleen tissues were taken and extracted its total RNA at 42 days old, then SSH was used to construct differential gene library and screen immune-related genes. A total of 119 differentially expressed sequence tags (ESTs) were isolated by SSH and 9 immune-related genes were screened out by Gene ontology analysis. Nine differentially expressed genes were identified by qRT-PCR. JCHAIN, FTH1, P2RX7, TLR7, IGF1R, SMAD7, and SLC7A6 were found to be significantly up-regulated in the treated group. Which was consistent with the results of SSH. These findings imply that probiotic Bacillus cereus PAS38-induced differentially expressed genes in spleen might play an important role in the improvement of immunity for broilers, which provided useful information for further understanding of the molecular mechanism of probiotics responsible to affect the poultry immunity.

mRNA and miRNA Transcriptome Profiling of Granulosa and Theca Layers From Geese Ovarian Follicles Reveals the Crucial Pathways and Interaction Networks for Regulation of Follicle Selection

Follicle development is characterized by the recruitment, growth, selection, and dominance of follicles, and follicle selection determines the lifetime reproductive performance. However, in birds, the molecular mechanisms underlying follicle selection still remain elusive. This study analyzed genome-wide changes in the mRNA and miRNA expression profiles in both the granulosa and theca layers of geese ovarian follicles before selection (4–6- and 8–10-mm follicles) and after selection (F5). The sequencing results showed that a higher number of both differentially expressed (DE) mRNAs and DE miRNAs were identified between 8–10-mm and F5 follicles compared with those between the 4–6- and 8–10-mm follicles, especially in the granulosa layer. Moreover, a Short Time-series Expression Miner analysis identified a large number of DE mRNAs and DE miRNAs that are associated with follicle selection. The functional enrichment analysis showed that DE genes in the granulosa layer during follicle selection were mainly enriched in five pathways related to junctional adhesion and two pathways associated with lipid metabolism. Additionally, an interaction network was constructed to visualize interactions among protein-coding genes, which identified 53 junctional adhesion- and 15 lipid regulation-related protein-coding genes. Then, a co-expression network between mRNAs and miRNAs in relation to junctional adhesion was also visualized and mainly included acy-miR-2954, acy-miR-218, acy-miR-2970, acy-miR-100, acy-miR-1329, acy-miR-199, acy-miR-425, acy-miR-181, and acy-miR-147. Furthermore, miRNA–mRNA interaction pairs related to lipid regulation were constructed including acy-miR-107, acy-miR-138, acy-miR-130, acy-miR-128, and acy-miR-101 during follicular selection. In summary, these data highlight the key roles of junctional adhesion and lipid metabolism during follicular selection and contribute to a better understanding of the mechanisms underlying follicle selection in birds.

Antioxidant Defence Systems and Oxidative Stress in Poultry Biology: An Update

Poultry in commercial settings are exposed to a range of stressors. A growing body of information clearly indicates that excess ROS/RNS production and oxidative stress are major detrimental consequences of the most common commercial stressors in poultry production. During evolution, antioxidant defence systems were developed in poultry to survive in an oxygenated atmosphere. They include a complex network of internally synthesised (e.g., antioxidant enzymes, (glutathione) GSH, (coenzyme Q) CoQ) and externally supplied (vitamin E, carotenoids, etc.) antioxidants. In fact, all antioxidants in the body work cooperatively as a team to maintain optimal redox balance in the cell/body. This balance is a key element in providing the necessary conditions for cell signalling, a vital process for regulation of the expression of various genes, stress adaptation and homeostasis maintenance in the body. Since ROS/RNS are considered to be important signalling molecules, their concentration is strictly regulated by the antioxidant defence network in conjunction with various transcription factors and vitagenes. In fact, activation of vitagenes via such transcription factors as Nrf2 leads to an additional synthesis of an array of protective molecules which can deal with increased ROS/RNS production. Therefore, it is a challenging task to develop a system of optimal antioxidant supplementation to help growing/productive birds maintain effective antioxidant defences and redox balance in the body. On the one hand, antioxidants, such as vitamin E, or minerals (e.g., Se, Mn, Cu and Zn) are a compulsory part of the commercial pre-mixes for poultry, and, in most cases, are adequate to meet the physiological requirements in these elements. On the other hand, due to the aforementioned commercially relevant stressors, there is a need for additional support for the antioxidant system in poultry. This new direction in improving antioxidant defences for poultry in stress conditions is related to an opportunity to activate a range of vitagenes (via Nrf2-related mechanisms: superoxide dismutase, SOD; heme oxygenase-1, HO-1; GSH and thioredoxin, or other mechanisms: Heat shock protein (HSP)/heat shock factor (HSP), sirtuins, etc.) to maximise internal AO protection and redox balance maintenance. Therefore, the development of vitagene-regulating nutritional supplements is on the agenda of many commercial companies worldwide.

Transcriptome analysis of ovary in relatively greater and lesser egg producing Jinghai Yellow Chicken

Egg production is determined by the function of ovary and is regulated by the hypothalamic-pituitary-ovary axis. The mechanism by which the ovary regulates egg production, however, is still poorly understood. The purpose of this study is to compare the transcriptome difference in ovary of relatively greater and lesser egg producing chickens, and to screen candidate genes related to egg production. A RNA sequencing was performed to analyze and compare the mRNA in ovarian tissues of relatively greater and lesser egg producing chickens. A total of 4 431 new genes expressed in the chicken ovary were mined. There were 305 differentially expressed genes (DEGs) identified between the relatively greater and lesser egg producing hens. Gene ontology analysis identified five candidate genes related to egg production, including ZP2, WNT4, AMH, IGF1, and CYP17A1 genes. Tissue expression profiles indicated these five candidate genes were highly expressed in chicken ovarian tissues, indicating a potential role in regulating chicken ovarian function and egg production. The KEGG analysis indicated the neuroactive ligand-receptor interaction pathway might have an important function in regulation of egg production. In addition, four known pathways related to reproduction were detected, including the calcium signaling, wnt signaling pathway, focal adhesion, and cytokine-cytokine receptor interaction pathways. Results of the present study indicate gene expression differences in the ovarian tissues of relatively greater and lesser egg producing chickens, and identified five important candidate genes related to egg production, which provided a theoretical basis for improving egg production of Jinghai Yellow Chickens.

Effect of 3-nitropropionic acid inducing oxidative stress and apoptosis of granulosa cells in geese

The mechanism of action by which oxidative stress induces granulosa cell apoptosis, which plays a vital role in initiating follicular atresia, is not well understood. In the present study, the effect of 3-nitropropionic acid (3-NPA) on oxidative stress and apoptosis in granulosa cells in geese was investigated. Our results showed that treatment with 3-NPA at 5.0 mmol/l for 24 h increased intracellular reactive oxygen species (ROS) production by 25.4% and decreased granulosa cell viability by 45.5% (P<0.05). Catalase and glutathione peroxidase gene expression levels in granulosa cells treated with 3-NPA were 1.32- and 0.49-fold compared with those of the control cells, respectively (P <0.05). A significant decrease in the expression level of B-cell lymphoma 2 (Bcl-2) protein and remarkable increases in the levels of Bax, p53 and cleaved-Caspase 3 proteins and the ratio of Bax/Bcl-2 expression in granulosa cells treated with 3-NPA were observed (P<0.05). Furthermore, a 38.43% increase in the percentage of early apoptotic cells was also observed in granulosa cells treated with 3-NPA (P<0.05). Moreover, the expression levels of NF-κB, Nrf2, Fhc, Hspa2 and Ho-1 in granulosa cells treated with 3-NPA were elevated 4.36-, 1.63-, 3.62-, 27.54- and 10.48-fold compared with those of the control cells (P<0.05), respectively. In conclusion, the present study demonstrates that treatment with 3-NPA induces ROS production and apoptosis and inhibits the viability of granulosa cells in geese. Furthermore, 3-NPA triggers increases in the expression of cleaved-Caspase 3 protein and the ratio of Bax/Bcl-2 expression, and induces the early apoptosis of granulosa cells.

Regulation of lipid peroxidation and ferroptosis in diverse species

This review by Conrad et al. reviews the functions and regulation of lipid peroxidation, ferroptosis, and the antioxidant network in diverse species, including humans, other mammals and vertebrates, plants, invertebrates, yeast, bacteria, and archaea, and discusses the potential evolutionary roles of lipid peroxidation and ferroptosis.

Lipid peroxidation is the process by which oxygen combines with lipids to generate lipid hydroperoxides via intermediate formation of peroxyl radicals. Vitamin E and coenzyme Q₁₀ react with peroxyl radicals to yield peroxides, and then these oxidized lipid species can be detoxified by glutathione and glutathione peroxidase 4 (GPX4) and other components of the cellular antioxidant defense network. Ferroptosis is a form of regulated nonapoptotic cell death involving overwhelming iron-dependent lipid peroxidation. Here, we review the functions and regulation of lipid peroxidation, ferroptosis, and the antioxidant network in diverse species, including humans, other mammals and vertebrates, plants, invertebrates, yeast, bacteria, and archaea. We also discuss the potential evolutionary roles of lipid peroxidation and ferroptosis.

RNA-Seq reveals seven promising candidate genes affecting the proportion of thick egg albumen in layer-type chickens

Eggs with a much higher proportion of thick albumen are preferred in the layer industry, as they are favoured by consumers. However, the genetic factors affecting the thick egg albumen trait have not been elucidated. Using RNA sequencing, we explored the magnum transcriptome in 9 Rhode Island white layers: four layers with phenotypes of extremely high ratios of thick to thin albumen (high thick albumen, HTA) and five with extremely low ratios (low thick albumen, LTA). A total of 220 genes were differentially expressed, among which 150 genes were up-regulated and 70 were down-regulated in the HTA group compared with the LTA group. Gene Ontology (GO) analysis revealed that the up-regulated genes in HTA were mainly involved in a wide range of regulatory functions. In addition, a large number of these genes were related to glycosphingolipid biosynthesis, focal adhesion, ECM-receptor interactions and cytokine-cytokine receptor interactions. Based on functional analysis, ST3GAL4, FUT4, ITGA2, SDC3, PRLR, CDH4 and GALNT9 were identified as promising candidate genes for thick albumen synthesis and metabolism during egg formation. These results provide new insights into the molecular mechanisms of egg albumen traits and may contribute to future breeding strategies that optimise the proportion of thick egg albumen.

Evidence for a role of ferritin heavy chain in mediating reproductive processes of geese

Ferritin heavy chain (FHC), which exhibits ferroxidase activity and mediates the primary functions of ferritin, plays a role in regulating reproduction in animals. However, the changes in the FHC mRNA and protein levels in the HPG axis of geese remain to be determined. In the current study, FHC mRNA expression level was quantitatively monitored in the hypothalamus, anterior pituitary and ovary stroma in prelaying and laying geese. In addition, the levels of FHC mRNA and protein were determined in follicles and ovarian stroma of laying geese. In comparison to prelaying geese, the FHC mRNA expression were 2.4, 1.8, and 13 times higher in the hypothalamus, anterior pituitary and ovarian stroma of laying geese, respectively (p<0.05). FHC mRNA and protein were detected in all examined follicles and ovarian stroma. FHC mRNA expression was higher in postovulatory follicles (POFs) and atretic follicles than in developing follicles and ovarian stroma. Furthermore, the FHC protein concentration in POF3 and atretic follicles were, respectively, 1.45 and 1.7 times higher compared with that of F1 (p<0.05). In conclusion, the presented results provided evidence of a link between FHC and goose reproduction, and supplied a theoretical foundation and a new approach for studying reproduction, in particular ovarian follicular development in birds.

Identification of differentially expressed genes in ovaries of chicken attaining sexual maturity at different ages

In poultry as well as in other birds, sexual maturity is one of the important factors influencing female reproduction and egg production. In this study, cDNA-amplified fragment length polymorphism (cDNA-AFLP) differential display approach was used to identify genes related to sexual maturity. Using 54 EcoR I/Mse I selective primer combinations, totally 403 differentially expressed transcript-derived fragments (TDFs) were isolated, 27 of which belong to 25 unigenes. By real-time quantitative PCR (qPCR), the expression pattern of 13 genes was confirmed; among them, four genes including ZNF183 (P < 0.01), KIAA0700, CCT6A, and 23e 15 (P < 0.05) are significantly up-regulated and one gene (Loc418883) is significantly down-regulated (P < 0.01) in sexually mature ovaries compared to immature ones. The mRNA expression dynamics of ZNF183, CCT6A, 23e 15 and Loc418883 were further investigated in ovaries of 70-, 300- and 500-day-old commercial egg-laying hens: the expression level of CCT6A was the highest in 300-day-old hens (P < 0.05), while that of Loc418883 in 500-day-old hens was significantly higher than the other two stages (P < 0.01). The expression levels of ZNF183 and 23e 15 in ovary increase significantly from 70-day-old hens (P < 0.01) and 300-day-old (P < 0.05) to 500-day-old hens, respectively. The consistence of CCT6A expression and egg-laying performance suggests that CCT6A likely plays important role in sexual maturity in hens.

A novel genetic marker of the ovomucoid gene associated with hatchability in Tsaiya ducks (Anas platyrhynchos)

Transcriptome analysis using a cDNA microarray was performed to identify differentially expressed genes that are correlated with hatchability, and a new PCR-RFLP marker of high hatchability among the identified genes was observed. We used the cDNA microarray technique for gene expression profiling of the magnum epithelium of laying Tsaiya ducks, and several regulated genes associated with hatchability were found. The results of real-time PCR and Western blotting analysis confirmed that the mRNA and protein levels of ovomucoid in the magnum epithelium of animals in the low-hatchability group were significantly higher than the levels in the high-hatchability group (P < 0.05). Primers TovF1 and TovR1, designed according to the ovomucoid EST sequence, were used to amplify genomic DNA samples of different individual Tsaiya ducks, and sequence analysis of the amplified DNA products showed deletion among the ducks from the low-hatchability group. Primers TovF2 and TovR2 were used to perform PCR-RFLP analysis on the amplified DNA products to classify the ducks into +/+, +/- and -/- genotypes. The animals of +/+ and +/- genotypes were identified as having significantly higher hatchability than those of the -/- genotype (P < 0.05). In contrast, no differences were observed between genotypes in terms of fertility, duration of fertility, egg weight or total number of eggs. Our results indicated that a novel PCR-RFLP marker of high hatchability, an ovomucoid gene polymorphism, can be used as a genetic marker for marker-assisted selection to improve hatchability in Tsaiya ducks.

Thymosins β-4 and β-10 are expressed in bovine ovarian follicles and upregulated in cumulus cells during meiotic maturation

β-Thymosins are small proteins that regulate the actin cytoskeleton and are involved in cell motility, differentiation, the induction of metalloproteinases, in anti-inflammatory processes and tumourigenesis. However, their roles in the ovary have not yet been elucidated. Using transcriptomics and real time reverse transcription-polymerase chain reaction validation, the present study demonstrates that thymosin β-4 (TMSB4) and thymosin β-10 (TMSB10) are upregulated in bovine cumulus cells (CCs) during in vitro maturation of cumulus-oocyte complexes (COCs) in parallel with an increase in mRNA expression of HAS2, COX2 and PGR genes. Using immunocytochemistry, both proteins were found to be localised mainly in granulosa cells, CCs and oocytes, in both the cytoplasm and nucleus, as well as being colocalised with F-actin stress fibres in CCs. Using different maturation mediums, we showed that the expression of TMSB10, but not TMSB4, was positively correlated with COC expansion and progesterone secretion and negatively correlated with apoptosis. Immunofluorescence, coupled with terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end-labelling (TUNEL), demonstrated the absence of TMSB4 and/or TMSB10 in apoptotic cells. TMSB10 expression was higher in COCs matured in vivo than in vitro, and differences related to the age of the animal were observed. TMSB4 and/or TMSB10 expression was unchanged, whereas HAS2 overexpressed in CCs from oocytes that developed to the blastocyst stage in vitro compared with those that did not. Thus, TMSB4 and/or TMSB10 ovarian expression patterns suggest that these two thymosins may be involved in cumulus modifications during maturation.

OVEX1, a novel chicken endogenous retrovirus with sex-specific and left-right asymmetrical expression in gonads

BACKGROUND

In chickens, as in most birds, female gonad morphogenesis is asymmetrical. Gonads appear first rather similarly, but only the left one undergoes full differentiation and gives rise to a functional ovary. The right gonad, in which the cortex does not develop, remains restricted to the medulla and finally regresses. Opportunity was taken of this left-right asymmetry to perform a suppression subtractive hybridization screening to select for transcripts preferentially expressed in the developing left ovary as compared to the right one, and thus identify genes that are potentially involved in the process of ovarian differentiation.

RESULTS

One of these transcripts, named Ovex1 according to its expression profile, corresponds to an endogenous retrovirus that has not been previously characterized. It is transcribed as full-length and singly spliced mRNAs and contains three uninterrupted open reading frames coding potentially for proteins with homology to Gag and Pro-Pol retroviral polyproteins and a third protein showing only a weak similarity with Env glycoproteins. Ovex1 is severely degenerated; it is devoid of typical long terminal repeats and displays some evidence of recombination. An orthologous Ovex1 locus was identified in the genome of zebra finch, a member of a different bird order, and similar sequences were detected in turkey, guinea fowl, and duck DNA. The relationship between these sequences follows the bird phylogeny, suggesting vertical transmission of the endogenous retrovirus for more than 100 million years. Ovex1 is transcribed in chicken gonads with a sex-dependent and left-right asymmetrical pattern. It is first expressed in the cortex of the left indifferent gonads of both sexes. Expression is transient in the left testis and absent in the right one. In developing ovaries, Ovex1 transcription increases sharply in the left cortex and is weakly detected in the medulla. After folliculogenesis, Ovex1-expressing cells constitute the follicular granulosa cell layer. Ovex1 expression highlights a striking desquamation process that leads to profound cortical remodeling associated with follicle morphogenesis.

CONCLUSION

Evidence for a selection pressure at the protein level suggests that this endogenous retrovirus, expressed in the ovarian supporting cell lineage, might play an active role in bird ovarian physiology.