Molecular cloning, expression profile and transcriptional modulation of two splice variants of very low density lipoprotein receptor during ovarian follicle development in geese (Anser cygnoide)

Integrated metabolome and transcriptome analysis reveals key genes and pathways associated with egg yolk percentage in chicken

Yolk percentage is a critical index in the egg product industry, reflecting both nutritional value and economic benefits. To elucidate the underlying mechanisms that contribute to variations in egg yolk percentage, we performed integrated transcriptome and metabolome analyses on the liver, ovary, and magnum tissues of Rhode Island Red chickens with high and low yolk percentages. A total of 322 differentially expressed genes (DEGs) and 128 significantly differential metabolites (SDMs) (VIP>1, P < 0.05) were identified in the liver, whereas 419 DEGs and 215 SDMs were detected in the ovary, and 238 DEGs along with 47 SDMs were found in the magnum. In the liver, genes such as HMGCR, DHCR7, MSMO1, and CYP7A1 were linked to cholesterol metabolism, essential for steroid hormone synthesis and yolk formation, while ACACB, ACSL1, ACSL4, LPL, and SGPP2 were involved in fatty acid biosynthesis, a key process for supplying energy and structural components of the yolk. In the ovary, COL6A6, COMP, CHAD, ITGA7, THBS2, and TNC contributed to extracellular matrix-receptor interactions, which are fundamental for follicle development and oocyte maturation. In the magnum, UGT1A1, MAOB, and ALDH3B2 participated in drug metabolism-cytochrome P450 and amino acid metabolism, ensuring a proper environment for egg white formation and potentially influencing nutrient allocation to the yolk. Metabolic pathway enrichment revealed that steroid hormone biosynthesis, glycerophospholipid metabolism, and betaine metabolism were predominant in the liver; pyruvate, taurine, and hypotaurine metabolism in the ovary; and phenylalanine metabolism in the magnum. Moreover, integrated analysis highlighted key metabolites and genes potentially regulating yolk deposition, including 7,8-dihydroneopterin and Pg 38:4 in the liver (related to immune modulation and lipid metabolism, respectively), thalsimine in the ovary, as well as DL-glutamine in the magnum, all of which may be crucial for maintaining metabolic homeostasis and supporting egg formation. Collectively, these findings deepen our understanding of how distinct molecular and metabolic pathways in the liver, ovary, and magnum orchestrate yolk proportion and deposition. Such insights may advance future strategies to improve egg quality and productivity in poultry breeding programs.

Immuno-Neutralization of Follistatin Bioactivity Enhances the Developmental Potential of Ovarian Pre-hierarchical Follicles in Yangzhou Geese

Simple Summary

Follistatin involves in the regulation of ovarian follicular development in mammals; however, the role of follistatin in goose ovarian follicular development has not been investigated. In this study, following immuno-neutralization of follistatin bioactivity in geese, the number of ovarian pre-ovulatory follicles significantly increased, and mRNA levels of genes involved in ovarian steroidogenesis and yolk deposition were upregulated in the granulosa layer of pre-hierarchical follicles. These results suggest that follistatin plays a limiting role in the development of ovarian pre-hierarchical follicles into pre-ovulatory follicles. These results also expand our understanding of the mechanism of follistatin on ovarian follicular development in geese.

Abstract

In order to explore the role of follistatin (FST) in ovarian follicular development and egg production in Yangzhou geese, sixty-four egg laying geese of the same genetic origin were selected and divided into two groups with equal numbers. One group was immunized against the recombinant goose FST protein by intramuscular injection, whereas the control group received bovine serum albumin (BSA) injection. Immunization against FST significantly increased the number of pre-ovulatory follicles. Furthermore, immunization against FST upregulated Lhr, Star, Vldlr, Smad3, and Smad4 mRNA levels in the granulosa layer of pre-hierarchical follicles. The results suggest that FST plays a limiting role in the development of ovarian pre-hierarchical follicles into pre-ovulatory follicles by decreasing follicular sensitivity to activin in geese. The mechanism may be achieved by regulating the SMAD3 signaling pathway, which affects progesterone synthesis and yolk deposition in pre-hierarchical follicles.

Molecular Characterisation, Tissue Distribution, and Expression Profiling of the Cathepsin B Gene during Ovarian Follicle Development in Geese

1. Although there is evidence that Cathepsin B (CTSB) regulates the degradation and absorption of yolk precursors during avian ovarian follicle development, nothing is known about its molecular characteristics, tissue distribution or expression profiles in goose ovarian follicular compartments.2. The intact 1023 bp coding sequence of the goose CTSB gene was obtained for the first time. It encoded a polypeptide of 340 amino acids (AA) containing two conserved functional domains (i.e., Propeptide_C1 and Peptidase_C1A_Cathpsin B) and three active amino acid residues (+108, +279, and +299). Both the nucleotide and AA sequences of goose CTSB gene showed more than 90% similarity with its respective homologs from other avian species.3. The qRT-PCR results showed that CTSB mRNA was ubiquitously expressed in all examined goose tissues, with moderate to high levels in the reproductive organs including the ovarian stroma and oviduct.4. Expression of goose CTSB mRNA in the granulosa layers increased gradually from the 2-4 mm F5 follicles but declined to relatively low levels in the F4-F1 follicles while remaining statistically unchanged in the theca layers throughout follicle development.5. High sequence similarity of goose CTSB gene to other avian species suggested functional conservation of avian CTSB genes, and its fluctuating levels in the granulosa layers may be associated with the orderly progression of goose follicle development. These data laid a foundation for further elucidating the role of CTSB in the avian ovary.

Differential actions of diacylglycerol acyltransferase (DGAT) 1 and 2 in regulating lipid metabolism and progesterone secretion of goose granulosa cells

Accumulating evidence shows that granulosa cells within both mammalian and avian ovaries have the ability to synthesize fatty acids through de novo lipogenesis and to accumulate triglycerides essential for oocyte and ovarian development. However, very little is known about the exact roles of key genes involved in the lipid metabolic pathway in granulosa cells. The goal of this study was to investigate the differential actions of diacylglycerol acyltransferase (DGAT) 1 and 2, which are recognized as the rate-limiting enzymes catalyzing the last step of triglyceride biosynthesis, in regulating lipid metabolism and steroidogenesis in granulosa cells of goose follicles at different developmental stages. It was observed that the mRNAs encoding DGAT1 and DGAT2 were ubiquitous in all examined granulosa cell layers but exhibited distinct expression profiles during follicle development. Notably, the mRNA levels of DGAT1, DGAT2, FSHR, LHR, STAR, CYP11A1, and 3βHSD remained almost constant in all except for 1-2 follicles within the 8-10 mm cohort, followed by an acute increase/decrease in the F5 follicles. At the cellular level, siRNA-mediated downregulation of DGAT1 or DGAT2 did not change the amount of lipids accumulated in both undifferentiated- and differentiated granulosa cells, while overexpression of DGAT2 promoted lipid accumulation and expression of lipogenic-related genes in these cells. Meanwhile, we found that interfering DGAT2 had no effect but interfering DGAT1 or overexpressing DGAT2 stimulated progesterone secretion in undifferentiated granulosa cells; in contrast, interference or overexpression of DGAT1/2 failed to change progesterone levels in differentiated granulosa cells but differently modulated expression of steroidogenic-related genes. Therefore, it could be concluded that DGAT1 is less efficient than DGAT2 in promoting lipid accumulation in both undifferentiated- and differentiated granulosa cells and that DGAT1 negatively while DGAT2 positively regulates progesterone production in undifferentiated granulosa cells.

Comparative Analysis of Metabolites in the Liver of Muscovy Ducks at Different Egg-Laying Stages Using Nontargeted Ultra-High-Performance Liquid Chromatography-Electrospray Mass Spectrometry-Based Metabolomics

Liver plays an important physiological function in the synthesis of yolk materials during egg laying in birds. Liver metabolite profiles of Muscovy ducks at different egg-laying stages from the perspective of nontargeted metabolomics were analyzed in this study. Twelve Muscovy ducks were selected at pre-laying (22 weeks, TT group), laying (40 weeks, FT group), and post-laying (60 weeks, ST group) stages, resulting in 36 hepatic metabolite profiles by using ultra-high-performance liquid chromatography-electrospray mass spectrometry. A total of 324 differential metabolites (156 increased and 168 decreased) in FT as compared to the TT (FT/TT) group and 332 differential metabolites (120 increased and 212 decreased) in ST as compared to the FT (ST/FT) group were screened out. Metabolic pathways enriched in FT/TT and ST/FT groups were mainly amino acid metabolism, glycerophospholipid metabolism, nucleotide metabolism, and vitamin metabolism. The amino acid metabolism pathways were upregulated in the FT/TT group and downregulated in the ST/FT group (P < 0.05). The glutathione and ascorbic acid abundances were downregulated, and the choline abundance was upregulated during egg laying (P < 0.05). The liver provides amino acids, lipids, nucleotides, vitamins, and choline, and so on, which are essential materials for yolk precursor synthesis. The decrease in the abundance of glutathione and ascorbic acid indicates that Muscovy ducks might be in a relatively stable physiological state during egg laying.

Transcriptomic and proteomic analyses of ovarian follicles reveal the role of VLDLR in chicken follicle selection

Background

Follicle selection in chickens refers to the process of selecting one follicle from a group of small yellow follicles (SY, 6–8 mm in diameter) for development into 12–15 mm hierarchical follicles (usually F6 follicles), which is an important process affecting laying performance in the poultry industry. Although transcriptomic analysis of chicken ovarian follicles has been reported, integrated analysis of chicken follicles for selection by using both transcriptomic and proteomic approaches is still rarely performed. In this study, we compared the proteomes and transcriptomes of SY and F6 follicles in laying hens and identified several genes involved in chicken follicle selection.

Results

Transcriptomic analysis revealed 855 differentially expressed genes (DEGs) between SY follicles and F6 follicles in laying hens, among which 202 were upregulated and 653 were downregulated. Proteomic analysis revealed 259 differentially expressed proteins (DEPs), including 175 upregulated and 84 downregulated proteins. Among the identified DEGs and DEPs, changes in the expression of seven genes, including VLDLR1, WIF1, NGFR, AMH, BMP15, GDF6 and MMP13, and nine proteins, including VLDLR, VTG1, VTG3, PSCA, APOB, APOV1, F10, ZP2 and ZP3L2, were validated. Further analysis indicated that the mRNA level of chicken VLDLR was higher in F6 follicles than in SY follicles and was also higher in granulosa cells (GCs) than in thecal cells (TCs), and it was stimulated by FSH in GCs.

Conclusions

By comparing the proteomes and transcriptomes of SY and F6 follicles in laying hens, we identified several differentially expressed proteins/genes that might play certain roles in chicken follicle selection. These data may contribute to the identification of functional genes and proteins involved in chicken follicle selection.

Transcriptome analysis to unravel the gene expression profile of ovarian follicular development in Magang goose

Magang geese exhibit a unique characteristic of follicular development, with eight largest orderly arranged pre-ovulatory follicles in the abdominal cavity. However, little is known about the mechanisms underlying this follicular development. This study aimed to compare gene expression profiles of granulosa cells (GCs) at different stages of follicular development and provide comprehensive insights into follicle selection and the mechanisms underlying the well-defined follicle hierarchy in Magang geese. GCs of large white follicles (LWFs), small yellow follicles (SYFs), F8, F4, and F1 were used for RNA-seq analysis; 374, 1117, 791, and 593 genes were differentially expressed in stages LWFs to SYFs, SYFs to F8, F8 to F4, and F4 to F1, respectively, suggesting that these genes contribute to follicle selection and development. Reliability of sequencing data was verified through qPCR analysis of 24 genes. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathways revealed a complex mechanism that remodels the extracellular matrix and turnover of extracellular matrix components in follicular development and ovulation and involves multiple pathway, such as focal adhesion, adherens junction, and extracellular matrix–receptor interaction. Some unique characteristics were observed during the different follicular development stages. For instance, some differentially expressed genes were enriched in progesterone-mediated oocyte maturation and steroid biosynthesis from stage SYFs to F8, whereas others were enriched in actin cytoskeleton regulation and vascular smooth muscle contraction from stage F4 to F1. These findings enhance our current understanding of GC function and ovarian follicles during the key stages of follicular development.

The Effects of Cholesterol Metabolism on Follicular Development and Ovarian Function

Cholesterol is an important substrate for the synthesis of ovarian sex hormones and has an important influence on follicular development. The cholesterol in follicular fluid is mainly derived from plasma. High-density lipoprotein (HDL) and lowdensity lipoprotein (LDL) play important roles in ovarian cholesterol transport. The knockout of related receptors in the mammalian HDL and LDL pathways results in the reduction or absence of fertility, leading us to support the importance of cholesterol homeostasis in the ovary. However, little is known about ovarian cholesterol metabolism and the complex regulation of its homeostasis. Here, we reviewed the cholesterol metabolism in the ovary and speculated that regardless of the functioning of cholesterol metabolism in the system or the ovarian microenvironment, an imbalance in cholesterol homeostasis is likely to have an adverse effect on ovarian structure and function.

A Functional Mutation in KIAA1462 Promoter Decreases Glucocorticoid Receptor Affinity and Affects Egg-Laying Performance in Yangzhou Geese

The identification of genetic markers is valuable for improving the egg-laying performance in goose production. The single-nucleotide polymorphism (SNP) rs1714766362 in an intron of the goose KIAA1462 gene was found to be relevant to laying performance in our previous study. However, its function remains unclear. In this study, the full-length coding sequence of KIAA1462 gene was firstly characterized in Yangzhou geese. Q-PCR (Quantitative Real Time Polymerase Chain Reaction) results showed that KIAA1462 was highly expressed in the liver, ovary, and mature F1 follicles. For SNP rs1714766362, geese with the AA genotype showed better laying performance than the TT ones and exhibited a higher KIAA1462 expression level in the ovary. Gain- and loss-of function experiments in granulosa cells revealed that KIAA1462 affected the expression of the apoptosis marker gene caspase-3. Considering that rs1714766362 locates in an intron area, we compared the KIAA1462 promoter regions of AA and TT individuals and identified the SNP c.-413C>G (Genbank ss2137504176), which was completely linked to SNP rs1714766362. According to the transcription factor prediction results, the glucocorticoid receptor (GR) would bind to the SNP site containing the C but not the G allele. In this study, we proved this hypothesis by an electrophoretic mobility shift assay (EMSA). In summary, we identified a novel mutation in the promoter of KIAA1462 gene which can modulate GR binding affinity and affect the laying performance of geese.

High-throughput sequencing reveals differential expression of miRNAs in prehierarchal follicles of laying and brooding geese

Broodiness is the primary factor influencing egg production in geese, in which several genes and miRNAs participate. Detailed spatiotemporal profiles of miRNAs encompassing follicle development levels, however, are lacking. In this study, we collected preovulatory follicles (classified as small white follicles, large white follicles, and small yellow follicles) from brooding and laying geese and aimed to analyze microRNA (miRNA or miR) during folliculogenesis. High-throughput sequencing and bioinformatics analysis were used to identify the miRNAs involved in follicle development. The let7 family, miR-10 family, and miR-143 family were abundant in these libraries, and they have been suggested to play a housekeeping role during folliculogenesis. Joint comparisons revealed 23 upregulated and 21 downregulated miRNAs (in at least two comparisons of follicles during brooding and laying, P < 0.1) in the laying stage. Unlike reproduction pathways reported for ovaries, GO and KEGG analysis suggested pathways for cell apoptosis and proliferation, such as the regulation of actin cytoskeleton, endocytosis, axon guidance, pathways in cancer, tight junctions, focal adhesion, the MAPK signaling pathway, cytokine-cytokine receptor interactions, and the Wnt signaling pathway in folliculogenesis. This study revealed the miRNAs that were directly involved in follicular atresia, and our results added to the understanding of the functional involvement of miRNAs during specific stages of follicle development.

Conservation of Regional Variation in Sex-Specific Sex Chromosome Regulation

Regional variation in sex-specific gene regulation has been observed across sex chromosomes in a range of animals and is often a function of sex chromosome age. The avian Z chromosome exhibits substantial regional variation in sex-specific regulation, where older regions show elevated levels of male-biased expression. Distinct sex-specific regulation also has been observed across the male hypermethylated (MHM) region, which has been suggested to be a region of nascent dosage compensation. Intriguingly, MHM region regulatory features have not been observed in distantly related avian species despite the hypothesis that it is situated within the oldest region of the avian Z chromosome and is therefore orthologous across most birds. This situation contrasts with the conservation of other aspects of regional variation in gene expression observed on the avian sex chromosomes but could be the result of sampling bias. We sampled taxa across the Galloanserae, an avian clade spanning 90 million years, to test whether regional variation in sex-specific gene regulation across the Z chromosome is conserved. We show that the MHM region is conserved across a large portion of the avian phylogeny, together with other sex-specific regulatory features of the avian Z chromosome. Our results from multiple lines of evidence suggest that the sex-specific expression pattern of the MHM region is not consistent with nascent dosage compensation.