Transcriptomic analysis of the liver in aged laying hens with different intensity of brown eggshell color

Transcriptome-based analysis reveals relationship between duck eggshell color and eggshell strength

BACKGROUND

The strength of duck eggshells is essential for their storage, transportation, and processing, with various studies indicating a correlation between eggshell color and strength.

RESULTS

Our research has demonstrated that green-shelled duck eggs exhibit higher eggshell strength compared to white-shelled eggs in the M2 Line Pekin Duck population. To this end, we established mRNA transcriptome profiles of 10 eggshell gland tissues and 10 liver tissues and constructed gene expression networks in the two tissues. RNA-Seq analysis suggests that genes associated with ion transport, transmembrane transport, and liver cell proliferation and differentiation in the eggshell gland could play important roles in eggshell formation. The liver of green shell duck has stronger cell proliferation ability to maintain its homeostasis, and the eggshell gland has stronger ability to secrete eggshell matrix protein, which may be the reason why the eggshell is stronger than that of white shell duck. Through Weighted gene co-expression network analysis (WGCNA), three related modules were found in eggshell gland and liver, respectively, and three key genes were screened in each tissue (eggshell gland: FKBP10, PPARG, MAP3K5, liver: PHLDA1, FLT3, CACNB4). They have important regulatory effects on eggshell color and eggshell strength respectively.

CONCLUSIONS

Through transcriptome analysis, we identified key genes associated with eggshell color (ESB) (Gland: ABCG2, SLC51B; Liver: COX1, DIO3, RBPJ) and eggshell strength (ESS) (Gland: MAP3K5, PPARG, FKBP10; Liver: PHLDA1, FLT3, CACNB4). We propose that these genes regulate ESB and ESS by modulating antioxidant capacity and bile acid synthesis in the liver and shell gland, leading to enhanced biliverdin deposition and stronger eggshells in green-shelled ducks. Additionally, the upregulation of ion transport, transmembrane transport, and liver cell proliferation-related genes in green-shelled ducks further supports the observed superiority in eggshell strength.

Comparative analysis of hepatic transcriptomes and metabolomes of Changshun green-shell laying hens based on different green eggshell color intensities

The eggshell color of avian species is an important trait that is predominantly determined by the pigments biliverdin and protoporphyrin. Various factors affect eggshell pigment deposition and coloration; however, the underlying mechanisms remain unclear. We analyzed the hepatic transcriptomes and metabolomes of Changshun green-shell hens laying dark green and light green eggs to investigate the potential role of the liver in regulating the intensity of the green eggshell color. In total, 350 differentially expressed genes and 211 differentially altered metabolites were identified. Gene set enrichment analysis revealed that the enriched pathways and Gene Ontology (GO) terms were mainly associated with energy, immunity, and nutrient metabolism. Metabolite set enrichment analysis revealed that the enriched pathways were mainly associated with amino acid, vitamin, bile acid, and lipid metabolism. Moreover, gene-metabolite interaction network analysis revealed 1 subnetwork. Most genes and metabolites in this subnetwork were determined to be related to melanin metabolism and transport. In conclusion, our results suggest that hepatic melanin metabolism and transport are critical for eggshell coloration. Six candidate genes (CDKN2B, DDC, PYCR1, ABCG5, SLC3A1, and P2RX2) and 7 candidate metabolites (serotonin, 5-hydroxyindoleacetic acid, ornithine, acetylcholine, L-tryptophan, D-ornithine, and ADP) were suggested to play important roles in this process. Meanwhile, this study suggests that changes in hepatic energy metabolism, immune status, antioxidation activity, nutrient availability, and bile acid synthesis can impair eggshell coloration.

Transcriptome and histological analyses on the uterus of freckle egg laying hens

BACKGROUND

In this study, we explored the characteristics and causes of freckle formation. We collected 15 normal and freckled eggs each for eggshell index testing and hypothesized that the structure and function of the uterus would have a direct effect on freckled egg production given that eggshells are formed in the uterus. To test this hypothesis, we collected uterine tissue from laying hens (418 days of age) that laid normal (Group C, n = 13) and freckled (Group T, n = 16) eggs for 7 consecutive days.

RESULTS

When we examined the eggshell quality, we found that the L value was significantly lower (P < 0.05) in the freckled site group of freckled eggs compared to the normal egg group during the detection of blunt pole, equator, and sharp pole of the eggshell color. The a-values of the three positions were significantly higher (P < 0.05) in the freckled site group of freckled eggs, and the a-values of the blunt pole were significantly lower (P < 0.05) in the background site group of freckled eggs, compared to the normal egg group. The b-values were significantly higher (P < 0.05) at three locations in the freckled site group of freckled eggs compared to the normal egg group. During the detection of eggshell thickness, the blunt pole was significantly higher (P < 0.05) in the freckled egg site group of freckled eggs compared to the normal egg group, and there was no significant difference between the other groups (P > 0.05). There was no significant difference (P > 0.05) between the transverse and longitudinal diameters of the eggs in each group.We then performed histopathology and transcriptome analyses on the collected tissue. When compared with group C, uterine junctional epithelial cells in group T showed significant defects and cilia loss, and epithelial tissue was poorly intact. From transcriptomics, genes that met (|log2FC|) ≥ 1 and P < 0.05 criteria were screened as differentially expressed genes (DEGs). We identified a total of 136 DEGs, with 101 up- and 35 down-regulated genes from our RNA-seq data. DEGs identified by enrichment analyses, which were potentially associated with freckled egg production were: IFI6, CCL19, AvBD10, AvBD11, S100A12, POMC, and UCN3. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses showed that pathways were associated with immunoreaction and stress stimulation, e.g., complement activation, interleukin-1 cell reactions, viral responses, cell reactions stimulated by corticotropin releasing hormone, steroid hormone mediated signaling pathways, staphylococcal infections, B cell receptor signaling pathways, and natural killer cell mediated cytotoxicity.

CONCLUSIONS

From these data, freckled areas deepen freckled eggshell color, but background areas are not affected. At the same time,we reasoned that freckle eggs may result from abnormal immune responses and impaired uterine functions induced by stress. Therefore, the uterus of laying hens in a state of stress and abnormal immune function can cause the appearance of freckled eggs.