Comparative N-Glycoproteomic Investigation of Eggshell Cuticle and Mineralized Layer Proteins

Transcriptomic and Metabolomic Analysis of the Uterine Tissue of Yaoshan Chicken and Its Crossbreeds to Reveal the Molecular Mechanism Influencing Eggshell Quality

Background/Objectives: Eggshell quality is a critical factor influencing consumer preference and the economic benefits of poultry enterprises, and the uterus is the key site for eggshell synthesis. Yaoshan chicken (YS), an indigenous chicken breed in China, is renowned for its flavorful meat and high-quality eggs. However, its egg production is lower compared to specialized strains. Therefore, the GYR crossbreed was developed by three-line hybridization for YS chicken, which can produce green-shelled eggs with better eggshell thickness and strength than YS chicken (p < 0.01). To explore the molecular mechanisms underlying the differences in eggshell quality between GYR and YS chickens, we conducted an integrated transcriptomic and metabolomic analysis. Methods: Twelve uterus samples (six from GYR and six from YS chickens) were collected during the period of eggshell calcification at 260 days of age. RNA sequencing (RNA-seq) and liquid chromatography-mass spectrometry (LC-MS/MS) were performed to identify differentially expressed genes (DEGs) and differential metabolites (DMs), respectively. Results: A total of 877 DEGs were identified in the GYR group, including 196 upregulated and 681 downregulated genes (|log2 (fold change)| > 1, p-value < 0.05). Additionally, 79 DMs were detected, comprising 50 upregulated and 29 downregulated metabolites (|log₂ (fold change)| > 1, VIP > 1). Notably, the key DEGs (SLCO1B3, SLCO1B1, PTGR1, LGR6, MELTF, CRISP2, GVINP1, and OVSTL), important DMs (prostaglandin-related DMs and biliverdin) and signaling pathways (calcium signaling, neuroactive ligand-receptor interaction, arachidonic acid metabolism, bile secretion, and primary bile acid biosynthesis) were major regulators of the eggshell quality. Furthermore, an integrated transcriptomic and metabolomic analysis revealed two significant gene-metabolite pairs associated with eggshell quality: PTGDS-prostaglandin E2 and PTGS1-prostaglandin E2. Conclusions: This study provides a theoretical foundation for the improved eggshell quality of Yaoshan chicken.

Storage deterioration and detection of egg multi-scale structure: A review

This review summarized the processes and mechanisms of deterioration in different components of eggs during storage. The mechanisms linked to reduced glycosylation, structural decay, and ovomucin degradation during egg-white thinning were elucidated, along with the weakening of lysozyme-ovomucin interactions. The degradation and S-conformation transformation of ovalbumin were studied, and the potential application of solubility-viscosity theory in egg-white thinning was discussed. Furthermore, the metabolic pathways of glycerophospholipids and glycerolipids during lipid hydrolysis in egg yolk were scrutinized, and the mechanism of fatty acid auto-oxidation was concluded. The review also delineated the mechanism of cuticle thinning and the impact of preservation strategies on cuticle quality. The reproductive and adaptive strategies of dominant bacteria during egg spoilage were addressed, summarizing the microbial perspective. Lastly, methods for assessing egg freshness were reviewed, encompassing both traditional destructive testing methods and advanced photoelectric nondestructive testing techniques.

Translucent eggs of laying hens: a review

Eggshell quality is a significant characteristic that influences consumer preferences. Eggshell translucency is a common defect in the appearance of eggshells, which are characterized by gray spots that are visible to the naked eye under natural light. The presence of various defects resulting from eggshell translucency has caused a decrease in consumer willingness to purchase eggs, leading to considerable economic losses in the egg industry. Although the impact of eggshell translucency on food safety, egg quality, and hatchability has been extensively investigated, the classification and causes of eggshell translucency remain unclear and lack a systematic summary. In recent studies, new interpretations of evaluation methods and causes of eggshell translucency have been proposed, along with numerous innovative solutions. Therefore, this paper aims to provide a comprehensive review of the evaluation methods, classification, causes, effects, and influencing factors of eggshell translucency and to summarize the treatments for translucent eggs. We believe that this review will serve as a valuable reference for researchers involved in the study of translucent eggs.

On the Structure and Role of Avian Eggshells: A 31P, 1H, and 13C Solid-State NMR Study

The eggshell is a composite and highly ordered structure formed by biomineralization. Besides other functions, it has a vital and intricate role in the protection of an embryo from various potentially harsh environmental conditions. Solid-state nuclear magnetic resonance (SSNMR) has been used for detailed structural investigations of the chicken, tinamou, and flamingo eggshell materials. 31P NMR spectra reveal that hydroxyapatite and β-tricalcium phosphate in the ratio 3:2 represent major constituents of phosphate species in the eggshells. All three eggshells exhibit similar spectra, except for the line widths, which implies different structural order of phosphate species in the chicken, tinamou, and flamingo eggshells. 1H NMR spectra for these materials are comparable, differentiating overlapped peaks in three spectral regions at around 7, 4-5, and 1-2 ppm. These spectral regions have been attributed to protons from NH or CaHCO3, water, and possibly isolated monomeric water molecules or hydroxyl groups in calcium-deficient hydroxyapatite. 1H-13C CP MAS NMR revealed the presence of organic matter in the form of lipids and proteins. Two overlapped resonances in the carbonyl region at around 173 and 169 ppm are assigned to the carbonyls of the peptide bonds and the bicarbonate unit in calcite, respectively. Fourier-transform infrared spectroscopy (FTIR) spectra confirmed the presence of structural units detected in the NMR spectra.

TMT-based quantitative proteomic analysis reveals eggshell matrix protein changes correlated with eggshell quality in Jing Tint 6 laying hens of different ages

The decline in eggshell quality resulting from aging hens poses a threat to the financial benefits of the egg industry. The deterioration of eggshell quality with age can be attributed to changes in its ultrastructure and chemical composition. Specific matrix proteins in eggshells have a role in controlling crystal growth and regulating structural organization. However, the variations in ultrastructure and organic matrix of eggshells in aging hens remain poorly understood. This study assessed the physical traits, mechanical quality, chemical content, as well as the microstructural and nanostructural properties of eggs from Jing Tint 6 hens at 38, 58, 78, and 108 wk of age. Subsequently, a quantitative proteomic analysis was conducted to identify differences in protein abundance in eggshells between the ages of 38 and 108 wk. The results indicated a notable decline in shell thickness, breaking strength, index, fracture toughness, and stiffness in the 108-wk-age group compared to the other groups (P < 0.05). The ultrastructure variations primarily involved an increased ratio of the mammillary layer and a reduced thickness of the effective layer of eggshell in the 108-wk-age group (P < 0.05). However, no significant differences in eggshell compositions were observed among the various age groups (P > 0.05). Proteomic analysis revealed the identification of 76 differentially expressed proteins (DEPs) in the eggshells of the 38-wk-age group and 108-wk-age group, which comprised proteins associated with biomineralization, calcium ion binding, immunity, as well as protein synthesis and folding. The downregulation of ovocleidin-116, osteopontin, and calcium-ion-related proteins, together with the upregulation of ovalbumin, lysozyme C, and antimicrobial proteins, has the potential to influence the structural organization of the eggshell. Therefore, the deterioration of eggshell quality with age may be attributed to the alterations in ultrastructure and the abundance of matrix proteins.