Abstract
Brown eggs are popular in many countries and consumers regard eggshell brownness as an important indicator of egg quality. However, the potential regulatory proteins and detailed molecular mechanisms regulating eggshell brownness have yet to be clearly defined. In the present study, we performed quantitative proteomics analysis with iTRAQ technology in the shell gland epithelium of hens laying dark and light brown eggs to investigate the candidate proteins and molecular mechanisms underlying variation in chicken eggshell brownness. The results indicated 147 differentially expressed proteins between these two groups, among which 65 and 82 proteins were significantly up-regulated in the light and dark groups, respectively. Functional analysis indicated that in the light group, the down-regulated iron-sulfur cluster assembly protein (Iba57) would decrease the synthesis of protoporphyrin IX; furthermore, the up-regulated protein solute carrier family 25 (mitochondrial carrier; adenine nucleotide translocator), member 5 (SLC25A5) and down-regulated translocator protein (TSPO) would lead to increased amounts of protoporphyrin IX transported into the mitochondria matrix to form heme with iron, which is supplied by ovotransferrin protein (TF). In other words, chickens from the light group produce less protoporphyrin IX, which is mainly used for heme synthesis. Therefore, the exported protoporphyrin IX available for eggshell deposition and brownness is reduced in the light group. The current study provides valuable information to elucidate variation of chicken eggshell brownness, and demonstrates the feasibility and sensitivity of iTRAQ-based quantitative proteomics analysis in providing useful insights into the molecular mechanisms underlying brown eggshell pigmentation.
Highlights
Brown eggs dominate commercial markets in many countries, such as China, Britain, France, Italy and Portugal
A total of 765 eggs from 281 hens were collected on three consecutive days, and eggshell color, egg shape index, eggshell strength, eggshell thickness and eggshell weight were measured
The LÃ value was used to represent the intensity of eggshell brownness, as verified by the high correlation coefficient between the LÃvalue and protoporphyrin IX quantity in the eggshell [11]
Summary
Brown eggs dominate commercial markets in many countries, such as China, Britain, France, Italy and Portugal. Eggshell color has low genetic correlation with external and internal egg quality traits [1]. Consumers still regard eggshell color as an important indicator of PLOS ONE | DOI:10.1371/journal.pone.0168750. Proteomic Analysis for Chicken Eggshell Brownness egg quality. Market tests suggest that consumers positively perceive brown eggs as being more nutritious and flavorful, and that hens laying brown eggs are thought to be organically fed [2]. Consumers who prefer brown eggs pay attention to the intensity of eggshell brownness, and exhibit a preference for uniformity in eggshell brownness [3]
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