Egg is an encapsulated source of macro and micronutrients that meet all requirements to support embryonic development until hatching. The perfect balance and diversity in its nutrients along with its ...high digestibility and its affordable price has put the egg in the spotlight as a basic food for humans. However, egg still has to face many years of nutritionist recommendations aiming at restricting egg consumption to limit cardiovascular diseases incidence. Most experimental, clinical, and epidemiologic studies concluded that there was no evidence of a correlation between dietary cholesterol brought by eggs and an increase in plasma total-cholesterol. Egg remains a food product of high nutritional quality for adults including elderly people and children and is extensively consumed worldwide. In parallel, there is compelling evidence that egg also contains many and still-unexplored bioactive compounds, which may be of high interest in preventing/curing diseases. This review will give an overview of (1) the main nutritional characteristics of chicken egg, (2) emerging data related to egg bioactive compounds, and (3) some factors affecting egg composition including a comparison of nutritional value between eggs from various domestic species.
During chicken embryonic development, skeleton calcification mainly relies on the eggshell, whose minerals are progressively solubilized and transported to the embryo via the chorioallantoic membrane ...(CAM). However, the molecular components involved in this process remain undefined. We assessed eggshell demineralization and calcification of the embryo skeleton after 12 and 16 d of incubation, and analyzed the expression of several candidate genes in the CAM: carbonic anhydrases that are likely involved in secretion of protons for eggshell dissolution (CA2, CA4, CA9), ions transporters and regulators (CALB1, SLC4A1, ATP6V1B2, SGK1, SCGN, PKD2) and vitamin-D binding protein (GC).
Our results confirmed that eggshell weight, thickness, and strength decreased during incubation, with a concomitant increase in calcification of embryonic skeletal system. In the CAM, the expression of CA2 increased during incubation while CA4 and CA9 were expressed at similar levels at both stages. SCL4A1 and SCGN were expressed, but not differentially, between the two stages, while the expression of ATP6V1B2 and PKD2 genes decreased. The expression of SGK1 and TRPV6 increased over time, although the expression of the latter gene was barely detectable. In parallel, we analyzed the expression of these candidate genes in the yolk sac (YS), which mediates the transfer of yolk minerals to the embryo during the first half of incubation. In YS, CA2 expression increases during incubation, similar to the CAM, while the expression of the other candidate genes decreases. Moreover, CALB1 and GC genes were found to be expressed during incubation in the YS, in contrast to the CAM where no expression of either was detected.
This study demonstrates that the regulation of genes involved in the mobilization of egg minerals during embryonic development is different between the YS and CAM extraembryonic structures. Identification of the full suite of molecular components involved in the transfer of eggshell calcium to the embryo via the CAM should help to better understand the role of this structure in bone mineralization.
Dimorphism between male and female embryos has been demonstrated in many animal species, including chicken species. Likewise, extraembryonic membranes such as the chorioallantoic membrane (CAM) are ...likely to exhibit a sex-specific profile. Analysis of the previously published RNA-seq data of the chicken CAM sampled at two incubation times, revealed 783 differentially expressed genes between the CAM of male and female embryos. The expression of some of these genes is sex-dependant only at one or other stage of development, while 415 genes are sex-dependant at both developmental stages. These genes include well-known sex-determining and sex-differentiation genes (DMRT1, HEGM, etc.), and are mainly located on sex chromosomes. This study provides evidence that gene expression of extra-embryonic membranes is differentially regulated between male and female embryos. As such, a better characterisation of associated mechanisms should facilitate the identification of new sex-specific biomarkers.
•The chorioallantoic membrane (CAM) expresses sex-specific genes.•Most CAM sex-dimorphic transcripts are located on Z or W chromosomes.•Most sex-dimorphic transcripts encode proteins.•CAM sex-dimorphic transcripts are likely to be similarly expressed, regardless of the breed.•The data provide new evidence that extraembryonic tissues exhibit a sex-specific transcriptome.
The pHu+ and pHu- lines, which were selected based on the ultimate pH (pHu) of the breast muscle, represent a unique model to study the genetic and physiological controls of muscle energy store in ...relation with meat quality in chicken. Indeed, pHu+ and pHu- chicks show differences in protein and energy metabolism soon after hatching, associated with a different ability to use energy sources in the muscle. The present study aimed to assess the extent to which the nutritional environment of the embryo might contribute to the metabolic differences observed between the two lines at hatching. Just before incubation (E0), the egg yolk of pHu+ exhibited a higher lipid percentage compared to the pHu- line (32.9% vs. 27.7%). Although
H-NMR spectroscopy showed clear changes in egg yolk composition between E0 and E10, there was no line effect. In contrast,
H-NMR analysis performed on amniotic fluid at embryonic day 10 (E10) clearly discriminated the two lines. The amniotic fluid of pHu+ was richer in leucine, isoleucine, 2-oxoisocaproate, citrate and glucose, while choline and inosine were more abundant in the pHu- line. Our results highlight quantitative and qualitative differences in metabolites and nutrients potentially available to developing embryos, which could contribute to metabolic and developmental differences observed after hatching between the pHu+ and pHu- lines.
Chicken diet essentially relies on soybean as the major source of proteins but there are increasing efforts to identify other protein-rich feedstuffs. Of these, some pea cultivars constitute ...interesting sources of proteins, although some of them contain anti-nutritional factors that may compromise the digestibility of their protein content. Consequently, chickens exhibit low performance, while undigested compounds rejected in feces have a negative environmental impact. In this article, we analyzed the intestinal content of chickens fed a pea-diet (Pisum sativum) to decipher the mechanisms that could explain such a low digestibility. Using gelatin zymography, we observed that the contents of chicken fed the pea diet exhibit altered proteolytic activities compared with intestinal contents from chickens fed a rapeseed, corn, or soybean diet. This pea-specific profile parallels the presence of a 34 kDa protein band that resists proteolysis during the digestion process. Using mass spectrometry analysis, we demonstrated that this band contains the pea-derived Bowman-Birk protease inhibitor (BBI) and three chicken proteases, the well-known chymotrypsinogen 2-like (CTRB2) and trypsin II-P39 (PRSS2), and the yet uncharacterized trypsin I-P38 (PRSS3). All three proteases are assumed to be protease targets of BBI. Molecular modeling of the interaction of pea BBI with PRSS2 and PRSS3 trypsins reveals that electrostatic features of PRSS3 may favor the formation of a BBI-PRSS3 complex at physiological pH. We hypothesize that PRSS3 is specifically expressed and secreted in the intestinal lumen to form a complex with BBI, thereby limiting its inhibitory effects on PRSS2 and chymotrypsinogen 2-like proteases. These data clearly demonstrate that in chickens, feedstuff containing active pea BBI affects intestinal proteolytic activities. Further studies on the effects of BBI on the expression of PRSS3 by digestive segments will be useful to better appreciate the impact of pea on intestine physiology and function. From these results, we suggest that PRSS3 protease may represent an interesting biomarker of digestive disorders in chickens, similar to human PRSS3 that has been associated with gut pathologies.
The seminal plasma is a very complex fluid, which surrounds sperm in semen. It contains numerous proteins including proteases and protease inhibitors that regulate proteolytic processes associated ...with protein activation and degradation. We previously identified a seminal protein, chicken liver trypsin inhibitor 1 (ClTI‐1) over expressed in semen of roosters with high fertility, suggesting a role in male fertility. In the present study, we showed that ClTI‐1 gene is actually SPINK2. Using normal healthy adult roosters, we showed that SPINK2 amount in seminal plasma was positively correlated with male fertility in chicken lines with highly contrasted genetic backgrounds (broiler and layer lines). Using affinity chromatography combined to mass spectrometry analysis and kinetic assays, we demonstrated for the first time that two chicken acrosin isoforms (acrosin and acrosin‐like proteins) are the physiological serine protease targets of SPINK2 inhibitor. SPINK2 transcript was overexpressed all along the male tract, and the protein was present in the lumen as expected for secreted proteins. Altogether, these data emphasize the role of seminal SPINK2 Kazal‐type inhibitor as an important actor of fertility in birds through its inhibitory action on acrosin isoforms proteins.
In the present paper, we demonstrate that the seminal SPINK2 Kazal‐type inhibitor is an important actor of fertility in birds through its inhibitory action on acrosin isoforms proteins.
The chicken chorioallantoic membrane (CAM) is an extraembryonic membrane that is vital for the embryo. It undergoes profound cell differentiation between 11 and 15 days of embryonic incubation (EID), ...which corresponds to the acquisition of its physiological functions. To gain insight into the functional genes that accompany these biological changes, RNA sequencing of the CAM at EID11 and EID15 was performed. Results showed that CAM maturation coincides with the overexpression of 4225 genes, including many genes encoding proteins involved in mineral metabolism, innate immunity, homeostasis, angiogenesis, reproduction, and regulation of hypoxia. Of these genes, some exhibit variability in expression depending on the chicken breed (broiler versus layer breeds). Besides the interest of these results for the poultry sector, the identification of new functional gene candidates opens additional research avenues in the field of developmental biology.
•The chorioallantoic membrane (CAM) ensures vital functions for the chicken embryo.•CAM cell differentiation and activity coincides with the overexpression of 4225 genes.•Active CAM gene expression highlights mineral ion transport and immunity functions.•Variable gene expression level between breeds suggests linkage to production traits.•The data opens new research avenues in developmental biology.
Nutrient availability in eggs can affect early metabolic orientation in birds. In chickens divergently selected on the Pectoralis major ultimate pH, a proxy for muscle glycogen stores, ...characterization of the yolk and amniotic fluid revealed a different nutritional environment. The present study aimed to assess indicators of embryo metabolism in pHu lines (pHu+ and pHu-) using allantoic fluids (compartment storing nitrogenous waste products and metabolites), collected at days 10, 14 and 17 of embryogenesis and characterized by 1H-NMR spectroscopy. Analysis of metabolic profiles revealed a significant stage effect, with an enrichment in metabolites at the end of incubation, and an increase in interindividual variability during development. OPLS-DA analysis discriminated the two lines. The allantoic fluid of pHu- was richer in carbohydrates, intermediates of purine metabolism and derivatives of tryptophan-histidine metabolism, while formate, branched-chain amino acids, Krebs cycle intermediates and metabolites from different catabolic pathways were more abundant in pHu+. In conclusion, the characterization of the main nutrient sources for embryos and now allantoic fluids provided an overview of the in ovo nutritional environment of pHu lines. Moreover, this study revealed the establishment, as early as day 10 of embryo development, of specific metabolic signatures in the allantoic fluid of pHu+ and pHu- lines.
As uricoletic animals, chickens produce cleidoic eggs, which are self-contained bacteria-resistant biological packages for extra-uterine development of the chick embryo. The eggshell constitutes a ...natural physical barrier against bacterial penetration if it forms correctly and remains intact. The eggshell's remarkable mechanical properties are due to interactions among mineral components and the organic matrix proteins. The purpose of our study was to identify novel eggshell proteins by examining the transcriptome of the uterus during calcification of the eggshell. An extensive bioinformatic analysis on genes over-expressed in the uterus allowed us to identify novel eggshell proteins that contribute to the egg's natural defenses.
Our 14 K Del-Mar Chicken Integrated Systems microarray was used for transcriptional profiling in the hen's uterus during eggshell deposition. A total of 605 transcripts were over-expressed in the uterus compared with the magnum or white isthmus across a wide range of abundance (1.1- to 79.4-fold difference). The 605 highly-expressed uterine transcripts correspond to 469 unique genes, which encode 437 different proteins. Gene Ontology (GO) analysis was used for interpretation of protein function. The most over-represented GO terms are related to genes encoding ion transport proteins, which provide eggshell mineral precursors. Signal peptide sequence was found for 54 putative proteins secreted by the uterus during eggshell formation. Many functional proteins are involved in calcium binding or biomineralization--prerequisites for interacting with the mineral phase during eggshell fabrication. While another large group of proteins could be involved in proper folding of the eggshell matrix. Many secreted uterine proteins possess antibacterial properties, which would protect the egg against microbial invasion. A final group includes proteases and protease inhibitors that regulate protein activity in the acellular uterine fluid where eggshell formation takes place.
Our original study provides the first detailed description of the chicken uterus transcriptome during formation of the eggshell. We have discovered a cache of about 600 functional genes and identified a large number of encoded proteins secreted into uterine fluid for fabrication of the eggshell and chemical protection of the egg. Some of these uterine genes could prove useful as biological markers for genetic improvement of phenotypic traits (i.e., egg and eggshell quality).
To better appreciate the dynamics of yolk proteins during embryonic development, we analyzed the protein quantitative changes occurring in the yolk plasma at the day of lay and after 12 days of ...incubation, by comparing unfertilized and fertilized chicken eggs. Of the 127 identified proteins, 69 showed relative abundance differences among conditions. Alpha-fetoprotein and two uncharacterized proteins (F1NHB8 and F1NMM2) were identified for the first time in the egg. After 12 days of incubation, five proteins (vitronectin, α-fetoprotein, similar to thrombin, apolipoprotein B, and apovitellenin-1) showed a major increase in relative abundance, whereas 15 proteins showed a significant decrease in the yolks of fertilized eggs. In unfertilized/table eggs, we observed an accumulation of proteins likely to originate from other egg compartments during incubation. This study provides basic knowledge on the utilization of egg yolk proteins by the embryo and gives some insight into how storage can affect egg quality.
PDF
