A study on eggshell pigmentation: biliverdin in blue-shelled chickens

Genome-wide association analysis of eggshell color of an F2 generation population reveals candidate genes in chickens

Eggshell color is an important visual characteristic that affects consumer preferences for eggs. Eggshell color, which has moderate to high heritability, can be effectively enhanced through molecular marker selection. Various studies have been conducted on eggshell color at specific time points. However, few longitudinal data are available on eggshell color. Therefore, the objective of this study was to investigate eggshell color using the Commission International de L'Eclairage L*a*b* system with multiple measurements at different ages (age at the first egg and at 32, 36, 40, 44, 48, 52, 56, 60, 66, and 72 weeks) within the same individuals from an F2 resource population produced by crossing White Leghorn and Dongxiang Blue chicken. Using an Affymetrix 600 single nucleotide polymorphism (SNP) array, we estimated the genetic parameters of the eggshell color trait, performed genome-wide association studies (GWASs), and screened for the potential candidate genes. The results showed that pink-shelled eggs displayed a significant negative correlation between L* values and both a* and b* values. Genetic heritability based on SNPs showed that the heritability of L*, a*, and b* values ranged from 0.32 to 0.82 for pink-shelled eggs, indicating a moderate to high level of genetic control. The genetic correlations at each time point were mostly above 0.5. The major-effect regions affecting the pink eggshell color were identified in the 10.3-13.0 Mb interval on Gallus gallus chromosome 20, and candidate genes were selected, including SLC35C2, PCIF1, and SLC12A5. Minor effect polygenic regions were identified on chromosomes 1, 6, 9, 12, and 15, revealing 11 candidate genes, including MTMR3 and SLC35E4. Members of the solute carrier family play an important role in influencing eggshell color. Overall, our findings provide valuable insights into the phenotypic and genetic aspects underlying the variation in eggshell color. Using GWAS analysis, we identified multiple quantitative trait loci (QTLs) for pink eggshell color, including a major QTL on chromosome 20. Genetic variants associated with eggshell color may be used in genomic breeding programs.

Production of biliverdin by biotransformation of exogenous heme using recombinant Pichia pastoris cells

Biliverdin, a bile pigment hydrolyzed from heme by heme oxygenase (HO), serves multiple functions in the human body, including antioxidant, anti-inflammatory, and immune response inhibitory activities. Biliverdin has great potential as a clinical drug; however, no economic and efficient production method is available currently. Therefore, the production of biliverdin by the biotransformation of exogenous heme using recombinant HO-expressing yeast cells was studied in this research. First, the heme oxygenase-1 gene (HO1) encoding the inducible plastidic isozyme from Arabidopsis thaliana, with the plastid transport peptide sequence removed, was recombined into Pichia pastoris GS115 cells. This resulted in the construction of a recombinant P. pastoris GS115-HO1 strain that expressed active HO1 in the cytoplasm. After that, the concentration of the inducer methanol, the induction culture time, the pH of the medium, and the concentration of sorbitol supplied in the medium were optimized, resulting in a significant improvement in the yield of HO1. Subsequently, the whole cells of GS115-HO1 were employed as catalysts to convert heme chloride (hemin) into biliverdin. The results showed that the yield of biliverdin was 132 mg/L when hemin was added to the culture of GS115-HO1 and incubated for 4 h at 30 °C. The findings of this study have laid a good foundation for future applications of this method for the economical production of biliverdin.

Genetics and breeding of a black-bone and blue eggshell chicken line. 3. Visual eggshell color and colorimeter parameters in 3 consecutive generations

The BG line, originated by crossing 2 Chinese indigenous breeds, Dongxiang blue eggshell and Jiangshan black-bone, has been bred for black carcass and blue-greenish eggs. Aiming to study the genetic parameters and selection aspects of these eggshell colors, the 4 colorimeter parameters (L*, a*, b*, SCI = L*-a*-b*) were measured on ∼5 eggs/hen/age (200 d and 300 d) from each hen in 3 generations (G4 = 452, G5 = 508, G6 = 498). Visual eggshell color was classified as either "Light," "Blue," "Green," or "Olive," and data from G4 and G5 indicated that visual eggshell color was more accurately determined by combining the classifications of single representative egg/hen by 4 independent observers. Based on the apparent gradual variation in visual color, the 4 colors were expressed numerically (Light = 1, Blue = 2, Green = 3, Olive = 4) and the averages of the 4 observers (AveObs) were used as quantitative expression of the visual color of each egg. This expression, in the range from Blue to Olive, was highly significantly correlated with L*, b* and SCI. The a* values were also associated with AveObs, but not linearly; AveObs between 2 (Blue) and 3 (Green) had lowest a*, and it increased as AveObs was more Light (<2) or more Olive (>3). The heritability estimates of the colorimeter parameters were mostly very high; those of b* and SCI ranged between 0.7 and 0.8, and those of L* and a* between 0.6 and 0.7, indicating that they can serve as criterions to select for blue and/or green eggshells. The phenotypic and genetic correlations between the colorimeter parameters were highly significant and favorable. It is suggested that effective breeding for blue eggs can be done by selecting hens laying eggs with highest SCI/L* or lowest b* (against green and olive shades), followed by selection for low a* (against light shades). Breeding for green eggs can be done by selecting hens laying eggs with SCI ≈ 75 and/or L* ≈ 80 and/or b* ≈ 12. Breeding for hens that lay either blue or green eggs can be done by selection for low a* values.

The Pigments in Eggshell with Different Color and the Pigment Regulatory Genes Expression in Corresponding Chicken’s Shell Gland

Eggshell colour is the unique appearance and economically valuable trait of eggs, whereas the colour is often short of uniformity, especially in the blue-shelled breeds, hence, their pigment differences and molecular mechanism need clarity. To investigate the relationship between the pigment content of eggshells and related gene expression in the eggshell glands of chickens, four subtypes of blue-shelled eggs ('Olive', 'Green', 'Blue', and 'Light') from the same blue-eggshell chicken line were selected; Hy-Line 'White' and 'Brown'-shelled eggs were used as control groups. The L*, a*, b* values, and protoporphyrin-IX and biliverdin contents in each group of eggshells were measured. In addition, the shell glands of the corresponding hens were collected to detect SLCO1B3 genotype and mRNA expression, and ABCG2 and HMOX1 transcription and protein expression. Eggshell colour L* values were negatively correlated with protoporphyrin-IX, b* values were positively correlated with total pigment content (P < 0.001), and a* values were positively correlated with protoporphyrin-IX (P < 0.001) but negatively with biliverdin. Moreover, all four blue-eggshell subtypes were SLCO1B3 homozygous, with SLCO1B3 mRNA expression in shell glands being significantly higher than in the White and Brown groups. ABCG2 and HMOX1 mRNA expression were highest in the Brown and Green groups, respectively (P < 0.05), and were positively correlated with protoporphyrin-IX (P < 0.001) and biliverdin contents in eggshells, respectively. Western blot and immunohistochemical results demonstrated that the Brown group had the highest ABCG2 expression (P < 0.05), followed by the Green and Olive groups. HMOX1 protein expression was higher in the Olive and Green groups (P < 0.05), and lowest in the White group. This study suggests that ABCG2 and HMOX1 have important regulatory roles in the production and transport of protoporphyrin-IX and biliverdin in blue-shelled chicken eggs, respectively.

Nanoparticles derived from naturally occurring metal chelators for theranostic applications

Metals are indispensable for the activities of all living things, from single-celled organisms to higher organisms, including humans. Beyond their intrinsic quality as metal ions, metals help creatures to maintain requisite biological processes by forming coordination complexes with endogenous ligands that are broadly distributed in nature. These types of naturally occurring chelating reactions are found through the kingdoms of life, including bacteria, plants and animals. Mimicking these naturally occurring coordination complexes with intrinsic biocompatibility may offer an opportunity to develop nanomedicine toward clinical applications. Herein, we introduce representative examples of naturally occurring coordination complexes in a selection of model organisms and highlight such bio-inspired metal-chelating nanomaterials for theranostic applications.

Uterine Metabolomic Analysis for the Regulation of Eggshell Calcification in Chickens

Eggshell quality is economically important for table eggs and functionally indispensable for hatching eggs. During the formation of eggshell in the uterus, organic matrixes in uterine fluid can control and modify the formation of calcified eggshell. At present, there are limited studies focusing on the effect of uterine organic metabolites on eggshell quality. In this study, an LC-MS-based metabolomic technology was performed to identify the crucial uterine metabolites that differently presented in hens producing eggs with divergent eggshell quality (eggshell strength, thickness, and weight). More than 1000 metabolites were identified in uterine fluid, and six putative metabolites, including phosphatidylcholine, diacylglycerol, verapamil, risedronate, coproporphyrinogen III, and biliverdin, were screened to play crucial roles in eggshell calcification. Then, two trials for oral administration and in vitro calcite crystal growth were conducted to verify the effect of potential different metabolites on the eggshell quality. Verapamil has a temporary effect on decreasing eggshell strength and eggshell thickness. Coproporphyrinogen III could induce smaller calcite crystals to improve eggshell strength while biliverdin could modify crystal morphology by forming rougher faces and rounder edges to strengthen the eggshell. The present study gives us new insight to understand the role of uterine fluid matrixes in eggshell calcification.

The Variability of Quality Traits of Table Eggs and Eggshell Mineral Composition Depending on Hens' Breed and Eggshell Color

The aim of the study was to evaluate the relationship between the eggshell color parameters and its mineral composition as well as the internal quality of eggs derived from various breeds of hens, varied by eggshell color: seledine from Araucana, brown from Marans, and white from Leghorn. The sample consisted of 180 eggs (60/group) The eggshell color was measured using CIE L*a*b* system. The quality evaluation included traits of whole egg (weight, specific gravity, proportions of elements, shape index), yolk (weight, color, index, pH), albumen (weight, height, pH), and shell (color, strength, weight, thickness, density). The mineral composition of eggshells was analyzed. The eggs origin affected the quality characteristics of particular egg elements (p < 0.001). However, the impact of analyzed colors on the egg quality traits varied, and in the case of whole egg and albumen traits the most favorable was the white color (p ≤ 0.05), while in the case of the strength of shell or its thickness it was the dark brown color (p ≤ 0.05). The eggshell color influenced variations in its mineral composition (p < 0.001) except potassium and sodium content, while the proportion of particular mineral elements in shell was correlated with the L*a*b* color space coordinates (p ≤ 0.05).

A single nucleotide polymorphism variant located in the cis-regulatory region of the ABCG2 gene is associated with mallard egg colour

Avian egg coloration is shaped by natural selection, but its genetic basis remains unclear. Here, we used genome-wide association analysis and identity by descent to finely map green egg colour to a 179-kb region of Chr4 based on the resequencing of 352 ducks (Anas platyrhynchos) from a segregating population resulting from the mating of Pekin ducks (white-shelled eggs) and mallards (green-shelled eggs). We further narrowed the candidate region to a 30-kb interval by comparing genome divergence in seven indigenous duck populations. Among the genes located in the finely mapped region, only one transcript of the ABCG2 gene (XM_013093252.2) exhibited higher uterine expression in green-shelled individuals than in white-shelled individuals, as supported by transcriptome data from four populations. ABCG2 has been reported to encode a protein that functions as a membrane transporter for biliverdin. Sanger sequencing of the whole 30-kb candidate region (Chr4: 47.41-47.44 Mb) and a plasmid reporter assay helped to identify a single nucleotide polymorphism (Chr4: 47,418,074 G>A) located in a conserved predicted promoter region whose variation may alter ABCG2 transcription activity. We provide a useful molecular marker for duck breeding and contribute data to the research on ecological evolution based on egg colour patterns among birds.

Albumen Quality of Fresh and Stored Table Eggs: Hen Genotype as a Further Chance for Consumer Choice

Simple Summary

Consumer interest in food products and their origins is increasing. Knowledge of egg production and quality of purebred hens during the productive period is required for a niche market sustaining and encouraging biodiversity and the peculiarities of the products that consumers can appreciate. Egg production and quality of the eggshell and albumen in fresh and stored eggs of two Italian dual-purpose purebreds (Ermellinata di Rovigo (ER); Robusta maculata (RM)) and two hybrid genotypes (Hy-Line Brown (HB); Hy-Line White (HW)) reared outdoors were compared throughout the laying period. RM breed (brown eggshell) showed fresh and stored eggs with a good eggshell thickness, and Haugh Units (HU) quite stable along the production period; RM total egg mass was lower than ER (light brown eggshell) which showed fresh and stored eggs with more variable HU, due also to a possible effect of lower eggshell thickness and pigmentation, and shape index. The hybrids produced a higher total egg mass than the purebreds and showed an intermediate variation of the egg quality, with HU higher than those of ER and RM only in 1 d eggs, but not in stored eggs.

Abstract

The quality of fresh (1 d) and stored (7–14–21 d, 21 °C) eggs was studied in Italian dual-purpose breeds (Ermellinata di Rovigo (ER), Robusta maculata (RM)) and hybrids (Hy-Line Brown (HB), Hy-Line White36 (HW)), reared outdoors (4 m²/bird) and fed commercial feed. The eggs were analyzed at 4 ages, throughout different seasonal environmental conditions, from summer (31, 35 weeks; 25 °C) until autumn (39, 43 weeks, 15 °C). Each genotype showed significant (p < 0.01) changes in egg quality. In 1 d eggs, the eggshell thickness changed in RM and HW (quadratic), decreased linearly in ER; Haugh Units (HU) changed (ER–cubic) and decreased (hybrids-linear). In 7 d and 14 d eggs, HU linearly (p < 0.01) decreased, except in RM. In 21 d eggs, HU (ER linear decrease; HB, HW quadratic) changed. Significant negative correlations between albumen pH and height were seen in ER (at 1 d, 14 d, 21 d) and HW (at each storage time) eggs, and in RM and HB only in 1 d eggs. RM showed a quite stable albumen quality and a lower total egg mass than ER which showed a more variable albumen quality, due also to a lower eggshell thickness and shape index. The hybrids produced a higher total egg mass than the purebreds and showed an intermediate variation of the egg quality, with an albumen quality higher than those of ER and RM only in 1 d egg, as a result of a higher albumen weight.

Expanding the eggshell colour gamut: uroerythrin and bilirubin from tinamou (Tinamidae) eggshells

To date, only two pigments have been identified in avian eggshells: rusty-brown protoporphyrin IX and blue-green biliverdin IXα. Most avian eggshell colours can be produced by a mixture of these two tetrapyrrolic pigments. However, tinamou (Tinamidae) eggshells display colours not easily rationalised by combination of these two pigments alone, suggesting the presence of other pigments. Here, through extraction, derivatization, spectroscopy, chromatography, and mass spectrometry, we identify two novel eggshell pigments: yellow–brown tetrapyrrolic bilirubin from the guacamole-green eggshells of Eudromia elegans, and red–orange tripyrrolic uroerythrin from the purplish-brown eggshells of Nothura maculosa. Both pigments are known porphyrin catabolites and are found in the eggshells in conjunction with biliverdin IXα. A colour mixing model using the new pigments and biliverdin reproduces the respective eggshell colours. These discoveries expand our understanding of how eggshell colour diversity is achieved. We suggest that the ability of these pigments to photo-degrade may have an adaptive value for the tinamous.

The shell gland in laying and natural moulting commercial egg-type chickens: A histomorphological and ultrastructural study

The purpose of the present study was to determine the histological and ultrastructural changes in the luminal epithelium of the shell gland associated with natural moulting. Samples of the shell gland from laying (32 weeks old) and moulting (75 weeks old) hens were studied using histological, histochemical and electron microscopic techniques. In addition, TUNEL was used to demonstrate the distribution of apoptotic cells in the luminal epithelium of the shell gland. Autophagy, characterized by the presence of autophagosomes and autolysosomes, was evident in the early stages of degeneration in non-ciliated, ciliated and mitochondrial cells. The intermediate and advanced stages of regression in non-ciliated as well as mitochondrial cells occurred via apoptosis, while both apoptotic and necrotic ciliated cells were observed during the later stages of degeneration. The results of the present study suggest that a synergy of autophagy, apoptosis and necrosis is involved in the involution of the shell gland during natural moulting.

The Impact of Eggshell Colour on the Quality of Table and Hatching Eggs Derived from Japanese Quail

Simple Summary

The eggshell is the first element in the assessment of both table and hatching eggs. It may be influenced by many factors, i.e., the birds’ genotype, their utility type, rearing system, environmental conditions and feed mineral additives. However, the eggshell colour may affect the shell itself as well as both the quality of eggs and their biological value. Among the standard coloured eggs of Japanese quail, the eggs with a uniform shell can be found, in white to celadon colour. Consumers have no preferences in this regard, they are satisfied with the small size and taste of the egg. However, breeders believe that these eggs may be worse in the case of internal quality, both in terms of consumption and hatching. The aim of the study was to evaluate table and hatching eggs of Japanese quails (Coturnix coturnix japonica) depending on the eggshell colour. It seems that Japanese quail eggs with uniform “blue” shells do not appear to be of poorer quality than those with brown-spotted shells if they are intended for consumption. However, in the aspect of hatching eggs, the eggshell colour may modify the hatching results and body weight of the chicks obtained.

Abstract

The aim of the study was to evaluate table and hatching eggs of Japanese quails (Coturnix coturnix japonica) depending on the eggshell colour. The research was carried out in two stages, in terms of table eggs’ quality and their biological value as hatching eggs depending on the eggshell colour. In both stages, 300 Japanese quail eggs were used in each (600 in total) divided into two equal groups: with a brown-spotted shell, with a uniform shell in shades of blue. In the 1st stage, quality characteristics of the whole egg (weight, specific gravity, proportions of particular elements), yolk (weight, colour, index), albumen (weight, height) and shell (colour, strength, weight, thickness, density) were evaluated. In the 2nd stage, eggs were incubated under standard conditions and following biological characteristics were analyzed: eggs fertility, embryo mortality, hatchability of fertile and set eggs, body weight of hatchlings and their proportion in egg weight. The shell colour, “blue” or spotted, of Japanese quail eggs, does not appear to influence their quality if they are intended for consumption. However, the hatching results and body weight of obtained chicks of Japanese quail may be affected by the eggshell colour.

Genetic evaluation of eggshell color based on additive and dominance models in laying hens

Objective

Eggshells with a uniform color and intensity are important for egg production because many consumers assess the quality of an egg according to the shell color. In the present study, we evaluated the influence of dominant effects on the variations in eggshell color after 32 weeks in a crossbred population.

Methods

This study was conducted using 7,878 eggshell records from 2,626 hens. Heritability was estimated using a univariate animal model, which included inbreeding coefficients as a fixed effect and animal additive genetic, dominant genetic, and residuals as random effects. Genetic correlations were obtained using a bivariate animal model. The optimal diagnostic criteria identified in this study were: L* value (lightness) using a dominance model, and a* (redness), and b* (yellowness) value using an additive model.

Results

The estimated heritabilities were 0.65 for shell lightness, 0.42 for redness, and 0.60 for yellowness. The dominance heritability was 0.23 for lightness. The estimated genetic correlations were 0.61 between lightness and redness, −0.84 between lightness and yellowness, and −0.39 between redness and yellowness.

Conclusion

These results indicate that dominant genetic effects could help to explain the phenotypic variance in eggshell color, especially based on data from blue-shelled chickens. Considering the dominant genetic variation identified for shell color, this variation should be employed to produce blue eggs for commercial purposes using a planned mating system.

Pigmentation of White, Brown, and Green Chicken Eggshells Analyzed by Reflectance, Transmittance, and Fluorescence Spectroscopy

We report on the reflectance, transmittance and fluorescence spectra (λ=200-1200 nm) of four types of chicken eggshells (white, brown, light green, dark green) measured in situ without pretreatment and after ablation of 20-100 μm of the outer shell regions. The color pigment protoporphyrin IX (PPIX) is embedded in the protein phase of all four shell types as highly fluorescent monomers, in the white and light green shells additionally as non-fluorescent dimers, and in the brown and dark green shells mainly as non-fluorescent poly-aggregates. The green shell colors are formed from an approximately equimolar mixture of PPIX and biliverdin. The axial distribution of protein and colorpigments were evaluated from the combined reflectances of both the outer and inner shell surfaces, as well as from the transmittances. For the data generation we used the radiative transfer model in the random walk and Kubelka-Munk approaches.

The SYNBREED chicken diversity panel: a global resource to assess chicken diversity at high genomic resolution

BACKGROUND

Since domestication, chickens did not only disperse into the different parts of the world but they have also undergone significant genomic changes in this process. Many breeds, strains or lines have been formed and those represent the diversity of the species. However, other than the natural evolutionary forces, management practices (including those that threaten the persistence of genetic diversity) following domestication have shaped the genetic make-up of and diversity between today's chicken breeds. As part of the SYNBREED project, samples from a wide variety of chicken populations have been collected across the globe and were genotyped with a high density SNP array. The panel consists of the wild type, commercial layers and broilers, indigenous village/local type and fancy chicken breeds. The SYNBREED chicken diversity panel (SCDP) is made available to serve as a public basis to study the genetic structure of chicken diversity. In the current study we analyzed the genetic diversity between and within the populations in the SCDP, which is important for making informed decisions for effective management of farm animal genetic resources.

RESULTS

Many of the fancy breeds cover a wide spectrum and clustered with other breeds of similar supposed origin as shown by the phylogenetic tree and principal component analysis. However, the fancy breeds as well as the highly selected commercial layer lines have reduced genetic diversity within the population, with the average observed heterozygosity estimates lower than 0.205 across their breeds' categories and the average proportion of polymorphic loci lower than 0.680. We show that there is still a lot of genetic diversity preserved within the wild and less selected African, South American and some local Asian and European breeds with the average observed heterozygosity greater than 0.225 and the average proportion of polymorphic loci larger than 0.720 within their breeds' categories.

CONCLUSIONS

It is important that such highly diverse breeds are maintained for the sustainability and flexibility of future chicken breeding. This diversity panel provides opportunities for exploitation for further chicken molecular genetic studies. With the possibility to further expand, it constitutes a very useful community resource for chicken genetic diversity research.

Genome-wide association study and a post replication analysis revealed a promising genomic region and candidate genes for chicken eggshell blueness

The eggshell blueness is an interesting object for chicken genetic studies and blue-shelled chicken industry, especially after the discovery of the causative mutation of chicken blue eggshell. In the present study, genome wide association study (GWAS) was conducted in Chinese Dongxiang blue-shelled chicken underlying four traits of blue eggshell pigments: quantity of biliverdin (QB), quantity of protoporphyrin (QP), quantity of total pigment (QT), and color density trait (CD). A total of 139 individuals were randomly collected for GWAS. We detected two SNPs in genome-wise significance and 35 in suggestive significance, 24 out of the 37 SNP were located either within intron/exon or near 15 genes in a range of ~1.17 Mb on GGA21. For further confirmation of the identified SNP loci by GWAS, the follow-up replication studies were performed in two populations. A total of 146 individuals of the second generation derived from the former GWAS population, as well as 280 individuals from an alternative independent population were employed for genotyping by MALDI-TOF MS in a genotype-phenotype association study. Eighteen SNPs evenly distributed on the GGA21 significant region were successfully genotyped in the two populations, of which 4 and 6 SNP loci were shown significantly associated with QB, QT and QP in the two repeat populations, respectively. Further, the SNPs were narrowed down to a region of ~ 653.819 Kb on GGA21 that harbors five candidate genes: AJAP1, TNFRSF9, C1ORF174, CAMTA1, and CEP104. Shell gland of chickens laying dark and light blue eggshell was chosen for detection of mRNA expression of the five candidate genes. The results showed differential expression levels of these genes in the two groups. The specific function of these genes has not yet been defined clearly in chickens and further in-depth studies are needed to explore the new functional role in chicken eggshell blueness.

Isolation of blue-green eggshell pigmentation-related genes from Putian duck through RNA-seq

Background

The diversity of avian eggshell colour plays important biological roles in ensuring successful reproduction. Eggshell colour is also an important trait in poultry, but the mechanisms underlying it are poorly understood in ducks. This study aimed to provide insights into the mechanism of blue-green eggshell colour generation.

Results

Here, white-shelled ducks (HBR) and blue-green-shelled ducks (HQR) were selected from Putian black ducks, and white-shelled ducks (BBR) were selected from Putian white ducks. Transcriptional changes in the shell gland were analysed using RNA-sequencing on the Illumina HiSeq 2500. Twenty-seven individual cDNA libraries were sequenced and generated an average of 7.35 million reads per library; 70.6% were mapped to the duck reference genome, yielding an average of 13,794 genes detected, which accounted for approximately 86.39% of all 15,967 annotated duck genes. A total of 899 differentially expressed genes (DEGs) were detected between the HQR and BBR groups, and 373 DEGs were detected between the HQR and HBR groups. We analysed the DEGs in the HQR-vs-BBR and HQR-vs-HBR comparisons. None of these DEGs were directly involved in the eggshell pigmentation process in HQR-vs-HBR, while UDP-glucuronosyltransferase 2A2 (UGT2A2) and UDP-glucuronosyltransferase 1–1-like (UGT1–1-like), which participate in biliverdin breakdown, were two of the DEGs in HQR-vs-BBR. In the RT-qPCR results, delta-aminolevulinic acid synthase 1 (ALAS1) and EPRS glutamyl-prolyl-tRNA synthetase were significantly upregulated in the HBR group compared with the HQR and BBR groups (P < 0.05). Haem oxygenase (HMOX1) was significantly downregulated in BBR compared with HQR and HBR (P < 0.05). Biliverdin reductase A (BLVRA), GUSB glucuronidase beta, cytochrome c-type haem lyase, protohaem IX farnesyltransferase and UGT2A2 were significantly upregulated in HBR and BBR compared with HQR (P < 0.05).

Conclusions

We conducted a comparative transcriptome analysis of the shell glands of Putian white ducks and Putian black ducks. None of the differentially regulated pathways were directly involved in the eggshell pigmentation process in the HQR-vs-HBR comparison, while 2 DEGs related to biliverdin breakdown were found in HQR-vs-BBR. Based on the RT-qPCR results, we can speculate that both HQR and HBR can produce biliverdin, but HBR cannot accumulate it. Compared with HQR, BBR produced less biliverdin and did not accumulate it.

Visible light biophotosensors using biliverdin from Antheraea yamamai

We report an endogenous photoelectric biomolecule and demonstrate that such a biomolecule can be used to detect visible light. We identify the green pigment abundantly present in natural silk cocoons of Antheraea yamamai (Japanese oak silkmoth) as biliverdin, using mass spectroscopy and optical spectroscopy. Biliverdin extracted from the green silk cocoons generates photocurrent upon light illumination with distinct colors. We further characterize the basic performance, responsiveness, and stability of the biliverdin-based biophotosensors at a photovoltaic device level using blue, green, orange, and red light illumination. Biliverdin could potentially serve as an optoelectric biomolecule toward the development of next-generation implantable photosensors and artificial photoreceptors.

Epigallocatechin-3-gallate protected vanadium-induced eggshell depigmentation via P38MAPK-Nrf2/HO-1 signaling pathway in laying hens

It has been demonstrated that tea polyphenol (TP) epigallocatechin-3-gallate (EGCG) can confer protection against vanadium (V) toxicity in laying hens; however, our understanding of the molecular mechanisms beyond this effect are still limited. In this study, 360 hens were randomly assigned to the 3 groups to study whether the potential mechanism P38MAPK-Nrf2/HO-1 signaling pathway is involved in the protective effect of EGCG on eggshell pigmentation in vanadium challenged laying hens. Treatments included a control group, a 10 mg/kg V (V10), and a V10 plus 130 mg/kg of EGCG group (V10+EGCG130). Both eggshell color and protoporphyrin IX were decreased in the V10 group compared with the control diet, while EGCG130 treatment partially improved shell color and protoporphyrin IX (P < 0.05). The V10 exposure induced higher cell apoptosis rate and oxidative stress in birds as evidenced by the histological apoptosis status, decreased uterine glutathione-S transferase (GST) and high abundance of malondialdehyde (MDA) compared with the control group, whereas EGCG130 markedly alleviated oxidative stress via reducing MDA generation (P < 0.05). Dietary vanadium reduced ferrochelatase, NF-E2-related factor 2 (Nrf2), and heme oxygenase (HO-1) mRNA expression, while EGCG up-regulated Nrf2 and HO-1 expression (P < 0.05). Protein levels of Nrf2, HO-1 and phospho-p38 (P-P38) MAPK were reduced in V10 group, while dietary supplementation with 130 mg/kg EGCG markedly increased Nrf2, HO-1 and P-P38 MAPK protein levels in the uterus compared with the V10 group (P < 0.01). In conclusion, EGCG improved eggshell color and antioxidant system in V10-challenged hens, which seems to be associated with P38MAPK-Nrf2/HO-1 signaling pathway.

Recent advances in avian egg science: A review

Eggs and egg products form an integral part of the food chain. As such, research into egg structure, function, and production has made an important contribution to the field of poultry science. The past decade has seen significant advances in avian egg science research, with work supplementing our understanding of the nature of the avian egg, and its biological, chemical, and physical properties. Eggshell color, strength, and chemical composition, poultry nutrition, and genetics have all been intensively studied recently, with significant progress being made in a number of these areas. Indeed, with the prevalence of robust theoretical techniques, it is now commonplace to combine experimental investigations with theory, providing a balanced and interdisciplinary perspective.

Study of formation of green eggshell color in ducks through global gene expression

The green eggshell color produced by ducks is a threshold trait that can be influenced by various factors, such as hereditary, environment and nutrition. The aim of this study was to investigate the genetic regulation of the formation of eggs with green shells in Youxian ducks. We performed integrative analysis of mRNAs and miRNAs expression profiling in the shell gland samples from ducks by RNA-Seq. We found 124 differentially expressed genes that were associated with various pathways, such as the ATP-binding cassette (ABC) transporter and solute carrier supper family pathways. A total of 31 differentially expressed miRNAs were found between ducks laying green eggs and white eggs. KEGG pathway analysis of the predicted miRNA target genes also indicated the functional characteristics of these miRNAs; they were involved in the ABC transporter pathway and the solute carrier (SLC) supper family. Analysis with qRT-PCR was applied to validate the results of global gene expression, which showed a correlation between results obtained by RNA-seq and RT-qPCR. Moreover, a miRNA-mRNA interaction network was established using correlation analysis of differentially expressed mRNA and miRNA. Compared to ducks that lay white eggs, ducks that lay green eggs include six up-regulated miRNAs that had regulatory effects on 35 down-regulated genes, and seven down-regulated miRNAs which influenced 46 up-regulated genes. For example, the ABC transporter pathway could be regulated by expressing gga-miR-144-3p (up-regulated) with ABCG2 (up-regulated) and other miRNAs and genes. This study provides valuable information about mRNA and miRNA regulation in duck shell gland tissues, and provides foundational information for further study on the eggshell color formation and marker-assisted selection for Youxian duck breeding.

Comparative transcriptome analysis provides clues to molecular mechanisms underlying blue-green eggshell color in the Jinding duck (Anas platyrhynchos)

BACKGROUND

In birds, blue-green eggshell color (BGEC) is caused by biliverdin, a bile pigment derived from the degradation of heme and secreted in the eggshell by the shell gland. Functionally, BGEC might promote the paternal investment of males in the nest and eggs. However, little is known about its formation mechanisms. Jinding ducks (Anas platyrhynchos) are an ideal breed for research into the mechanisms, in which major birds lay BGEC eggs with minor individuals laying white eggs. Using this breed, this study aimed to provide insight into the mechanisms via comparative transcriptome analysis.

RESULTS

Blue-shelled ducks (BSD) and white-shelled ducks (WSD) were selected from two populations, forming 4 groups (3 ducks/group): BSD1 and WSD1 from population 1 and BSD2 and WSD2 from population 2. Twelve libraries from shell glands were sequenced using the Illumina RNA-seq platform, generating an average of 41 million clean reads per library, of which 55.9% were mapped to the duck reference genome and assembled into 31,542 transcripts. Expression levels of 11,698 genes were successfully compared between all pairs of 4 groups. Of these, 464 candidate genes were differentially expressed between cross-phenotype groups, but not for between same-phenotype groups. Gene Ontology (GO) annotation showed that 390 candidate genes were annotated with 2234 GO terms. No candidate genes were directly involved in biosynthesis or transport of biliverdin. However, the integral components of membrane, metal ion transport, cholesterol biosynthesis, signal transduction, skeletal system development, and chemotaxis were significantly (P < 0.05) overrepresented by candidate genes.

CONCLUSIONS

This study identified 464 candidate genes associated with duck BGEC, providing valuable information for a better understanding of the mechanisms underlying this trait. Given the involvement of membrane cholesterol contents, ions and ATP levels in modulating the transport activity of bile pigment transporters, the data suggest a potential association between duck BGEC and the transport activity of the related transporters.

Haematocrit, eggshell colouration and sexual signaling in the European starling (Sturnus vulgaris)

Background

One hypothesis to explain the blue–green colour of the eggs of many bird species is that it is a sexually-selected signal of the laying female’s quality, which males use to determine their investment. This hypothesis requires that eggshell pigmentation carries a cost or is otherwise linked to female quality. One potential cost is that biliverdin, a haem derivative and the pigment responsible for eggshell colouration, is limiting. To assess this potential cost, we attempted to manipulate haematocrit and haemoglobin in free-living European starlings (Sturnus vulgaris Linnaeus). Upon collecting unmanipulated first clutches, we treated females with phenylhydrazine (PHZ), a haemolytic agent, and measured the blue–green chroma and reproductive performance of replacement clutches. We also investigated whether eggshell colour was associated with haematocrit or haemoglobin levels in unmanipulated first clutches. To test whether eggshell colour might act as a sexual signal, we examined associations between eggshell colour and reproductive performance, as well as the provisioning rate of the male.

Results

PHZ-treatment did not affect eggshell colour in replacement clutches. In unmanipulated first clutches, eggshell colour was not correlated with haematocrit or haemoglobin levels. Eggshell colour was correlated with female mass in unmanipulated first clutches but not replacement clutches. Chicks from eggs with higher eggshell colour had higher haemoglobin levels and longer tarsi just prior to fledging, suggesting that eggshell colour could reflect brood quality. However, eggshell colour was not correlated with the provisioning rate of the male or any other measure of reproductive performance.

Conclusions

We found no evidence to support the hypothesis that the availability of resources required for the synthesis of pigment limits eggshell colour in European starlings, or that eggshell colour is used by males to determine their level of reproductive investment. We found little evidence that eggshell colour is correlated with female or offspring quality in this species.

Electronic supplementary material

The online version of this article (doi:10.1186/s12898-016-0084-x) contains supplementary material, which is available to authorized users.

Genome-wide association study reveals novel variants for growth and egg traits in Dongxiang blue-shelled and White Leghorn chickens

This study was designed to investigate the genetic basis of growth and egg traits in Dongxiang blue-shelled chickens and White Leghorn chickens. In this study, we employed a reduced representation sequencing approach called genotyping by genome reducing and sequencing to detect genome-wide SNPs in 252 Dongxiang blue-shelled chickens and 252 White Leghorn chickens. The Dongxiang blue-shelled chicken breed has many specific traits and is characterized by blue-shelled eggs, black plumage, black skin, black bone and black organs. The White Leghorn chicken is an egg-type breed with high productivity. As multibreed genome-wide association studies (GWASs) can improve precision due to less linkage disequilibrium across breeds, a multibreed GWAS was performed with 156 575 SNPs to identify the associated variants underlying growth and egg traits within the two chicken breeds. The analysis revealed 32 SNPs exhibiting a significant genome-wide association with growth and egg traits. Some of the significant SNPs are located in genes that are known to impact growth and egg traits, but nearly half of the significant SNPs are located in genes with unclear functions in chickens. To our knowledge, this is the first multibreed genome-wide report for the genetics of growth and egg traits in the Dongxiang blue-shelled and White Leghorn chickens.

Not so colourful after all: eggshell pigments constrain avian eggshell colour space

Birds' eggshells are renowned for their striking colours and varied patterns. Although often considered exceptionally diverse, we report that avian eggshell coloration, sampled here across the full phylogenetic diversity of birds, occupies only 0.08-0.10% of the avian perceivable colour space. The concentrations of the two known tetrapyrrole eggshell pigments (protoporphyrin and biliverdin) are generally poor predictors of colour, both intra- and interspecifically. Here, we show that the constrained diversity of eggshell coloration can be accurately predicted by colour mixing models based on the relative contribution of both pigments and we demonstrate that the models' predictions can be improved by accounting for the reflectance of the eggshell's calcium carbonate matrix. The establishment of these proximate links between pigmentation and colour will enable future tests of hypotheses on the functions of perceived avian eggshell colours that depend on eggshell chemistry. More generally, colour mixing models are not limited to avian eggshell colours but apply to any natural colour. Our approach illustrates how modelling can aid the understanding of constraints on phenotypic diversity.

Eggshell color in brown-egg laying hens - a review

The major pigment in eggshells of brown-egg laying hens is protoporphyrin IX, but traces of biliverdin and its zinc chelates are also present. The pigment appears to be synthesized in the shell gland. The protoporphyrin IX synthetic pathway is well defined, but precisely where and how it is synthesized in the shell gland of the brown-egg laying hen is still ambiguous. The pigment is deposited onto all shell layers including the shell membranes, but most of it is concentrated in the outermost layer of the calcareous shell and in the cuticle. Recently, the genes that are involved in pigment synthesis have been identified, but the genetic control of synthesis and deposition of brown pigment in the commercial laying hen is not fully understood. The brown coloration of the shell is an important shell quality parameter and has a positive influence on consumer preference. The extent of pigment deposition is influenced by the housing system, hen age, hen strain, diet, stressors, and certain diseases such as infectious bronchitis. In this article, the physiological and biochemical characteristics of the brown pigment in commercial brown-egg layers are reviewed in relation to its various functions in the poultry industry.

Molecular phylogenetic analysis of Chinese indigenous blue-shelled chickens inferred from whole genomic region of the SLCO1B3 gene

In total, 246 individuals from 8 Chinese indigenous blue- and brown-shelled chicken populations (Yimeng Blue, Wulong Blue, Lindian Blue, Dongxiang Blue, Lushi Blue, Jingmen Blue, Dongxiang Brown, and Lushi Brown) were genotyped for 21 SNP markers from the SLCO1B3 gene to evaluate phylogenetic relationships. As a representative of nonblue-shelled breeds, White Leghorn was included in the study for reference. A high proportion of SNP polymorphism was observed in Chinese chicken populations, ranging from 89% in Jingmen Blue to 100% in most populations, with a mean of 95% across all populations. The White Leghorn breed showed the lowest polymorphism, accounting for 43% of total SNPs. The mean expected heterozygosity varied from 0.11 in Dongxiang Blue to 0.46 in Yimeng Blue. Analysis of molecular variation (AMOVA) for 2 groups of Chinese chickens based on eggshell color type revealed 52% within-group and 43% between-group variations of the total genetic variation. As expected, FST and Reynolds' genetic distance were greatest between White Leghorn and Chinese chicken populations, with average values of 0.40 and 0.55, respectively. The first and second principal coordinates explained approximately 92% of the total variation and supported the clustering of the populations according to their eggshell color type and historical origins. STRUCTURE analysis showed a considerable source of variation among populations for the clustering into blue-shelled and nonblue-shelled chicken populations. The low estimation of genetic differentiation (FST) between Chinese chicken populations is possibly due to a common historical origin and high gene flow. Remarkably similar population classifications were obtained with all methods used in the study. Aligning endogenous avian retroviral (EAV)-HP insertion sequences showed no difference among the blue-shelled chickens.

Comparison of protoporphyrin IX content and related gene expression in the tissues of chickens laying brown-shelled eggs

Protoporphyrin IX (PpIX), an immediate precursor of heme, is the main pigment resulting in the brown coloration of eggshell. The brownness and uniformity of the eggshell are important marketing considerations. In this study, 9 chickens laying darker brown shelled eggs and 9 chickens laying lighter brown shelled eggs were selected from 464 individually caged layers in a Rhode Island Red pureline. The PpIX contents were measured with a Microplate Reader at the wavelength of 412 nm and were compared in different tissues of the 2 groups. Although no significant difference in serum, bile, and excreta was found between the 2 groups, PpIX content in the shell gland and eggshell of the darker group was higher than in those of the lighter group, suggesting that PpIX was synthesized in the shell gland. We further determined the expression levels of 8 genes encoding enzymes involved in the heme synthesis and transport in the liver and shell gland at 6 h postoviposition by quantitative PCR. The results showed that expression of aminolevulinic acid synthase-1 (ALAS1) was higher in the liver of hens laying darker brown shelled eggs, whereas in the shell gland the expression levels of ALAS1, coproporphyrinogen oxidase (CPOX), ATP-binding cassette family members ABCB7 and ABCG2, and receptor for feline leukemia virus, subgroup C (FLVCR) were significantly higher in the hens laying darker brown shelled eggs. Our results demonstrated that hens laying darker brown shelled eggs could deposit more PpIX onto the eggshell and the brownness of the eggshell was dependent on the total quantity of PpIX in the eggshell. More heme was synthesized in the liver and shell gland of hens laying darker brown shelled eggs than those of hens laying lighter brown shelled eggs. High expression level of ABCG2 might facilitate the accumulation of PpIX in the shell gland.

Endogenous retrovirus EAV-HP linked to blue egg phenotype in Mapuche fowl

Oocyan or blue/green eggshell colour is an autosomal dominant trait found in native chickens (Mapuche fowl) of Chile and in some of their descendants in European and North American modern breeds. We report here the identification of an endogenous avian retroviral (EAV-HP) insertion in oocyan Mapuche fowl and European breeds. Sequencing data reveals 100% retroviral identity between the Mapuche and European insertions. Quantitative real-time PCR analysis of European oocyan chicken indicates over-expression of the SLCO1B3 gene (P<0.05) in the shell gland and oviduct. Predicted transcription factor binding sites in the long terminal repeats (LTR) indicate AhR/Ar, a modulator of oestrogen, as a possible promoter/enhancer leading to reproductive tissue-specific over-expression of the SLCO1B3 gene. Analysis of all jungle fowl species Gallus sp. supports the retroviral insertion to be a post-domestication event, while identical LTR sequences within domestic chickens are in agreement with a recent de novo mutation.

Comparison of HMOX1 expression and enzyme activity in blue-shelled chickens and brown-shelled chickens

Blue egg coloring is attributed to biliverdin derived from the oxidative degradation of heme through catalysis by heme oxygenase (HO). The pigment is secreted into the eggshell by the shell gland. There is uncertainty as to whether the pigment is synthesized in the shell gland or in other tissues. To investigate the site of pigment biosynthesis, the expression of heme oxygenase (decycling) 1 (HMOX1), a gene encoding HO, and HO activity in liver and spleen were compared between blue-shelled chickens (n = 12) and brown-shelled chickens (n = 12). There were no significant differences in HMOX1 expression and HO activity in these tissues between the two groups. Since the liver and spleen, two important sites outside the shell gland where heme is degraded into biliverdin, CO and Fe(2+), did not differ in HO expression and activity we conclude that the pigment is most likely synthesized in the shell gland.

Immune function is related to adult carotenoid and bile pigment levels, but not dietary carotenoid access during development, in female mallard ducks

Immune function can be modulated by multiple physiological factors, including nutrition and reproductive state. Because these factors can vary throughout an individual’s lifetime due to environmental conditions (e.g. nutrition) or life-history stage (e.g. adult reproduction), we must carefully examine the degree to which developmental versus adult conditions shape performance of the immune system. We investigated how variation in dietary access to carotenoid pigments – a class of molecules with immunostimulatory properties that females deposit into egg yolks – during three different developmental time points affected adult immunological and reproductive traits in female mallard ducks (Anas platyrhynchos). In males and females of other avian species, carotenoid access during development affects carotenoid assimilation ability, adult sexual ornamentation, and immune function, while carotenoid access at adulthood can increase immune response and reproductive investment (e.g. egg-laying capacity, biliverdin deposition in eggshells). We failed to find effects of developmental carotenoid supplementation on adult immune function (phytohemagglutinin-induced cutaneous immune response, antibody production in response to the novel antigen keyhole limpet hemocyanin [KLH], or oxidative burst, assessed by change in circulating nitric oxide levels), carotenoid-pigmented beak coloration, ovarian development, circulating carotenoid levels, or concentration of bile pigments in the gall bladder. However, we did uncover positive relationships between circulating carotenoid levels at adulthood and KLH-specific antibody production, and a negative relationship between biliverdin concentration in bile and KLH-specific antibody production. These results are consistent with the view that adult physiological parameters better predict current immune function than do developmental conditions and highlight a possible, previously unstudied relationship between biliverdin and immune system performance.

Go green: the anti-inflammatory effects of biliverdin reductase

Biliverdin (BV) has emerged as a cytoprotective and important anti-inflammatory molecule. Conversion of BV to bilirubin (BR) is catalyzed by biliverdin reductase (BVR) and is required for the downstream signaling and nuclear localization of BVR. Recent data by others and us make clear that BVR is a critical regulator of innate immune responses resulting from acute insult and injury and moreover, that a lack of BVR results in an enhanced proinflammatory phenotype. In macrophages, BVR is regulated by its substrate BV which leads to activation of the PI3K–Akt-IL-10 axis and inhibition of TLR4 expression via direct binding of BVR to the TLR4 promoter. In this review, we will summarize recent findings on the role of BVR and the bile pigments in inflammation in context with its activity as an enzyme, receptor, and transcriptional regulator.

Expression and activity analysis reveal that heme oxygenase (decycling) 1 is associated with blue egg formation

Biliverdin is responsible for the coloration of blue eggs and is secreted onto the eggshell by the shell gland. Previous studies confirmed that a significant difference exists in biliverdin content between blue eggs and brown eggs, although the reasons are still unknown. Because the pigment is derived from oxidative degradation of heme catalyzed by heme oxygenase (HO), this study compared heme oxygenase (decycling) 1 (HMOX1), the gene encoding HO expression and HO activity, in the shell glands of the Dongxiang blue-shelled chicken (n = 12) and the Dongxiang brown-shelled chicken (n = 12). Results showed that HMOX1 was highly expressed at the mRNA (1.58-fold; P < 0.05) and protein levels in blue-shelled chickens compared with brown-shelled chickens. At the functional level, blue-shelled chickens also showed 1.40-fold (P < 0.05) higher HO activity than brown-shelled chickens. To explore the reasons for the differential expression of HMOX1, an association study of 6 SNP capturing the majority of HMOX1 variants with the blue egg coloration was performed. Results showed no significant association between SNP and the blue egg coloration in HMOX1 (P > 0.05). Taken together, these results show that blue egg formation is associated with high expression of HMOX1 in the shell gland of Dongxiang blue-shelled chickens, and suggest that differential expression of HMOX1 in the 2 groups of chickens is most likely to arise from an alteration in the trans-acting factor.

Localisation of the genomic sequence interval for the blue eggshell gene using an F2 resource population of Dongxiang chickens

1. In order to identify the molecular interval containing the blue shell gene (O locus), linkage analysis was conducted with three microsatellite markers, (TTA)(n), (TG)(n) and (tg)(n), and a SNP in intron 1 of SLCO1C1 (solute carrier organic anion transporter family, member 1C1; A locus) to map the O locus in an F2 resource population of Dongxiang chickens. 2. Linkage analysis based on 98 F2 hens resulted in estimation of the best map order of the O locus with other linked markers as: (TTA)(n)-(TG)(n)-A-O-(tg)(n). 3. Based on these results, we inferred that the O locus was located between the A and (tg)(n) loci, that is, Chr1:67,296,991-69,140,571, which is the first genomic sequence interval to be established for the blue eggshell gene.

Developmental phenotypic-genotypic associations of tyrosinase and melanocortin 1 receptor genes with changing profiles in chicken plumage pigmentation

The tyrosinase (TYR) and melanocortin 1 receptor (MC1R) genes have been accepted as major genes involved in the plumage pigmentation of chickens. The co-segregation of plumage coloration and sequence polymorphism in TYR and MC1R genes were investigated using an intercross between black and white plumage color types of the Dongxiang blue-shelled chicken. Profiles of plumage color changing and genes expression levels of TYR and MC1R were observed from hatch to 112 d of age using quantitative real-time reverse transcription-PCR. Intercrossed offspring were classified by phenotypes of plumage colors. The phenotypes of black and amber chicks with genotypes of E_C_ exhibited a black feather pattern, whereas white, gray, and buff chicks with genotypes of E_cc and eecc belonged to the white feather pattern. Although TYR in cooperation with MC1R determined the coloration feather patterns, the different phenotypes did not correspond completely with the genotypes. During the period studied, plumage phenotype changed dramatically, and the buff and gray down were gradually replaced by whiteness feathers. Real-time reverse transcription-PCR studies showed that 1) expression levels of TYR declined dramatically with age, and expression at hatch was highest (P<0.01) during the ages studied; 2) expression level of MC1R was higher at 28 d than at younger and older ages; and 3) expression of TYR in chickens carrying E/E and E/e alleles on MC1R loci were higher than those carrying e/e alleles from hatch to 28 d.