Association of Cellular Retinol-binding Protein 2 (CRBP2) Gene Polymorphism with Egg Production in Erlang Mountainous Chicken

Quantitative proteomic analyses during formation of chicken egg yolk

A quantitative comparison of the proteomes during different periods of the formation of egg yolk, from yellow follicles (YF), small hierarchical follicles (9-12 mm, SF), and the largest hierarchical follicle (LF), was performed. The abundance of major egg yolk proteins (apolipoprotein B and vitellogenins) changed significantly during the yolk formation, and several protein hydrolases and isomerases, which may be related to the processing of egg yolk proteins, also varied significantly. The binding proteins for three vitamins (retinol, riboflavin, and vitamin D) and cholesterol were all most abundant in the LF period, suggesting that these nutrients were transported mainly at the final period of the egg yolk formation. Immunoglobulins decreased and complement proteins increased as formation progressed, indicating the dynamic nature of the egg yolk immune system. These results are helpful for understanding the nutrient composition, the formation of assembly structure, the preservation and processing properties of egg yolk.

Identification of SNPs in Cellular Retinol Binding Protein 1 and Cellular Retinol Binding Protein 3 Genes and Their Associations with Laying Performance Traits in Erlang Mountainous Chicken

CRBP1 (cellular retinol binding protein 1) and CRBP3 (cellular retinol binding protein 3), are important components of the retinoid signaling pathway and take part in vitamin A absorption, transport and metabolism. Based on the role of vitamin A in chicken laying performance, we investigated the polymorphism of CRBP1 and CRBP3 genes in 349 chickens using single strand conformation polymorphism and DNA sequencing methods. Only one polymorphism was identified in the third intron of CRBP1, two polymorphisms were detected in CRBP3; they were located in the second intron and the third intron respectively. The association studies between these three SNPs and laying performance traits were performed in Erlang mountainous chicken. Notably, the SNP g.14604G>T of CRBP1 was shown to be significantly associated with body weight at first egg (BWFE), age at first egg (AFE), weight at first egg (WFE) and total number of eggs with 300 age (EN). The CRBP3 polymorphism g.934C>G was associated with AFE, and the g.1324A>G was associated with AFE and BWFE, but none of these polymorphisms were associated with egg quality traits. Haplotype combinations constructed on these two SNPs of CRBP3 gene were associated with BWFE and AFE. In particular, diplotype H2H2 had positive effect on AFE, BWFE, EN, and average egg-laying interval. We herein describe for the first time basic research on the polymorphism of chicken CRBP1 and CRBP3 genes that is predictive of genetic potential for laying performance in chicken.

Characterization of the expression profile of CRBP1 and CRBP3 gene in chicken

In this study, we quantified the expression of CRBP1 and CRBP3 in Roman layer (R) and Erlang mountainous chickens (SD02 and SD03), to discern the tissue, breed and age-related expression patterns in order to discover potential involvement in egg production and other related reproduction traits. Real-time quantitative PCR assays were developed for accurate measurement of CRBP1 and CRBP3 mRNA levels in different tissues from chickens at four ages (12, 20, 32 and 45 weeks). We found that the CRBP1 and CRBP3 were expressed in all six tissues examined in all three breeds of chicken at 32 weeks. CRBP1 mRNA levels in SD02 kidneys were slightly higher than those in SD03 and R at 12 weeks, whereas, at the other three time points, the expression levels of CRBP1 in SD03 were higher than those in SD02 and R. In addition, there was higher hepatic expression of CRBP3 mRNA in layers (R) compared to broilers (SD02 and SD03) at 20 and 32 weeks. An age-related expression pattern of CRBP1 gene was evident in liver (P < 0.01), but not in pituitary (P > 0.05). Overall, the expression level of CRBP1 gene in kidney, ovary and oviduct at the different ages had a "decline-rise-decline" trend in all three breeds. In contrast, in pituitary, hypothalamus, liver and kidney CRBP3 mRNA expression levels were significantly different at various ages (P < 0.05) and exhibited a "rise-decline-rise" pattern in all three breeds. Our results show that the expression of CRBP1 and CRBP3 in chicken tissues exhibit specific developmental changes and age-related patterns.

Expression Profiles of Cellular Retinol-binding Protein, Type II (CRBP II) in Erlang Mountainous Chickens

Cellular retinol-binding protein II (CRBP II) belongs to the family of cellular retinol-binding proteins and plays a major role in absorption, transport, and metabolism of vitamin A. In addition, because vitamin A is correlated with reproductive performance, we measured CRBP II mRNA abundance in erlang mountainous chickens by real-time PCR using the relative quantification method. The expression of CRBP II showed a tissue-specific pattern and egg production rate-dependent changes. The expression was very high (p<0.05) in jejunum and liver, intermediate in kidney, ovary, and oviduct, and lowest (p<0.05) in heart, hypothalamus, and pituitary. In the hypothalamus, oviduct, ovary, and pituitary, CRBP II mRNA abundance were correlated to egg production rate, which increased from 12 wk to 32 wk, peaked at 32 wk relative to the other time points, and then decreased from 32 wk to 45 wk. In contrast, the expression of CRBP II mRNA in heart, jejunum, kidney, and liver was not different at any of the ages evaluated in this study. These data may help to understand the genetic basis of vitamin A metabolism, and suggest that CRBP II may be a candidate gene to affect egg production traits in chickens.

Genetic effects of polymorphisms in the prolactin receptor gene on chicken reproductive traits

Prolactin receptor (PRLR) is a single transmembrane protein through which prolactin plays a wide variety of physiological roles in vertebrates. Markers of alleles for the PRLR gene were assessed for the association with six reproductive traits (bodyweight at first egg; egg weight at first egg; age at first egg; number of eggs at 300 days of age; bodyweight at 300 days of age; and egg weight at 300 days of age) in a single generation of the Erlang Mountain Chicken. Five single-nucleotide polymorphisms were detected in the PRLR gene by sequencing pooled DNA samples. Genotypes were identified using PCR-single strand conformational polymorphism and direct PCR-sequencing methods. The GLM procedure was used to estimate the association between genotypes and reproductive traits. The results showed that at the P1 locus, individuals with genotype TT had shorter age at first egg and greater number of eggs at 300 days of age than those with genotype CC (P < 0.01). Our findings suggest that the single-nucleotide polymorphism g.-14A > G at P1 locus could be a potential genetic marker for age at first egg and number of eggs at 300 days of age in the Erlang Mountain Chicken and haplotype ATGTT might be advantageous for reproductive traits.

Genetic effect of the prolactin receptor gene on egg production traits in chickens

The identification and utilization of potential candidate genes with significant effects on economically important traits have become increasingly important in poultry breeding programs. The prolactin (PRLR) receptor is a specific receptor for prolactin, which is an anterior pituitary peptide hormone involved in various physiological activities and is essential for reproductive success. In chickens, the PRLR gene resides on the Z chromosome. We used a pooled DNA sequencing approach for identifying SNPs of the PRLR gene. Three hundred and nine-six Erlang Mountainous chicken hens were genotyped for six SNPs using PCR-SSCP and PCR-sequencing methods; the association with chicken egg production traits was studied using general linear model procedures. Three linked SNPs (G14952A, A14969C and G14984A) at the P1 locus, two linked SNPs (G17560A and T17626A) at the P2 locus, and one SNP (T20868C) at the P3 locus were identified. Eight haplotypes were reconstructed on the basis of the six SNPs. The general linear model analysis indicated that there were significant associations of certain genotypes and haplotypes with some egg production traits. We conclude that chicken PRLR gene polymorphisms are associated with egg production traits and have potential as molecular markers for chicken breeding.