Association between MyoG Gene Polymorphism and Egg Quality of Egg Quail

In this experiment, egg quails were 80 China quails with yellow feathers, 80 Beijing quails with white feathers and 80 Korean quails. All egg quails were females. Blood samples (5ml each) were collected at vein in wings and stored in heparin sodium anticoagulant tubes which were then kept in a refrigerator under -20 oC. DNA was extracted by poultry whole blood DNA kit and kept under -20 oC. Egg quality indices included egg weight, egg shape index, yolk index, yolk weight, shell thickness and egg white height.

For PCR amplification, primers at loci A and B in the control region of MyoG 5’ were designed with references to the design of Wang et al. (2007) which were listed in Table I. Primers were synthesized by Beijing Dongguo Changsheng Biotechnology Co., Ltd. Pre-denaturation at 94oC for 4 min, then denaturation at 94oC for 40 s, annealing at 57-60oC for 1 min, annealing at 72oC for 20 seconds, denaturation, annealing and elongation were carried out for 35 cycles, then elongation at 72oC and finally the reaction was completed and cooled and preserved at 4oC.

For SSCP analysis in this experiment, 5μL denatured upper sample buffer and 5μL PCR products were mixed evenly, which was degenerated for 10 min under 98oC. The mixture was treated by electrophoresis with 10% acrylamide gel for 15 min under 220V, and then treated by electrophoresis for 6h under 90V. Finally, the mixture was developed by silver staining under lights. Pictures were taken and stored.

For data analysis, analytical model used was Yijkl=μ+Bi+Wj+Mk+eijkl, where Yijkl is the phenotype value of traits, μ is the total mean value, Bi is the first variety effect (i = 1, 2, 3), Wj is the j age effect(j=9, 10, 11, 12, 13,14, 15, 16, 17, 18), Mk is the k genotype effect, eijkl is the residual effect.

The SNPs in the control region of MyoG 5’ are shown in Figure 1. The target fragment gained from amplification of locus A is 203bp and the target fragment gained from amplification of locus B is 236bp. These agree with expectations and show good specificity. These target fragments can be applied in subsequent experiments.

Figure 2 shows genotype test results at loci A and B of the control region of MyoG 5’ of three egg quails. A total of 6 genotypes are discovered at locus A, which are AA, BB, CC, AB, AC and BC. AB and BC are not observed in Korean quail. Nine genotypes are detected at loci B, namely, AA, BB, CC, DD, EE, AB, AC, AD and AE. BB and AC are not detected in Beijing white quails, and CC and AC are not detected in Korean quail.

Gene frequency and genotype frequency at loci A and B in the control region of MyoG 5’ in three egg quail groups are shown in Table II. Obviously, The C allele frequency of China yellow quail, Beijing white quail and Korean quail is the highest, valuing 0.461, 0.528 and 0.579, respectively. In short, genetic polymorphism of China yellow quail, Beijing white quail and Korean quail is relatively abundant (He>0.5). All three quail groups are moderate polymorphism (0.25<PIC<0.5). For locus B, A allele frequency of China yellow quail, Beijing white quail and Korean quail is the highest, valuing 0.612, 0.623 and 0.633, respectively. Genetic polymorphism of China yellow quail, Beijing white quail and Korean quail is high (He>0.5). All three quail groups are highly polymorphism (PIC>0.5).

Association analysis between MyoG and egg quality of egg quail is obvious in Table III. It can be seen, that for locus A, there’s no significant difference among AA, AB, AC, BB, BC and CC (P>0.05). For locus B, egg shape index of CC is significantly higher than that of EE (P<0.05), CC and EE show similar egg shape index with AA, AB, AC, AD, AE, BB and DD (P>0.05). Yolk index of AC and CC is significantly higher compared with that of AB and BB (P<0.05), Yolk index of BB is greatly lower compared with those of other genotypes (P<0.05). Egg weight, yolk weight, shell thickness and egg white height are similar among different genotypes (P>0.05).

Wei et al. (2014) found 2 mutation sites and 6 genotypes in the third exon of MyoG of Bian chicken.

Note: In the table, there are significant differences between different lowercase letters on the shoulder of the same column (P < 0.05), but there are no significant differences between the same letters (P > 0.05).

Tang et al. (2013, 2015) discovered 1 mutation site at exon 1 and exon 3 of MyoG of Jinghai yellow chicken, which involved 3 genotypes. Zhao et al. (2016) discovered 1, 2 and 3 mutation sites in exons 1, 2 and 3 of MyoG of three ear duck. Wang et al. (2007) discovered 1 mutation site and 3 genotypes at locus A in the control region of MyoG5’ of broiler chicken, and found 3 SNPs loci and 6 genotypes at loci B. In this study, polymorphism in 3 egg quail groups at loci A and B in the control region of MyoG 5’ was detected. Six genotypes were found at locus A and 9 genotypes were found at locus B. These revealed that MyoG had rich polymorphism in egg quail groups, which was similar with polymorphism research results on other poultries.

In studies on correlation between MyoG polymorphism and production performance of poultries, Zhao et al. (2016) concluded that two mutations of MyoG could influence breast muscle rate, weight and carcass net weight of duck significantly (P<0.05). Wang et al. (2007) discussed correlation of MyoG polymorphism with slaughter traits and meat quality of broiler chicken, finding significantly positive correlation between MyoG and muscle fiber growth of chicken (P<0.05). Tang et al. (2013) discovered 3 genotypes (AA, AB and BB) on exon 1 of MyoG of Jinghai yellow chicken, the body weight of BB at 2nd, 4th and 6th week was far higher than those of AB, and the body weight of BB at 8th week was higher than that of AA, showing significant differences (P<0.05). Wei et al. (2014) found 2 same sense mutation sites on MyoG, polymorphisms of these two mutation sites were correlated with growth performance of Bian chicken (P<0.05). This study significant correlations of locus B in the control region of MyoG 5’ with egg shape index and yolk index of egg quail are discovered (P<0.05), however, locus A has no significant impacts on egg quality of egg quail (P>0.05). Correlation between loci A and B in the control region of MyoG 5’ with egg quality of egg quail has to be further studied.

Sincere gratitude goes to the sponsor of National Natural Science Foundation (31201777) and Industry-University-Research Cooperation Project in Henan Province (152107000095.0).

The authors declare that there is no conflict of interset.