Eggshell colors have a significant effect on sale of eggs. The aim of this study is to identify sequence variants associated with color variation of chicken brown eggs in the ABCG2, a protoporphyrin transport-related gene. Three successive eggs were collected from each of 381 Lueyang black-boned hens at the 31 weeks old. Eggshell color was quantified via the L*a*b color space. g.18378442T>C (a non-synonymous mutation C21R), g.18383682A>G and g.18391548A>T were genotyped via the MassARRAY platform. The associations of genotypes with color indexes were tested by one-way ANOVA. The conservation of the C21R locus was analyzed by multiple alignment of 52 avian genomes from the UCSC database. We predicted 3D structures of ABCG2 with C21 and R21 by homology modelling using the MODELLER program to analyze effect of C21R on protein structures. Results showed that g.18378442T>C was significantly associated with L and b values. The L value (75.3±4.0) of CC was significantly lower than ones of CT (76.6±4.3) and TT (78.0±4.4) genotypes. The b value (16.2±3.5) of CC was significantly higher than ones of CT (15.7±3.6) and TT (15.7±3.6). g.18383682A>G was only associated with the L value (P<0.05). There was no any association between g.18391548A>T and three color indexes (P>0.05)。The C21 was completely conserved among 45 bird species. In contrast, the R21 was only present in two species of Psittaciformes. Structure comparisons showed that C21R potentially cause 468 structure alternations, of which 49.6% belong to hydrogen bond alternations, 38.8% for solvent accessible, 8.1% for positive φ angle and 3.5% for changes of secondary structures. In conclusion, this study identifies C21R as a molecular marker that is associated with color variation of chicken brown eggs and has a potential effect on protein structures. The CC genotype of C21R is associated with dark brown color and the TT for light brown.
蛋壳颜色变异是影响蛋品销售的一个重要因素。本研究以蛋壳色素原卟啉转运基因ABCG2为对象，旨在筛选出与鸡褐壳颜色变异关联的功能突变。选取381只31周龄的略阳乌鸡，每只母鸡收集3枚蛋，用L*a*b色度空间量化蛋壳颜色。用MassARRAY质谱法检测g.18378442T>C (错义突变C21R)、g.18383682A>G和g.18391548A>T的基因型，用单因素方差分析检验基因型与色度指标的关联性。在UCSC数据库调取52种鸟类物种的同源基因组序列，经序列比对，分析C21R位点的保守性。用MODELLER程序执行同源建模，分别构建C21和R21的蛋白3D结构，研究C21R对ABCG2蛋白结构的影响。结果表明，g.18378442T>C的CC基因型L值(75.3±4.0)显著低于CT (76.6±4.3)和TT (78.0±4.4)，b值(16.2±3.5)显著高于CT (15.7±3.6)和TT型(14.7±3.2)。g.18383682A>G仅与L值显著关联。g.18391548A>T与3个色度指标的关联性均不显著。C21在45种鸟类物种中均完全保守，R21仅在两个鹦形目物种中出现。结构比对结果显示，C21R将引起468个结构改变，涉及氢键(49.6%)、溶剂可及性(38.8%)、正φ转角(8.1%)和二级结构(3.5%)变化。综上所述，C21R是一个与鸡褐壳颜色变异显著关联、对ABCG2结构有潜在影响的突变；其中，CC基因型与深褐壳关联，TT与浅褐壳关联。.
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