The Chicken Frizzle Feather Is Due to an α-Keratin (<em>KRT75</em>) Mutation That Causes a Defective Rachis

Feathers have complex forms and are an excellent model to study the development and evolution of morphologies. Existing chicken feather mutants are especially useful for identifying genetic determinants of feather formation. This study focused on the gene F, underlying the frizzle feather trait that has a characteristic curled feather rachis and barbs in domestic chickens. Our developmental biology studies identified defects in feather medulla formation, and physical studies revealed that the frizzle feather curls in a stepwise manner. The frizzle gene is transmitted in an autosomal incomplete dominant mode. A whole-genome linkage scan of five pedigrees with 2678 SNPs revealed association of the frizzle locus with a keratin gene-enriched region within the linkage group E22C19W28_E50C23. Sequence analyses of the keratin gene cluster identified a 69 bp in-frame deletion in a conserved region of KRT75, an α-keratin gene. Retroviral-mediated expression of the mutated F cDNA in the wild-type rectrix qualitatively changed the bending of the rachis with some features of frizzle feathers including irregular kinks, severe bending near their distal ends, and substantially higher variations among samples in comparison to normal feathers. These results confirmed KRT75 as the F gene. This study demonstrates the potential of our approach for identifying genetic determinants of feather forms.羽毛具有复杂的形态结构，是研究形态发育与演化的绝佳模型。现有的家鸡羽毛突变体，在鉴定羽毛形成的遗传决定因子方面具有重要应用价值。本研究聚焦于作为家鸡卷羽性状遗传基础的F基因，该性状的典型特征为羽轴与羽枝发生卷曲。我们的发育生物学研究发现羽髓形成存在缺陷，而物理特性分析则显示卷羽的卷曲过程呈阶梯式进行。卷羽基因以常染色体不完全显性的方式进行遗传。我们利用2678个单核苷酸多态性（Single Nucleotide Polymorphisms, SNPs）标记，对5个家系开展全基因组连锁扫描，结果显示卷羽基因座与连锁群E22C19W28_E50C23内的角蛋白基因富集区域存在显著关联。对该角蛋白基因簇的序列分析显示，α角蛋白基因KRT75的保守区域存在一段69 bp的框内缺失。通过逆转录病毒介导，将突变型F基因的互补DNA（cDNA）导入野生型尾羽中表达后，羽轴的弯曲特性发生了定性改变，呈现出卷羽的部分特征：包括不规则扭结、远端严重弯曲，且样本间的变异程度显著高于正常尾羽。上述实验结果证实KRT75即为F基因。本研究证明了我们的方法在鉴定羽毛形态遗传决定因子方面具有应用潜力。