Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843, USA.
Key Laboratory of Agricultural Animal Genetics, Breeding and Reproduction of Ministry of Education, College of Animal Science and Technology, Huazhong Agricultural University, 430070 Wuhan, Hubei, China.
G3 (Bethesda). 2021 Feb 9;11(2). doi: 10.1093/g3journal/jkaa048.
The Crest mutation in chicken shows incomplete dominance and causes a spectacular phenotype in which the small feathers normally present on the head are replaced by much larger feathers normally present only in dorsal skin. Using whole-genome sequencing, we show that the crest phenotype is caused by a 197 bp duplication of an evolutionarily conserved sequence located in the intron of HOXC10 on chromosome 33. A diagnostic test showed that the duplication was present in all 54 crested chickens representing eight breeds and absent from all 433 non-crested chickens representing 214 populations. The mutation causes ectopic expression of at least five closely linked HOXC genes, including HOXC10, in cranial skin of crested chickens. The result is consistent with the interpretation that the crest feathers are caused by an altered body region identity. The upregulated HOXC gene expression is expanded to skull tissue of Polish chickens showing a large crest often associated with cerebral hernia, but not in Silkie chickens characterized by a small crest, both homozygous for the duplication. Thus, the 197 bp duplication is required for the development of a large crest and susceptibility to cerebral hernia because only crested chicken show this malformation. However, this mutation is not sufficient to cause herniation because this malformation is not present in breeds with a small crest, like Silkie chickens.
鸡的 Crest 突变表现为不完全显性，导致一种显著的表型，即通常位于头部的小羽毛被替换为仅在背部皮肤中存在的更大的羽毛。使用全基因组测序，我们表明 Crest 表型是由位于 33 号染色体 HOXC10 内含子中的一个 197bp 重复序列引起的，该重复序列在进化上是保守的。一个诊断测试表明，该重复序列存在于所有 54 只 Crest 鸡中，代表八个品种，而不存在于所有 433 只非 Crest 鸡中，代表 214 个种群。该突变导致至少五个紧密连锁的 HOXC 基因在 Crest 鸡的颅皮中异位表达，包括 HOXC10。这一结果与 Crest 羽毛是由身体区域身份改变引起的解释一致。上调的 HOXC 基因表达扩展到波兰鸡的颅骨组织，这些鸡通常表现出与脑疝相关的大 Crest，但在 Silkie 鸡中则没有，Silkie 鸡的 Crest 很小，两者都是该重复序列的纯合子。因此，197bp 的重复是产生大 Crest 和易患脑疝的必要条件，因为只有 Crest 鸡才会出现这种畸形。然而，这种突变不足以导致脑疝，因为在具有小 Crest 的品种中，如 Silkie 鸡，不存在这种畸形。
