A novel sex-linked mutant affecting tail formation in Hongshan chicken

Molecular genetic foundation of a sex-linked tailless trait in Hongshan chicken by whole genome data analysis

As a Chinese local chicken breed, Hongshan chickens have 2 kinds of tail feather phenotypes, normal and taillessness. Our previous studies showed that taillessness was a sex-linked dominant trait. Abnormal development of the tail vertebrae could be explained this phenomenon in some chicken breeds. However, the number of caudal vertebrae in rumpless Hongshan chickens was normal, so rumplessness in Hongshan chicken was not related to the development of the caudal vertebrae. Afterwards, we found that rumplessness in Hongshan was due to abnormal development of tail feather rather than abnormal development of caudal vertebrae. In order to understand the genetic foundation of the rumplessness of Hongshan chickens, we compared and reanalyzed 2 sets of data in normal and rumpless Hongshan chickens from our previous studies. By joint analysis of genome-wide selection signature analysis and genome-wide association approach, we found that 1 overlapping gene (EDIL3) and 16 peak genes (ENSGALG00000051843, ENSGALG00000053498, ENSGALG00000054800, KIF27, PTPRD, ENSGALG00000047579, ENSGALG00000041052, ARHGEF28, CAMK4, SERINC5, ENSGALG00000050776, ERCC8, MCC, ADAMTS19, ENSGALG00000053322, CHRNA8) located on the Z chromosome was associated with the rumpless trait. The results of this study furtherly revealed the molecular mechanism of the rumpless trait in Hongshan chickens, and identified the candidate genes associated with this trait. Our results will help to improve the shape of chicken tail feathers and to rise individual economic value in some specific market in China.

Genomic Regions Related to White/Black Tail Feather Color in Dwarf Chickens Identified Using a Genome-Wide Association Study

Although the genetic foundation of chicken body feather color has been extensively explored, that of tail feather color remains poorly understood. In the present study, we used a synthetic chicken dwarf line (DW), derived from hybrids bred between a black tail chicken breed, Rhode Island Red (RIR), and a white tail breed, dwarf layer (DL), to investigate the genetic rules associated white/black tail color. Even though the body feathers are predominantly red, the DW line still comprises individuals with black or white tails after more than 10 generations of self-crossing and selection for the body feather color. We first performed four crosses using the DW chickens, including black-tailed males to females, reciprocal crosses between the black and white, and white males to females to elucidate the inheritance pattern of the white/black tail. We also performed a genome-wide association (GWA) analysis to determine the candidate genomic regions underlying the tail feather color using black tail chickens from the RIR and DW lines and white individuals from the DW line. In the crossing experiment, we found that (i) the white/black tail feather color is independent of body feather color; (ii) the phenotype is a simple autosomal trait; and (iii) the white is dominant to the black in the DW line. The GWA results showed that seven single-nucleotide polymorphisms (SNPs) on chromosome 24 were significantly correlated with tail feather color. The significant region (3.97-4.26 Mb) comprises nine known genes (NECTIN1, THY1, gga-mir-1466, USP2, C1QTNF5, RNF26, MCAM, CBL, and CCDC153) and five anonymous genes. This study revealed that the white/black tail feather trait is autosome-linked in DW chickens. Fourteen genes were found in the significant ~0.29 Mb genomic region, and some, especially MCAM, are suggested to play critical roles in the determination of white/black tail feather color. Our research is the first study on the genetics underlying tail feather color and could help further the understanding of feather pigmentation in chickens.

Integrating Genomic and Transcriptomic Data to Reveal Genetic Mechanisms Underlying Piao Chicken Rumpless Trait

Piao chicken, a rare Chinese native poultry breed, lacks primary tail structures, such as pygostyle, caudal vertebra, uropygial gland, and tail feathers. So far, the molecular mechanisms underlying tail absence in this breed remain unclear. In this study, we comprehensively employed comparative transcriptomic and genomic analyses to unravel potential genetic underpinnings of rumplessness in Piao chicken. Our results reveal many biological factors involved in tail development and several genomic regions under strong positive selection in this breed. These regions contain candidate genes associated with rumplessness, including Irx4, Il18, Hspb2, and Cryab. Retrieval of quantitative trait loci (QTL) and gene functions implies that rumplessness might be consciously or unconsciously selected along with the high-yield traits in Piao chicken. We hypothesize that strong selection pressures on regulatory elements might lead to changes in gene activity in mesenchymal stem cells of the tail bud. The ectopic activity could eventually result in tail truncation by impeding differentiation and proliferation of the stem cells. Our study provides fundamental insights into early initiation and genetic basis of the rumpless phenotype in Piao chicken.

Genome-wide re-sequencing and transcriptome analysis reveal candidate genes associated with the pendulous comb phenotype in domestic chickens

To determine the causative variations associated with two chicken comb phenotypes, pendulous comb (PC) or upright comb (UC), two pooled genomic DNA samples from PC and UC chickens were re-sequenced by Next-Generation Sequencer, and genome-wide Single nucleotide polymorphisms (SNPs) were detected. Using three selective sweep approaches, F_ST , θπ, and Tajima's D, with top 5% window values serving as the threshold, a total of 84 positively selective genes (PSGs) were identified. There were no SNPs in exons of the PSGs with significant differences in allele frequencies between the two comb phenotype groups. Then, 515 differentially expressed genes (DEGs) between the PC and UC were identified by RNA-seq. Three genes including CD36 (CD36 molecule), ADAMTSL3 (ADAMTS-like 3), and AOX1 (aldehyde oxidases 1) are overlapped between PSGs and DEGs. After genotyping seven candidate SNPs in the regulatory regions of the three overlapping genes in 120 chickens from two other breeds, two variants (rs14607046 and rs731818051) in the regulatory regions of AOX1 and ADAMTSL3 were found to have significant differences in allele frequency between the PC and UC, suggesting that the two variants may be causative mutations for PC. Overall, our study shed light on the genetic basis underlying the PC phenotype in chickens.

Genome-wide association study confirms that the chromosome Z harbours a region responsible for rumplessness in Hongshan chickens

Rumplessness in Hongshan chickens has been reported as a novel sex-linked characteristic. Re-sequencing data suggest that a pseudogene on the Z chromosome, LOC431648, is affiliated with this phenotype. In this study, we chose 23 rumpless and 25 normal Hongshan chickens to localize the potential variation by means of a genome-wide association study using a high density microarray. A region on the Z chromosome was found to be closely associated with rumplessness in Hongshan chickens. The region, located in gene LINGO2, was approximately 3 Mb away from pseudogene LOC431648. The function of this gene has not yet been studied in birds. Differential expression of the candidate genes in the tail feather follicles was not detected by q-PCR, which suggests that the rumplessness trait could be attributed to other genetic mechanisms.