Characteristics of Reversion to Early Feathering Phenotype in the Late Feathering Line of Nagoya Breed Chickens

dPRLR causes differences in immune responses between early and late feathering chickens after ALV-J infection

To understand the differences in immune responses between early feathering (EF) and late feathering (LF) chickens after infection with avian leukosis virus, subgroup J (ALV-J), we monitored the levels of prolactin, growth hormone and the immunoglobulins IgG and IgM in the serum of LF and EF chickens for 8 weeks. Moreover, we analysed the expression of immune-related genes in the spleen and the expression of PRLR, SPEF2 and dPRLR in the immune organs and DF-1 cells by qRT–PCR. The results showed that ALV-J infection affected the expression of prolactin, growth hormone, IgG and IgM in the serum. Regardless of whether LF and EF chickens were infected with ALV-J, the serum levels of the two hormones and two immunoglobulins in EF chickens were higher than those in LF chickens (P  < 0.05). However, the expression of immune-related genes in the spleen of positive LF chickens was higher than that in the spleen of positive EF chickens. In the four immune organs, PRLR and SPEF2 expression was also higher in LF chickens than in EF chickens. Furthermore, the dPRLR expression of positive LF chickens was higher than that of negative LF chickens. After infection with ALV-J, the expression of PRLR in DF-1 cells significantly increased. In addition, overexpression of PRLR or dPRLR in DF-1 cells promoted replication of ALV-J. These results suggested that the susceptibility of LF chickens to ALV-J might be induced by dPRLR.

Endogenous viral gene ev21 is not responsible for the expression of late feathering in chickens

The late-feathering (LF) gene K on the Z chromosome is an important gene in the chicken industry, which is frequently utilized for the feather sexing, a type of autosexing, of neonatal chicks. The K gene is closely associated with the endogenous ev21 gene from an avian leukosis virus and the incomplete duplication (ID) of prolactin receptor (PRLR) and sperm flagellar protein 2 (SPEF2) genes, and ev21 has been used as a molecular marker to detect LF birds. In the present study, a comprehensive survey for the presence or absence of ev21 and ID across 1,994 birds from 52 chicken breeds, three commercial hybrid groups, and the Red Jungle Fowl revealed that almost all LF breeds have both ev21 and ID. However, only one LF breed (Ingie) has only ID and no ev21. Moreover, this study revealed that almost all early (normal)-feathering (EF) breeds lack both ev21 and ID, but only one breed (White Plymouth Rock) included EF birds with ev21 but no ID. Therefore, regarding LF expression, the results indicated that ID is responsible, but ev21 is not required. Henceforth, ID should be used as a molecular marker to detect LF birds instead of ev21. Because ev21 contains the full genome of an avian leukosis virus, there is a risk of disease development in breeds with this gene. Therefore, the Ingie breed, which has no ev21 at the K locus, represents excellent material for the establishment of new LF stocks.

Early and late feathering in turkey and chicken: same gene but different mutations

BACKGROUND

Sex-linked slow (SF) and fast (FF) feathering rates at hatch have been widely used in poultry breeding for autosexing at hatch. In chicken, the sex-linked K (SF) and k+ (FF) alleles are responsible for the feathering rate phenotype. Allele K is dominant and a partial duplication of the prolactin receptor gene has been identified as the causal mutation. Interestingly, some domesticated turkey lines exhibit similar slow- and fast-feathering phenotypes, but the underlying genetic components and causal mutation have never been investigated. In this study, our aim was to investigate the molecular basis of feathering rate at hatch in domestic turkey.

RESULTS

We performed a sequence-based case-control association study and detected a genomic region on chromosome Z, which is statistically associated with rate of feathering at hatch in turkey. We identified a 5-bp frameshift deletion in the prolactin receptor (PRLR) gene that is responsible for slow feathering at hatch. All female cases (SF turkeys) were hemizygous for this deletion, while 188 controls (FF turkeys) were hemizygous or homozygous for the reference allele. This frameshift mutation introduces a premature stop codon and six novel amino acids (AA), which results in a truncated PRLR protein that lacks 98 C-terminal AA.

CONCLUSIONS

We present the causal mutation for feathering rate in turkey that causes a partial C-terminal loss of the prolactin receptor, and this truncated PRLR protein is strikingly similar to the protein encoded by the slow feathering K allele in chicken.