Naturally Occurring Frameshift Mutations in the tvb Receptor Gene Are Responsible for Decreased Susceptibility of Chicken to Infection with Avian Leukosis Virus Subgroups B, D, and E

Insertion/deletion mutations within tva receptor gene confer chicken resistance to infection by avian leukosis virus subgroups A and K

The classic subgroup A (ALV-A) and newly emerging subgroup K (ALV-K) of avian leukosis virus are two major pathogens responsible for avian leukemia in chickens, posing substantial threats to global poultry industry. Both viruses share a Tva protein encoded by the tva gene as a receptor to gain the entry into the host cells. In this study, we described the identifications of two alleles of the tva receptor gene in Qingyuan partridge chicken, which possesses an 11-nucleotide (GCTGCCCACCC) insertion and a 6-nucleotide (ACCTCC) deletion independently located in exon 1 of the tva receptor gene. The natural 11-nucleotide insertion causes a frameshift in the reading frame of the tva cDNA, which presumably blocks the expression of the normal tva allele and results resistance in chicken against infection by ALV-A and ALV-K. The natural 6-nucleotide deletion leads to a Tva receptor protein missing the amino acids residues T21 and S22, which appeared dysfunctional to mediate the viral entry. As a result, we observed that the deletion mutation in the tva receptor gene significantly reduced the susceptibility to infection by ALV-A and ALV-K in vitro and in vivo, and significantly reduced the binding capacity of the Tva receptor protein to the envelope glycoproteins of ALV-A and ALV-K in our subsequent analysis. Taken together, these findings not only provide evidence that the insertion and deletion mutations within the tva receptor gene confer chicken resistance to infection by ALV-A and ALV-K but also provide ideal targets for selective breeding of ALV-A and ALV-K resistance in chicken.

Molecular characteristics of avian leukosis viruses isolated from indigenous chicken breeds in Yunnan Province, Southwestern China

Indigenous chicken breeds have a large market share in China due to their superior production traits, including high meat quality and disease resistance. Yunnan Province is recognized as a major source of domestic chickens globally and boasts a diverse array of indigenous chicken resources. Avian leukosis virus (ALV) induces various tumors and immunosuppression, endangering the poultry industry. However, the prevalence of ALV infection among indigenous chickens in Yunnan Province remains unclear. In this study, we aimed to investigate the presence of ALV in these breeds. To this end, we collected 1,470 plasma samples from six indigenous chicken breeds in Yunnan province, 309 of which tested positive. The results confirmed the presence of exogenous ALV in local chicken, with a positivity rate ranging from 8.20 %-41.46 %. Furthermore, eight exogenous ALV isolates were successfully identified: four ALV subtype J (ALV-J) strains, three ALV subtype A (ALV-A) strains and one ALV subtype B (ALV-B) strain. The four ALV-J strains share relatively high sequence identity (99.55 %-99.80 %) with the GX14ZS14 strain isolated from Guangxi in 2014 and was closely related to the prototype strain HPRS103 and belongs to clade 1.1. Several substitutions were observed in gp85 proteins in the three ALV-A and ALV-B strains isolated in this study. Additionally, the four ALV-J strains exhibited 203 bp deletions in the rTM and DR1 regions, a feature commonly observed in viruses in clades 1.2 and 1.3. Overall, this study confirmed the presence of multiple ALVs in these six indigenous chicken breeds from Yunnan Province. This study provides molecular characterization of ALV in indigenous chicken breeds in Yunnan Province and provides a reference for the further eradication of ALV in China. The complex background of ALV infection highlights the urgent need for intensifying eradication efforts.

Rapid and sensitive visual detection of avian leukosis virus by reverse transcription loop-mediated isothermal amplification combined with a lateral flow immunochromatographic strip assay

Considering that avian leukosis virus (ALV) infection has inflicted massive economic losses on the poultry breeding industry in most countries, its early diagnosis remains an important measure for timely treatment and control of the disease, for which a rapid and sensitive point-of-care test is required. We established a user-friendly, economical, and rapid visualization method for ALV amplification products based on reverse transcription loop-mediated isothermal amplification (RT-LAMP) combined with an immunochromatographic strip in a lateral flow device (LFD). Using the ALVp27 gene as the target, five RT-LAMP primers and one fluorescein-isothiocyanate-labeled probe were designed. After 60 min of RT-LAMP amplification at 64 °C, the products could be visualized directly using the LFD. The detection limit of this assay for ALV detection was 102 RNA copies/μL, and the sensitivity was 100 times that of reverse transcription polymerase chain reaction (RT-PCR), showing high specificity and sensitivity. To verify the clinical practicality of this assay for detecting ALV, the gold standard RT-PCR method was used for comparison, and consistent results were obtained with both assays. Thus, the assay described here can be used for rapid detection of ALV in resource-limited environments.

Advances on genetic and genomic studies of ALV resistance

Avian leukosis (AL) is a general term for a variety of neoplastic diseases in avian caused by avian leukosis virus (ALV). No vaccine or drug is currently available for the disease. Therefore, the disease can result in severe economic losses in poultry flocks. Increasing the resistance of poultry to ALV may be one effective strategy. In this review, we provide an overview of the roles of genes associated with ALV infection in the poultry genome, including endogenous retroviruses, virus receptors, interferon-stimulated genes, and other immune-related genes. Furthermore, some methods and techniques that can improve ALV resistance in poultry are discussed. The objectives are willing to provide some valuable references for disease resistance breeding in poultry.

Avian Leucosis Virus-Host Interaction: The Involvement of Host Factors in Viral Replication

Avian leukosis virus (ALV) causes various diseases associated with tumor formation and decreased fertility. Moreover, ALV induces severe immunosuppression, increasing susceptibility to other microbial infections and the risk of failure in subsequent vaccination against other diseases. There is growing evidence showing the interaction between ALV and the host. In this review, we will survey the present knowledge of the involvement of host factors in the important molecular events during ALV infection and discuss the futuristic perspectives from this angle.

Conservation of chicken male germline by orthotopic transplantation of primordial germ cells from genetically distant donors†

Successful derivation and cultivation of primordial germ cells (PGCs) opened the way to efficient transgenesis and genome editing in the chicken. Furthermore, implantation of male PGCs from non-chicken galliform species into the chicken embryos resulted in cross-species germline chimeras and viable offspring. We have recently improved the PGC technology by demonstrating that chicken male PGCs transplanted into the testes of adult cockerel recipients mature into functional sperms. However, the availability of this orthotopic transplantation for cross-species transfer remains to be explored. Here we tested the capacity of genetically distant male PGCs to mature in the microenvironment of adult testes. We derived PGCs from the Chinese black-bone Silkie and transplanted them into infertile White Leghorn cockerels. Within 15-18 weeks after transplantation, we observed restoration of spermatogenesis in recipient cockerels and production of healthy progeny derived from the transplanted PGCs. Our findings also indicate the possibility of cross-species orthotopic transplantation of PGCs. Thus, our results might contribute to the preservation of endangered avian species and maintaining the genetic variability of the domestic chicken.