Prototype endogenous avian retroviruses of the genus Gallus

Detection of long terminal repeat loci derived from endogenous retrovirus in junglefowl using whole-genome sequencing

Endogenous retroviruses (ERVs) are genetic elements present in the genome that retain traces of past viral infections. Characterization of ERVs can provide crucial insights into avian evolution. This study aimed to identify novel long terminal repeat (LTR) loci derived from ERVs (ERV-LTRs) absent in the reference genome using whole-genome sequencing data of red junglefowl, gray junglefowl, Ceylon junglefowl, and green junglefowl. In total, 835 ERV-LTR loci were identified across the four Gallus species. The numbers of ERV-LTRs loci detected in red junglefowl and its subspecies gray junglefowl, Ceylon junglefowl, and green junglefowl were 362, 216, 193, and 128, respectively. The phylogenetic tree was congruent with previously reported trees, suggesting the potential for inferring relationships among past junglefowl populations from the identified ERV-LTR loci. Of the detected loci, 306 ERV-LTRs were identified near or within the genes, and some were associated with cell adhesion. The detected ERV-LTR sequences were classified as endogenous avian retrovirus family, avian leukosis virus subgroup E, Ovex-1, and murine leukemia virus-related ERVs. In addition, the sequence of the EAV family was divided into four patterns by combining the U3, R, and U5 regions. These findings contribute to a more comprehensive understanding of the characteristics of junglefowl ERVs.

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.

Fasting and overfeeding affect the expression of the immunity- or inflammation-related genes in the liver of poultry via endogenous retrovirus

It is known that nutrition and immunity are connected, but the mechanism is not very clear. Endogenous retroviruses (ERV) account for 8 to 10% of the human and mouse genomes and play an important role in some biological processes of animals. Recent studies indicate that the activation of ERV can affect the expression of the immunity- or inflammation-related genes, and the activities of ERV are subjected to regulation of many factors including nutritional factors. Therefore, we hypothesize that nutritional status can affect the expression of the immunity- or inflammation-related genes via ERV. To verify this hypothesis, the nutritional status of animals was altered by fasting or overfeeding, and the expression of intact ERV (ERVK18P, ERVK25P) and immunity- or inflammation-related genes (DDX41, IFIH1, IFNG, IRF7, STAT3) in the liver was determined by quantitative PCR, followed by overexpressing ERVK25P in goose primary hepatocytes and determining the expression of the immunity- or inflammation-related genes. The data showed that compared with the control group (no fasting), the expression of ERV and the immunity- or inflammation-related genes was increased in the liver of the fasted chickens but decreased in the liver of the fasted geese. Moreover, compared with the control group (routinely fed), the expression of ERV and the immunity- or inflammation-related genes was increased in the liver of the overfed geese. In addition, overexpression of ERVK25P in goose primary hepatocytes can induce the expression of the immunity- or inflammation-related genes. In conclusion, these findings suggest that ERV mediate the effects of fasting and overfeeding on the expression of the immunity- or inflammation-related genes, the mediation varied with poultry species, and ERV and the immunity- or inflammation-related genes may be involved in the development of goose fatty liver. This study provides a potential mechanism for the connection between nutrition and immunity.

GGERV20, a recently integrated, segregating endogenous retrovirus in Gallus gallus

Endogenous retroviruses (ERVs) are widespread in vertebrate genomes. The recent availability of whole eukaryotic genomes has enabled their characterization in many organisms, including Gallus gallus (red jungle fowl), the progenitor of the domesticated chicken. Our bioinformatics analysis of a G. gallus ERV previously designated GGERV20 identified 35 proviruses with complete long terminal repeats (LTRs) and gag-pol open reading frames (ORFs) in the Genome Reference Consortium Chicken Build 6a, of which 8 showed potential for translation of functional retroviral polyproteins, including the integrase and reverse transcriptase enzymes. No elements were discovered with an env gene. Fifteen loci had LTR sequences with 100 % identity, indicative of recent integration. Chicken embryo fibroblast RNA-seq datasets showed reads representing the entire length of the GGERV20 provirus, supporting their potential for expressing viral proteins. To investigate the possibility that GGERV20 elements may not be fixed in the genome, we assessed the integration status of five loci in a meat-type chicken. PCRs targeting a GGERV20 locus on G. gallus chromosome one (GGERV20_1-1) reproducibly amplified both LTRs and the preintegration state, indicating that the bird from which the DNA was sampled was hemizygous at this locus. The four other loci examined only produced the preintegration state amplicons. These results reveal that GGERV20 is not fixed in the G. gallus population, and taken together with the lack of mutations seen in several provirus LTRs and their transcriptional activity, suggest that GGERV20 retroviruses have recently been and continue to be active in the chicken genome.

Mosquito-Borne Viruses and Insect-Specific Viruses Revealed in Field-Collected Mosquitoes by a Monitoring Tool Adapted from a Microbial Detection Array

Several mosquito-borne diseases affecting humans are emerging or reemerging in the United States. The early detection of pathogens in mosquito populations is essential to prevent and control the spread of these diseases. In this study, we tested the potential applicability of the Lawrence Livermore Microbial Detection Array (LLMDA) to enhance biosurveillance by detecting microbes present in Aedes aegypti, Aedes albopictus, and Culex mosquitoes, which are major vector species globally, including in Texas. The sensitivity and reproducibility of the LLMDA were tested in mosquito samples spiked with different concentrations of dengue virus (DENV), revealing a detection limit of >100 but <1,000 PFU/ml. Additionally, field-collected mosquitoes from Chicago, IL, and College Station, TX, of known infection status (West Nile virus [WNV] and Culex flavivirus [CxFLAV] positive) were tested on the LLMDA to confirm its efficiency. Mosquito field samples of unknown infection status, collected in San Antonio, TX, and the Lower Rio Grande Valley (LRGV), TX, were run on the LLMDA and further confirmed by PCR or quantitative PCR (qPCR). The analysis of the field samples with the LLMDA revealed the presence of cell-fusing agent virus (CFAV) in A. aegypti populations. Wolbachia was also detected in several of the field samples (A. albopictus and Culex spp.) by the LLMDA. Our findings demonstrated that the LLMDA can be used to detect multiple arboviruses of public health importance, including viruses that belong to the Flavivirus, Alphavirus, and Orthobunyavirus genera. Additionally, insect-specific viruses and bacteria were also detected in field-collected mosquitoes. Another strength of this array is its ability to detect multiple viruses in the same mosquito pool, allowing for the detection of cocirculating pathogens in an area and the identification of potential ecological associations between different viruses. This array can aid in the biosurveillance of mosquito-borne viruses circulating in specific geographical areas.IMPORTANCE Viruses associated with mosquitoes have made a large impact on public and veterinary health. In the United States, several viruses, including WNV, DENV, and chikungunya virus (CHIKV), are responsible for human disease. From 2015 to 2018, imported Zika cases were reported in the United States, and in 2016 to 2017, local Zika transmission occurred in the states of Texas and Florida. With globalization and a changing climate, the frequency of outbreaks linked to arboviruses will increase, revealing a need to better detect viruses in vector populations. With the capacity of the LLMDA to detect viruses, bacteria, and fungi, this study highlights its ability to broadly screen field-collected mosquitoes and contribute to the surveillance and management of arboviral diseases.

Enhancing Targeted Genomic DNA Editing in Chicken Cells Using the CRISPR/Cas9 System

The CRISPR/Cas9 system has enabled highly efficient genome targeted editing for various organisms. However, few studies have focused on CRISPR/Cas9 nuclease-mediated chicken genome editing compared with mammalian genomes. The current study combined CRISPR with yeast Rad52 (yRad52) to enhance targeted genomic DNA editing in chicken DF-1 cells. The efficiency of CRISPR/Cas9 nuclease-induced targeted mutations in the chicken genome was increased to 41.9% via the enrichment of the dual-reporter surrogate system. In addition, the combined effect of CRISPR nuclease and yRad52 dramatically increased the efficiency of the targeted substitution in the myostatin gene using 50-mer oligodeoxynucleotides (ssODN) as the donor DNA, resulting in a 36.7% editing efficiency after puromycin selection. Furthermore, based on the effect of yRad52, the frequency of exogenous gene integration in the chicken genome was more than 3-fold higher than that without yRad52. Collectively, these results suggest that ssODN is an ideal donor DNA for targeted substitution and that CRISPR/Cas9 combined with yRad52 significantly enhances chicken genome editing. These findings could be extensively applied in other organisms.

Expression patterns of endogenous avian retrovirus ALVE1 and its response to infection with exogenous avian tumour viruses

Endogenous retroviruses (ERVs) are genomic elements that are present in a wide range of vertebrates and have been implicated in a variety of human diseases, including cancer. However, the characteristic expression patterns of ERVs, particularly in virus-induced tumours, is not fully clear. DNA methylation was analysed by bisulfite pyrosequencing, and gene expression was analysed by RT-qPCR. In this study, we first found that the endogenous avian retrovirus ALVE1 was highly expressed in some chicken tissues (including the heart, bursa, thymus, and spleen) at 2 days of age, but its expression was markedly decreased at 35 days of age. In contrast, the CpG methylation level of ALVE1 was significantly lower in heart and bursa at 2 days than at 35 days of age. Moreover, we found that the expression of ALVE1 was significantly inhibited in chicken embryo fibroblast cells (CEFs) and MSB1 cells infected with avian leukosis virus subgroup J (ALVJ) and reticuloendotheliosis virus (REV) at the early stages of infection. In contrast, the expression of the ALVE1 env gene was significantly induced in CEFs and MSB1 cells infected with Marek's disease virus (MDV). However, the methylation and expression levels of the ALVE1 long terminal repeat (LTR) did not show obvious alterations in response to viral infection. The present study revealed the expression patterns of ALVE1 in a variety of chicken organs and tissues and in chicken cells in response to avian tumour virus infection. These findings may be of significance for understanding the role and function of ERVs that are present in the host genome.

Expression of the env gene from the avian endogenous retrovirus ALVE and regulation by miR-155

Endogenous retroviruses (ERVs) are important retroelements that reside in host genomes. However, ERV expression patterns and regulatory mechanisms are poorly understood. In this study, chicken embryo fibroblasts (CEFs) and MSB1 cells infected with Marek's disease virus (MDV) exhibited significantly increased expression of env from the endogenous retrovirus ALVE. In contrast, env expression was significantly lower in CEF and MSB1 cells infected with exogenous avian leukosis virus J (ALVJ) at the early infection stage. Furthermore, env was found to be ubiquitously expressed in various chicken tissues, with high expression in certain tissues at 2 days of age and low levels in most tissues, including immune organs (thymus, spleen and bursa) as well as the brain and heart, at 35 days of age. Sequence analysis revealed miR-155 target sites in env transcripts, which was verified using a firefly luciferase reporter assay, and treatment with miR-155 agomir significantly decreased levels of env transcripts in MSB1 and CEF cells. Together, these findings suggest that the env gene from the endogenous retrovirus ALVE is regulated by miR-155.

Endogenous avian leukosis viral loci in the Red Jungle Fowl genome assembly

The current build (galGal4) of the genome of the ancestor of the modern chicken, the Red Jungle Fowl, contains a single endogenous avian leukosis viral element (ALVE) on chromosome 1 (designated RSV-LTR; family ERVK). The assembly shows the ALVE provirus juxtaposed with a member of a second family of avian endogenous retroviruses (designated GGERV20; family ERVL); however, the status of the 3' end of the ALVE element as well as its flanking region remain unclear due to a gap in the reference genome sequence. In this study, we filled the gap in the assembly using a combination of long-range PCR (LR-PCR) and a short contig present in the unassembled portion of the reference genome database. Our results demonstrate that the ALVE element (ALVE-JFevB) is inserted into the putative envelope region of a GGERV20 element, roughly 1 kbp from its 3' end, and that ALVE-JFevB is complete, and depending on its expression status, potentially capable of directing the production of virus. Moreover, the unassembled portion of the genome database contains junction fragments for a second, previously characterized endogenous proviral element, ALVE-6.