Abstract
Two environmental factors, Newcastle disease and heat stress, are concurrently negatively impacting poultry worldwide and warrant greater attention into developing genetic resistance within chickens. Using two genetically distinct and highly inbred layer lines, Fayoumi and Leghorn, we explored how different genetic backgrounds affect the bursal response to a treatment of simultaneous Newcastle disease virus (NDV) infection at 6 days postinfection (dpi) while under chronic heat stress. The bursa is a primary lymphoid organ within birds and is crucial for the development of B cells. We performed RNA-seq and ChIP-seq targeting histone modifications on bursa tissue. Differential gene expression revealed that Leghorn, compared to Fayoumi, had significant down-regulation in genes involved in cell proliferation, cell cycle, and cell division. Interestingly, we also found greater differences in histone modification levels in response to treatment in Leghorns than Fayoumis, and biological processes enriched in associated target genes of H3K27ac and H3K4me1 were similarly associated with cell cycle and receptor signaling of lymphocytes. Lastly, we found candidate variants between the two genetic lines within exons of differentially expressed genes and regulatory elements with differential histone modification enrichment between the lines, which provides a strong foundation for understanding the effects of genetic variation on NDV resistance under heat stress. This study provides further understanding of the cellular mechanisms affected by NDV infection under heat stress in chicken bursa and identified potential genes and regulatory regions that may be targets for developing genetic resistance within chickens.
Highlights
Infection with the paramyxovirus, Newcastle disease virus (NDV), in chickens has resulted in devastating economic losses across both commercial and backyard poultry farms with mortality rates as high as 100% (Alexander, 2000)
By performing RNA-seq in four groups, four comparisons were made for differential gene analysis on bursa samples from 6 dpi that included withinline comparisons [treated Fayoumis (TF) vs. control Fayoumis (CF) and treated Leghorn (TL) vs. control Leghorn (LC)] and between-line comparisons (CF vs. CL and TF vs. TL)
For differentially enriched regions (DERs) identified for H3K4me1, we found that both within-line analyses have very similar terms and pathways that relate to the immune system and, especially interestingly, are ones relevant to B-cell biology such as B-cell homeostasis, B cell receptor (BCR) signaling, and B-cell activation (Table 1)
Summary
Newcastle disease virus (NDV), in chickens has resulted in devastating economic losses across both commercial and backyard poultry farms with mortality rates as high as 100% (Alexander, 2000). The most effective method in preventing and controlling the spread of Newcastle disease (ND) is through biosecurity and vaccines, which when administered effectively can provide up to 100% survival against lethal, velogenic NDV infection in chickens (Stone et al, 1980; Miller et al, 2013). An additional protective measure that has not been extensively explored is the use of genomics and genetics to improve NDV resistance. Our efforts have been in identifying genetic variation that is associated with NDV resistance as a method for mitigating the potentially devastating effects of virulent NDV. Variation in NDV resistance has previously been observed between different breeds and lines that were first observed during previous outbreaks (Albiston and Gorrie, 1942)
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