Unique Genetic Responses Revealed in RNA-seq of the Spleen of Chickens Stimulated with Lipopolysaccharide and Heat

Climate change and disease have large negative impacts on poultry production, but little is known about the interactions of responses to these stressors in chickens. Fayoumi (heat and disease resistant) and broiler (heat and disease susceptible) chicken lines were stimulated at 22 days of age, using a 2x2x2 factorial design including: breed (Fayoumi or broiler), inflammatory stimulus [lipopolysaccharide (LPS) or saline], and temperature (35°C or 25°C). Transcriptional changes in spleens were analyzed using RNA-sequencing on the Illumina HiSeq 2500. Thirty-two individual cDNA libraries were sequenced (four per treatment) and an average of 22 million reads were generated per library. Stimulation with LPS induced more differentially expressed genes (DEG, log2 fold change ≥ 2 and FDR ≤ 0.05) in the broiler (N=283) than the Fayoumi (N=85), whereas heat treatment resulted in fewer DEG in broiler (N=22) compared to Fayoumi (N=107). The double stimulus of LPS+heat induced the largest numbers of changes in gene expression, for which broiler had 567 DEG and Fayoumi had 1471 DEG of which 399 were shared between breeds. Further analysis of DEG revealed pathways impacted by these stressors such as Remodelling of Epithelial Adherens Junctions due to heat stress, Granulocyte Adhesion and Diapedesis due to LPS, and Hepatic Fibrosis/Hepatic Stellate Cell Activation due to LPS+heat. The genes and pathways identified provide deeper understanding of the response to the applied stressors and may serve as biomarkers for genetic selection for heat and disease tolerant chickens. Overall design: At 22 days of age, divergent chicken breeds (Fayoumi and broiler) were treated with a thermal treatment (heat stress at 35C, or thermoneutral at 25C as a control) for 3.5 hours, then stimulated subcutaneously with an inflammatory stimulus (LPS, or saline as a control) for another 3.5 hours. Chickens were euthanized and spleens were harvested. A total of 32 indivudally coded cDNA libraries were prepared using TruSeq v2 library preparation kit which selects for polyA mRNA. In this 2x2x2 full factorial design with the factors of breed, thermal treatment, and inflammatory stimulus, there were a total of 8 treatment groups. Each treatment group had a total of 4 animal biological replicates. Therefore, a total of 32 individual barcoded samples were sequenced. A total of 8 individually barcoded cDNA libraries were sequenced per lane using the HiSeq Illumina 2500, and we used 4 lanes total. Reads were mapped to Galgal 2.0.