Screening of Streptococcus Suis serotype 2 resistance genes with GWAS and transcriptomic microarray analysis (mRNA)

Swine streptococcosis has caused great economic loss in the swine industry, and the major pathogen responsible for this disease is Streptococcus Suis serotype 2 (SS2). Disease resistance breeding is a fundamental way of resolving this problem. With the development of GWAS and transcriptomic microarray technology, we now have powerful research tools to identify SS2 resistance genes. In this research, we generated an F2 generation of SS2 resistant C57BL/6 and SS2 susceptive A/J mice. With the F2 generation of these two mice strains and GWAS analysis, we identified 286 significant mouse genome SNPs sites associated with the SS2 resistance trait. Gene expression profiles for C57BL/6 and A/J were analyzed under SS2 infection pressure by microarray. In total, 251 differentially expressed genes were identified between these two mouse strains during SS2 infection. After combining the GWAS and gene expression profile data, we located two genes that were significantly associated with SS2 resistance, which were the UBA domain containing 1 gene (Ubac1) and Epsin 1 gene (Epn 1). GO classification and over-representation analysis revealed nine up-regulated related to immune function, which could potentially be involved in the C57BL/6 SS2 resistance trait. This is the first study to use both SNP chip and gene express profile chip for SS2 resistance gene identification in mouse, and these results will contribute to Swine SS2 resistance breeding. The SS2 inoculum for experimental infection was adjusted to a concentration of 1×108 CFU/mL. Seventy male and seventy female F2 mice were injected i.p. with a 1 mL inoculum per mouse. F2 mice surviving for fewer than 3 days following infection were regarded as susceptible (22 males and 22 females), while those surviving for more than 15 days were regarded as resistant (23 males and 21 females). Blood samples were collected aseptically from susceptible and resistant F2 mice. Genomic DNA was extracted from blood using TIANamp Genomic DNA Kit, and then amplified and hybridized to an Affymetrix Mouse Diversity Genotyping Array (Affymetrix) according to the manufacturer’s instructions (Affymetrix Inc.).