Vaccine Induced Differential Expressions of Mirnas at Cytolytic Stage in Chickens Resistant or Susceptible to Marek's Disease

Gene expression regulation is critical for all cellular processes since dysregulation of it often results in elevated disease risk and compromised cellular immunity. MicroRNAs (miRNAs) directly regulate gene expression post-transcriptionally through base-pairing with regions in the 3’-untranslated sequences of the target gene mRNAs. MicroRNAs also indirectly regulate gene expression through regulation of other epigenetic factors. This study was designed to identify miRNAs differentially expressed in chickens induced by Marek’s disease (MD) vaccines. Chickens from two inbred lines (6₃ and 7₂) were included in this study. The line 6₃ is relatively resistant to MD whereas the line 7₂ is highly susceptible. Small RNA libraries were constructed with total RNAs extracted from spleen samples collected at 5 days post vaccine inoculation. Analyses of deep sequencing data resulted in 58 and 17 miRNAs differentially expressed between the HVT and non-vaccinated groups, 17 and 57 miRNAs between the CVI988/Rispens and non-vaccinated groups for line 6₃ and line 7₂, respectively (Log₂ fold change > 1.5). HVT and CVI988/Rispens apparently induced strikingly differed numbers of differentially expressed miRNAs between the MD resistant and susceptible lines of chickens. The reciprocally different numbers of differentially expressed miRNAs are anticipated highly relevant to the differences of vaccine protective efficacy observed between the lines of chickens in challenge trials. Analyses for target genes of the identified miRNAs will follow. These results might lead to better understanding on what microRNAs are involved in modulating vaccine protective efficacy in chickens.