Identification and expression analysis of infectious laryngotracheitis virus encoding microRNAs

MicroRNAs (miRNAs) are a class of small non-coding RNA molecules that play a pivotal role in the regulation of gene expression at the post transcriptional level. Infectious laryngotracheitis virus (ILTV) is an alphaherpesvirus belonging to the herpesviridae family. It causes an acute respiratory disorder in chicken resulting in high mortality rates. ILTV encoding miRNAs have been identified in cell cultures infected by ILTV. Seven candidates ILTV encoding miRNAs were identified by the 454 FLX genome sequencing method. Five ILTV miRNAs identified in this study were identical to those previously reported by Waidner et al. (Virology 388:128, 2009). Two unique ILTV miRNAs, iltv-miR-I1-3p and iltv-miR-I7-3p, were identified in this study. The iltv-miR-I1-3p is the passenger strand of I1-5p, which was previously known. The iltv-miR-I7-3p showed a perfect match with the complementary passenger strand in contrast to other miRNA species showing imperfect complementarity with the passenger strand. The I7-3p was mapped in the replication origin (oriL) of the palindrome stem loop sequence of the ILTV genome. Expression of all ILTV miRNAs were confirmed by the end point PCR using small RNA libraries generated from either ILTV infected or uninfected control chicken embryo kidney (CEK) cells.