ABSTRACT: We previously reported widespread differential expression of long non-protein-coding RNAs (ncRNAs) in response to virus infection. Here, we expanded the study through small RNA transcriptome sequencing analysis of the host response to both severe acute respiratory syndrome coronavirus (SARS-CoV) and influenza virus infections across four founder mouse strains of the Collaborative Cross, a recombinant inbred mouse resource for mapping complex traits. We observed differential expression of over 200 small RNAs of diverse classes during infection. A majority of identified microRNAs (miRNAs) showed divergent changes in expression across mouse strains with respect to SARS-CoV and influenza virus infections and responded differently to a highly pathogenic reconstructed 1918 virus compared to a minimally pathogenic seasonal influenza virus isolate. Novel insights into miRNA expression changes, including the association with pathogenic outcomes and large differences between in vivo and in vitro experimental systems, were further elucidated by a survey of selected miRNAs across diverse virus infections. The small RNAs identified also included many non-miRNA small RNAs, such as small nucleolar RNAs (snoRNAs), in addition to nonannotated small RNAs. An integrative sequencing analysis of both small RNAs and long transcripts from the same samples showed that the results revealing differential expression of miRNAs during infection were largely due to transcriptional regulation and that the predicted miRNA-mRNA network could modulate global host responses to virus infection in a combinatorial fashion. These findings represent the first integrated sequencing analysis of the response of host small RNAs to virus infection and show that small RNAs are an integrated component of complex networks involved in regulating the host response to infection. IMPORTANCE: Most studies examining the host transcriptional response to infection focus only on protein-coding genes. However, mammalian genomes transcribe many short and long non-protein-coding RNAs (ncRNAs). With the advent of deepsequencing technologies, systematic transcriptome analysis of the host response, including analysis of ncRNAs of different sizes, is now possible. Using this approach, we recently discovered widespread differential expression of host long (>200 nucleotide[nt]) ncRNAs in response to virus infection. Here, the samples described in the previous report were again used, but we sequenced another fraction of the transcriptome to study very short (about 20 to 30 nt) ncRNAs. We demonstrated that virus infection also altered expression of many short ncRNAs of diverse classes. Putting the results of the two studies together, we show that small RNAs may also play an important role in regulating the host response to virus infection. The small RNA transcriptome deep sequencing analysis was performed on lung samples from our previously published study (Unique signatures of long noncoding RNA expression in response to virus infection and altered innate immune signaling , X Peng, MBio. 2010 Oct 26;1(5). pii: e00206-10.). We infected four of the eight founder mouse strains used in generating the Collaborative Cross, a recombinant inbred mouse resource for mapping complex traits (41). These strains included 129S1/SvImJ (129/S1), WSB/EiJ (WSB), PWK/PhJ (PWK), and CAST/EiJ (CAST) mice. Ten-week-old mice were intranasally infected with phosphate-buffered saline (PBS) alone or with 1X10^5 PFU of mouse adapted severe acute respiratory syndrome coronavirus (SARS-CoV; rMA15), or 500 PFU of influenza A virus strain A/Pr/8/34 (H1N1; PR8). To match the previous whole-transcriptome analysis, we performed small RNA transcriptome sequencing analysis on the same eight samples from mice with SARS-CoV infections, including one SARS-CoV rMA15-infected mouse and one matched mock-infected mouse from each of the four strains at 2 days postinfection (dpi). In addition, we sequenced the small RNA transcriptome for 12 samples obtained from influenza virus infected mice, including two PR8-infected mice and one matched mockinfected mouse from each of the four strains at 2 dpi.
