| Summary: | 碩士 === 國立陽明大學 === 生物醫學資訊研究所 === 99 === MicroRNAs (miRNAs) are endogenous small RNA molecules that can regulate gene expression at the post-transcriptional level. Being a kind of primary gene regulators in metazoans, miRNAs were considered to have great impact on gene regulatory networks. However, the preferences and properties of miRNA regulation on transcription network hierarchy have not been well investigated. We first collected transcription factor (TF) and target gene relationships from online databases and constructed the transcriptional regulatory networks for four species (human, mouse, rat, and fly). Next, we divided each network into four levels: top, middle, bottom, and non-TF (non-regulator), based on their positions in regulatory hierarchies. Finally, the miRNA-target relationships were integrated into the networks. Thus, the topological properties of miRNA regulation on those hierarchies could be analyzed. We found that miRNAs tend to regulate middle level in transcriptional network hierarchy, suggesting a dense cross-regulation of TFs and miRNAs in the middle level. Such cross-regulation may enable the cooperatively control of downstream gene expression. In addition, we also observed that miRNAs have preference to regulate the feed-forward loop structure in the hierarchy, implying that the feed-forward loop structure in regulatory network may have more complex behaviors than we thought before. Our study provides a novel view for miRNA regulation in transcriptional regulatory network. These identified characteristics may provide useful clues for further experiments on metazoan gene regulation model.
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