In the past, most research on gene regulation has focused on transcriptional regulation and post-translational regulation. Recently, the post-transcriptional regulation by small non-coding RNAs has drawn much attention. This mode of regulation was found in both prokaryotes and eukaryotes. In this study, the authors integrate transcriptional and post-transcriptional regulation into four different kinds of microRNA-mediated motifs and investigate the mechanism of microRNAs regulation from the viewpoints of dynamics. Theoretical analysis and numerical simulations show that all the four motifs exhibit strong robustness to external and stochastic perturbations.