  miRNAs serve as crucial post-transcriptional regulators in various essential
cell fate decision. However, the contribution of the mRNA-miRNA mutual
regulation to bistability is not fully understood. Here, we built a set of
mathematical models of mRNA-miRNA interactions and systematically analyzed the
sensitivity of response curves under various conditions. First, we found that
mRNA-miRNA reciprocal regulation could manifest ultrasensitivity to subserve
the generation of bistability when equipped with a positive feedback loop.
Second, the region of bistability is expanded by a stronger competing mRNA
(ceRNA). Interesting, bistability can be emerged without feedback loop if
multiple miRNA binding sites exist on a target mRNA. Thus, we demonstrated the
importance of simple mRNA-miRNA reciprocal regulation in cell fate decision.
