Before revision:  First, we found that mRNA-miRNA reciprocal regulation manifests great versatility, such as subsensitive activation, ultrasensitive and subsensitive inhibition, depending on parameters such as the miRNA recycle ratio and the mRNA-miRNA complex degradation rate constant. Second, ultrasensitivity from reciprocal mRNA-miRNA regulation contributes to generation of bistability .
After revision:  First, we found that mRNA-miRNA reciprocal regulation could manifest ultrasensitivity to subserve the generation of bistability .