Before revision:  Second, ultrasensitivity from reciprocal mRNA-miRNA regulation contributes to generation of bistability . Furthermore, the degree of ultrasensitivity is amplified by a stronger competing mRNA (ceRNA).
After revision:  Second, ultrasensitivity from reciprocal mRNA-miRNA regulation contributes to generation of bistability when equipped with a positive feedback loop. Second, the region of bistability is expanded by a stronger competing mRNA (ceRNA).