Competitive endogenous RNAs (ceRNAs). (a) Transcripts A (blue) and B (red) are a pair of ceRNAs sharing microRNA response sequences (MREs, boxes) for two microRNAs (blue and yellow). The two ceRNAs can influence the expression level of each other through competitive microRNA binding (dotted lines). MicroRNAs are represented as line structures bound to the MREs. (b) These transcripts co-regulate each other's expression level through competition for shared microRNA (yellow) binding on MREs. In the steady state (middle), ceRNAs and targeting microRNAs are in equilibrium. Overexpression of transcript A (left) reduces the concentration of free microRNAs, thereby increasing expression of transcript B. Decreased expression of transcript A (right) leads to an increase of available microRNAs to bind transcript B and consequently suppresses its expression level. Figure adapted, with permission, from .