Conditions of appreciable influence of microRNA on a large number of target mRNAs.

In eukaryotic cells, messenger RNAs (mRNAs) can be regulated by microRNAs (miRNAs) via association and subsequent degradation. Each miRNA is now believed to potentially have hundreds of target mRNAs. Employing a generic kinetic model with physically reasonable parameters, we have quantified the mutual influence of miRNA and mRNAs in the case when the number of target mRNAs is large (e.g., 100). The decrease in the population of mRNAs due to interaction with miRNA is found to be appreciable (about 1.5-2-fold) only if the rate of the miRNA synthesis is very high. In the absence of the miRNA-mRNA interaction, it should be sufficient to maintain the miRNA population in the order of 10(4) per cell. In addition, the average mRNA population should not be too high (lower than or comparable to 100 for each kind of mRNA). For lower miRNA synthesis rates, the significant influence of miRNA on mRNAs is only possible provided that the average mRNA population is very low (of the order of 10). These general findings are complemented by a brief discussion of some relevant recent experimental results.