Regulatory mechanisms. The two proposed regulatory mechanisms of functional host to miRNA relationships. (A) An antagonistic effect can be achieved by miRNA-mediated downregulation of a gene with perturbing effect on a pathway or biological process regulated by the host gene. (B) Synergistic effect by miRNA-mediated fine tuning of a target gene with common contribution of host and target gene to a pathway or biological process. Proposed corresponding gene expression patterns are shown below the two motif figures. Genes are marked by rounded rectangles, miRNAs by ellipses. Host and intronic miRNA relations are indicated by an edge with a dot. MiRNA target tuning regulation is indicated by a blank triangle, inhibition is indicated with a stop.