The incoherent and coherent feed-forward loops. Arrows mean activation, the turned over T-bars indicate repression. TF-transcription factor, miR-miRNA, Target - target protein. A: 1In - type 1 incoherent FFL, TF activates both target mRNA and miRNA synthesis. B: 1C - type 1 coherent FFL, TF represses traget mRNA and activates miRNA synthesis. C: 2In - type 2 incoherent FFL, TF represses both target mRNA and miRNA synthesis. D: 2C - type 2 coherent FFL, TF activates target mRNA and represses miRNA synthesis.