gene 2 Nerve cells Neuron-specific enhancer P2 T Ex2Ex3 Ex4I3I2 Cell-specific gene expression gene 1 P1 T Ex1Ex2 Ex3I2I1 Ex1 I1 Skin cell-specific enhancer TF gene 2 P2 T Ex2Ex3 Ex4I3I2 gene 1 P1 T Ex1Ex2 Ex3I2I1 Ex1 I1 Skin cell-specific enhancer S Neuron-specific enhancer TF Skin cells Cell-specific gene expression: histone pattern! 1. Type of transcription factor expressed in a cell 2. The accessibility of the regulatory region of a gene

Steroid hormone activation GRE: glucocorticoid response element GRE DNA cytoplasm Nucleus glucocorticoid receptor inhibitor (hsp90) steroid Signal transduction

Interferon-γ activation RE: response element IFN: interferon JAK: Janus activated kinase STAT-1  : transcription factor RE DNA cytoplasm nucleus IFN-γ receptor JAK kinase IFN-γ STAT-1  P P Signal transduction

RNA interference – Dicing Dicer Slicer RISC RISC* (activated) mRNA RNase Helicase siRNAs (21-23 base pairs) siRNA: small interfering RNA RISC: RNAi silencing complex RISC*: activated RISC Slicer: it cleaves mRNA RNase: ribonuclease Double-stranded RNA 1

Dicer siRNAs RNA-dependent RNA polymerase Amplified double- stranded RNA mRNA many siRNAs Dicer RNA interference – amplification Double-stranded RNA siRNA: small interfering RNA RISC: RNAi silencing complex RISC*: activated RISC Slicer: it cleaves mRNA RNase: ribonuclease 2