Figure for the reviewAdvances in myelofibrosis: a clinical case approach published in the October edition (2013) of Haematologica. It shows the regulation of transcription by two types of chromatin modifying agents. HDAC inhibitors (HDACI) inhibit the enzymatic activity of HDACs which result in hyperacetylation of histones. DNA methyltransferase inhibitors (DNMTI) inhibit the methylation of DNA sequences by inhibiting the catalytic activity of DNMT. Increased acetylation of histones and reduction in DNA promoter site methylation allow for transcription of genes that result in a variety of different biological effects, including growth and cell cycle arrest, cellular differentiation, inhibition of angiogenesis, apoptosis, and immune surveillance.