Interestingly, however, fixation of tissue samples for tissue inclusion involves the usage of formaldehyde (FA), the same reagent that is currently used to fix new cells for standard chromatin preparations. expression and other nuclear events, driving improper proliferation of malignancy cells. New technologies are beginning to allow global analyses of the epigenetic profile of the genome (the so-called epigenome) (4,5), which have revealed at an unprecedented resolution the position of both DNA and histone modifications and dramatically extended our understanding of the structural determinants of the epigenome. These technologies, based on massively parallel sequencing of DNA fragments, are being applied systematically to the study of the epigenome in model cell lines (68). In these studies, chromatin-associated DNA is usually immunoprecipitated using antibodies against specific histone PTMs and then sequenced to obtain a genome-wide map of each specific PTM (ChIP-Seq) (9). Application of these technologies to clinically derived patient samples represents the logical next step of these approaches. It would allow a better definition of the role of epigenetic alterations in human diseases and provide useful biomarkers for their management (10). Regrettably, the study of patient samples presents a number of technical hurdles. The small quantity of cells that can be obtained in most cases (such as from bioptic material) is limiting for several methodologies, although recent approaches have been explained to partially circumvent this problem (1113). Paraffin-embedded tissues, linked to individual clinical information, represent an invaluable source of clinical samples, because their preparation is indispensable for Rabbit Polyclonal to PAK2 (phospho-Ser197) the diagnosis and clinical management of the vast majority of diseases. Large archives of paraffin-embedded tissues are available in most hospitals and have been extensively utilized for DNA and RNA analyses. To preserve tissue architecture and allow sectioning for histology-based analyses, patient-derived materials are first fixed and subsequently embedded in paraffin, a procedure that is generally perceived as too harsh to preserve complex cellular structures such as chromatin. Interestingly, however, fixation of tissue samples for tissue inclusion involves the usage of formaldehyde (FA), the same reagent that is currently used to fix new cells for standard chromatin preparations. Here we statement the setup of a protocol (PAT-ChIP, for pathology tissuechromatin immunoprecipitation) that allows high-quality chromatin purification from paraffin-embedded samples for genome-wide epigenetic studies (PAT-ChIP-Seq). == Results == == Setup of a Protocol for ChIP from Paraffin-Embedded Pathology Tissues. == In standard pathology analyses, tissues derived from surgery or biopsies are cross-linked with FA at high concentrations (4%) for an extended period (usually overnight). Subsequently, fixed tissues are dehydrated and included in paraffin (Materials Thiotepa and Methods). Extraction of chromatin from tissue sections after the harsh conditions of FA fixation and paraffin embedding (FFPE) are considered a limiting step for efficient ChIP protocols, in which single-cell suspensions are cross-linked for short periods Thiotepa (1015 min) using lower concentrations of FA (1%). In the setup of a ChIP protocol for Thiotepa paraffin-embedded pathology tissues (PAT-ChIP), we used an in-house murine model of human acute promyelocytic leukemia (APL) to compare the PAT-ChIP process with the canonical ChIP assay performed on isolated cells (14). In this model, leukemic blasts invade the spleen and completely subvert its normal architecture, resulting in massive splenomegaly. Importantly, splenic tissue under these conditions is Thiotepa usually very easily minced to obtain a single-cell suspension, which can then be treated according to standard ChIP protocols. We therefore divided the spleen of each leukemic mouse into two halves that were subjected either to standard ChIP (Cells-ChIP inFig. 1Aand below), or to overnight.