J Biol Chem. determine a new compaction pathway of mammalian pericentric heterochromatin relying on Tip60 that might be dependent on BRD2 recruitment by H4K12 acetylation. We propose that the underexpression of Tip60 observed in many human being tumors can promote genetic instability via defective pericentric heterochromatin. Intro The structure of mammalian heterochromatin around centromeres, that is, in pericentric regions of each chromosome, takes on a central part in genomic integrity: it silences the manifestation of deleterious sequences, such as transposons; prevents deleterious recombination events that can happen in repeated sequences; and allows right chromosome Harmane segregation (Elgin and Grewal, 2003 ). Therefore the factors involved in the formation of such condensed constructions or in their maintenance are crucial for genetic stability. Among these factors, Suv39H1 and Suv39H2 proteins methylate histone H3 on lysine 9, advertising the recruitment of heterochromatin protein 1 (HP1; Peters harbor histone H4 acetylated on K12 (Turner ideals of the difference between the two cell populations are indicated above the graphs. Note that natural ideals of DAPI CV strongly assorted from one experiment to another, depending on the settings utilized for image acquisition. (C) Suv39H?value of the difference between the two cell populations is indicated above the graphs. (C) Suv39H?(Zhou 0.05) or not normally ( 0.05) distributed. Because at least one of the lists was not normally distributed, we applied the MannCWhitneyCWilcoxon test. Immunofluorescence Cells seeded on coverslips were fixed in 4% paraformaldehyde and incubated with main anti-HP1 and secondary anti-mouse (Euromedex, Souffelweyersheim, France) antibodies before becoming stained with DAPI, mounted, and observed, as previously explained (Escaffit em et?al. /em , 2007 ). RNA extraction, reverse transcription, and quantitative PCR analysis RNA extraction were performed with TRIzol reagent and then treated Harmane with DNase I and DNase Z for 1.5 h at 37C. DNases were then precipitated and eliminated with lysis answer and MPC protein precipitation reagent from Epicentre (Tebu-Bio, Le Perrey-en-Yvelines, France). After reverse transcription using random primers and AMV reverse transcriptase (Promega, Madison, WI), quantitative PCR (qPCR) analysis was performed using iQ qPCR blend and a real-time PCR device (Bio-Rad, Marnes-la-Coquette, France) according to the manufacturers instructions. qPCRs were performed in triplicate. Chromatin immunoprecipitation Chromatin immunoprecipitation experiments were performed essentially as explained. Briefly, cells were fixed Harmane in 1% formaldehyde (15 min), and glycine was added to block the reaction. Nuclei were prepared and sonicated to generate DNA fragments with lengths between 500 and 1500 foundation pairs. After preclearing and obstructing steps, immunoprecipitations were performed over night with specific antibodies or without antibody as bad control. After centrifugation to remove background, recovery of the immune complexes was performed from the incubation of samples with a mixture of clogged protein A/protein G beads (Sigma-Aldrich) on a rotating wheel (1 h at 4C). After washing, the DNACprotein cross-link was reversed by the addition of RNase A to the samples (30 min at 37C) and heating under agitation at 70C over night. After proteinase K digestion (1.5 h), DNA was purified using a GFX DNA Purification kit (GE Healthcare, Vandoeuvre-les-Nancy, France) and then quantified by qPCR using iQ qPCR blend and a real-time PCR device (Bio-Rad) according to the manufacturers instructions. qPCRs were performed in triplicate. Supplementary Material Supplemental Materials: Click here to view. Acknowledgments We say thanks to Thomas Jenuwein for providing cell models and Saadi Khochbin and all members of the Trouche lab for helpful discussions. We especially say thanks to Catherine Chailleux for technical help in automatized imaging analysis, as well as Marion Aguirrebengoa for statistical analysis Nr4a1 of these data. Operetta high-throughput analysis, cytometry, and fluorescence imaging microscopy were performed in the Toulouse Rseau.