Research Report 2010 - MDC

Above: Tip of chromosom3L showing the Z4 in interbands red (IIF) andthe DNA in blue. Inserts indicate the chromatid organisation in bands(30 nm fiber) and interbands (10 nm fiber) respectively. Below: Schemeof the Z4-complex with Chriz- (C), Z4- (Z), MBD-R2- (M) and other yetuncharacterized proteins that results in recruitment of the H3S10kinase Jil-1 and H3S10 phosphorylation (yellow flag) followed by otherchromatin modifications like H3K4 trimethylation (red flag).ments that insulate nearby regulatory elements or thespreading of adjacent heterochromatin. Thus, besidesfor scientific curiosity, the knowledge of chromosomaldomain structure and their boundaries is of immediatemedical importance, in particular in gene therapy.Formation of boundaries is part of a concept, thateukaryotic genomes are organized into functionallyindependent chromosomal domains. A well knownchromosomal domain is the globin domain in man,mouse and chicken whose boundary function essentiallyrequires the CTCF protein. The Drosophila homologuedCTCF is found at a restricted number of interbandson polytene chromosomes and is required forboundary formation in homeotic gene clusters. It interactswith the protein CP190 present at band interbandboundaries At some sites CP190 is essential for dCTCFchromosomal binding. dCTCF and CP190 binding wasmapped genome-wide by ChIP on Chip experimentsand found to be correlated to active promoters andinsulators.On Drosophila polytene chromosomes chromosomaldomains differing in their degree of condensationbecome apparent as a conserved pattern of dark bands(chromatids as >30 nm fibers) and light interbands(chromatids as ~10 nm fibers). The pattern is conservedbetween tissues, suggesting a constitutive chromosomaldomain organisation established and maintainedby chromatin boundaries. By localization, isolating andcharacterizing DNA sequences from band/interbandunits, their associated proteins and histone modificationswe try to understand the process of chromosomaldomain formation. Mutation of the interband specificzinc finger protein Z4 results in a dramatic loss ofband/interband structure, presumably by affecting themaintenance of chromosomal boundaries. The Z4 proteinis complexed with other interband proteins likethose organizing dosage compensation on the X chromosomesand the histone kinase Jil-1 [Gan PhD thesisHumboldt University 2009]. Tethering Jil-1 kinase inchromatin results in local decondensation and Z4-mutations affect interband specific histone H3S10phosphorylation and H3K4 trimethylation. Z4 interactsin a protein complex with the novel chromodomainproteins Chriz and MBD-R2. Chriz is required for Jil-1 andZ4 binding, H3S10 interphase phosphorylation and themaintenance of chromosome structure [Gan PhD thesisHumboldt University 2009]. The DNA regionrequired for Z4/Chriz complex binding was mapped onpolytene chromosomes by high resolution in situhybridization and by ChIP on chromatin of diploid cellswe could show that the complex binds to the sameregion in these cells too, suggesting its general role in aconstituting a chromatin structure that is sharedbetween cells of different tissues.Selected PublicationsBartkuhn M, Straub T, Herold M, Herrmann M, Rathke C, Saumweber H,Gilfillan GD, Becker PB, Renkawitz R. (2009) Active promoters and insulatorsare marked by the centrosomal protein 190. EMBO J. 2009 28, 877-888.Mohan, M., Bartkuhn, M., Herold, M., Philippen, A., Heinl, N., Leers, J., White,R. A. H., Renkawitz-Pohl, R., Saumweber, H., and Renkawitz, R. (2007) EMBOJ 26, 4203-4214-Mendjan, S, Taipale, M, Kind, J, Holz, H, Gebhard, P, Schelder, M, Vermeulen,M, Buscaino, A, Duncan, K, Mueller, J, Wilm, M, Stunnenberg, H,Saumweber, H and Akhtar, A (2006) Nucleoporins are involved in thetranscriptional regulation of dosage compensation in Drosophila. MolCell 21, 1-13.Gortchakov, A., Eggert, H., Gan, M., Mattow, J., Zhimulev, I.F., Saumweber,H. (2005) Chriz, a chromodomain protein specific for the interbands ofDrosophila melanogaster. Chromosoma 114, 54-66.Eggert, H., Gortchakov, A, Saumweber H. (2004) Identification of theDrosophila interband-specific protein Z4 as a DNA binding zinc-fingerprotein determining chromosomal structure. J. Cell Sci. 117, 4253-4264.Cancer Research 107