TY  - JOUR
AB  - Noncycling and terminally differentiated (TD) cells display differences in radiosensitivity and DNA damage response. Unlike other TD cells, Sertoli cells express a mixture of proliferation inducers and inhibitors in vivo and can reenter the cell cycle. Being in a G1-like cell cycle stage, TD Sertoli cells are expected to repair DSBs by the error-prone nonhomologous end-joining pathway (NHEJ). Recently, we have provided evidence for the involvement of Ku-dependent NHEJ in protecting testis cells from DNA damage as indicated by persistent foci of the DNA double-strand break (DSB) repair proteins phospho-H2AX, 53BP1, and phospho-ATM in TD Sertoli cells of Ku70-deficient mice. Here, we analyzed the kinetics of 53BP1 foci induction and decay up to 12 h after 0.5 Gy gamma irradiation in DNA-PKcs-deficient (Prkdc (scid) ) and wild-type Sertoli cells. In nonirradiated mice and Prkdc (scid) Sertoli cells displayed persistent DSBs foci in around 12 % of cells and a fivefold increase in numbers of these DSB DNA damage-related foci relative to the wild type. In irradiated mice, Prkdc (scid) Sertoli cells showed elevated levels of DSB-indicating foci in 82 % of cells 12 h after ionizing radiation (IR) exposure, relative to 52 % of irradiated wild-type Sertoli cells. These data indicate that Sertoli cells respond to and repair IR-induced DSBs in vivo, with repair kinetics being slow in the wild type and inefficient in Prkdc (scid) . Applying the same dose of IR to Prdkc (-/-) and Ku (-/-) mouse embryonic fibroblast (MEF) cells revealed a delayed induction of 53BP1 DSB-indicating foci 5 min post-IR in Prdkc (-/-) cells. Inefficient DSB repair was evident 7 h post-IR in DNA-PKcs-deficient cells, but not in Ku (-/-) MEFs. Our data show that quiescent Sertoli cells repair genotoxic DSBs by DNA-PKcs-dependent NEHJ in vivo with a slower kinetics relative to somatic DNA-PKcs-deficient cells in vitro, while DNA-PKcs deficiency caused inefficient DSB repair at later time points post-IR in both conditions. These observations suggest that DNA-PKcs contributes to the fast and slow repair of DSBs by NHEJ.
AU  - Ahmed, E.A.*
AU  - Vélaz, E.*
AU  - Rosemann, M.
AU  - Gilbertz, K.P.*
AU  - Scherthan, H.*
C1  - 48528
C2  - 41138
TI  - DNA repair kinetics in SCID mice Sertoli cells and DNA-PKcs-deficient mouse embryonic fibroblasts.
JO  - Chromosoma
PY  - 2016
SN  - 0009-5915
ER  - 

TY  - JOUR
AB  - The large-scale chromatin organization of retrovirus and retroviral gene vector integration loci has attracted little attention so far. We compared the nuclear organization of transcribed integration loci with the corresponding loci on the homologous chromosomes. Loci containing gamma-retroviral gene transfer vectors in mouse hematopoietic precursor cells showed small but significant repositioning of the integration loci towards the nuclear interior. HIV integration loci in human cells showed a significant repositioning towards the nuclear interior in two out of five cases. Notably, repositioned HIV integration loci also showed chromatin decondensation. Transcriptional activation of HIV by sodium butyrate treatment did not lead to a further enhancement of the differences between integration and homologous loci. The positioning relative to splicing speckles was indistinguishable for integration and homologous control loci. Our data show that stable retroviral integration can lead to alterations of the nuclear chromatin organization, and has the potential to modulate chromatin structure of the host cell. We thus present an example where a few kb of exogenous DNA are sufficient to significantly alter the large-scale chromatin organization of an endogenous locus.
AU  - Nagel, J.*
AU  - Gross, B.*
AU  - Meggendorfer, M.
AU  - Preiss, C.*
AU  - Grez, M.*
AU  - Brack-Werner, R.
AU  - Dietzel, S.*
C1  - 8386
C2  - 29933
SP  - 353-367
TI  - Stably integrated and expressed retroviral sequences can influence nuclear location and chromatin condensation of the integration locus.
JO  - Chromosoma
VL  - 121
IS  - 4
PB  - Springer
PY  - 2012
SN  - 0009-5915
ER  - 

TY  - JOUR
AB  - Mediator (TRAP/ARC/PC2) is a large (22–28 subunit) protein complex that binds RNA polymerase II and controls transcription from class II genes. The evolutionarily conserved core of Mediator is found in all eukaryotes. It binds RNA polymerase II and is probably critical for basal transcription but it also mediates activation and repression of transcription. During evolution the complex has acquired additional species-specific subunits. These serve as an interface for regulatory factors and support specific signalling pathways. Recent mechanistic studies are consistent with the hypothesis that Mediator marks genes for binding by RNA polymerase II whereupon it subsequently activates the preinitiation complex. It is further likely that Mediator coordinates the recruitment of chromatin-modifying cofactor activities.
AU  - Blazek, E.
AU  - Mittler, G.*
AU  - Meisterernst, M.
C1  - 3701
C2  - 22892
SP  - 399-408
TI  - The mediator of RNA polymerase II.
JO  - Chromosoma
VL  - 113
IS  - 8
PY  - 2005
SN  - 0009-5915
ER  - 

TY  - JOUR
AB  - Dosage compensation in Drosophila is controlled by a complex (DCC) of proteins and noncoding RNA that binds specifically to the male X chromosome and leads to fine-tuning of transcription. Here, we employ male SL2 cells to characterize DCC function and dynamics during steady state of dosage compensation. Knocking down the key regulator of dosage compensation, male-specific-lethal 2 (MSL2), leads to loss of propagation of histone H4 lysine 16 acetylation and of the twofold elevation of transcription characteristic of the compensated male X chromosome. Surprisingly, lack of dosage compensation does not impair cell viability. Targeting of MSL2 to a reporter gene suffices to initiate dosage compensation in the cell model. Using photobleaching techniques in living cells, we found the association of MSL2 with the X chromosome to be exceptionally stable, essentially excluding dynamic redistribution of the DCC during interphase. This immobility distinguishes MSL2 from most other chromosomal proteins. Our findings have profound implications for the mechanism underlying dosage compensation and furthermore provide a new, conceptual reference of stability in an otherwise highly dynamic nuclear environment.
AU  - Straub, T.*
AU  - Neumann,M.F.*
AU  - Prestel, M.*
AU  - Kremmer, E.
AU  - Käther, Ch.*
AU  - Haass, Ch.*
C1  - 437
C2  - 23049
SP  - 352-364
TI  - Stable chromosomal association of MSL2 defines a dosage-compensated nuclear compartment.
JO  - Chromosoma
VL  - 114
IS  - 5
PY  - 2005
SN  - 0009-5915
ER  -