Karin Schubart

Max Planck Institute of Molecular Cell Biology and Genetics, Dresden, Saxony, Germany

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Publications (5)48.53 Total impact

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    ABSTRACT: Oct1 is a ubiquitously expressed transcription factor that is induced in response to DNA damage to modulate gene expression. Herein, Oct1 deficient mouse embryonic fibroblasts were used as a model to study the importance of Oct1 in cellular stress response. Cells lacking Oct1 kept proliferating and bypassed the G(1) cell cycle arrest induced by glucose or amino acid starvation. Indeed, mTOR-mediated regulation of proliferation was abolished in Oct1(-/-) cells starved for glucose or amino acids and Oct1(-/-) cells were also insensitive to mTOR inhibition by rapamycin. Furthermore, in wild-type cells, Oct1 controls the transcription of the CDK inhibitor p27(Kip1) downstream of the mTOR pathway and Oct1-null cells failed to upregulate p27(Kip1) in response to rapamycin or glucose starvation. p27(Kip1) is required for rapamycin or nutrient starvation-induced G(1)-arrest, as p27(-/-) fibroblasts were largely insensitive to rapamycin treatment or glucose starvation. Thus, Oct1 appears to be a critical mediator of the growth arrest induced by mTOR inhibition via the control of p27(Kip1) expression.
    Cell cycle (Georgetown, Tex.) 10/2010; 9(19):3933-44. · 5.24 Impact Factor
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    ABSTRACT: Oct1 (Pou2f1) is a transcription factor of the POU-homeodomain family that is unique in being ubiquitously expressed in both embryonic and adult mouse tissues. Although its expression profile suggests a crucial role in multiple regions of the developing organism, the only essential function demonstrated so far has been the regulation of cellular response to oxidative and metabolic stress. Here, we describe a loss-of-function mouse model for Oct1 that causes early embryonic lethality, with Oct1-null embryos failing to develop beyond the early streak stage. Molecular and morphological analyses of Oct1 mutant embryos revealed a failure in the establishment of a normal maternal-embryonic interface due to reduced extra-embryonic ectoderm formation and lack of the ectoplacental cone. Oct1(-/-) blastocysts display proper segregation of trophectoderm and inner cell mass lineages. However, Oct1 loss is not compatible with trophoblast stem cell derivation. Importantly, the early gastrulation defect caused by Oct1 disruption can be rescued in a tetraploid complementation assay. Oct1 is therefore primarily required for the maintenance and differentiation of the trophoblast stem cell compartment during early post-implantation development. We present evidence that Cdx2, which is expressed at high levels in trophoblast stem cells, is a direct transcriptional target of Oct1. Our data also suggest that Oct1 is required in the embryo proper from late gastrulation stages onwards.
    Development 09/2010; 137(21):3551-60. · 6.60 Impact Factor
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    ABSTRACT: Transcription of the gene encoding the transcriptional coactivator Oct-binding factor 1 (OBF-1)/OCA-B/Bob.1 is largely restricted to B cells. During B cell development OBF-1 expression shows two peaks, one in immature B cells in the bone marrow and the other in germinal center B cells. Promoter analysis has identified a cAMP response element (CRE)-binding site present in the OBF-1 proximal promoter that is crucial for activity in B cells and for the induction of OBF-1 expression upon stimulation with CD40 ligand/IL-4. Here we address the question of how transcription of the OBF-1 gene is restricted to B cells. Surprisingly, in transient transfection assays the OBF-1 proximal promoter exhibited an equally strong activity in B and non-B cells. In contrast, upstream promoter regions displayed B cell-specific properties, partly overlapping with DNaseI hypersensitive sites identified in this study. In mice, expression of a neomycin resistance gene under the control of a Polyoma enhancer/TK promoter cassette was restricted to B cells when integrated into the OBF-1 locus, but was ubiquitous when integrated into two other loci, Oct-1 or the large subunit of RNA polymerase II.Therefore, lineage commitment of the OBF-1 gene is promoter independent and is achieved by regulating the entire locus in a B cell-specific manner.
    European Journal of Immunology 11/2003; 33(10):2864-74. · 4.97 Impact Factor
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    ABSTRACT: Oct-2 and OBF-1 (also called OCA-B or Bob-1) are B cell-specific transcription factors that bind to the conserved octamer site of immunoglobulin promoters, yet their role in immunoglobulin transcription has remained unclear. We generated mice in which the lymphoid compartment was reconstituted with cells that lack both Oct-2 and OBF-1. Even in the absence of these two transcription factors, B cells develop normally to the membrane immunoglobulin M-positive (IgM+) stage and immunoglobulin gene transcription is essentially unaffected. These observations imply that the ubiquitous factor Oct-1 plays a previously unrecognized role in the control of immunoglobulin gene transcription and suggest the existence of another, as yet unidentified, cofactor. In addition, both factors are essential for germinal center formation, although OBF-1 is more important than Oct-2 for IgG production after immunization.
    Nature Immunology 02/2001; 2(1):69-74. · 26.20 Impact Factor
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    ABSTRACT: OBF-1 is a B cell-restricted transcriptional coactivator that is recruited to octamer-containing promoters by interacting with the POU domain of Oct-1 or Oct-2. We have shown earlier that mice lacking OBF-1 were dramatically impaired in their ability to mount humoral immune responses and did not develop germinal centers in the spleen; however, they had a largely normal B cell development in the bone marrow. In this study, we demonstrate that OBF-1-deficient mice also have an early defect in B cell development and show that OBF-1-/- immature B cells are greatly impaired at the transition from the bone marrow to the spleen. In addition, when the OBF-1 mutation is combined to a mutation in the gene encoding Bruton's tyrosine kinase, a striking phenotype is observed. These double-deficient animals lack peripheral B cells and have virtually no serum Igs, thus closely resembling human X chromosome-linked agammaglobulinemia.
    The Journal of Immunology 02/2000; 164(1):18-22. · 5.52 Impact Factor