Luminal-like breast tumor cells express estrogen receptor ␣ (ER␣),

BackgroundMYC is a key transcription factor involved in central cellular processes such as regulation of the cell cycle, histone acetylation and ribosomal biogenesis. It is overexpressed in the majority of human tumors including aggressive B-cell lymphoma. Especially Burkitt lymphoma (BL) is a highlight example for MYC overexpression due to a chromosomal translocation involving the c-MYC gene. However, no genome-wide analysis of MYC-binding sites by chromatin immunoprecipitation (ChIP) followed by next generation sequencing (ChIP-Seq) has been conducted in BL so far.Methodology/Principal FindingsChIP-Seq was performed on 5 BL cell lines with a MYC-specific antibody giving rise to 7,054 MYC-binding sites after bioinformatics analysis of a total of approx. 19 million sequence reads. In line with previous findings, binding sites accumulate in gene sets known to be involved in the cell cycle, ribosomal biogenesis, histone acetyltransferase and methyltransferase complexes demonstrating a regulatory role of MYC in these processes. Unexpectedly, MYC-binding sites also accumulate in many B-cell relevant genes. To assess the functional consequences of MYC binding, the ChIP-Seq data were supplemented with siRNA- mediated knock-downs of MYC in BL cell lines followed by gene expression profiling. Interestingly, amongst others, genes involved in the B-cell function were up-regulated in response to MYC silencing.Conclusion/SignificanceThe 7,054 MYC-binding sites identified by our ChIP-Seq approach greatly extend the knowledge regarding MYC binding in BL and shed further light on the enormous complexity of the MYC regulatory network. Especially our observations that (i) many B-cell relevant genes are targeted by MYC and (ii) that MYC down-regulation leads to an up-regulation of B-cell genes highlight an interesting aspect of BL biology.

Mice with targeted genetic alterations are the most effective tools for deciphering organismal gene function. We generated an ENU-based parallel C3HeB/FeJ sperm and DNA archive characterized by a high probability to identify allelic variants of target genes as well as high efficiencies in allele retrieval and model revitalization. Our archive size of over 17,000 samples contains approximately 340,000 independent alleles (20 functional mutations per individual sample). Based on an estimated number of approximately 30,000 mouse genes, the parallel sperm/DNA archive should permit the identification and recovery of ten or more alleles per average target gene which translates to a calculated 99% success rate in the discovery of five allelic variants for any given average gene. The low rate of unrelated ENU-induced passenger mutations has no practical impact on the analysis of the allele-specific phenotype at the G3 generation because of dilution and free segregation of such unrelated passenger mutations. To date 39 mouse models representing 33 different genes have been recovered from our archive using in vitro fertilization techniques. The generation time for a murine model heterozygous for a mutation in a gene of interest is less than 2 months, i.e., three to four times faster compared with current embryonic stem-cell-based technologies. We conclude that ENU-based targeted mutagenesis is a powerful tool for the fast and high-throughput production of murine gene-specific models for biomedical research.

Pine is known to respond to ozone by the induction of stilbene synthase (STS) and cinnamyl alcohol dehydrogenase (CAD) activities. Here we describe the in¯uence of ozone on STS and CAD transcript levels, as well as on the amounts of actin mRNA and chlorophyll a/b-binding protein (cab) mRNA in needles of young Scots pine (Pinus sylvestris L.) seedlings. A single ozone pulse of 0.3 lL á L A1 for 8 h resulted in transient increases in STS, and CAD mRNA levels. In contrast, actin and cab transcript levels were reduced. Treatment of Scots pine seedlings with ozone (0.3 lL á L A1 , 8 h á d A1 ) over a period of 12.5 d resulted in a constant high CAD mRNA level. In contrast STS transcripts were transiently induced over 6 d under these conditions. These results indicate selective ozone responses by the two genes. Compared with results for ozone fumigation alone, combined ozone/UV-B treatment led to a slightly higher increase in STS mRNA in primary needles, as well as in cotyledons. This points to an additive eect by the two stressors. In-situ hybridization with STS and CAD antisense mRNAs revealed an enhanced uniform labeling of mesophyll cells in tissue cross-sections of ozone-treated needles, whereas in the epidermal cell layer the amount of silver grains was unaltered in comparison with controls.Abbreviations: cab chlorophyll a/b-binding protein; CAD cinnamyl alcohol dehydrogenase; STS stilbene synthase