"Replicative stress" is one of the main factors underlying neoplasia from its early stages. Genes involved in DNA synthesis may therefore represent an underexplored source of potential prognostic markers for cancer. To this aim, we generated gene expression profiles from two independent cohorts (France, n = 206; United Kingdom, n = 117) of patients with previously untreated primary breast cancers. We report here that among the 13 human nuclear DNA polymerase genes, DNA Polymerase θ (POLQ) is the only one significantly up-regulated in breast cancer compared with normal breast tissues. Importantly, POLQ up-regulation significantly correlates with poor clinical outcome (4.3-fold increased risk of death in patients with high POLQ expression), and this correlation is independent of Cyclin E expression or the number of positive nodes, which are currently considered as markers for poor outcome. POLQ expression provides thus an additional indicator for the survival outcome of patients with high Cyclin E tumor expression or high number of positive lymph nodes. Furthermore, to decipher the molecular consequences of POLQ up-regulation in breast cancer, we generated human MRC5-SV cell lines that stably overexpress POLQ. Strong POLQ expression was directly associated with defective DNA replication fork progression and chromosomal damage. Therefore, POLQ overexpression may be a promising genetic instability and prognostic marker for breast cancer.specialized DNA replication | prognosis marker | S-phase checkpoint B esides the "replicative" DNA polymerases POLA, POLD, and POLE, which are involved in conventional DNA replication of the undamaged genome, mammalian nuclei contain 10 additional specialized DNA polymerases that play a role in replication, repair, and recombination of damaged DNA (1, 2) and thus may be of paramount importance to preserve the integrity of the genome.Specialized DNA polymerases are frequently deregulated in neoplasia (3-10). Indeed, the intracellular balance between the error-free, replicative polymerases POLA, POLD, and POLE and the error-prone, specialized DNA polymerases (POLH, POLL, POLM, POLN, POLK, POLB, POLI, POLQ, POLZ/REV3L, and REV1) appears to be of great importance for the maintenance of genome stability (11)(12)(13)(14). Here, we wondered whether misregulation of DNA polymerases could be a signature of breast cancer progression. Indeed, beside the standard classification used by pathologists, there is a clear lack of tools to accurately predict the clinical outcome of many patients.We specifically measured the expression levels of the 13 human replicative and specialized DNA polymerases in 206 breast carcinomas. We report that, differently from the replicative and the other specialized DNA polymerases, POLQ was significantly upregulated in most of the breast tumors analyzed. Such up-regulation was associated with poor clinical outcome.POLQ is an error-prone, specialized DNA polymerase that might operate during "normal" genomic replication because it bypasses some endogenous DNA lesions an...

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dDeveloping lymphocytes somatically diversify their antigen-receptor loci through V(D)J recombination. The process is associated with allelic exclusion, which results in monoallelic expression of an antigen receptor locus. Various cis-regulatory elements control V(D)J recombination in a developmentally regulated manner, but their role in allelic exclusion is still unclear. At the immunoglobulin heavy chain locus (IgH), the E enhancer plays a critical role in V(D)J recombination. We generated a mouse line with a replacement mutation in the constant region of the locus that duplicates the E enhancer and allows premature expression of the ␥3 heavy chain. Strikingly, IgM expression was completely and specifically excluded in cis from the mutant allele. This cis exclusion recapitulated the main features of allelic exclusion, including differential exclusion of variable genes. Notably, sense and antisense transcription within the distal variable domain and distal V H -DJ H recombination were inhibited. cis exclusion was established and stably maintained despite an active endogenous E enhancer. The data reveal the importance of the dynamic, developmental stage-dependent interplay between IgH locus enhancers and signaling in the induction and maintenance of allelic exclusion. Developing B and T lymphocytes have the capacity to somatically alter their genomes and diversify their antigen receptor loci through V(D)J recombination. This developmentally regulated process is initiated by the lymphoid-specific RAG1/2 complex, which recognizes conserved recombination signal sequences (RSSs) flanking the V, D, and J segments in the variable domain of antigen receptor (IgH, IgL, and TCR) loci (1, 2). V(D)J recombination correlates with chromatin modifications, germ line transcription of rearranging V, D, and J segments, and large-scale chromosome dynamics within nuclear compartments (3-5).The mouse IgH locus contains ϳ200 V H genes, which are subdivided into V H gene families. The most prominent are the distal V H genes, notably the large V HJ558 gene family, and the proximal V H genes. These are followed by a dozen D segments (ϳ60 kb), 4 J H segments (ϳ2 kb), and 8 constant genes (ϳ200 kb) (6, 7).In B lymphocytes, V(D)J assembly starts at the IgH locus, where D segments are first recombined to J H segments on both alleles. Although they have the potential to undergo V H -DJ H recombination on the two alleles, the vast majority of B lymphocytes are subject to allelic exclusion, i.e., a given B cell expresses only one IgH allele. A productive V(D)J rearrangement allows production of the heavy chain, which associates with surrogate light chains and signals an arrest of V H -DJ H recombination on the second IgH allele. If the first V H -DJ H rearrangement is not productive, then the second allele can undergo V H -DJ H recombination (1, 8). Nonetheless, in rare B cells, productive rearrangements can occur on both alleles (i.e., allelic inclusion), but only one heavy chain from only one allele can associate with surrogate light chains...