Loss of Caenorhabditis elegans BRCA1 promotes genome stability during replication in smc-5 mutants.

DNA damage by ultraviolet (UV) light poses a risk for mutagenesis and a potential hindrance for cell cycle progression. Cells cope with UV-induced DNA damage through two general strategies to repair the damaged nucleotides and to promote cell cycle progression in the presence of UV-damaged DNA. Defining the genetic pathways and understanding how they function together to enable effective tolerance to UV remains an important area of research. The structural maintenance of chromosomes (SMC) proteins form distinct complexes that maintain genome stability during chromosome segregation, homologous recombination, and DNA replication. Using a forward genetic screen, we identified two alleles of smc-5 that exacerbate UV sensitivity in Caenorhabditis elegans. Germ cells of smc-5-defective animals show reduced proliferation, sensitivity to perturbed replication, chromatin bridge formation, and accumulation of RAD-51 foci that indicate the activation of homologous recombination at DNA double-strand breaks. Mutations in the translesion synthesis polymerase polh-1 act synergistically with smc-5 mutations in provoking genome instability after UV-induced DNA damage. In contrast, the DNA damage accumulation and sensitivity of smc-5 mutant strains to replication impediments are suppressed by mutations in the C. elegans BRCA1/BARD1 homologs, brc-1 and brd-1. We propose that SMC-5/6 promotes replication fork stability and facilitates recombination-dependent repair when the BRC-1/BRD-1 complex initiates homologous recombination at stalled replication forks. Our data suggest that BRC-1/BRD-1 can both promote and antagonize genome stability depending on whether homologous recombination is initiated during DNA double-strand break repair or during replication stalling.

Genome maintenance and transcription integrity in aging and disease.

DNA damage contributes to cancer development and aging. Congenital syndromes that affect DNA repair processes are characterized by cancer susceptibility, developmental defects, and accelerated aging (Schumacher et al., 2008). DNA damage interferes with DNA metabolism by blocking replication and transcription. DNA polymerase blockage leads to replication arrest and can gives rise to genome instability. Transcription, on the other hand, is an essential process for utilizing the information encoded in the genome. DNA damage that interferes with transcription can lead to apoptosis and cellular senescence. Both processes are powerful tumor suppressors (Bartek and Lukas, 2007). Cellular response mechanisms to stalled RNA polymerase II complexes have only recently started to be uncovered. Transcription-coupled DNA damage responses might thus play important roles for the adjustments to DNA damage accumulation in the aging organism (Garinis et al., 2009). Here we review human disorders that are caused by defects in genome stability to explore the role of DNA damage in aging and disease. We discuss how the nucleotide excision repair system functions at the interface of transcription and repair and conclude with concepts how therapeutic targeting of transcription might be utilized in the treatment of cancer.

Next Generation Sequencing of miRNAs - Strategies, Resources and Methods.

miRNAs constitute a family of small RNA species that have been demonstrated to play a central role in regulating gene expression in many organisms. With the advent of next generation sequencing, new opportunities have arisen to identify and quantify miRNAs and elucidate their function. The unprecedented sequencing depth reached by next generation sequencing technologies makes it possible to get a comprehensive miRNA landscape but also poses new challenges for data analysis. We provide an overview of strategies used for miRNA sequencing, public miRNA resources, and useful methods and tools that are available for data analysis.