Multiple Regulatory Mechanisms to Inhibit Untimely Initiation of DNA Replication Are Important for Stable Genome Maintenance

Genomic instability is a hallmark of human cancer cells. To prevent genomic instability, chromosomal DNA is faithfully duplicated in every cell division cycle, and eukaryotic cells have complex regulatory mechanisms to achieve this goal. Here, we show that untimely activation of replication origins during the G1 phase is genotoxic and induces genomic instability in the budding yeast Saccharomyces cerevisiae. Our data indicate that cells preserve a low level of the initiation factor Sld2 to prevent untimely initiation during the normal cell cycle in addition to controlling the phosphorylation of Sld2 and Sld3 by cyclin-dependent kinase. Although untimely activation of origin is inhibited on multiple levels, we show that deregulation of a single pathway can cause genomic instability, such as gross chromosome rearrangements (GCRs). Furthermore, simultaneous deregulation of multiple pathways causes an even more severe phenotype. These findings highlight the importance of having multiple inhibitory mechanisms to prevent the untimely initiation of chromosome replication to preserve stable genome maintenance over generations in eukaryotes

Ethnobotany of the Himalayas: The Nepal, Bhutanese, and Tibetan Himalayas

Plant use in the Nepal Himalaya, recorded in the 6500-year-old text of the Rigveda, ranks among the earliest uses of medicinal plants (Malla and Shakya 1984). Another early account, the Saushrut Nighantu, is perhaps the oldest Nepali medicinal plant book, which was produced during the rule of the Great King Mandev in the fifth century, and records the uses of 278 Nepalese medicinal plants (Subedi and Tiwari 2000; Gewali and Awale 2008). Later compendia of herbal pharmacopoeias such as Chandra Nighantu and Nepali Nighantu published in the nineteenth and twentieth centuries, respectively, described 750 plants and 971 articles (IUCN Nepal 2004)

Topoisomerase 1 suppresses replication stress and genomic instability by preventing interference between replication and transcription.

International audienceTopoisomerase I (Top1) is a key enzyme acting at the interface between DNA replication, transcription and mRNA maturation. Here, we show that Top1 suppresses genomic instability in mammalian cells by preventing conflicts between transcription and DNA replication. Using DNA combing and ChIP-on-chip, we found that Top1-deficient cells accumulate stalled replication forks and chromosome breaks in S phase and that breaks occur preferentially at gene-rich regions of the genome. Strikingly, these phenotypes were suppressed by preventing the formation of RNA-DNA hybrids (R-loops) during transcription. Moreover, these defects could be mimicked by depletion of the splicing factor ASF/SF2, which interacts functionally with Top1. Taken together, these data indicate that Top1 prevents replication fork collapse by suppressing the formation of R-loops in an ASF/SF2-dependent manner. We propose that interference between replication and transcription represents a major source of spontaneous replication stress, which could drive genomic instability during early stages of tumorigenesis