Low Levels of DNA Polymerase Alpha Induce Mitotic and Meiotic Instability in the Ribosomal DNA Gene Cluster of Saccharomyces cerevisiae

The ribosomal DNA (rDNA) genes of Saccharomyces cerevisiae are located in a tandem array of about 150 repeats. Using a diploid with markers flanking and within the rDNA array, we showed that low levels of DNA polymerase alpha elevate recombination between both homologues and sister chromatids, about five-fold in mitotic cells and 30-fold in meiotic cells. This stimulation is independent of Fob1p, a protein required for the programmed replication fork block (RFB) in the rDNA. We observed that the fob1 mutation alone significantly increased meiotic, but not mitotic, rDNA recombination, suggesting a meiosis-specific role for this protein. We found that meiotic cells with low polymerase alpha had decreased Sir2p binding and increased Spo11p-catalyzed double-strand DNA breaks in the rDNA. Furthermore, meiotic crossover interference in the rDNA is absent. These results suggest that the hyper-Rec phenotypes resulting from low levels of DNA polymerase alpha in mitosis and meiosis reflect two fundamentally different mechanisms: the increased mitotic recombination is likely due to increased double-strand DNA breaks (DSBs) resulting from Fob1p-independent stalled replication forks, whereas the hyper-Rec meiotic phenotype results from increased levels of Spo11-catalyzed DSBs in the rDNA

A Comprehensive Genome-Wide Map of Autonomously Replicating Sequences in a Naive Genome

Eukaryotic chromosomes initiate DNA synthesis from multiple replication origins. The machinery that initiates DNA synthesis is highly conserved, but the sites where the replication initiation proteins bind have diverged significantly. Functional comparative genomics is an obvious approach to study the evolution of replication origins. However, to date, the Saccharomyces cerevisiae replication origin map is the only genome map available. Using an iterative approach that combines computational prediction and functional validation, we have generated a high-resolution genome-wide map of DNA replication origins in Kluyveromyces lactis. Unlike other yeasts or metazoans, K. lactis autonomously replicating sequences (KlARSs) contain a 50 bp consensus motif suggestive of a dimeric structure. This motif is necessary and largely sufficient for initiation and was used to dependably identify 145 of the up to 156 non-repetitive intergenic ARSs projected for the K. lactis genome. Though similar in genome sizes, K. lactis has half as many ARSs as its distant relative S. cerevisiae. Comparative genomic analysis shows that ARSs in K. lactis and S. cerevisiae preferentially localize to non-syntenic intergenic regions, linking ARSs with loci of accelerated evolutionary change

Pollen viability and pollen vigor

Investigations were carried out to correlate pollen viability, assessed on the basis of a fluorochromatic reaction (FCR) test, with pollen vigor, assessed on the basis of the time taken for in vitro germination in pollen grains subjected to high humidity (> 95% RH) and temperature (38°C) or storage stress of Nicotiana tabacum, Agave sp., Tradescantia virginiana, and Iris sp. Both high RH and temperature, as well as storage stresses, affected pollen vigor before affecting pollen viability. The results are discussed in the light of available data on the viability and vigor of stressed pollen and of aged seeds. The need for consideration of pollen vigor, particularly in stored pollen, the inadequacy of the methods presently used, and some of the methods suitable to assess pollen vigor are elaborated

Responses of tobacco pollen to high humidity and heat stress: viability and germinability in vitro and in vivo

Responses of pollen grains of Nicotiana tabacum to high humidity (95% RH, 4 h) and temperature (38°/45°C, 4 h) stresses were investigated. Pollen grains were subjected to only RH or only temperature, or to both of these stresses. Their viability was assessed on the basis of the fluorochromatic reaction (FCR) test, and vigour was assessed on the basis of the time taken for in vitro germination as well as on the emergence of pollen tubes through the cut end of semi-vivo implanted styles. None of the stress conditions affected pollen viability and high RH or high temperature stress did not individually affect pollen vigour. However, pollen vigour was markedly affected when both the stresses were given together. Pollen grains subjected to high RH at 38°C took a longer time to germinate in vitro and the pollen tubes emerged later from the cut end of the semi-vivo styles; division of the generative cell was also delayed. Pollen grains subjected to high RH at 45° C failed to germinate in vitro, but did germinate on the stigma. Many pollen tubes subjected to this treatment showed abnormalities, and the growth of pollen tubes in the pistil was much slower than that observed in other treatments. Pollen samples subjected to all of the stress conditions were able to induce fruit and seed set. The implications of these results on the relationship between the FCR test and viability, and between viability and vigour, especially in stressed pollen, are discussed

Genetic and serological markers to identify phenotypic subgroups in a Dutch Crohn' s disease population. Digestive & Liver Disease

Abstract Background and aims. Both genetic and microbial factors seem to play a pivotal role in the aetiopathogenesis of Crohn's disease. The CARD15 frameshift mutation might link host genetic factors and the indigenous microbial flora, since CARD15 expression is stimulated by peptidoglycan, thereby activating NF-B. It is hypothesised that CARD15 mutation carriers have defective anti-microbial reactions, resulting in more penetrating lesions and antibody responses, which are now being used as highly specific markers for Crohn's disease. The serological marker anti-Saccharomyces cerevisiae antibody directed against cell wall oligomannosidic epitopes has high specificity for Crohn's disease. Perinuclear anti-neutrophil cytoplasmic antibodies have been found in a subgroup of Crohn's disease patients, mostly with colonic involvement. Methods. We investigated the incidence of two CARD15 mutations (3020insC and 2722G > C), anti-S. cerevisiae antibody, and perinuclear anti-neutrophil cytoplasmic antibody in 108 (73F/35M) patients with Crohn's disease with a mean duration of disease since diagnosis of 16 (1-41) years in relation to their phenotype, according to the Vienna classification. Results. The prevalence of CARD15 frameshift mutation was 21%. Of all patients, 62% were anti-S. cerevisiae antibody positive, and 9% had perinuclear anti-neutrophil cytoplasmic antibodies. The prevalence of both anti-S. cerevisiae antibodies and perinuclear anti-neutrophil cytoplasmic antibodies was higher in the mutation carriers compared to non-carriers. Remarkably, all patients with a CARD15 mutation and positive anti-S. cerevisiae antibody had ileal disease. Carriership of the mutation was significantly associated with penetrating behaviour of the disease and weakly associated with stricturing behaviour. Furthermore, anti-S. cerevisiae antibody was associated with ileal disease involvement. Finally, most perinuclear anti-neutrophil cytoplasmic antibody positive patients showed ulcerative-like behaviour of disease (by means of colonic localisation). Conclusions. Genetic and serologic markers might be useful in defining patient subgroups. This may result in a more accurate prediction of disease behaviour, prognosis and therapeutic approach