Both endonucleolytic and exonucleolytic cleavage mediate ITS1 removal during human ribosomal RNA processing

Human ribosome production is up-regulated during tumorogenesis and is defective in many genetic diseases (ribosomopathies). We have undertaken a detailed analysis of human precursor ribosomal RNA (pre-rRNA) processing because surprisingly little is known about this important pathway. Processing in internal transcribed spacer 1 (ITS1) is a key step that separates the rRNA components of the large and small ribosomal subunits. We report that this was initiated by endonuclease cleavage, which required large subunit biogenesis factors. This was followed by 3′ to 5′ exonucleolytic processing by RRP6 and the exosome, an enzyme complex not previously linked to ITS1 removal. In contrast, RNA interference–mediated knockdown of the endoribonuclease MRP did not result in a clear defect in ITS1 processing. Despite the apparently high evolutionary conservation of the pre-rRNA processing pathway and ribosome synthesis factors, each of these features of human ITS1 processing is distinct from those in budding yeast. These results also provide significant insight into the links between ribosomopathies and ribosome production in human cells.     

Threshold response of Madagascar's littoral forest to sea-level rise

Aim Coastal biodiversity hotspots are globally threatened by sea‐level rise. As such it is important to understand how ecosystems resist, respond and adapt to sea‐level rise. Using pollen, geochemistry, charcoal and diatom records in conjunction with previously published palaeoclimatic records, we investigated the mechanism, interactions and ecosystem response and resilience of Madagascar's littoral forest to late Holocene sea‐level rise. Location Sediment sequences were collected along the south‐east coast of Madagascar in two adjacent habitats in Mandena; the highly diverse littoral forest fragment and species‐poor Erica‐matrix. Methods We used a multi‐proxy approach to investigate the relative influence of environmental changes on the littoral ecosystem. We reconstructed past vegetation and fire dynamics over the past 6500 years at two sites in the littoral forest using fossil pollen and macrofossil charcoal contained in sedimentary sequences. Alongside these records we reconstructed past marine transgressions from the same sedimentary sequences using geochemical analyses, and a salinity and drought index through the analysis of fossil diatoms. Results Our findings indicated that it was the synergistic effect of sea‐level rise coupled with rainfall deficits that triggered a threshold event with a switch from two types of littoral forest (an open Uapaca forest and a closed littoral forest fragment) to an Erica–Myrica heath/grassland occurring in approximately less than 100 years. Resilience to sea‐level rise differed in the two adjacent habitats, suggesting that the littoral forest fragment was more resilient to the impacts of sea‐level change and aridity than the open Uapaca woodland. Conclusions We demonstrated that the littoral ecosystem was influenced by late Holocene sea‐level rise and climatic desiccation. While climate change‐integrated conservation strategies address the effects of climate change on species distribution and dispersal, our work suggests that more attention should be paid to the impacts of interactive climatic variables that affect ecosystem thresholds.     

Low-dose Ad26.COV2.S protection against SARS-CoV-2 challenge in rhesus macaques

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Mannitol Does Not Enhance Tobramycin Killing of Pseudomonas aeruginosa in a Cystic Fibrosis Model System of Biofilm Formation

Cystic Fibrosis (CF) is a human genetic disease that results in the accumulation of thick, sticky mucus in the airways, which results in chronic, life-long bacterial biofilm infections that are difficult to clear with antibiotics. Pseudomonas aeruginosa lung infection is correlated with worsening lung disease and P. aeruginosa transitions to an antibiotic tolerant state during chronic infections. Tobramycin is an aminoglycoside currently used to combat lung infections in individuals with CF. While tobramycin is effective at eradicating P. aeruginosa in the airways of young patients, it is unable to completely clear the chronic P. aeruginosa infections in older patients. A recent report showed that co-addition of tobramycin and mannitol enhanced killing of P. aeruginosa grown in vitro as a biofilm on an abiotic surface. Here we employed a model system of bacterial biofilms formed on the surface of CF-derived airway cells to determine if mannitol would enhance the antibacterial activity of tobramycin against P. aeruginosa grown on a more clinically relevant surface. Using this model system, which allows the growth of robust biofilms with high-level antibiotic tolerance analogous to in vivo biofilms, we were unable to find evidence for enhanced antibacterial activity of tobramycin with the addition of mannitol, supporting the observation that this type of co-treatment failed to reduce the P. aeruginosa bacterial load in a clinical setting.     

An apoptosis-inducing genotoxin differentiates heterozygotic carriers for Werner helicase mutations from wild-type and homozygous mutants

Immortalized B lymphocytes from Werner syndrome subjects are shown to be hypersensitive to 4-nitroquinoline-1-oxide (4NQO), supporting earlier work on T lymphocytes. We also show that B cell lines from clinically normal heterozygous carriers exhibit sensitivities to this genotoxic agent, which are intermediate to those of wild-type and homozygous mutants. 4NQO is shown to induce an apoptotic response. These data encourage research on DNA repair with such cell lines and raise the question of an enhanced sensitivity of the relatively prevalent heterozygous carriers to certain environmental genotoxic agents. Received: 21 April 1997 / Accepted: 25 July 1997