Bone marrow failure and developmental delay caused by mutations in poly(A)-specific ribonuclease (PARN).

BACKGROUND: Deadenylation regulates RNA function and fate. Poly(A)-specific ribonuclease (PARN) is a deadenylase that processes mRNAs and non-coding RNA. Little is known about the biological significance of germline mutations in PARN. METHODS: We identified mutations in PARN in patients with haematological and neurological manifestations. Genomic, biochemical and knockdown experiments in human marrow cells and in zebrafish have been performed to clarify the role of PARN in the human disease. RESULTS: We identified large monoallelic deletions in PARN in four patients with developmental delay or mental illness. One patient in particular had a severe neurological phenotype, central hypomyelination and bone marrow failure. This patient had an additional missense mutation on the non-deleted allele and severely reduced PARN protein and deadenylation activity. Cells from this patient had impaired oligoadenylation of specific H/ACA box small nucleolar RNAs. Importantly, PARN-deficient patient cells manifested short telomeres and an aberrant ribosome profile similar to those described in some variants of dyskeratosis congenita. Knocking down PARN in human marrow cells and zebrafish impaired haematopoiesis, providing further evidence for a causal link with the human disease. CONCLUSIONS: Large monoallelic mutations of PARN can cause developmental/mental illness. Biallelic PARN mutations cause severe bone marrow failure and central hypomyelination.

Primary Care Physicians' Knowledge, Perceptions, and Comfort Level in Managing Patients Fasting in Ramadan.

Background: Once a year, Muslims fast from dawn to sunset during the month of Ramadan. While fasting has many positive health implications, it may pose risks to individuals with underlying health issues. Despite the exemption from fasting for those who are ill, many Muslims with chronic conditions choose to fast. It is unclear how many Muslim patients receive counseling on fasting. As such, the purpose of this pilot project was to assess the knowledge, perception, and comfort level of primary care physicians (PCPs) at Dalhousie University's Department of Family Medicine in managing patients choosing to fast during Ramadan. Methods: A 16-item anonymous, self-administered, structured online survey was distributed to PCPs with an academic affiliation with the Department of Family Medicine at Dalhousie University. Participants rated their level of comfort, objective knowledge, and perceptions of managing patients fasting in Ramadan. Results: Many PCPs perceived the importance of understanding Ramadan fasting and its relevance to their patients' health, however, they did not have adequate knowledge about the matter. The majority of PCPs felt they received inadequate training in this area and did not feel comfortable counseling and managing the health of these patients. Conclusions: The findings of this study have outlined a knowledge gap that exists within our PCP community and will help inform and prioritize educational needs and direct efforts to ensure safe patient management during Ramadan.

Development and validation of a sensitive and specific HPLC assay of cladribine for pharmacokinetics studies in rats.

PURPOSE: To develop and validate a sensitive and specific HPLC assay for cladribine (CdA) in plasma for pharmacokinetic studies in rats. METHODS: CdA and the internal standard AZT were purchased from Sigma-Aldrich Chem. The HPLC system consisted of a Shimadzu LC-9A pump, a 3 im, 250 x 2.0 mm I.D. high speed C18 column (Jupitertrade mark), preceded by a 5 im 4 4 mm I.D. C18 guard column (Licrocarttrade mark), an Agilent Model 1050 UV-VIS detector and a 3395 Integrator. The mobile phase was made up of 0.01M KH2PO4 (pH 5): methanol: acetonitrile 90:5:5). The system was operated at ambient temperature with a flow rate of 0.3 mL/min, and UV wavelength at 265 nm, and an operating pressure of ca. 1.56 kpsi. Extraction of cladribine and AZT from plasma was achieved by solid phase extraction using 100 mg/mL C18 SPE columns Extra-septrade mark). The assay was validated for sensitivity, precision, specificity and application for pharmacokinetic study in rats. RESULTS: Under these conditions, the average retention times of CdA and AZT were 13.5 and 21 min, respectively, and recoveries were between 80 - 95%. Standard curve constructed from plasma standards was linear from 0.1 ug/mL to 1 ug/mL with regression coefficient (r2) 0.99 or greater. Sensitivity assessed by on column injection was < 1 ng. Using a 50-uL plasma sample size, the mean intra assay variations 0.1 ug/mL were 7%, and inter assay variations over a period of 3 months for 5 separate batches were less than 20%. The assay was used to study a single dose pharmacokinetic study of CdA in rats after a 2 mg/kg subcutaneous injection. CONCLUSION: The described HPLC assay has adequate sensitivity and specificity to study pharmacokinetics of CdA in rats, and could be adapted also to clinical pharmacokinetic studies.

A Shigella flexneri virulence plasmid encoded factor controls production of outer membrane vesicles.

Shigella spp. use a repertoire of virulence plasmid-encoded factors to cause shigellosis. These include components of a Type III Secretion Apparatus (T3SA) that is required for invasion of epithelial cells and many genes of unknown function. We constructed an array of 99 deletion mutants comprising all genes encoded by the virulence plasmid (excluding those known to be required for plasmid maintenance) of Shigella flexneri. We screened these mutants for their ability to bind the dye Congo red: an indicator of T3SA function. This screen focused our attention on an operon encoding genes that modify the cell envelope including virK, a gene of partially characterized function. We discovered that virK is required for controlled release of proteins to the culture supernatant. Mutations in virK result in a temperature-dependent overproduction of outer membrane vesicles (OMVs). The periplasmic chaperone/protease DegP, a known regulator of OMV production in Escherichia coli (encoded by a chromosomal gene), was found to similarly control OMV production in S. flexneri. Both virK and degP show genetic interactions with mxiD, a structural component of the T3SA. Our results are consistent with a model in which VirK and DegP relieve the periplasmic stress that accompanies assembly of the T3SA.

Hace1 controls ROS generation of vertebrate Rac1-dependent NADPH oxidase complexes.

The Hace1-HECT E3 ligase is a tumor suppressor that ubiquitylates the activated GTP-bound form of the Rho family GTPase Rac1, leading to Rac1 proteasomal degradation. Here we show that, in vertebrates, Hace1 targets Rac1 for degradation when Rac1 is localized to the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase holoenzyme. This event blocks de novo reactive oxygen species generation by Rac1-dependent NADPH oxidases, and thereby confers cellular protection from reactive oxygen species-induced DNA damage and cyclin D1-driven hyper-proliferation. Genetic inactivation of Hace1 in mice or zebrafish, as well as Hace1 loss in human tumor cell lines or primary murine or human tumors, leads to chronic NADPH oxidase-dependent reactive oxygen species elevation, DNA damage responses and enhanced cyclin D1 expression. Our data reveal a conserved ubiquitin-dependent molecular mechanism that controls the activity of Rac1-dependent NADPH oxidase complexes, and thus constitutes the first known example of a tumor suppressor protein that directly regulates reactive oxygen species production in vertebrates.