Actin nucleators safeguard replication forks by limiting nascent strand degradation.

Accurate genome replication is essential for all life and a key mechanism of disease prevention, underpinned by the ability of cells to respond to replicative stress (RS) and protect replication forks. These responses rely on the formation of Replication Protein A (RPA)-single stranded (ss) DNA complexes, yet this process remains largely uncharacterized. Here, we establish that actin nucleation-promoting factors (NPFs) associate with replication forks, promote efficient DNA replication and facilitate association of RPA with ssDNA at sites of RS. Accordingly, their loss leads to deprotection of ssDNA at perturbed forks, impaired ATR activation, global replication defects and fork collapse. Supplying an excess of RPA restores RPA foci formation and fork protection, suggesting a chaperoning role for actin nucleators (ANs) (i.e. Arp2/3, DIAPH1) and NPFs (i.e, WASp, N-WASp) in regulating RPA availability upon RS. We also discover that ß-actin interacts with RPA directly in vitro, and in vivo a hyper-depolymerizing ß-actin mutant displays a heightened association with RPA and the same dysfunctional replication phenotypes as loss of ANs/NPFs, which contrasts with the phenotype of a hyper-polymerizing ß-actin mutant. Thus, we identify components of actin polymerization pathways that are essential for preventing ectopic nucleolytic degradation of perturbed forks by modulating RPA activity.

Actin nucleators safeguard replication forks by limiting nascent strand degradation.

Accurate genome replication is essential for all life and a key mechanism of disease prevention, underpinned by the ability of cells to respond to replicative stress (RS) and protect replication forks. These responses rely on the formation of Replication Protein A (RPA)-single stranded (ss) DNA complexes, yet this process remains largely uncharacterized. Here we establish that actin nucleation-promoting factors (NPFs) associate with replication forks, promote efficient DNA replication and facilitate association of RPA with ssDNA at sites of RS. Accordingly, their loss leads to deprotection of ssDNA at perturbed forks, impaired ATR activation, global replication defects and fork collapse. Supplying an excess of RPA restores RPA foci formation and fork protection, suggesting a chaperoning role for actin nucleators (ANs) (i.e., Arp2/3, DIAPH1) and NPFs (i.e, WASp, N-WASp) in regulating RPA availability upon RS. We also discover that ß-actin interacts with RPA directly in vitro , and in vivo a hyper-depolymerizing ß-actin mutant displays a heightened association with RPA and the same dysfunctional replication phenotypes as loss of ANs/NPFs, which contrasts with the phenotype of a hyper-polymerizing ß-actin mutant. Thus, we identify components of actin polymerization pathways that are essential for preventing ectopic nucleolytic degradation of perturbed forks by modulating RPA activity.

RECON syndrome is a genome instability disorder caused by mutations in the DNA helicase RECQL1.

Despite being the first homolog of the bacterial RecQ helicase to be identified in humans, the function of RECQL1 remains poorly characterized. Furthermore, unlike other members of the human RECQ family of helicases, mutations in RECQL1 have not been associated with a genetic disease. Here, we identify 2 families with a genome instability disorder that we have named RECON (RECql ONe) syndrome, caused by biallelic mutations in the RECQL gene. The affected individuals had short stature, progeroid facial features, a hypoplastic nose, xeroderma, and skin photosensitivity and were homozygous for the same missense mutation in RECQL1 (p.Ala459Ser), located within its zinc binding domain. Biochemical analysis of the mutant RECQL1 protein revealed that the p.A459S missense mutation compromised its ATPase, helicase, and fork restoration activity, while its capacity to promote single-strand DNA annealing was largely unaffected. At the cellular level, this mutation in RECQL1 gave rise to a defect in the ability to repair DNA damage induced by exposure to topoisomerase poisons and a failure of DNA replication to progress efficiently in the presence of abortive topoisomerase lesions. Taken together, RECQL1 is the fourth member of the RecQ family of helicases to be associated with a human genome instability disorder.

The surgical management of acute type A aortic dissection: Current options and future trends.

OBJECTIVE: Acute type A aortic dissection (ATAAD) is a catastrophic condition that can be fatal if not treated immediately. We sought to examine the literature and identify evidence behind each method of surgical intervention. METHOD: A comprehensive electronic literature search was done to identify the articles that reported outcomes and discussed surgical techniques in ATAAD. No limits were placed on timing or type of the articles; all results are summarized in a narrative manner within each relevant section. RESULTS: Different units have different approaches for extensive ATAAD; experienced and high-volume units tend to perform aortic root and total-arch replacement, whereas others tend to perform only hemiarch replacement. The evidence shows no significant differences in long-term outcomes. Frozen elephant trunk and endovascular repair play key roles in managing the rest of the aortic dissection that involve the thoracic aorta, and the evidence evolve with their impact on false lumen patency. CONCLUSION: The management of ATAAD is tailored by individual surgeons and unit experience to save lives. Future directions for reducing mortality depend on effective early recognition and accessibility to centralized specialist centers with experience in a wide range of surgical techniques.

Accelerated infliximab infusions for inflammatory bowel disease improve effectiveness.

AIM: To study the safety and effectiveness associated with accelerated infliximab infusion protocols in patients with inflammatory bowel disease (IBD). METHODS: Original protocols and infusion rates were developed for the administration of infliximab over 90-min and 60-min. Then the IBD patients on stable maintenance infliximab therapy were offered accelerated infusions. To be eligible for the study, patients needed a minimum of four prior infusions. An initial infusion of 90-min was given to each patient; those tolerating the accelerated infusion were transitioned to a 60-min infusion protocol at their next and all subsequent visits. Any patient having significant infusion reactions would be reverted to the standard 120-min protocol. A change in a patient's dose mandated a single 120-min infusion before accelerated infusions could be administered again. RESULTS: The University of Virginia Medical Center's Institutional Review Board approved this study. Fifty IBD patients treated with infliximab 5 mg/kg, 7.5 mg/kg and 10 mg/kg were offered accelerated infusions. Forty-six patients consented to participate in the study. Nineteen (41.3%) were female, five (10.9%) were African American and nine (19.6%) had ulcerative colitis. The mean age was 42.6 years old. Patients under age 18 were excluded. Ten patients used immunosuppressive drugs concurrently out of which six were taking azathioprine, three were taking 6-mercaptopurine and one was taking methotrexate. One of the 46 study patients used corticosteroid therapy for his IBD. Seventeen of the patients used prophylactic medications prior to receiving infusions; six patients received corticosteroids as pre-medication. Four patients had a history of distant transfusion reactions to infliximab. These reactions included shortness of breath, chest tightness, flushing, pruritus and urticaria. These patients all took prophylactic medications before receiving infusions. 46 patients (27 males and 19 females) received a total of fifty 90-min infusions and ninety-three 60-min infusions. No infusion reactions were reported. There were no adverse events, including drug-related infections. None of the patients developed cancer of any type during the study timeframe. Total cost savings for administration of the both 90-min and 60-min accelerated infusions compared to standard 120-min infusions was estimated to be $53 632 ($116 965 vs $63 333, P = 0.001). One hundred and eighteen hours were saved in the administration of the accelerated infusions (17 160 min vs 10 080 min, P = 0.001). In the study population, overweight females [body mass index (BMI) > 25.00 kg/m(2)] were found to have statistically higher BMIs than overweight males (mean BMI 35.07 ± 2.66 kg/m(2) vs 30.08 ± 0.99 kg/m(2), P = 0.05), finding which is of significance since obesity was described as being one of the risk factors for Crohn's disease. CONCLUSION: We are the first US group to report substantial cost savings, increased safety and patient satisfaction associated with accelerated infliximab infusion.

Differential selection according to the degree of cheating in a status signal.

The maintenance of honesty in a badge-of-status system is not fully understood, despite numerous empirical and theoretical studies. Our experiment examined the relationship between a status signal and winter survival, and the long-term costs of cheating, by manipulating badge size in male house sparrows, Passer domesticus. The effect of badge-size manipulation on survival was complex owing to the significant interactions between the treatments and original (natural) badge size, and between the treatments and age classes (yearlings and older birds). Nevertheless, in the experimental (badge-enlargement) group, males with originally large badges had increased winter survival, while males with originally small badges had decreased survival. This indicates that differential selection can act on a trait according to the degree of cheating.