Rad17 phosphorylation is required for claspin recruitment and Chk1 activation in response to replication stress

The ATR-mediated checkpoint is not only critical for responding to genotoxic stress but also essential for cell proliferation. The RFC-related checkpoint protein Rad17, a phosphorylation substrate of ATR, is critical for ATR-mediated checkpoint signaling and cell survival. Here, we show that phosphorylation of Rad17 by ATR is important for genomic stability and restraint of S phase but is not essential for cell survival. The phosphomutant Rad17AA exhibits distinct defects in hydroxyurea- (HU) and ultraviolet- (UV) induced Chk1 activation, indicating that separate Rad17 functions are required differently in response to different types of replication interference. Although cells expressing Rad17AA can initiate Chk1 phosphorylation after HU treatment, they fail to sustain Chk1 phosphorylation after withdrawal of HU and are profoundly sensitive to HU. Importantly, we found that phosphorylated Rad17 interacts with Claspin and regulates its phosphorylation. These findings reveal a phosphorylation-dependent function of Rad17 in an ATR-Rad17-Claspin-Chk1-signaling cascade that responds to specific replication stress.     

Copine A is expressed in prestalk cells and regulates slug phototaxis and thermotaxis in developing Dictyostelium

Copines are calcium-dependent membrane-binding proteins found in many eukaryotic organisms. We are studying the function of copines using the model organism, Dictyostelium discoideum. When under starvation conditions, Dictyostelium cells aggregate into mounds that become migrating slugs, which can move toward light and heat before culminating into a fruiting body. Previously, we showed that Dictyostelium cells lacking the copine A (cpnA) gene are not able to form fruiting bodies and instead arrest at the slug stage. In this study, we compared the slug behavior of cells lacking the cpnA gene to the slug behavior of wild-type cells. The slugs formed by cpnA- cells were much larger than wild-type slugs and exhibited no phototaxis and negative thermotaxis in the same conditions that wild-type slugs exhibited positive phototaxis and thermotaxis. Mixing as little as 5% wild-type cells with cpnA- cells rescued the phototaxis and thermotaxis defects, suggesting that CpnA plays a specific role in the regulation of the production and/or release of a signaling molecule. Reducing extracellular levels of ammonia also partially rescued the phototaxis and thermotaxis defects of cpnA- slugs, suggesting that CpnA may have a specific role in regulating ammonia signaling. Expressing the lacZ gene under the cpnA promoter in wild-type cells indicated cpnA is preferentially expressed in the prestalk cells found in the anterior part of the slug, which include the cells at the tip of the slug that regulate phototaxis, thermotaxis, and the initiation of culmination into fruiting bodies. Our results suggest that CpnA plays a role in the regulation of the signaling pathways, including ammonia signaling, necessary for sensing and/or orienting toward light and heat in the prestalk cells of the Dictyostelium slug.     

Independent effects of ocean warming versus acidification on the growth,survivorship and physiology of two Acropora corals

Coral Reefs - Climate change is the greatest threat to coral reef ecosystems. Importantly, gradual changes in seawater chemistry compounds upon increasing temperatures leading to declines in...     

Genetic background modifies CNS‐mediated sensorimotor decline in the AD‐BXD mouse model of genetic diversity in Alzheimer's disease

Many patients with Alzheimer's dementia (AD) also exhibit noncognitive symptoms such as sensorimotor deficits, which can precede the hallmark cognitive deficits and significantly impact daily activities and an individual's ability to live independently. However, the mechanisms underlying sensorimotor dysfunction in AD and their relationship with cognitive decline remains poorly understood, due in part to a lack of translationally relevant animal models. To address this, we recently developed a novel model of genetic diversity in Alzheimer's disease, the AD‐BXD genetic reference panel. In this study, we investigated sensorimotor deficits in the AD‐BXDs and the relationship to cognitive decline in these mice. We found that age‐ and AD‐related declines in coordination, balance and vestibular function vary significantly across the panel, indicating genetic background strongly influences the expressivity of the familial AD mutations used in the AD‐BXD panel and their impact on motor function. Although young males and females perform comparably regardless of genotype on narrow beam and inclined screen tasks, there were significant sex differences in aging‐ and AD‐related decline, with females exhibiting worse decline than males of the same age and transgene status. Finally, we found that AD motor decline is not correlated with cognitive decline, suggesting that sensorimotor deficits in AD may occur through distinct mechanisms. Overall, our results suggest that AD‐related sensorimotor decline is strongly dependent on background genetics and is independent of dementia and cognitive deficits, suggesting that effective therapeutics for the entire spectrum of AD symptoms will likely require interventions targeting each distinct domain involved in the disease.     

Augmented sympathetic tone alters muscle metabolism with exercise: lack of evidence for functional sympatholysis

Shoemaker, J. Kevin, Prasant Pandey, Michael D. Herr, DavidH. Silber, Qing X. Yang, Michael B. Smith, Kristen Gray, and LawrenceI. Sinoway. Augmented sympathetic tone alters muscle metabolismwith exercise: lack of evidence for functional sympatholysis. J. Appl. Physiol. 82(6):1932-1938, 1997.It is unclear whether sympathetic tone opposesdilator influences in exercising skeletal muscle. We examined highlevels of sympathetic tone, evoked by lower body negative pressure(LBNP, 60 mmHg) on intramuscular pH and phosphocreatine (PCr)levels (³¹P-nuclear magnetic resonance spectroscopy) duringgraded rhythmic handgrip (30 contractions/min; ~17, 34, 52 and 69%maximal voluntary contraction). Exercise was performedwith LBNP and without LBNP (Control). At the end of exercise, LBNPcaused lower levels of muscle pH (6.59 ± 0.09) comparedwith Control (6.78 ± 0.05; P < 0.05). PCr recovery, an index of mitochondrial respiration, was lessduring the recovery phase of the LBNP trial. Exercise mean arterialpressure was not altered by LBNP. The protocols were repeated withmeasurements of forearm blood flow velocity and deep venous samples(active forearm) of hemoglobin (Hb) saturation, pH, and lactate. WithLBNP, mean blood velocity was reduced at rest, during exercise, andduring recovery compared with Control (P < 0.05). Also, venous Hbsaturation and pH levels during exercise and recovery were lower withLBNP and lactate was higher compared with Control(P < 0.05). We concludethat LBNP enhanced sympathetic tone and reduced oxygen transport. Athigh workloads, there was a greater reliance on nonoxidativemetabolism. In other words, sympatholysis did not occur.

     

Impairment in Task-Specific Modulation of Muscle Coordination Correlates with the Severity of Hand Impairment following Stroke

Significant functional impairment of the hand is commonly observed in stroke survivors. Our previous studies suggested that the inability to modulate muscle coordination patterns according to task requirements may be substantial after stroke, but these limitations have not been examined directly. In this study, we aimed to characterize post-stroke impairment in the ability to modulate muscle coordination patterns across tasks and its correlation with hand impairment. Fourteen stroke survivors, divided into a group with severe hand impairment (8 subjects) and a group with moderate hand impairment (6 subjects) according to their clinical functionality score, participated in the experiment. Another four neurologically intact subjects participated in the experiment to serve as a point of comparison. Activation patterns of nine hand and wrist muscles were recorded using surface electromyography while the subjects performed six isometric tasks. Patterns of covariation in muscle activations across tasks, i.e., muscle modules, were extracted from the muscle activation data. Our results showed that the degree of reduction in the inter-task separation of the multi-muscle activation patterns was indicative of the clinical functionality score of the subjects (mean value = 26.2 for severely impaired subjects, 38.1 for moderately impaired subjects). The values for moderately impaired subjects were much closer to those of the impaired subjects (mean value = 46.1). The number of muscle modules extracted from the muscle activation patterns of a subject across six tasks, which represents the degree of motor complexity, was found to be correlated with the clinical functionality score (R = 0.68). Greater impairment was also associated with a change in the muscle module patterns themselves, with greater muscle coactivation. A substantial reduction in the degrees-of-freedom of the multi-muscle coordination post-stroke was apparent, and the extent of the reduction, assessed by the stated metrics, was strongly associated with the level of clinical impairment.     

Quantify patient-specific coronary material property and its impact on stress/strain calculations using in vivo IVUS data and 3D FSI models: a pilot study

Biomechanics and Modeling in Mechanobiology - Computational models have been used to calculate plaque stress and strain for plaque progression and rupture investigations. An intravascular...     

Molecular vehicles for targeted drug delivery

Targeted drug delivery by cell-specific cytokines and antibodies promises greater drug efficacy and reduced side effects. We describe a novel strategy for assembly of drug delivery vehicles that does not require chemical modification of targeting proteins. The strategy relies on a noncovalent binding of standardized "payload" modules to targeting proteins expressed with a "docking" tag. The payload modules are constructed by linking drug carriers to an adapter protein capable of binding to a docking tag. Using fragments of bovine ribonuclease A as an adapter protein and a docking tag, we have constructed vascular endothelial growth factor (VEGF) based vehicles for gene delivery and for liposome delivery. Assembled vehicles displayed remarkable selectivity in drug delivery to cells overexpressing VEGF receptors. We expect that our strategy can be employed for targeted delivery of many therapeutic or imaging agents by different recombinant targeting proteins.