Microbial community changes in a female rat model of Rett syndrome

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder that is predominantly caused by alterations of the methyl-CpG-binding protein 2 (MECP2) gene. Disease severity and the presence of comorbidities such as gastrointestinal distress vary widely across affected individuals. The gut microbiome has been implicated in neurodevelopmental disorders such as Autism Spectrum Disorder (ASD) as a regulator of disease severity and gastrointestinal comorbidities. Although the gut microbiome has been previously characterized in humans with RTT compared to healthy controls, the impact of MECP2 mutation on the composition of the gut microbiome in animal models where the host and diet can be experimentally controlled remains to be elucidated. By evaluating the microbial community across postnatal development as behavioral symptoms appear and progress, we have identified microbial taxa that are differentially abundant across developmental timepoints in a zinc-finger nuclease rat model of RTT compared to WT. We have additionally identified p105 as a key translational timepoint. Lastly, we have demonstrated that fecal SCFA levels are not altered in RTT rats compared to WT rats across development. Overall, these results represent an important step in translational RTT research.

Can digital technology help reduce smoke exposure and protect health in extreme air quality events?

Background

In the southern hemisphere summer of 2019-2020, Australia experienced its most severe bushfire season on record. Smoke from fires affected 80% of the population, with large exceedances of the Australian National Air Quality Standard for particulate air pollution recorded in all major population centres during this period. We examined if emerging and innovative digital technology can assist extreme smoke-affected populations to reduce their exposure and protect their health.

Methods

AirRater is a free smartphone app that tracks air quality and user symptoms in near real-time. We distributed an online survey to over 13,000 app users to assess how they used this information during the 2019-20 bushfire season, and if the app was helpful in decision-making around reducing personal smoke exposure.

Results

We received responses from 1732 users (13.3%). Respondents reported that the app was highly useful, supporting informed decisions regarding daily activities during the smoke-affected period. Commonly reported activities supported by information provided through the app were staying inside (76%), rescheduling or planning outdoor activities (64%), changing locations to less affected areas (29%) and informing decisions on medication use (15%).

Conclusions

Smartphone apps enable users to reduce smoke exposure and protect their health by providing individual-level and location-specific data. Furthermore, digital technology such as AirRater provides the potential to provide insight into the community impacts of environmental hazards such as bushfire smoke.

Key messages

Smartphone apps enable users to reduce their smoke exposure and protect their health. These emerging technologies can help public health authorities to understand the community impact of environmental hazards.

A Fermi-degenerate three-dimensional optical lattice clock

Strontium optical lattice clocks have the potential to simultaneously interrogate millions of atoms with a high spectroscopic quality factor of 4 × 10¹⁷ Previously, atomic interactions have forced a compromise between clock stability, which benefits from a large number of atoms, and accuracy, which suffers from density-dependent frequency shifts. Here we demonstrate a scalable solution that takes advantage of the high, correlated density of a degenerate Fermi gas in a three-dimensional (3D) optical lattice to guard against on-site interaction shifts. We show that contact interactions are resolved so that their contribution to clock shifts is orders of magnitude lower than in previous experiments. A synchronous clock comparison between two regions of the 3D lattice yields a measurement precision of 5 × 10^-19 in 1 hour of averaging time.

Anchoring of protein kinase A by ERM (ezrin-radixin-moesin) proteins is required for proper netrin signaling through DCC (deleted in colorectal cancer)

Netrin-1, acting through its principal receptor DCC (deleted in colorectal cancer), serves as an axon guidance cue during neural development and also contributes to vascular morphogenesis, epithelial migration, and the pathogenesis of some tumors. Several lines of evidence suggest that netrin-DCC signaling can regulate and be regulated by the cAMP-dependent protein kinase, PKA, although the molecular details of this relationship are poorly understood. Specificity in PKA signaling is often achieved through differential subcellular localization of the enzyme by interaction with protein kinase A anchoring proteins (AKAPs). Here, we show that AKAP function is required for DCC-mediated activation of PKA and phosphorylation of cytoskeletal regulatory proteins of the Mena/VASP (vasodilator-stimulated phosphoprotein) family. Moreover, we show that DCC and PKA physically interact and that this association is mediated by the ezrin-radixin-moesin (ERM) family of plasma membrane-actin cytoskeleton cross-linking proteins. Silencing of ERM protein expression inhibits DCC-PKA interaction, DCC-mediated PKA activation, and phosphorylation of Mena/VASP proteins as well as growth cone morphology and neurite outgrowth. Finally, although expression of wild-type radixin partially rescued growth cone morphology and tropism toward netrin in ERM-knockdown cells, expression of an AKAP-deficient mutant of radixin did not fully rescue growth cone morphology and switched netrin tropism from attraction to repulsion. These data support a model in which ERM-mediated anchoring of PKA activity to DCC is required for proper netrin/DCC-mediated signaling.

An optical lattice clock with accuracy and stability at the 10(-18) level

Progress in atomic, optical and quantum science has led to rapid improvements in atomic clocks. At the same time, atomic clock research has helped to advance the frontiers of science, affecting both fundamental and applied research. The ability to control quantum states of individual atoms and photons is central to quantum information science and precision measurement, and optical clocks based on single ions have achieved the lowest systematic uncertainty of any frequency standard. Although many-atom lattice clocks have shown advantages in measurement precision over trapped-ion clocks, their accuracy has remained 16 times worse. Here we demonstrate a many-atom system that achieves an accuracy of 6.4 × 10(-18), which is not only better than a single-ion-based clock, but also reduces the required measurement time by two orders of magnitude. By systematically evaluating all known sources of uncertainty, including in situ monitoring of the blackbody radiation environment, we improve the accuracy of optical lattice clocks by a factor of 22. This single clock has simultaneously achieved the best known performance in the key characteristics necessary for consideration as a primary standard-stability and accuracy. More stable and accurate atomic clocks will benefit a wide range of fields, such as the realization and distribution of SI units, the search for time variation of fundamental constants, clock-based geodesy and other precision tests of the fundamental laws of nature. This work also connects to the development of quantum sensors and many-body quantum state engineering (such as spin squeezing) to advance measurement precision beyond the standard quantum limit.

Comparison of two independent Sr optical clocks with 1×10(-17) stability at 10(3) s

Many-particle optical lattice clocks have the potential for unprecedented measurement precision and stability due to their low quantum projection noise. However, this potential has so far never been realized because clock stability has been limited by frequency noise of optical local oscillators. By synchronously probing two ^{87}Sr lattice systems using a laser with a thermal noise floor of 1×10(-15), we remove classically correlated laser noise from the intercomparison, but this does not demonstrate independent clock performance. With an improved optical oscillator that has a 1×10(-16) thermal noise floor, we demonstrate an order of magnitude improvement over the best reported stability of any independent clock, achieving a fractional instability of 1×10(-17) in 1000 s of averaging time for synchronous or asynchronous comparisons. This result is within a factor of 2 of the combined quantum projection noise limit for a 160 ms probe time with ~10(3) atoms in each clock. We further demonstrate that even at this high precision, the overall systematic uncertainty of our clock is not limited by atomic interactions. For the second Sr clock, which has a cavity-enhanced lattice, the atomic-density-dependent frequency shift is evaluated to be -3.11×10(-17) with an uncertainty of 8.2×10(-19).

Protein kinase A activity and anchoring are required for ovarian cancer cell migration and invasion

Epithelial ovarian cancer (EOC) is the deadliest of the gynecological malignancies, due in part to its clinically occult metastasis. Therefore, understanding the mechanisms governing EOC dissemination and invasion may provide new targets for antimetastatic therapies or new methods for detection of metastatic disease. The cAMP-dependent protein kinase (PKA) is often dysregulated in EOC. Furthermore, PKA activity and subcellular localization by A-kinase anchoring proteins (AKAPs) are important regulators of cytoskeletal dynamics and cell migration. Thus, we sought to study the role of PKA and AKAP function in both EOC cell migration and invasion. Using the plasma membrane-directed PKA biosensor, pmAKAR3, and an improved migration/invasion assay, we show that PKA is activated at the leading edge of migrating SKOV-3 EOC cells, and that inhibition of PKA activity blocks SKOV-3 cell migration. Furthermore, we show that while the PKA activity within the leading edge of these cells is mediated by anchoring of type-II regulatory PKA subunits (RII), inhibition of anchoring of either RI or RII PKA subunits blocks cell migration. Importantly, we also show--for the first time--that PKA activity is up-regulated at the leading edge of SKOV-3 cells during invasion of a three-dimensional extracellular matrix and, as seen for migration, inhibition of either PKA activity or AKAP-mediated PKA anchoring blocks matrix invasion. These data are the first to demonstrate that the invasion of extracellular matrix by cancer cells elicits activation of PKA within the invasive leading edge and that both PKA activity and anchoring are required for matrix invasion. These observations suggest a role for PKA and AKAP activity in EOC metastasis.

Protein kinase A regulates 3-phosphatidylinositide dynamics during platelet-derived growth factor-induced membrane ruffling and chemotaxis

Spatial regulation of the cAMP-dependent protein kinase (PKA) is required for chemotaxis in fibroblasts; however, the mechanism(s) by which PKA regulates the cell migration machinery remain largely unknown. Here we report that one function of PKA during platelet-derived growth factor (PDGF)-induced chemotaxis was to promote membrane ruffling by regulating phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) dynamics. Inhibition of PKA activity dramatically altered membrane dynamics and attenuated formation of peripheral membrane ruffles in response to PDGF. PKA inhibition also significantly decreased the number and size of PIP(3)-rich membrane ruffles in response to uniform stimulation and to gradients of PDGF. This ruffling defect was quantified using a newly developed method, based on computer vision edge-detection algorithms. PKA inhibition caused a marked attenuation in the bulk accumulation of PIP(3) following PDGF stimulation, without effects on PI3-kinase (PI3K) activity. The deficits in PIP(3) dynamics correlated with a significant inhibition of growth factor-induced membrane recruitment of endogenous Akt and Rac activation in PKA-inhibited cells. Simultaneous inhibition of PKA and Rac had an additive inhibitory effect on growth factor-induced ruffling dynamics. Conversely, the expression of a constitutively active Rac allele was able to rescue the defect in membrane ruffling and restore the localization of a fluorescent PIP(3) marker to membrane ruffles in PKA-inhibited cells, even in the absence of PI3K activity. These data demonstrate that, like Rac, PKA contributes to PIP(3) and membrane dynamics independently of direct regulation of PI3K activity and suggest that modulation of PIP(3)/3-phosphatidylinositol (3-PI) lipids represents a major target for PKA in the regulation of PDGF-induced chemotactic events.

Differential effects of Usp14 and Uch-L1 on the ubiquitin proteasome system and synaptic activity

The ubiquitin proteasome pathway has been implicated in the pathogenesis of many neurodegenerative diseases, and alterations in two different deubiquitinating enzymes, Uch-L1 and Usp14, result in neurological phenotypes in mice. We identified a new mutation in Uch-L1 and compared the roles of Uch-L1 and Usp14 in the ubiquitin proteasome system. Deficiencies in either Uch-L1 or Usp14 result in decreased levels of ubiquitin, suggesting that they both regulate ubiquitin stability in the nervous system. However, the effect of ubiquitin depletion on viability and onset of symptoms is more severe in the Usp14-deficient mice, and changes in hippocampal synaptic transmission were only observed in Usp14-deficient mice. In addition, while Usp14 appears to function at the proteasome, Uch-L1 deficiency resulted in up-regulation of lysosomal components, indicating that Uch-L1 and Usp14 may differentially affect the ubiquitin proteasome system and synaptic activity by regulating different pools of ubiquitin in the cell.

Efficacy and safety of dirlotapide in the management of obese dogs evaluated in two placebo-controlled, masked clinical studies in North America

Dirlotapide was evaluated in the management of obesity in dogs in two multicenter, clinical studies in North America. A total of 335 obese dogs of various breeds were randomized to dirlotapide or placebo in a 2:1 ratio. Dirlotapide was administered orally once daily to dogs at an initial dose of 0.05 mg/kg, increased after 14 days to 0.1 (study B, label dose) or 0.2 mg/kg (study A) and then adjusted according to individual weight loss at 28-day intervals. Dogs were examined and weighed, and body condition scores (BCSs) were recorded every 28 days. Study A had three consecutive phases: weight loss (16 weeks, day 0-112); weight management (12 weeks); and post-treatment (8 weeks). Study B had a weight loss phase only. For dirlotapide-treated dogs, mean weight loss by day 112 was 11.8-14.0% compared with 3.0-3.9% for placebo (P = 0.0001). In study A, weight losses for dirlotapide were 19.3% after 12 weeks of weight management and 16.7% (regain of 3.4%) by 8 weeks after dirlotapide was discontinued. In both studies, dogs in both treatments had emesis, lethargy, anorexia, diarrhea, and mildly elevated hepatic transaminase activity, that resolved spontaneously with time. These were experienced more frequently with dirlotapide. Improved activity levels and BCS for >50% dogs were reported with dirlotapide. Dirlotapide was safe and effective in the reduction and management of body weight in obese dogs.

Biologic activity of dirlotapide, a novel microsomal triglyceride transfer protein inhibitor, for weight loss in obese dogs

Dirlotapide is a novel microsomal triglyceride transfer protein inhibitor intended for the treatment and management of obesity in dogs. The biologic effects of dirlotapide, weight loss, decreased food intake, increased fecal fat, decreased serum cholesterol, and body composition, were evaluated in a controlled, blinded study. Sixteen obese beagles were randomized to treatment with placebo (n = 4) or dirlotapide (n = 12) following a 2-week acclimation period in which baseline data were collected. The dirlotapide dose, adjusted to produce weight loss for 3 months and then stabilize body weight for 1 month (weight management), produced a significant difference (expressed as a percentage of baselines) in weekly weight loss, food intake, fecal fat, serum cholesterol concentration, and body composition (measured by dual energy X-ray absorptiometry) compared with placebo treatment (P < 0.05). The initial dirlotapide dosage of 0.5 mg/kg (10 times the initial label dose) resulted in a high rate of weight loss (3.3% weekly) and anorexia, emesis, and loose stools for some dogs. A 25% dose reduction (mean dosage: 0.36 mg/kg) followed by biweekly 25% dose adjustments based on individual weight loss, produced 1-2% weekly weight loss and total weight loss of 18.8% in 12 weeks at a final mean dosage of 0.41 mg/kg (range: 0.15-0.60); a dosage range of 0.10-0.34 mg/kg stabilized body weight. Body weight changes for placebo-treated dogs were -0.8% to +0.9% weekly; total weight gain during the weight loss phase was 10.6%. No apparent change in food intake, percentage of fecal fat, and serum cholesterol was observed in the placebo group. Food intake and body weight increased when dirlotapide was discontinued. Dirlotapide produced weight loss by both reducing appetite (about 90% of the weight loss activity) and by increasing fecal fat excretion (about 10% of the weight loss activity).

Differential distribution of Kir4.1 in spinal cord astrocytes suggests regional differences in K+ homeostasis

Neuronal activity in the spinal cord results in extracellular potassium accumulation that is significantly higher in the dorsal horn than in the ventral horn. This is suggestive of differences in K(+) clearance, widely thought to involve diffusional K(+) uptake by astrocytes. We previously identified the inward rectifying K(+) channel Kir4.1 as the major K(+) conductance in spinal cord astrocytes in situ and hence hypothesized that different expression levels of Kir4.1 may account for the observed differences in potassium dynamics in spinal cord. Our results with immunohistochemical staining demonstrated highest Kir4.1 channel expression in the ventral horn and very low levels of Kir4.1 in the apex of the dorsal horn. Western blots from tissue of these two regions similarly confirmed much lower levels of Kir4.1 in the apex of the dorsal horn. Whole cell patch-clamp recordings from astrocytes in rat spinal cord slices also showed a difference in inwardly rectifying currents in these two regions. However, no statistical difference in either fast-inactivating (Ka) or delayed rectifying potassium currents (Kd) was observed, suggesting these differences were specific to Kir currents. Importantly, when astrocytes in each region were challenged with high [K(+)](o), astrocytes from the dorsal horn showed significantly smaller (60%) K(+) uptake currents than astrocytes from the ventral horn. Taken together, these data support the conclusion that regional differences in astrocytic expression of Kir4.1 channels result in marked changes in potassium clearance rates in these two regions of the spinal cord.

Functional expression of Kir4.1 channels in spinal cord astrocytes

Spinal cord astrocytes (SCA) have a high permeability to K+ and hence have hyperpolarized resting membrane potentials. The underlying K+ channels are believed to participate in the uptake of neuronally released K+. These K+ channels have been studied extensively with regard to their biophysics and pharmacology, but their molecular identity in spinal cord is currently unknown. Using a combination of approaches, we demonstrate that channels composed of the Kir4.1 subunit are responsible for mediating the resting K+ conductance in SCA. Biophysical analysis demonstrates astrocytic Kir currents as weakly rectifying, potentiated by increasing [K+]o, and inhibited by micromolar concentrations of Ba2+. These currents were insensitive to tolbutemide, a selective blocker of Kir6.x channels, and to tertiapin, a blocker for Kir1.1 and Kir3.1/3.4 channels. PCR and Western blot analysis show prominent expression of Kir4.1 in SCA, and immunocytochemistry shows localization Kir4.1 channels to the plasma membrane. Kir4.1 protein levels show a developmental upregulation in vivo that parallels an increase in currents recorded over the same time period. Kir4.1 is highly expressed throughout most areas of the gray matter in spinal cord in vivo and recordings from spinal cord slices show prominent Kir currents. Electrophysiological recordings comparing SCA of wild-type mice with those of homozygote Kir4.1 knockout mice confirm a complete and selective absence of Kir channels in the knockout mice, suggesting that Kir4.1 is the principle channel mediating the resting K+ conductance in SCA in vitro and in situ.

Glutamate transporters regulate excitability in local networks in rat neocortex

Excitatory postsynaptic currents (EPSCs) in the neocortex are principally mediated by glutamate receptors. Termination of excitation requires rapid removal of glutamate from the synaptic cleft following release. Glutamate transporters are involved in EPSC termination but the effect of uptake inhibition on excitatory neurotransmission varies by brain region. Epileptiform activity is largely mediated by a synchronous synaptic activation of cells in local cortical circuits, presumably associated with a large release of glutamate. The role of glutamate transporters in regulating epileptiform activity has not been addressed. Here we examine the effect of glutamate transport inhibition on EPSCs and epileptiform events in layer II/III pyramidal cells in rat neocortex. Inhibiting glutamate transporters with DL-threo-beta-benzyloxyaspartic acid (TBOA; 30 microM) had no effect on the amplitude or decay time of evoked, presumably alpha-amino-3-hydroxyl-5-methyl-isoxazolepropionic acid-mediated, EPSCs. In contrast, the amplitude and duration of epileptiform discharges were significantly enhanced. TBOA resulted also in a decreased threshold for evoking epileptiform activity and an increased probability of occurrence of spontaneous epileptiform discharges. TBOA's effects were not inhibited by the group I and II metabotropic glutamate receptors antagonist (S)-alpha-methyl-4-carboxyphenylglycine or the kainate receptor antagonist [(3S,4aR, 6S, 8aR)-6-((4-carboxyphenyl)methyl-1,2,3,4,4a,5,6,7,8,8a-decahydroisoquinoline-3-carboxylic acid]. D-(-)-2-amino-5-phosphonovaleric acid could both prevent excitability changes by TBOA and block already induced changes. Dihydrokainate (300 microM) had effects similar to TBOA suggesting involvement of the glial transporter GLT-1. Inhibiting glutamate transport increases local network excitability under conditions where there is an enhanced release of glutamate. Our results indicate that uptake inhibition produces an elevation of extracellular glutamate levels and activation of N-methyl-D-aspartate receptors.

Molecular basis for Rac1 recognition by guanine nucleotide exchange factors

Rho GTPases are activated by a family of guanine nucleotide exchange factors (GEFs) known as Dbl family proteins. The structural basis for how GEFs recognize and activate Rho GTPases is presently ill defined. Here, we utilized the crystal structure of the DH/PH domains of the Rac-specific GEF Tiam1 in complex with Rac1 to determine the structural elements of Rac1 that regulate the specificity of this interaction. We show that residues in the Rac1 beta2-beta3 region are critical for Tiam1 recognition. Additionally, we determined that a single Rac1-to-Cdc42 mutation (W56F) was sufficient to abolish Rac1 sensitivity to Tiam1 and allow recognition by the Cdc42-specific DH/PH domains of Intersectin while not impairing Rac1 downstream activities. Our findings identified unique GEF specificity determinants in Rac1 and provide important insights into the mechanism of DH/PH selection of GTPase targets.

The insert region of Rac1 is essential for membrane ruffling but not cellular transformation

The Rho family of Ras-related proteins, which includes Rac1, RhoA, and Cdc42, is distinguished from other members of the Ras superfamily of small GTPases in that its members possess additional sequences positioned between beta-strand 5 and alpha-helix 4, designated the insert region. Previous studies have established the importance of an intact insert region for the transforming, but not actin cytoskeletal reorganization, activities of Cdc42 and RhoA. Similarly, the insert region was determined to be essential for Rac1-mediated mitogenesis. Additionally, an intact insert region was also determined to be required for the antiapoptotic activity of Rac1 as well as for Rac1 activation of reactive oxygen species and the NF-kappaB transcription factor. However, it has not been determined whether the insert region is important for Rac1-mediated growth transformation. In this study, we assessed the requirement for the insert region in Rac1 transformation and signaling in NIH 3T3 cells. Unexpectedly, we found that a mutant of constitutively activated Rac1 that lacked the insert region retained potent transforming activity. The insert region of Rac1 was dispensable for Rac1 stimulation of transcription from the cyclin D1 promoter and for activation of the c-Jun, NF-kappaB, and E2F-1 transcription factors but was essential for Rac1 induction of serum response factor activity. While an intact insert region was dispensable for inducing reactive oxygen species production in vivo, it was required for Rac1 induction of lamellipodia. When taken together, these results show that the insert region of Rac1 serves roles in regulating actin organization and cell growth that are distinct from those of the analogous regions of Cdc42 and RhoA and support its involvement in regulating specific downstream effector interactions.

Elucidation of binding determinants and functional consequences of Ras/Raf-cysteine-rich domain interactions

Raf-1 is a critical downstream target of Ras and contains two distinct domains that bind Ras. The first Ras-binding site (RBS1) in Raf-1 has been shown to be essential for Ras-mediated translocation of Raf-1 to the plasma membrane, whereas the second site, in the Raf-1 cysteine-rich domain (Raf-CRD), has been implicated in regulating Raf kinase activity. While recognition elements that promote Ras.RBS1 complex formation have been characterized, relatively little is known about Ras/Raf-CRD interactions. In this study, we have characterized interactions important for Ras binding to the Raf-CRD. Reconciling conflicting reports, we found that these interactions are essentially independent of the guanine nucleotide bound state, but instead, are enhanced by post-translational modification of Ras. Specifically, our findings indicate that Ras farnesylation is sufficient for stable association of Ras with the Raf-CRD. Furthermore, we have also identified a Raf-CRD variant that is impaired specifically in its interactions with Ras. NMR data also suggests that residues proximal to this mutation site on the Raf-CRD form contacts with Ras. This Raf-CRD mutant impairs the ability of Ras to activate Raf kinase, thereby providing additional support that Ras interactions with the Raf-CRD are important for Ras-mediated activation of Raf-1.

Vav2 is an activator of Cdc42, Rac1, and RhoA

Vav and Vav2 are members of the Dbl family of proteins that act as guanine nucleotide exchange factors (GEFs) for Rho family proteins. Whereas Vav expression is restricted to cells of hematopoietic origin, Vav2 is widely expressed. Although Vav and Vav2 share highly related structural similarities and high sequence identity in their Dbl homology domains, it has been reported that they are active GEFs with distinct substrate specificities toward Rho family members. Whereas Vav displayed GEF activity for Rac1, Cdc42, RhoA, and RhoG, Vav2 was reported to exhibit GEF activity for RhoA, RhoB, and RhoG but not for Rac1 or Cdc42. Consistent with their distinct substrate targets, it was found that constitutively activated versions of Vav and Vav2 caused distinct transformed phenotypes when expressed in NIH 3T3 cells. In contrast to the previous findings, we found that Vav2 can act as a potent GEF for Cdc42, Rac1, and RhoA in vitro. Furthermore, we found that NH(2)-terminally truncated and activated Vav and Vav2 caused indistinguishable transforming actions in NIH 3T3 cells that required Cdc42, Rac1, and RhoA function. In addition, like Vav and Rac1, we found that Vav2 activated the Jun NH(2)-terminal kinase cascade and also caused the formation of lamellipodia and membrane ruffles in NIH 3T3 cells. Finally, Vav2-transformed NIH 3T3 cells showed up-regulated levels of Rac-GTP. We conclude that Vav2 and Vav share overlapping downstream targets and are activators of multiple Rho family proteins. Therefore, Vav2 may mediate the same cellular consequences in nonhematopoietic cells as Vav does in hematopoietic cells.

Dependence of Dbl and Dbs transformation on MEK and NF-kappaB activation

Dbs was identified initially as a transforming protein and is a member of the Dbl family of proteins (>20 mammalian members). Here we show that Dbs, like its rat homolog Ost and the closely related Dbl, exhibited guanine nucleotide exchange activity for the Rho family members RhoA and Cdc42, but not Rac1, in vitro. Dbs transforming activity was blocked by specific inhibitors of RhoA and Cdc42 function, demonstrating the importance of these small GTPases in Dbs-mediated growth deregulation. Although Dbs transformation was dependent upon the structural integrity of its pleckstrin homology (PH) domain, replacement of the PH domain with a membrane localization signal restored transforming activity. Thus, the PH domain of Dbs (but not Dbl) may be important in modulating association with the plasma membrane, where its GTPase substrates reside. Both Dbs and Dbl activate multiple signaling pathways that include activation of the Elk-1, Jun, and NF-kappaB transcription factors and stimulation of transcription from the cyclin D1 promoter. We found that Elk-1 and NF-kappaB, but not Jun, activation was necessary for Dbl and Dbs transformation. Finally, we have observed that Dbl and Dbs regulated transcription from the cyclin D1 promoter in a NF-kappaB-dependent manner. Previous studies have dissociated actin cytoskeletal activity from the transforming potential of RhoA and Cdc42. These observations, when taken together with those of the present study, suggest that altered gene expression, and not actin reorganization, is the critical mediator of Dbl and Rho family protein transformation.

Increasing complexity of Ras signaling

The initial discovery that ras genes endowed retroviruses with potent carcinogenic properties and the subsequent determination that mutated ras genes were present in a wide variety of human cancers, prompted a strong suspicion that the growth-promoting actions of mutated Ras proteins contribute to their aberrant regulation of growth stimulatory signaling pathways. In 1993, a remarkable convergence of experimental observations from genetic analyses of Drosophila, S. cerevisiae and C. elegans as well as biochemical and biological studies in mammalian cells came together to define a clear role for Ras in signal transduction. What emerged was an elegant linear signaling pathway where Ras functions as a relay switch that is positioned downstream of cell surface receptor tyrosine kinases and upstream of a cytoplasmic cascade of kinases that included the mitogen-activated protein kinases (MAPKs). Activated MAPKs in turn regulated the activities of nuclear transcription factors. Thus, a signaling cascade where every component between the cell surface and the nucleus was defined and conserved in worms, flies and man. This was a remarkable achievement in our efforts to appreciate how the aberrant function of Ras proteins may contribute to the malignant growth properties of the cancer cell. However, the identification of this pathway has proven to be just the beginning, rather than the culmination, of our understanding of Ras in signal transduction. Instead, we now appreciate that this simple linear pathway represents but a minor component of a very complex signaling circuitry. Ras signaling has emerged to involve a complex array of signaling pathways, where cross-talk, feedback loops, branch points and multi-component signaling complexes are recurring themes. The simplest concept of a signaling cascade, where each component simply relays the same message to the next, is clearly not the case. In this review, we summarize our current understanding of Ras signal transduction with an emphasis on new complexities associated with the recognition and/or activation of cellular effectors, and the diverse array of signaling pathways mediated by interaction between Ras and Ras-subfamily proteins with multiple effectors.

Rho family proteins and Ras transformation: the RHOad less traveled gets congested

The Rho family of small GTPases has attracted considerable research interest over the past 5 years. During this time, we have witnessed a remarkable increase in our knowledge of the biochemistry and biology of these Ras-related proteins. Thus, Rho family proteins have begun to rival, if not overshadow, interest in their more celebrated cousins, the Ras oncogene proteins. The fascination in Rho family proteins is fueled primarily by two major observations. First, like Ras, Rho family proteins serve as guanine nucleotide-regulated binary switches that control signaling pathways that in turn regulate diverse cellular processes. Rho family proteins are key components in cellular processes that control the organization of the actin cytoskeleton, activate kinase cascades, regulate gene expression, regulate membrane trafficking, promote growth transformation and induce apoptosis. Second, at least five Rho family proteins have been implicated as critical regulators of oncogenic Ras transformation. Thus, it is suspected that Rho family proteins contribute significantly to the aberrant growth properties of Ras-transformed cells. Rho family proteins are also critical mediators of the transforming actions of other transforming proteins and include Dbl family oncogene proteins, G protein-coupled receptors and G protein alpha subunits. Thus, Rho family proteins may be key components for the transforming actions of diverse oncogene proteins. Major aims of Rho family protein studies are to define the molecular mechanism by which Rho family proteins regulate such a diverse spectrum of cellular behavior. These efforts may reveal novel targets for the development of anti-Ras and anti-cancer drugs.

14-3-3 zeta negatively regulates raf-1 activity by interactions with the Raf-1 cysteine-rich domain

Although Raf-1 is a critical effector of Ras signaling and transformation, the mechanism by which Ras promotes Raf-1 activation is complex and remains poorly understood. We recently reported that Ras interaction with the Raf-1 cysteine-rich domain (Raf-CRD, residues 139-184) may be required for Raf-1 activation. The Raf-CRD is located in the NH2-terminal negative regulatory domain of Raf-1 and is highly homologous to cysteine-rich domains found in protein kinase C family members. Recent studies indicate that the structural integrity of the Raf-CRD is also critical for Raf-1 interaction with 14-3-3 proteins. However, whether 14-3-3 proteins interact directly with the Raf-CRD and how this interaction may mediate Raf-1 function has not been determined. In the present study, we demonstrate that 14-3-3 zeta binds directly to the isolated Raf-CRD. Moreover, mutation of Raf-1 residues 143-145 impairs binding of 14-3-3, but not Ras, to the Raf-CRD. Introduction of mutations that impair 14-3-3 binding resulted in full-length Raf-1 mutants with enhanced transforming activity. Thus, 14-3-3 interaction with the Raf-CRD may serve in negative regulation of Raf-1 function by facilitating dissociation of 14-3-3 from the NH2 terminus of Raf-1 to promote subsequent events necessary for full activation of Raf-1.

Structural and functional analysis of a mutant Ras protein that is insensitive to nitric oxide activation

Ras proteins cycle between active, guanosine triphosphate (GTP)-bound and inactive, guanosine diphospate (GDP)-bound states to mediate signal transduction pathways that promote cell growth and differentiation. It is believed that the major physiological mechanism for Ras activation is via interaction with guanine-nucleotide exchange factors (GEFs). This interaction is highly regulated and results in elevated levels of Ras-GTP by facilitating GDP dissociation. Recently, a novel mechanism of Ras activation has been proposed, whereby nitric oxide (NO) modification of Cys-118, like GEF interaction, populates Ras in its biologically active form by stimulating GDP release. Here, we describe characterization of a variant of Ras, C118S, that is insensitive to NO modification. We have measured the GTPase activity and the GDP dissociation rate of the C118S mutant and found them to be similar to wild-type Ras. We have also analyzed the structure of this mutant using multidimensional heteronuclear NMR methods. Analysis of chemical shifts and distance restraints demonstrates that this mutation has not disrupted the structure of the protein. These results suggest that NO modification of Cys-118 may not alter Ras structure and that the basis of Ras activation by NO is destabilization of a crucial interaction between residues in the GDP-binding pocket and the nucleotide. We have also found that this mutant is a more stable form of Ras at concentrations required for NMR studies, probably due to the removal of a surface-accessible cysteine residue. This stable variant may facilitate structural and biochemical investigations of Ras and other guanine-nucleotide-binding proteins containing a cysteine at this position.

The solution structure of the Raf-1 cysteine-rich domain: a novel ras and phospholipid binding site

The Raf-1 protein kinase is the best-characterized downstream effector of activated Ras. Interaction with Ras leads to Raf-1 activation and results in transduction of cell growth and differentiation signals. The details of Raf-1 activation are unclear, but our characterization of a second Ras-binding site in the cysteine-rich domain (CRD) and the involvement of both Ras-binding sites in effective Raf-1-mediated transformation provides insight into the molecular aspects and consequences of Ras-Raf interactions. The Raf-1 CRD is a member of an emerging family of domains, many of which are found within signal transducing proteins. Several contain binding sites for diacylglycerol (or phorbol esters) and phosphatidylserine and are believed to play a role in membrane translocation and enzyme activation. The CRD from Raf-1 does not bind diacylglycerol but interacts with Ras and phosphatidylserine. To investigate the ligand-binding specificities associated with CRDs, we have determined the solution structure of the Raf-1 CRD using heteronuclear multidimensional NMR. We show that there are differences between this structure and the structures of two related domains from protein kinase C (PKC). The differences are confined to regions of the CRDs involved in binding phorbol ester in the PKC domains. Since phosphatidylserine is a common ligand, we expect its binding site to be located in regions where the structures of the Raf-1 and PKC domains are similar. The structure of the Raf-1 CRD represents an example of this family of domains that does not bind diacylglycerol and provides a framework for investigating its interactions with other molecules.

Involvement of the switch 2 domain of Ras in its interaction with guanine nucleotide exchange factors

While Ras proteins are activated by stimulated GDP release, which enables acquisition of the active GTP-bound state, little is known about how guanine nucleotide exchange factors (GEFs) interact with Ras to promote this exchange reaction. Here we report that mutations within the switch 2 domain of Ras (residues 62-69) inhibit activation of Ras by the mammalian GEFs, Sos1, and GRF/CDC25Mm. While mutations in the 62-69 region blocked upstream activation of Ras, they did not disrupt Ras effector functions, including transcriptional activation and transformation of NIH 3T3 cells. Biochemical analysis indicated that the loss of GEF responsiveness of a Ras(69N) mutant was due to a loss of GEF binding, with no change in intrinsic nucleotide exchange activity. Furthermore, structural analysis of Ras(69N) using NMR spectroscopy indicated that mutation of residue 69 had a very localized effect on Ras structure that was limited to alpha-helix 2 of the switch 2 domain. Together, these results suggest that the switch 2 domain of Ras forms a direct interaction with GEFs.

Triple compliance: FMLA, ADA, and workers' comp

The major nightmare many employers have encountered is that they fail to notify an employee out on workers' comp leave in writing that the FMLA leave period began when they stopped working.

Assessing the efficacy of three dentifrices in the treatment of dentinal hypersensitivity

A multicenter clinical trial conducted by the authors compared the desensitizing efficacy of a new 5 percent potassium nitrate: 0.243 percent sodium fluoride dentifrice along with two clinically proven, commercially available desensitizing dentifrices to a placebo dentifrice. Sensitivity to cold air and tactile stimulation, along with patients' subjective assessments, were evaluated to assess the dentinal desensitizing efficacy of the test dentifrices. Results demonstrated that after four weeks, participants who used the new dentifrice formulation experienced significant decreases in dentinal sensitivity compared to the placebo group for all measured indexes.

Ras interaction with two distinct binding domains in Raf-1 may be required for Ras transformation

Although Raf-1 is a critical Ras effector target, how Ras mediates Raf-1 activation remains unresolved. Raf-1 residues 55-131 define a Ras-binding domain essential for Raf-1 activation. Therefore, our identification of a second Ras-binding site in the Raf-1 cysteine-rich domain (residues 139-184) was unexpected and suggested a more complex role for Ras in Raf-1 activation. Both Ras recognition domains preferentially associate with Ras-GTP. Therefore, mutations that impair Ras activity by perturbing regions that distinguish Ras-GDP from Ras-GTP (switch I and II) may disrupt interactions with either Raf-1-binding domain. We observed that mutations of Ras that impaired Ras transformation by perturbing its switch I (T35A and E37G) or switch II (G60A and Y64W) domain preferentially diminished binding to Raf-1-(55-131) or the Raf-1 cysteine-rich domain, respectively. Thus, these Ras-binding domains recognize distinct Ras-GTP determinants, and both may be essential for Ras transforming activity. Finally, since Ha-Ras T35A and E37G mutations prevent Ras interaction with full-length Raf-1, we suggest that Raf-Cys is a cryptic binding site that is unmasked upon Ras interaction with Raf-1-(55-131).

The comparative efficacy of two commercial tartar control dentifrices in preventing calculus development and facilitating easier dental cleanings

Tartar control dentifrices have been proven effective in reducing the build-up of supragingival calculus deposits between professional tooth cleanings. In addition to providing consumers with a cleaner dentition, these formulations can, in principle, contribute to easier professional tooth cleaning. Until recently, clinical methods for evaluating the effects of tartar control dentifrices were limited to the assessment of area coverage of calculus on the tooth surface. The development of the Quanticalc dental scaler permits the quantitative clinical measurement of force and stroke number associated with supragingival calculus debridement. In this clinical study, two commercial tartar control dentifrices, one containing 5.0% pyrophosphate as the tartar control agent and the other containing a combination of 1.3% pyrophosphate and 1.5% Gantrez copolymer, were compared for efficacy in reducing the development of supragingival calculus between prophylaxes, and in facilitating easier calculus removal in subsequent scaling. Results showed that the two commercial dentifrices were equally effective in reducing calculus extent between prophylaxes. In contrast, the 5.0% pyrophosphate dentifrice was observed to be almost twice as effective on a percentage basis as the lower dosage pyrophosphate dentifrice in facilitating easier calculus removal. The enhanced activity of the 5.0% pyrophosphate dentifrice may be postulated to be due to elevated dosage of tartar control crystallization inhibitor or to potential side effects of copolymer in the other commercial dentifrice. Importantly, these results substantiate that the clinical benefits of tartar control dentifrices are not completely described by actions in reducing calculus build-up as assessed by VMI, and that important clinical benefits and differences in efficacy may be provided by these formulations in facilitating easier dental cleaning of supragingival calculus.

Chylothorax associated with constrictive pericarditis in a dog

Chylothorax was associated with constrictive pericarditis in a 6-year-old mixed-breed dog. Clinical signs included hepatomegaly, bilateral jugular pulses, muffled heart sounds, and dyspnea. Pleural effusion was identified on thoracic radiographs. Thoracentesis yielded 3 L of chylous effusion, confirmed by the cholesterol/triglyceride ratio (0.14). Echocardiography revealed a thickened pericardium, with numerous fibrin tags, which was suggestive of constrictive pericarditis. Central venous, right atrial, and right ventricular pressures were high and on right ventricular diastolic pressure tracings, the square-root sign, which is indicative of constrictive pericarditis, was evident. Exploratory thoracotomy and pericardiectomy were performed. Histopathologic findings were consistent with chronic non-suppurative pericarditis. The dog's condition improved after surgery. On reevaluation 11 months later, central venous pressure and results of physical examination and thoracic radiography were normal. On the basis of these findings, we concluded that chylothorax was caused by constrictive pericarditis in this dog. Chylothorax is often associated with disorders that have a poor prognosis, but if constrictive pericarditis can be identified as the cause of the chylothorax, exploratory thoracotomy and pericardiectomy can provide a cure.

Frequency and frequency-ratio resolution by possessors of absolute and relative pitch: examples of categorical perception

The methodology derived from the trace-context theory of intensity resolution (Durlach and Braida, 1969; Macmillan et al., 1988) was applied to resolution over an octave range along two continua: a sequential-frequency-ratio continuum for possessors of relative pitch (RP), and a pure-tone frequency continuum for possessors of absolute pitch (AP). The performance of both RP and AP possessors was exceptional in that total identification sensitivity along both continua was much greater than identification sensitivity along unidimensional psychophysical continua characterized by the 7 +/- 2 rule. In addition, the performance of RP possessors was exceptional in that, on average, total sensitivity for identification resolution was greater than sensitivity for resolution in discrimination. Finally, identification sensitivity between category prototypes (chromatic semits) along both continua was approximately the same as identification sensitivity between phonemic category prototypes along speech continua, despite the fact that both the discrimination ranges and the total number of categories are much larger for the two pitch continua.

Uni- and multidimensional identification of rise time, spectral slope, and cutoff frequency

Absolute identification of rise time, spectral slope, and cutoff frequency was evaluated using complex tones comprising the first 40 harmonics of 200 Hz. Ranges of each dimension were restricted to those with relevance to natural music and speech. Baseline unidimensional fixed-background tasks yielded 1.5-2.0 bits of information, indicating that listeners could consistently identify at least three to four categories per dimension. Fixed-and roved-background information transfers implied rise time was perceptually separable from the other dimensions. Spectral slope and cutoff frequency displayed substantial integrality (ratios of fixed-background to roved-background information transfers of 1.08-5.03), but the extent decreased with experience (retest ratios of 1.03-2.64). Stimulus combinations that maximized differences in high-frequency spectral regions were associated with increased information transfer and greater separability, suggesting a functional role for "sharpness" in timbre identifications. Total multidimensional information transfer was closely approximated by the sum of the corresponding unidimensional roved-background values, supporting both the general additivity of information transfer and the feasibility of using unidimensional roved-background tasks to estimate multidimensional resolution efficiently.

Pressure transfer function and absorption cross section from the diffuse field to the human infant ear canal

The diffuse-field pressure transfer function from a reverberant field to the ear canal of human infants, ages 1, 3, 6, 12, and 24 months, has been measured from 125-10700 Hz. The source was a loudspeaker using pink noise, and the diffuse-field pressure and the ear-canal pressure were simultaneously measured using a spatial averaging technique in a reverberant room. The results in most subjects show a two-peak structure in the 2-6-kHz range, corresponding to the ear-canal and concha resonances. The ear-canal resonance frequency decreases from 4.4 kHz at age 1 month to 2.9 kHz at age 24 months. The concha resonance frequency decreases from 5.5 kHz at age 1 month to 4.5 kHz at age 24 months. Below 2 kHz, the diffuse-field transfer function shows effects due to the torsos of the infant and parent, and varies with how the infant is held. Comparisons are reported of the diffuse-field absorption cross section for infants relative to adults. This quantity is a measure of power absorbed by the middle ear from a diffuse sound field, and large differences are observed in infants relative to adults. The radiation efficiencies of the infant and the adult ear are small at low frequencies, near unity at midfrequencies, and decrease at higher frequencies. The process of ear-canal development is not yet complete at age 24 months. The results have implications for experiments on hearing in infants.

Longitudinal measurements of spontaneous otoacoustic emissions in infants

It has previously been shown [E. M. Burns, K. H. Arehart, and S. L. Campbell, J. Acoust. Soc. Am. 91, 1575-1581 (1992)] that both the overall prevalence of spontaneous otoacoustic emissions (SOAEs) and most of the various gender- and ear-related prevalence tendencies are not significantly different in 1-month-olds and adults. However, large differences were found between the neonates and adults in the distributions of the frequencies and levels of SOAEs. Both the average level and the median frequency were significantly higher in infants. To obtain longitudinal SOAE data, infants from this original group of 1-month-olds were tested at ages 3, 6, 12, and 24 months. In general, individual SOAEs decrease in level with age, and high-frequency SOAEs tend to show the largest decreases. No substantial shifts occur in the frequencies of individual SOAEs. The frequency and level distributions at 24 months of age are still not adult-like. SOAEs which show short-term instabilities in frequency and/or amplitude at 1 month of age typically continue to evidence such instabilities at later ages. These results suggest the cochlea is adult-like at birth, and imply that the observed SOAE changes reflect developmental changes in the external and middle ear.

Prevalence of spontaneous otoacoustic emissions in neonates

The prevalence of spontaneous otoacoustic emissions (SOAEs) was measured in a group of 100 neonates and in a group of 50 normal-hearing young adults. The prevalence of SOAEs in the adult group (0.62) is at the high end of the range of prevalences reported in other surveys of adult SOAEs based on measurements using similar microphones. The prevalence of SOAEs in neonates (0.64) is not significantly different from that in adults. The various tendencies that have been found to be significant in the pooled results of other surveys are also evident in our adult group: more SOAEs in right ears, a higher prevalence of SOAEs in females, and a dependence between ears for the occurrence of SOAEs. The above-mentioned tendencies are also significant in the infant data. The major differences between the infant and adult results are the predominant SOAE frequency range and the average levels of SOAEs. The majority of adult SOAEs are between 1.0 and 2.0 kHz, whereas the majority of neonatal SOAEs are between 2.5 and 5.0 kHz. The average SOAE level is -2.6 dB SPL for adults and 8.5 dB SPL for infants.

The decade takes shape: computers in healthcare for the 90's

The healthcare industry in the 1990s will continue to be driven by the three primary issues that emerged in the '80s--the need to improve productivity, profitability and quality of care. The critical difference for the '90s, however, is that these issues will reach a crisis point that will demand resolution.

Factors associated with dysphonia in high school cheerleaders

Questionnaire responses that encompassed the severity of acute, cheering-related dysphonia, typical vocal use, vocal history, medical history, smoking and drinking behaviors, and A-Scale personality characteristics were obtained from 146 female high school cheerleaders. Multiple-regression analysis was chosen to examine the degree to which the dysphonia severity items could be associated with the remaining items. The results indicated that acute, cheering-related dysphonia may be preceded or accompanied by a compact set of clinical signs that could be incorporated easily into a screening protocol for prospective cheerleaders.

Measurement of blood flow and lipolysis in the hindquarter tissues of the fat-tailed sheep in vivo

Karakul and Namaqua-Afrikander sheep, both of which are fat-tailed breeds, were examined for suitability as models for studying lipid metabolism in vivo. The anatomy of the blood supply to the hindquarters of both breeds was examined, and a technique developed for sampling the venous outflow from the fat tail. The composition of the tail and the rest of the hindquarters was determined and found to be similar in both breeds. The hindquarters contained 35% fat, about half of which was located in the tail (72-74% fat). Rates of blood flow through the whole hindquarters, tail adipose tissue and leg muscle of Karakul ewes were measured. Tritiated water (TOH) was used for measurement of specific blood flow and p-aminohippuric acid (PAH) for measurement of absolute blood flow. The specific blood flow rate for tail adipose tissue was 3.62 +/- 0.12 ml X min-1 X 100 g-1 and absolute blood flow was estimated as 74 +/- 7 ml X min-1. The absolute flow through the rest of the adipose tissue in the hindquarters was similar to that flowing through the tail, and together they represented about 15% of the total absolute flow through the whole hindquarters, 794 +/- 131 ml X min-1, measured directly using PAH. Total blood flow through the hindquarters estimated from the specific flow rate (using (TOH) and the mass of the hindquarters was 761 +/- 50 ml X min-1. The absolute blood flow through the hindquarters of Namaqua-Afrikander ewes (626 +/- 39 ml X min-1) was lower than that measured in the Karakul ewes, but the difference was not significant (P greater than 0.10). The rates of net release from tail adipose tissue of Karakul ewes measured in vivo were 3.0 +/- 0.6 and 2.0 +/- 0.2 mumol X min-1 X 100 g-1 for free fatty acids and glycerol respectively. Intravenous infusion of noradrenaline (2 micrograms X min-1 X kg-1 liveweight) increased venoarterial differences of both free fatty acids and glycerol 2- to 3-fold and blood flow increased by about 60%. As a result, in response to noradrenaline, net releases for both free fatty acids and glycerol increased 4-fold.

In vivo 31P nuclear magnetic resonance saturation transfer measurements of phosphate exchange reactions in the yeast Saccharomyces cerevisiae

31P saturation transfer techniques have been used to measure phosphate kinetics in the yeast Saccharomyces cerevisiae. The phosphate consumption rate observed in acetate grown mid-log cells was combined with measurements of O2 consumption to yield P/O ratios of 2.2 and 2.9, for cells respiring on glucose and ethanol, respectively. However, no phosphate consumption activity was observed in saturation transfer experiments on anaerobic glucose fed cells. The phosphate consumption rates measured by saturation transfer in cells respiring on glucose and ethanol was attributed to the unidirectional rates of mitochondrial ATP synthesis.