Kinase domain of the muscle-specific receptor tyrosine kinase (MuSK) is sufficient for phosphorylation but not clustering of acetylcholine receptors: Required role for the MuSK ectodomain?

Formation of the neuromuscular junction (NMJ) depends upon a nerve-derived protein, agrin, acting by means of a muscle-specific receptor tyrosine kinase, MuSK, as well as a required accessory receptor protein known as MASC. We report that MuSK does not merely play a structural role by demonstrating that MuSK kinase activity is required for inducing acetylcholine receptor (AChR) clustering. We also show that MuSK is necessary, and that MuSK kinase domain activation is sufficient, to mediate a key early event in NMJ formation—phosphorylation of the AChR. However, MuSK kinase domain activation and the resulting AChR phosphorylation are not sufficient for AChR clustering; thus we show that the MuSK ectodomain is also required. These results indicate that AChR phosphorylation is not the sole trigger of the clustering process. Moreover, our results suggest that, unlike the ectodomain of all other receptor tyrosine kinases, the MuSK ectodomain plays a required role in addition to simply mediating ligand binding and receptor dimerization, perhaps by helping to recruit NMJ components to a MuSK-based scaffold.     

From the Cover: Supercell tornadoes are much stronger and wider than damage-based ratings indicate

Tornadoes cause damage, injury, and death when intense winds impact structures. Quantifying the strength and extent of such winds is critical to characterizing tornado hazards. Ratings of intensity and size are based nearly entirely on postevent damage surveys [R. Edwards et al., Bull. Am. Meteorol. Soc. 94, 641–653 (2013)]. It has long been suspected that these suffer low bias [C. A. Doswell, D. W. Burgess, Mon. Weather Rev. 116, 495–501 (1988)]. Here, using mapping of low-level tornado winds in 120 tornadoes, we prove that supercell tornadoes are typically much stronger and wider than damage surveys indicate. Our results permit an accurate assessment of the distribution of tornado intensities and sizes and tornado wind hazards, based on actual wind-speed observations, and meaningful comparisons of the distribution of tornado intensities and sizes with theoretical predictions. We analyze data from Doppler On Wheels (DOW) radar measurements of 120 tornadoes at the time of peak measured intensity. In striking contrast to conventional damage-based climatologies, median tornado peak wind speeds are ∼60 m⋅s⁻¹, capable of causing significant, Enhanced Fujita Scale (EF)-2 to -3, damage, and 20% are capable of the most intense EF-4/EF-5 damage. National Weather Service (NWS) EF/wind speed ratings are 1.2 to 1.5 categories (∼20 m⋅s⁻¹) lower than DOW observations for tornadoes documented by both the NWS and DOWs. Median tornado diameter is 250 to 500 m, with 10 to 15% >1 km. Wind engineering tornado-hazard-model predictions and building wind resistance standards may require upward adjustment due to the increased wind-damage risk documented here.

Tornadoes cause direct harm to people, infrastructure, and communities (1). Quantifying tornado risk requires accurate knowledge of their wind speeds and the size of the areas at risk from these intense winds. However, since direct measurements of tornado winds are rare, tornado intensity and size are nearly always inferred indirectly from postevent damage surveys applying the Fujita (F) or Enhanced Fujita (EF) scales (2–5) to infer maximum wind speeds. Statistics concerning tornado frequency, intensity, and size are derived from these surveys. However, because most tornadoes do not damage well-engineered structures, from which the most intense wind speeds can be inferred, and many occur in primarily rural areas, damage-based tornado wind speed and size estimations are likely severely low biased (6–11). A limited climatology (12), using Doppler On Wheels (DOW) radar data (13–15), suggested that tornadoes may be larger and more intense than indicated by these surveys. In-situ observations of wind speeds reliably demonstrable to be inside the radius of maximum winds of tornadoes are very rare (16, 17) and inadequate for deriving a statistically meaningful climatology. It is no exaggeration to state that, until now, statistics concerning even the most basic characteristics of tornadoes, including intensity and size, could not be quantified with confidence.     

Musashi2 sustains the mixed-lineage leukemia–driven stem cell regulatory program

Leukemia stem cells (LSCs) are found in most aggressive myeloid diseases and contribute to therapeutic resistance. Leukemia cells exhibit a dysregulated developmental program as the result of genetic and epigenetic alterations. Overexpression of the RNA-binding protein Musashi2 (MSI2) has been previously shown to predict poor survival in leukemia. Here, we demonstrated that conditional deletion of Msi2 in the hematopoietic compartment results in delayed leukemogenesis, reduced disease burden, and a loss of LSC function in a murine leukemia model. Gene expression profiling of these Msi2-deficient animals revealed a loss of the hematopoietic/leukemic stem cell self-renewal program and an increase in the differentiation program. In acute myeloid leukemia patients, the presence of a gene signature that was similar to that observed in Msi2-deficent murine LSCs correlated with improved survival. We determined that MSI2 directly maintains the mixed-lineage leukemia (MLL) self-renewal program by interacting with and retaining efficient translation of Hoxa9, Myc, and Ikzf2 mRNAs. Moreover, depletion of MLL target Ikzf2 in LSCs reduced colony formation, decreased proliferation, and increased apoptosis. Our data provide evidence that MSI2 controls efficient translation of the oncogenic LSC self-renewal program and suggest MSI2 as a potential therapeutic target for myeloid leukemia.     

Preoperative Predictors of Postoperative Opioid Usage,Pain Scores,and Referral to a Pain Management Service in Total Knee Arthroplasty

Background

Little is known about preoperative predictors of postoperative pain and referral to a recuperative pain management service after total knee arthroplasty (TKA).

Questions/Purposes

We sought to identify the preoperative predictors of postoperative pain scores, referral to a pain management service, and narcotic usage in patients undergoing primary total knee arthroplasty.

Methods

We performed a prospective cohort study of 97 TKAs from a single surgeon. Pre and 6-week postoperative WOMAC, visual analog pain scale (VAS) scores, narcotic usage, and catastrophizing pain scores were collected.

Results

After adjusting for all other variables, higher age and catastrophizing pain scores were associated with lower odds of postoperative opioid usage. Increasing age and BMI were associated with lower odds of being referred to pain management. There was no relationship between self-reported preoperative pain tolerance and postoperative change in WOMAC or VAS pain scores.

Conclusions

This information may help surgeons advise their patients preoperatively and set expectations during the recovery period.

Electronic supplementary material

The online version of this article (doi:10.1007/s11420-014-9418-4) contains supplementary material, which is available to authorized users.     

Relationships Between Dimensions of Disability Experienced by Adults Living with HIV: A Structural Equation Model Analysis

As individuals age with HIV it is increasingly important to consider the health-related consequences of HIV and multiple morbidities, known as disability. We assessed relationships between four dimensions of disability among adults living with HIV. We conducted a structural equation modeling analysis using data from 913 participants in the Ontario HIV Treatment Network Cohort Study to determine relationships between four latent variables of disability in the Episodic Disability Framework: physical symptoms and impairments, mental health symptoms and impairments, difficulties with day-to-day activities, and challenges to social inclusion. Results indicated that physical symptoms and impairments, mental health symptoms and impairments and difficulties with day-to-day activities directly or indirectly predicted challenges to social inclusion for adults living with HIV. Challenges to social inclusion were directly predicted by mental health symptoms and indirectly by physical health symptoms via (mediated by) having difficulties carrying out day-to-day activities and mental health symptoms and impairments. These findings provide a basis for conceptualizing disability experienced by people living with HIV.     

Muscle thixotropy as a tool in the study of proprioception

When a muscle relaxes after a contraction, cross-bridges between actin and myosin in sarcomeres detach, but about 1 % spontaneously form new, non-force-generating attachments. These bridges give muscle its thixotropic property. They remain in place for long periods if the muscle is left undisturbed and give the muscle a passive stiffness in response to a stretch. They are detached by stretch, but reform at the new length. If the muscle is then shortened, the presence of these bridges prevents muscle fibres from shortening and they fall slack. So, resting muscle can be in one of two states, where it presents in response to a stretch with a high stiffness, if no slack is present, or with a compliant response in the presence of slack. Intrafusal fibres of muscle spindles show thixotropic behaviour. For spindles, after a conditioning contraction, they are left stretch sensitive, with a high level of background discharge. Alternatively, if after the contraction the muscle is shortened, intrafusal fibres fall slack, leaving spindles with a low level of background activity and insensitivity to stretch. Muscle spindles are receptors involved in the senses of human limb position and movement. The technique of muscle conditioning can be used to help understand the contribution of muscle spindles to these senses and how the brain interprets signals arising in spindles. When, in a two-arm position-matching task, elbow muscles of the two arms are deliberately conditioned in opposite ways, the blindfolded subject makes large position errors of which they are unaware. The evidence suggests that the brain is concerned with the difference signal coming from the antagonists acting at the elbow and with the overall difference in signal from the two arms. Another way of measuring position sense is to use a single arm and indicate its perceived position with a pointer. Here, there is no access to a signal from the other limb, and position sense relies on referral to a central map of the body, the postural schema.