Microtubule specialization by +TIP networks: from mechanisms to functional implications.

To fulfill their actual cellular role, individual microtubules become functionally specialized through a broad range of mechanisms. The 'search and capture' model posits that microtubule dynamics and functions are specified by cellular targets that they capture (i.e., a posteriori), independently of the microtubule-organizing center (MTOC) they emerge from. However, work in budding yeast indicates that MTOCs may impart a functional identity to the microtubules they nucleate, a priori. Key effectors in this process are microtubule plus-end tracking proteins (+TIPs), which track microtubule tips to regulate their dynamics and facilitate their targeted interactions. In this review, we discuss potential mechanisms of a priori microtubule specialization, focusing on recent findings indicating that +TIP networks may undergo liquid biomolecular condensation in different cell types.

Multivalency ensures persistence of a +TIP body at specialized microtubule ends.

Microtubule plus-end tracking proteins (+TIPs) control microtubule specialization and are as such essential for cell division and morphogenesis. Here we investigated interactions and functions of the budding yeast Kar9 network consisting of the core +TIP proteins Kar9 (functional homologue of APC, MACF and SLAIN), Bim1 (orthologous to EB1) and Bik1 (orthologous to CLIP-170). A multivalent web of redundant interactions links the three +TIPs together to form a '+TIP body' at the end of chosen microtubules. This body behaves as a liquid condensate that allows it to persist on both growing and shrinking microtubule ends, and to function as a mechanical coupling device between microtubules and actin cables. Our study identifies nanometre-scale condensates as effective cellular structures and underlines the power of dissecting the web of low-affinity interactions driving liquid-liquid phase separation in order to establish how condensation processes support cell function.

Structure and regulation of the microtubule plus-end tracking protein Kar9.

In many eukaryotes, coordination of chromosome segregation with cell cleavage relies on the patterned interaction of specific microtubules with actin filaments through dedicated microtubule plus-end tracking proteins (+TIPs). However, how these +TIPs are spatially controlled is unclear. The yeast +TIP Kar9 drives one of the spindle aster microtubules along actin cables to align the mitotic spindle with the axis of cell division. Here, we report the crystal structure of Kar9's folded domain, revealing spectrin repeats reminiscent of the +TIPs MACF/ACF7/Shot and PRC1/Ase1. Point mutations abrogating spectrin-repeat-mediated dimerization of Kar9 reduced and randomized Kar9 distribution to microtubule tips, and impaired spindle positioning. Six Cdk1 sites surround the Kar9 dimerization interface. Their phosphomimetic substitution inhibited Kar9 dimerization, displaced Kar9 from microtubules, and affected its interaction with the myosin motor Myo2. Our results provide molecular-level understanding on how diverse cell types may regulate and pattern microtubule-actin interactions to orchestrate their divisions.

Surface tensiometry of phase separated protein and polymer droplets by the sessile drop method.

Phase separated macromolecules play essential roles in many biological and synthetic systems. Physical characterization of these systems can be challenging because of limited sample volumes, particularly for phase-separated proteins. Here, we demonstrate that a classic method for measuring the surface tension of liquid droplets, based on the analysis of the shape of a sessile droplet, can be effectively scaled down to measure the interfacial tension between a macromolecule-rich droplet phase and its co-existing macromolecule-poor continuous phase. The connection between droplet shape and surface tension relies on the density difference between the droplet and its surroundings. This can be determined with small sample volumes in the same setup by measuring the droplet sedimentation velocity. An interactive MATLAB script for extracting the capillary length from a droplet image is included in the ESI.

Enhancing the performance of beech-timber concrete hybrids by a wood surface pre-treatment using sol-gel chemistry.

Timber-concrete composites require reliable connections between both components, which are usually obtained by metal fasteners or slots in the wood. In this study, an alternative approach is presented based on a fully glued connection in combination with a primer treated wood surface, to enhance the compatibility and the adhesion properties at the interface between beech wood and concrete. Prior to the gluing and the concrete application in a wet-on-wet process, the wood surface was functionalised with a xerogel obtained by means of a sol-gel process, consisting of two layers of silane nanofilms, with different functional groups, which are capable of undergoing further chemical crosslinking reactions with the adhesive. The coating with its functionalities allows for reducing the penetration of the epoxy adhesives into the wood structure and an additional chemical connection to the adhesive can be established. The main objective of this study was to analyse the effect of the surface treatment on the mechanical properties of such composites in 3-point and 4-point bending tests as well as push-out-tests. The results showed that the pre-treatment can improve the load bearing capacity of the timber-concrete composites, but that a ductile behaviour cannot be achieved with the tested adhesives.

Compliance with guidelines for disease management in diabetes: results from the SwissDiab Registry.

OBJECTIVE: Tight glycemic control and aggressive treatment of additional cardiovascular risk factors can substantially reduce risk of diabetes-related complications. In 2013, the Swiss Society of Endocrinology and Diabetology (SSED) established national criteria on good disease management in diabetes, but little is known about compliance in clinical care. Here we assessed to what extent patients from two tertiary care centers in the German-speaking part of Switzerland enrolled in the Swiss Diabetes (SwissDiab) Registry adhere to the SSED criteria. RESEARCH DESIGN AND METHODS: SwissDiab is a prospective observational cohort study of patients regularly treated at Swiss tertiary diabetes centers. Data were collected through standardized annual health examinations. Baseline participant descriptive statistics, stratified by diabetes mellitus type 1 (DM1) and type 2 (DM2), were compared with SSED targets for glycemic control, blood pressure, blood lipids, weight maintenance, and ophthalmic examination. RESULTS: By the end of 2016, 604 participants with DM1 (40%) and DM2 (60%) had data available for analyses, 36% and 29% women, respectively. At baseline, all the SSED targets were met with two exceptions: a glycated hemoglobin A1c value <7% was measured in 32% of participants with DM1 (SSED target: ≥40%) and 47% and 56% of overweight or obese participants with DM1 and DM2, respectively, received nutritional counseling in the previous year (SSED target: ≥80%). CONCLUSIONS: The SSED targets for good disease management in diabetes were achieved in the majority of participants at the time of enrollment, but results also highlight areas where disease management can be improved, particularly the role of nutrition counseling.

[Arthroscopic meniscal repair with an all-inside suture system].

OBJECTIVE: Application of an arthroscopic suture system to restore the form and function of the meniscus by adaptation of a longitudinal tear close to the base. INDICATIONS: Unstable longitudinal tears near the base of the meniscus, mainly in the posterior horn of the medial or lateral of the meniscus. Dislocated bucket-handle tears of the medial and lateral meniscus close to the base. CONTRAINDICATIONS: Poor tissue quality with fibrillated meniscal tissue. Meniscal tears in the avascular zone (zone I). Insufficient blood supply from the joint capsule and the base of the meniscus. Degenerative meniscal lesions. Anterior or posterior knee joint instability. Allergic reactions to nonresorbable suture material. SURGICAL TECHNIQUE: Standard anterior arthroscopic portals. Arthroscopic assessment of the meniscal tear using the probe. Revitalization of the tear margins and perforation of the meniscal base to induce bleeding. Adaptation of the tear margins and fixation with a suture-anchor system using an ipsilateral standard portal for tears in the posterior horn or by way of a contralateral standard portal for tears in the lateral horn. POSTOPERATIVE MANAGEMENT: Full weight bearing with the knee in extension in a knee immobilizer, relative to the pain threshold in the 1st postoperative week. Range of motion exercises without weight bearing from full extension to 90 degrees knee flexion (0/0/90). If simultaneous reconstruction of the anterior cruciate ligament (ACL) is being performed, rehabilitation protocols follow the principles for ACL reconstruction. RESULTS: Since the year 2000, meniscal tears in more than 300 patients have been repaired with the all-inside suture system. In the context of a multicenter study by ESSKA (European Society for Sports Medicine, Surgery and Arthroscopy) involving 20 patients, the result was evaluated by direct MRI arthrography (gadolinium). The suture bar anchors were generally not detectable, the incision channels produced a hypodense signal in the meniscus tissue. If re-rupture occurred, it was because the meniscus had pulled out of the suture loop. Cartilaginous lesions were not found. There were no complications related to the nonresorbable suture bar anchors.