Differential motion dynamics of synaptic vesicles undergoing spontaneous and activity-evoked endocytosis

Synaptic vesicle exo- and endocytosis are usually driven by neuronal activity but can also occur spontaneously. The identity and differences between vesicles supporting evoked and spontaneous neurotransmission remain highly debated. Here we combined nanometer-resolution imaging with a transient motion analysis approach to examine the dynamics of individual synaptic vesicles in hippocampal terminals under physiological conditions. We found that vesicles undergoing spontaneous and stimulated endocytosis differ in their dynamic behavior, particularly in the ability to engage in directed motion. Our data indicate that such motional differences depend on the myosin family of motor proteins, particularly myosin II. Analysis of synaptic transmission in the presence of myosin II inhibitor confirmed a specific role for myosin II in evoked, but not spontaneous, neurotransmission and also suggested a functional role of myosin II-mediated vesicle motion in supporting vesicle mobilization during neural activity.     

Dispersal and diversity – unifying scale‐dependent relationships within the neutral theory

The response of species diversity to dispersal capability is inherently scale‐dependent: increasing dispersal capability is expected to increase diversity at the local scale, while decreasing diversity at the metacommunity scale. However, these expectations are based on model formulations that neglect dispersal limitation and species segregation at the local scale. We developed a unifying framework of dispersal–diversity relationships and tested the generality of these expectations. For this purpose we used a spatially‐explicit neutral model with various combinations of survey area (local scale) and landscape size (metacommunity scale). Simulations were conducted using landscapes of finite and of conceptually infinite size. We analyzed the scale‐dependence of dispersal‐diversity relationships for exponentially‐bounded versus fat‐tailed dispersal kernels, several levels of speciation rate and contrasting assumptions on recruitment at short dispersal distances. We found that the ratio of survey area to landscape size is a major determinant of dispersal–diversity relationships. With increasing survey‐to‐landscape area ratio the dispersal–diversity relationship switches from monotonically increasing through a U‐shaped pattern (with a local minimum) to a monotonically decreasing pattern. Therefore, we provide a continuous set of dispersal–diversity relationships, which contains the response shapes reported previously as extreme cases. We suggest the mean dispersal distance with the minimum of species diversity (minimizing dispersal distance) for a certain scenario as a key characteristic of dispersal–diversity relationships. We show that not only increasing mean dispersal distances, but also increasing variances of dispersal can enhance diversity at the local scale, given a diverse species pool at the metacommunity scale. In conclusion, the response of diversity to variations of dispersal capability at spatial scales of interest, e.g. conservation areas, can differ more widely than expected previously. Therefore, land use and conservation activities, which manipulate dispersal capability, need to consider the landscape context and potential species pools carefully.     

Dopant‐Free Partial Rear Contacts Enabling 23% Silicon Solar Cells

Over the past five years, there has been a significant increase in both the intensity of research and the performance of crystalline silicon devices which utilize metal compounds to form carrier‐selective heterocontacts. Such heterocontacts are less fundamentally limited and have the potential for lower costs compared to the current industry dominating heavily doped, directly metalized contacts. A low temperature (≤230 °C), TiO_x/LiF_x/Al electron heterocontact is presented here, which achieves mΩcm² scale contact resistivities ρ_c on lowly doped n‐type substrates. As an extreme demonstration of the potential of this heterocontact, it is trialed in a newly developed, high efficiency n‐type solar cell architecture as a partial rear contact (PRC). Despite only contacting ≈1% of the rear surface area, an efficiency of greater than 23% is achieved, setting a new benchmark for n‐type solar cells featuring undoped PRCs and confirming the unusually low ρ_c of the TiO_x/LiF_x/Al contact. Finally, in contrast to previous versions of the n‐type undoped PRC cell, the performance of this cell is maintained after annealing at 350–400 °C, suggesting its compatibility with conventional surface passivation activation and sintering steps.     

In situ tissue classification during laser ablation using acoustic signals

We suggest a novel method to classify the type of tissue that is being ablated, using the recorded acoustic sound waves during pulsed ultraviolet laser ablation. The motivation of the current research is tissue classification during vascular interventions, where the identification of the ablated tissue is vital. We classify the acoustic signatures using Mel‐frequency cepstral coefficients (MFCCs) feature extraction with a Support Vector Machine (SVM) algorithm, and in addition, use a fully connected deep neural network (FC‐DNN) algorithm. First, we classify three different liquids using our method as a preliminary proof of concept. Then, we classify ex vivo porcine aorta and bovine tendon tissues in the presence of saline. Finally, we classify ex vivo porcine aorta and bovine tendon tissues where the acoustic signals are recorded through chicken breast medium. The results for tissue classification in saline and through chicken breast both show high accuracy (>98%), based on tens of thousands of acoustic signals for each experiment. The experiments were conducted in a noisy and challenging setting that tries to imitate practical working conditions. The obtained results could pave the way towards practical tissue classification in various important medical procedures, achieving enhanced efficacy and safety.     

Thylakoid membrane perforations and connectivity enable intracellular traffic in cyanobacteria

Cyanobacteria, the progenitors of plant and algal chloroplasts, enabled aerobic life on earth by introducing oxygenic photosynthesis. In most cyanobacteria, the photosynthetic membranes are arranged in multiple, seemingly disconnected, concentric shells. In such an arrangement, it is unclear how intracellular trafficking proceeds and how different layers of the photosynthetic membranes communicate with each other to maintain photosynthetic homeostasis. Using electron microscope tomography, we show that the photosynthetic membranes of two distantly related cyanobacterial species contain multiple perforations. These perforations, which are filled with particles of different sizes including ribosomes, glycogen granules and lipid bodies, allow for traffic throughout the cell. In addition, different layers of the photosynthetic membranes are joined together by internal bridges formed by branching and fusion of the membranes. The result is a highly connected network, similar to that of higher-plant chloroplasts, allowing water-soluble and lipid-soluble molecules to diffuse through the entire membrane network. Notably, we observed intracellular membrane-bounded vesicles, which were frequently fused to the photosynthetic membranes and may play a role in transport to these membranes.     

Genetic admixture, adipocytokines, and adiposity in Black Americans: the Health, Aging, and Body Composition study

Adipocytokines are a subset of cytokines produced by adipose tissue and are associated with risk of type II diabetes and atherosclerosis. Levels of adipocytokines differ between Black and White Americans, even after adjustment for differences in adiposity, diseases associated with adipocytokines including type 2 diabetes and cardiovascular disease, and general socioeconomic status indicators such as income. We used a series of ancestry informative markers to estimate genetic ancestry in a population-based study of older Black Americans, and examined the association between genetic ancestry and adipocytokines and soluble receptors to help determine which of these may be most amenable to admixture mapping. We typed 35 ancestry informative markers in 1,241 self-reported Black Americans with available DNA from the Health, Aging, and Body Composition (Health ABC) study with available DNA and used a maximum likelihood approach to estimate percent European ancestry. We used linear regression models to determine the association between these adipocytokines and percent ancestry, and staged models to examine whether adiposity or other measures affected the associations of genetic ancestry and adipocytokines. Mean European ancestry was 22.3 ± 15.9%. In multivariate adjusted models, the strongest associations observed were between higher European ancestry and interleukin-6 soluble receptor (IL-6 SR), C-reactive protein (CRP), and adiponectin levels, with interleukin-2 soluble receptor (IL-2 SR) and soluble tumor necrosis factor receptor II (TNF-α SR II) also showing more modest but significant associations. The association with adiponectin became stronger after adjustment for adiposity. These novel findings suggest that admixture mapping may identify genetic factors influencing the levels of IL-6 SR, CRP, IL-2 SR, and adiponectin. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The polycomb protein Ring1B generates self atypical mixed ubiquitin chains required for its in vitro histone H2A ligase activity

Polycomb complexes mediate gene silencing, in part by modifying histones. Ring1B and Bmi1 are RING finger proteins that are members of the Polycomb repressive complex 1 (PRC1). Ring1B is an E3 that mediates its own polyubiquitination and monoubiquitination of histone H2A. In contrast, Bmi1 has no self-ubiquitinating activity. We show that unlike other RING finger proteins that are believed to mediate their own ubiquitination and degradation, Ring1B and Bmi1 are degraded by an exogenous E3, independent of their RING domain. The RING domains of both proteins mediate their association and subsequent stabilization. Consistent with the nonproteolytic self-ligase activity of Ring1B, it generates atypical mixed K6-, K27-, and K48-based polyubiquitin chains, which require the presence of all these lysine residues on the same ubiquitin molecule. The modification is required for Ring1B ability to monoubiquitinate H2A in vitro, unraveling an as yet undescribed mechanism for ligase activation via noncanonical self-ubiquitination.     

Nutritionally induced diabetes in desert rodents as models of type 2 diabetes: Acomys cahirinus (spiny mice) and Psammomys obesus (desert gerbil)

The dietary effects of hyperglycemia increasingly result in type 2 diabetes in humans. Two species, the spiny mice (Acomys cahirinus) and the desert gerbil (Psammomys obesus), which have different metabolic responses to such effects, are discussed. Spiny mice exemplify a pathway that leads to diabetes without marked insulin resistance due to low supply of insulin on abundant nutrition, possibly characteristic of a desert animal. They respond with obesity and glucose intolerance, beta-cell hyperplasia, and hypertrophy on a standard rodent diet supplemented with fat-rich seeds. The accompanying hyperglycemia and hyperinsulinemia are mild and intermittent but after a few months, the enlarged pancreatic islets suddenly collapse, resulting in loss of insulin and ketosis. Glucose and other secretagogues produce only limited insulin release in vivo and in vitro, pointing to the inherent disability of the beta-cells to respond with proper insulin secretion despite their ample insulin content. On a 50% sucrose diet there is marked lipogenesis with hyperlipidemia without obesity or diabetes, although beta-cell hypertrophy is evident. P.obesus is characterized by muscle insulin resistance and the inability of insulin to activate the insulin signaling on a high-energy (HE) diet. Insulin resistance imposes a vicious cycle of Hyperglycemia and compensatory hyperinsulinemia, leading to beta-cell failure and increased secretion of proinsulin. Ultrastructural studies reveal gradual disappearance of beta-cell glucokinase, GLUT 2 transporter, and insulin, followed by apoptosis of beta-cells. Studies using the non-insulin-resistant HE diet-fed animals maintained as a control group are discussed. The insulin resistance that is evident to date in the normoglycemic state on a low-energy diet indicates sparing of glucose fuel in muscles of a desert-adapted animal for the benefit of glucose obligatory tissues. Also discussed are the effect of Psammomys age on the disabetogenicity of the HE diet; the impaired function of several components of the insulin signal transduction pathway in muscles, which reduces the availability of GLUT4 transporter; the testing of several antidiabetic modalities for the prevention of nutritional diabetes in Psammomys; and various complications related to the diabetic condition.     

Two‐polymerase mechanisms dictate error‐free and error‐prone translesion DNA synthesis in mammals

DNA replication across blocking lesions occurs by translesion DNA synthesis (TLS), involving a multitude of mutagenic DNA polymerases that operate to protect the mammalian genome. Using a quantitative TLS assay, we identified three main classes of TLS in human cells: two rapid and error‐free, and the third slow and error‐prone. A single gene, REV3L, encoding the catalytic subunit of DNA polymerase ζ (polζ), was found to have a pivotal role in TLS, being involved in TLS across all lesions examined, except for a TT cyclobutane dimer. Genetic epistasis siRNA analysis indicated that discrete two‐polymerase combinations with polζ dictate error‐prone or error‐free TLS across the same lesion. These results highlight the central role of polζ in both error‐prone and error‐free TLS in mammalian cells, and show that bypass of a single lesion may involve at least three different DNA polymerases, operating in different two‐polymerase combinations.     

A high-density microsatellite map of the ataxia-telangiectasia locus

The locus of the autosomal recessive disorder ataxia-telangiectasia (A-T) has been assigned by linkage analysis with biallelic markers to a 4-Mb interval on chromosome 11q22-23, between GRIA4 and D11S1897. We have undertaken to saturate the A-T region with highly polymorphic microsatellite markers. To this end, we have identified seven new polymorphic CA-repeats in this region, and have mapped to it five new markers generated by Genethon and the Cooperative Human Linkage Center. These markers are in addition to 12 others that we have previously mapped or generated at the A-T locus. All 24 markers have been integrated into a high-density microsatellite map spanning some 6 Mb DNA. This map, which contains the A-T locus and flanking sequences, allows the construction of extensive, highly informative haplotypes.