Molecular Relay Stations in Membrane Nanotubes: IRSp53 Involved in Actin-Based Force Generation.

Membrane nanotubes are cell protrusions that grow to tens of micrometres and functionally connect cells. Actin filaments are semi-flexible polymers, and their polymerisation provides force for the formation and growth of membrane nanotubes. The molecular bases for the provision of appropriate force through such long distances are not yet clear. Actin filament bundles are likely involved in these processes; however, even actin bundles weaken when growing over long distances, and there must be a mechanism for their regeneration along the nanotubes. We investigated the possibility of the formation of periodic molecular relay stations along membrane nanotubes by describing the interactions of actin with full-length IRSp53 protein and its N-terminal I-BAR domain. We concluded that I-BAR is involved in the early phase of the formation of cell projections, while IRSp53 is also important for the elongation of protrusions. Considering that IRSp53 binds to the membrane along the nanotubes and nucleates actin polymerisation, we propose that, in membrane nanotubes, IRSp53 establishes molecular relay stations for actin polymerisation and, as a result, supports the generation of force required for the growth of nanotubes.

Food Purchase Behavior during The First Wave of COVID-19: The Case of Hungary.

Coronavirus disease (SARSCoV-2) appeared in 2019 was confirmed as pandemic by the WHO on 11 March 2020. Stay-at-home order had an impact on consumers' food purchase habits, as people around the world were able to leave their homes solely in extremely severe or urgent cases. In our research, we delve into the impact of COVID-19 pandemic on consumers' food purchase habits. The research involved 3000 consumers during the first wave of coronavirus. The sample represents the Hungarian population by gender and age. To achieve the research goals, we applied multivariate statistical tools. The findings suggest that the pandemic could not change consumer attitude significantly, but the order of factors influencing purchases changed. Consumer motivation factors were organized into four well-distinguished factors: Healthy, domestic, and environmentally friendly choice; Usual taste and quality; Reasonable price; Shelf life. Due to the lack of outstanding data during segmentation, we developed four segments by hierarchical cluster analysis: Health- and environment-conscious women; Price sensitive young people; Taste-oriented men; Quality-oriented intellectuals. The results confirm that food manufacturers and traders need to be prepared for further restrictions in the future.

Live cell superresolution-structured illumination microscopy imaging analysis of the intercellular transport of microvesicles and costimulatory proteins via nanotubes between immune cells.

Membrane nanotubes are transient long-distance connections between cells that can facilitate intercellular communication. These tethers can form spontaneously between many cell types, including cells of the immune and nervous systems. Traffic of viral proteins, vesicles, calcium ions, mRNA, miRNA, mitochondria, lysosomes and membrane proteins/raft domains have all been reported so far via the open ended tunneling nanotubes (TNTs). Recently we reported on existence of plasma membrane derived GM1/GM3 ganglioside enriched microvesicles and costimulatory proteins in nanotubes connecting B lymphocytes, the way they are formed and transported across TNTs, however, still remained unclear. Here, using live cell confocal and Structured Illumination (SR-SIM) superresolution imaging, we show that B cells respond to bacterial (Cholera) toxin challenge by their subsequent internalization followed by rapid formation of intracellular microvesicles (MVs). These MVs are then transported between adjacent B cells via nanotubes. Selective transport-inhibition analysis of two abundant motor proteins in these cell types demonstrated that actin-based non-muscle myosin 2A dominantly mediates intercellular MV-transport via TNTs, in contrast to the microtubule-based dynein, as shown by the unchanged transport after inhibition of the latter. As suggested by SR-SIM images of GFP-CD86 transfected macrophages, these costimulatory molecules may be transferred by unusually shaped MVs through thick TNTs connecting macrophages. In contrast, in B cell cultures the same GFP-CD86 is dominantly transported along the membrane wall of TNTs. Such intercellular molecule-exchange can consequently improve the efficiency of antigen-dependent T cell activation, especially in macrophages with weak costimulator expression and T cell activation capacity. Such improved T cell activating potential of these two cell types may result in a more efficient cellular immune response and formation of immunological memory. The results also highlight the power of superresolution microscopy to uncover so far hidden structural details of biological processes, such as microvesicle formation and transport.

Context- and Output Layer-Dependent Long-Term Ensemble Plasticity in a Sensory Circuit.

Sensory information is translated into ensemble representations by various populations of projection neurons in brain circuits. The dynamics of ensemble representations formed by distinct channels of output neurons in diverse behavioral contexts remains largely unknown. We studied the two output neuron layers in the olfactory bulb (OB), mitral and tufted cells, using chronic two-photon calcium imaging in awake mice. Both output populations displayed similar odor response profiles. During passive sensory experience, both populations showed reorganization of ensemble odor representations yet stable pattern separation across days. Intriguingly, during active odor discrimination learning, mitral but not tufted cells exhibited improved pattern separation, although both populations showed reorganization of ensemble representations. An olfactory circuitry model suggests that cortical feedback on OB interneurons can trigger both forms of plasticity. In conclusion, we show that different OB output layers display unique context-dependent long-term ensemble plasticity, allowing parallel transfer of non-redundant sensory information to downstream centers. VIDEO ABSTRACT.

Evaluation of ambiguous associations in the amygdala by learning the structure of the environment.

Recognizing predictive relationships is critical for survival, but an understanding of the underlying neural mechanisms remains elusive. In particular, it is unclear how the brain distinguishes predictive relationships from spurious ones when evidence about a relationship is ambiguous, or how it computes predictions given such uncertainty. To better understand this process, we introduced ambiguity into an associative learning task by presenting aversive outcomes both in the presence and in the absence of a predictive cue. Electrophysiological and optogenetic approaches revealed that amygdala neurons directly regulated and tracked the effects of ambiguity on learning. Contrary to established accounts of associative learning, however, interference from competing associations was not required to assess an ambiguous cue-outcome contingency. Instead, animals' behavior was explained by a normative account that evaluates different models of the environment's statistical structure. These findings suggest an alternative view of amygdala circuits in resolving ambiguity during aversive learning.