Integrated Calendar

A wide variety of chemical transformations can be induced by the application of force or stress to reactive systems. In some cases, these reactions are undesired, including some tribochemical (friction-induced) reactions and bond-breaking in polymers under stress. A large and growing set of examples shows that mechanochemistry can be harnessed for useful chemical transformations, making the case for mechanochemistry as a general-purpose tool to advance chemical innovation. In order to realize this vision, we require greater understanding of how force and stress can be focused on particular bonds and reaction coordinates, and how this enhances chemical reactivity and selectivity. In this talk, I will outline strategies for applying stress to quantum-mechanical models of reactive chemical systems and for understanding the resulting mechanochemical reaction pathways. I will also describe the development of interatomic potential models that can enable larger-scale models of mechanochemical and piezoelectric effects in molecules, 2D materials, and polar solids.

Spontaneous neuronal activity in sensory brain regions is spatiotemporally structured, suggesting that this ongoing activity may have a functional role. Nevertheless, the neuronal interactions underlying these spontaneous activity patterns, and their biological relevance, remain elusive. We addressed these questions using two-photon and light-sheet Ca2+ imaging of intact zebrafish larvae to monitor the fine structure of the spontaneous activity in the zebrafish optic tectum (the fish's main visual center. We observed that the spontaneous activity was organized in topographically compact assemblies, grouping functionally similar neurons rather than merely neighboring ones, reflecting the tectal retinotopic map. Assemblies represent all-or-none-like sub-networks shaped by competitive dynamics, mechanisms advantageous for visual detection in noisy natural environments. Furthermore, the spontaneous activity structure also emerged in “naive” tecta (tecta of enucleated larvae before the retina connected to the tectum). We thus suggest that the formation of the tectal network circuitry is genetically prone for its functional role. This capability is an advantageous developmental strategy for the prompt execution of vital behaviors, such as escaping predators or catching prey, without requiring prior visual experience.
Mutant zebrafish larvae for the mecp2 gene display an abnormal spontaneous tectal activity, thus representing an ideal control to shed light on the biological relevance of the tectal functional connectivity. We found that the tectal assemblies limit the span of the visual responses, probably improving visual spatial resolution.

Despite favorable initial response to therapy, a third of cancer patients will develop recurrent disease and succumb to it within five years of diagnosis. While there has been much progress in characterizing the pathways that contribute to stable genetic drug resistance, the mechanisms underlying early reversible resistance, also known as persisters-driven resistance, remain largely unknown. It has long been believed that persisters represent a subset of cells that happen to be non-proliferating at the time of treatment, and therefore can survive drugs that preferentially kill rapidly proliferating cells. However, in my talk I will describe a rare persister population which, despite not harboring any resistance-conferring mutation, can maintain proliferative capacity in the presence of drug. To study this rare, transiently-resistant, cycling persister population, we developed Watermelon, a high-complexity expressed barcode lentiviral library for simultaneous tracing of each cell’s clonal origin and proliferative and transcriptional states. We combine single cell transcriptomics with imaging and metabolomics to show that cycling and non-cycling persisters arise from different cell lineages with distinct transcriptional and metabolic programs. Finally, I will describe how by studying persister cells we can gain critical insights on cellular memory, fate, and evolution, which can guide the development of better anti-cancer treatments.

Alzheimer’s disease (AD) is an age-related neurodegenerative disorder, which is the most common cause of dementia. Among the key hallmarks of AD are neurofibrillary tangles, abnormal amyloid beta (A) aggregation, neuroinflammation and neuronal loss; altogether manifested in progressive cognitive decline. Numerous attempts were made to arrest or slow disease progression by directly targeting these factors, with a limited successes in having a meaningful effect on cognition. In the recent years, the focus of AD research has been extended towards exploring the local and systemic immune response. Yet, the role of the two main myeloid populations, the central nerve system (CNS) resident immune cells, microglia and blood-borne monocyte-derived macrophages (MDM) remain unclear. In my PhD, together with members of the teams, using behavioral, immunological, biochemical and single-cell resolution molecular techniques, we deciphered the distinct role of microglia and MDM in transgenic mouse models of AD pathology. Using single cell RNA sequencing (scRNA-seq) in 5xFAD amyloidosis mouse model, we have identified a new state of microglia, which we named disease associated microglia (DAM) that were found in close proximity to A plaques. The full activation of these cells was found to be dependent on Triggering receptor expressed on myeloid cells 2 (TREM2), a well-known risk factor in late onset AD. To get an insight to the role of MDM relative to microglia, we used an experimental paradigm of boosting the systemic immunity by modestly blocking the inhibitory immune checkpoint pathway, PD-1/PD-L1, which was previously shown to be beneficial in ameliorating AD in 5xFAD mice, via facilitating homing of MDM to the brain. We found that the same treatment is efficient also in mouse model of tauopathy and that the MDM homing to the brain following the treatment expressed a unique set of scavenger molecules, including macrophage scavenger receptor 1 (MSR1). We found that MDM expressing MSR1 are essential for the disease modification. Using the same immune-modulatory treatment in a mouse model deficient in TREM2 (Trem2-/-5xFAD) and thus in DAM, allowed us to distinguish between the contribution to the disease modification of MDM and DAM. We found, that MDM display a Trem2-independent role in the cognitive improvement. In both Trem2-/-5xFAD and Trem2+/+5xFAD mice the treatment effect on behavior was accompanied by a reduction in the levels of hippocampal water-soluble Aβ1-42, a fraction of A that contains toxic oligomers. In Trem2+/+5xFAD mice, the same treatment seemed to activate additional Trem2-dependent mechanism, that could involve facilitation of removal of Aβ plaques by DAM or by other TREM2-expressing microglia. Collectively, our finding demonstrates the distinct role of activated microglia and MDM in therapeutic mechanism of AD pathology. They also support the approach of empowering the immune system to facilitate MDM mobilization as a common mechanism for treating AD, regardless of primary disease etiology and TREM2 genetic polymorphism.