Integrated Calendar

In this seminar, two new models will be presented. The first new model is a first-principles description of the propagation of light in a cloud, based on a classical solution to Maxwell's equations rather than radiative transfer theory. The second new model is a fully three-dimensional, time-dependent model of the regions of possible sprite inception in the mesosphere, based on the classical method of images from electrostatics rather than finite differencing in space. The reason why each model is unique, the problems each model can solve, and the kinds of results each model can produce will be discussed

Cell-cell communication is essential for growth, development and function. Cells can communicate mechanically by responding to mechanical deformations generated by their neighbors in the extracellular matrix (ECM).We use a 2D cardiac tissue model to study the role of mechanical communication between cardiac cells in the normal conduction wave. We quantify the mechanical coupling between cells in a monolayer and use this to identify a critical threshold of mechanical coupling, below which spiral waves are induced in the tissue. We demonstrate that normal conduction wave can be recovered only using mechanical stimulation. We further show that mechanical coupling reduces the sensitivity to geometrical defects in the tissue.We show that due to the dynamic viscoelastic properties of collagen hydrogels (a major component of the cardiac ECM), the shape of the mechanical signal changes in a frequency dependent manner as it propagates through the gel, leading to a frequency dependent mechanical communication. Moreover, we show that the sensitivity of cardiac cell response to the shape of the mechanical signal results from its sensitivity to the loading rate. We also show that an optimal loading rate exists for mechanical communication, implying that there are ideal viscoelastic properties for effective mechanical communication.FOR THE LATEST UPDATES AND CONTENT ON SOFT MATTER AND BIOLOGICAL PHYSICS AT THE WEIZMANN, VISIT OUR WEBSITE: https://www.biosoftweizmann.com/

There are two major classes of theories about the basal ganglia. The first class hypothesizesthat the basal ganglia are the site where cortical sensorimotor and dopaminergic rewardinformation interact to potentiate and select actions. These theories predict that contentspecificity of information emerges from within the basal ganglia. The second class oftheories posits that information is manipulated within the basal ganglia through processessuch as dimensionality reduction. These theories are primarily based on the fact that thereis a large reduction in the number of neurons from the input to the output stages of the basalganglia. These theories posit that there are changes in the coding properties of neuronsrather than the emergence of content specificity.In this talk, I will present a set of studies where we analyzed the eye movement system ofmonkeys to compare single-neuron activity in the basal ganglia with activity in thecerebellum and the frontal cortex. We used tasks that manipulated both eye movementsand expected rewards. We found that rather than coding specific sensorimotor or rewardparameters, the basal ganglia were unique in how they coded these parameters, both interms of the signal-to-noise ratio of responses and in the variety of their temporal patterns.These results strongly suggest that the basal ganglia play a role in manipulating rather thangenerating reward and sensorimotor signals.

The pre-industrial Holocene is unique among pastinterglacials due to a modest, but notable increase inatmospheric CO2 and methane (CH4) during the latter halfof the period despite an expected decrease given orbitalparameters. Although the causes for this increase,anthropogenic or natural are debated, all climate modelssimulate an increase in global mean temperature inresponse to the increase in the greenhouse gases. Yet,many proxy reconstructions, interpreted to reflect themean annual temperatures, indicate peak temperatures inthe first half of the Holocene, arguably exceeding modernmean annual temperatures followed by cooling through thepreindustrial period. This significant model-datadiscrepancy, known as the Holocene temperatureconundrum, and the debate on the cause of the CO2increase has undermined confidence in future climatemodel predications. In this talk I’ll offer new perspectiveson both issues.

As life expectancy increases, age-related diseases are becoming more prevalent. While these conditions are traditionally studied in isolation, mounting evidence points to shared, systemic mechanisms underlying these conditions. Our research highlights the vasculature as  a key player in organ homeostasis and repair, and a system shared across all organs—making its dysfunction potential driver of age-related pathologies.We demonstrate that manipulating VEGF signaling to counteract age-related microvascular rarefaction promotes comprehensive geroprotection, preserving organ function and delaying disease onset. Our findings also reveal a link between vascular rarefaction and altered RNA splicing. While hypoxia-driven and age-related changes in alternative RNA splicing have been studied independently, we propose a unifying mechanism that links the two. To explore this further, we also employ patient-derived organoids, which retain their biological age in culture, providing a robust in vitro platform to test anti-aging interventions.Our findings support a vascular theory of aging, identifying vascular health as a promising target to mitigate age-related diseases and promote healthier aging.

While sexual dimorphisms in brain structure and function are well-documented across species, the specific features and mechanisms underlying sex differences in individual neurons and how these differences drive behavior remain largely unknown. Most research has focused on sex-specific neurons, limiting insight into how shared neural circuits diverge between sexes. Using C. elegans, we investigated sex differences in shared neuronal modules through two approaches: 1. To explore circuit-level sex differences we dissected the neuronal properties of a sexually dimorphic circuit shared by both sexes, focusing on the circuit responsible for mechanosensation (the detection of mechanical stimulation), specifically touch sensation, in both sexes of C. elegans. We discovered that touch is detected through a distinctly different set of neurons in each sex, and this process involves unique molecules and receptors that operate in a sex-specific manner. One of these key molecules is the ion channel TMC-1, critical for hearing in humans. This study identified for the first time that touch can be sensed differently by the two sexes of an organism. 2. To investigate genetic sex differences at the level of individual sex-shared neurons, we mapped the nervous system of C. elegans in both sexes using single-cell RNA sequencing. By analyzing gene expression patterns in the nervous system of both sexes derived from the transcriptomic profiles, we discovered novel sexually dimorphic neurons and their relevance to behavior and neuronal function. We further conducted computational analysis on our single-cell data set to predict synaptic connectivity regulators based on gene expression, leading to the identification of several candidate genes now under investigation. Taken together, our work revealed multiple cellular and molecular pathways that operate differently between the sexes, shedding light on how an organism's sexual identity shapes the organization of its nervous system.