Mechanics of post-fusion exocytotic vesicle

From cells to sensations: A window to the physics of mind

Principles of methods for studying particles and fields that cannot be sensed by third-person observers by routine methods can be used to understand the physics of first-person properties of mind. Accordingly, whenever a system exhibits disparate features at multiple levels, unique combination of constraints offered by them direct us towards a solution that will be the first principle of that system. Using this method, it was possible to arrive at a third-person observable solution-point of brain-mind interface. Examination of this location identified a set of unique features that can allow an associatively learned (cue) stimulus to spark hallucinations that form units of first-person internal (inner) sensations reminiscent of stimuli from the associatively learned second item in timescales of milliseconds. It allows us to peep into a virtual space of mind where different modifications and integrations of units of internal sensations generate their different net conformations ranging from perception to an inner sense of hidden relationships that form a hypothesis. Since sparking of inner sensations of the late arriving (when far away) or non-arriving (when hidden) features of items started providing survival advantage, the focus of evolution might have been to optimize this property. Hence, the circuity that generates it can be considered as the primary circuitry of the system. The solution provides several testable predictions. By taking readers through the process of deriving the solution and by explaining how it interconnects disparate findings, it is hoped that the factors determining the physics of mind will become evident.

Biophysics at the coffee shop: lessons learned working with George Oster

Over the past 50 years, the use of mathematical models, derived from physical reasoning, to describe molecular and cellular systems has evolved from an art of the few to a cornerstone of biological inquiry. George Oster stood out as a pioneer of this paradigm shift from descriptive to quantitative biology not only through his numerous research accomplishments, but also through the many students and postdocs he mentored over his long career. Those of us fortunate enough to have worked with George agree that his sharp intellect, physical intuition, and passion for scientific inquiry not only inspired us as scientists but also greatly influenced the way we conduct research. We would like to share a few important lessons we learned from George in honor of his memory and with the hope that they may inspire future generations of scientists.

The Actomyosin Cytoskeleton Drives Micron-Scale Membrane Remodeling In Vivo Via the Generation of Mechanical Forces to Balance Membrane Tension Gradients

The remodeling of biological membranes is crucial for a vast number of cellular activities and is an inherently multiscale process in both time and space. Seminal work has provided important insights into nanometer-scale membrane deformations, and highlighted the remarkable variation and complexity in the underlying molecular machineries and mechanisms. However, how membranes are remodeled at the micron-scale, particularly in vivo, remains poorly understood. Here, we discuss how using regulated exocytosis of large (1.5-2.0 μm) membrane-bound secretory granules in the salivary gland of live mice as a model system, has provided evidence for the importance of the actomyosin cytoskeleton in micron-scale membrane remodeling in physiological conditions. We highlight some of these advances, and present mechanistic hypotheses for how the various biochemical and biophysical properties of distinct actomyosin networks may drive this process.

Effect of Osmotic Pressure on Cellular Stiffness as Evaluated Through Force Mapping Measurements

Atomic force microscopy (AFM) has been used to measure cellular stiffness at different osmolarities to investigate the effect of osmotic pressure on cells. However, substantial direct evidence is essential to clarify the phenomena derived from the experimental results. This study used both the single-point and force mapping methods to measure the effective Young's modulus of the cell by using temporal and spatial information. The single-point force measurements confirmed the positive correlation between cellular stiffness and osmolarity. The force mapping measurements provided local stiffness on the cellular surface and identified the cytoskeleton distribution underneath the plasma membrane. At hyper-osmolarity, the cytoskeleton was observed to cover most of the area underneath the plasma membrane, and the effective Young's modulus on the area with cytoskeleton support was determined to be higher than that at iso-osmolarity. The overall increase in cellular Young's modulus confirmed the occurrence of cytoskeleton compression at hyper-osmolarity. On the other hand, although the average Young's modulus at hypo-osmolarity was lower than that at iso-osmolarity, we observed that the local Young's modulus measured on the areas with cytoskeleton support remained similar from iso-osmolarity to hypo-osmolarity. The reduction of the average Young's modulus at hypo-osmolarity was attributed to reduced cytoskeleton coverage underneath the plasma membrane.