Ode to being In-Between

A poem about melancholy, loneliness, airports, and travelling

Gasdermins in Apoptosis: New players in an Old Game.

Apoptosis is a form of programmed cell death (PCD) that plays critical physiological roles in removing superfluous or dangerous cell populations that are unneeded or threatening to the health of the host organism. Although the molecular pathways leading to activation of the apoptotic program have been extensively studied and characterized starting in the 1970s, new evidence suggests that members of the gasdermin superfamily are novel pore-forming proteins that augment apoptosis by permeabilizing the mitochondria and participate in the final stages of the apoptotic program by inducing secondary necrosis/pyroptosis. These findings may explain outstanding questions in the field such as why certain gasdermin members sensitize cells to apoptosis, and why some apoptotic cells also show morphological features of necrosis. Furthermore, the interplay between the gasdermins and apoptosis may also explain why genetic and epigenetic alterations in these genes cause diseases and disorders like cancer and hearing loss. This review focuses on our current understanding of the function of several gasdermin superfamily members, their role in apoptosis, and how they may contribute to pathophysiological conditions

Minimal energy packings and collapse of sticky tangent hard-sphere polymers

We enumerate all minimal energy packings (MEPs) for small single linear and ring polymers composed of spherical monomers with contact attractions and hard-core repulsions, and compare them to corresponding results for monomer packings. We define and identify ``dividing surfaces" in polymer packings, which reduce the number of arrangements that satisfy hard-sphere and covalent bond constraints. Compared to monomer MEPs, polymer MEPs favor intermediate structural symmetry over high and low symmetries. We also examine the packing-preparation dependence for longer single chains using molecular dynamics simulations. For slow temperature quenches, chains form crystallites with close-packed cores. As quench rate increases, the core size decreases and the exterior becomes more disordered. By examining the contact number, we connect suppression of crystallization to the onset of isostaticity in disordered packings. These studies represent a significant step forward in our ability to predict how the structural and mechanical properties of compact polymers depend on collapse dynamics.Comment: Supplementary material is integrated in this versio

Isostaticity at Frictional Jamming

Amorphous packings of frictionless, spherical particles are isostatic at jamming onset, with the number of constraints (contacts) equal to the number of degrees of freedom. Their structural and mechanical properties are controlled by the interparticle contact network. In contrast, amorphous packings of frictional particles are typically hyperstatic at jamming onset. We perform extensive numerical simulations in two dimensions of the geometrical asperity (GA) model for static friction, to further investigate the role of isostaticity. In the GA model, interparticle forces are obtained by summing up purely repulsive central forces between periodically spaced circular asperities on contacting grains. We compare the packing fraction, contact number, mobilization distribution, and vibrational density of states using the GA model to those generated using the Cundall-Strack (CS) approach. We find that static packings of frictional disks obtained from the GA model are mechanically stable and isostatic when we consider interactions between asperities on contacting particles. The crossover in the structural and mechanical properties of static packings from frictionless to frictional behavior as a function of the static friction coefficient coincides with a change in the type of interparticle contacts and the disappearance of a peak in the density of vibrational modes for the GA model. These results emphasize that mesoscale features of the model for static friction play an important role in determining the properties of granular packings.Comment: 4.5 pages, 5 figures, http://prl.aps.org/covers/110/1