Seminars

Fall 2021

Modeling cell motility - shape, polarity, and the cytoskeleton
Brian Camley, Department of Biophysics, Johns Hopkins University
November 19, 2021, 10:00 am – 11:00 am Virtual MS Teams Link.

Abstract:

Crawling eukaryotic cells are soft matter driven out of equilibrium by active forces - and their physical properties also strongly constrain cell function. I will present two stories from recent work from my group, one on cell polarity, and one on cytoskeletal dynamics and active gels. First, I will discuss the group's recent work on how reaction-diffusion processes on the cell's surface can become sensitive to cell shape. This shape sensing can lead to surprising new behaviors, like single cells developing a spontaneous circular motion, but can be disrupted by membrane roughness. Secondly, I will discuss the statistics of extreme events in cytoskeletal dynamics. Recent experimental work suggests that tracers attached to the cell's cortex undergo diffusion with rare large jumps - diffusion with heavy tails. I will show how heavy tails arise naturally from a classical theory of actively-driven gels, and how this depends on the mechanics and geometry of the cortex.

Modeling Spatial Waves of Wolbachia Invasion for Controlling Mosquito-Borne Diseases
Zhuolin Qu, Department of Mathematics, University of Texas at San Antonio
October 29, 2021, 10:00 am – 11:00 am Virtual MS Teams Link.

Abstract
Wolbachia is a natural bacterium that can infect mosquitoes and reduce their ability to transmit mosquito-borne diseases, such as dengue, Zika, and chikungunya. Field trials and modeling studies have shown that the fraction of infection among the mosquitoes must exceed a threshold for the infection to persist. To capture this threshold, it is critical to consider the spatial heterogeneity in the distributions of the infected and uninfected mosquitoes, which is created by the release of the infected mosquitoes. We develop and analyze partial differential equation models to study the invasion dynamics of Wolbachia infection among mosquitoes in the field. Our reaction-diffusion-type models account for both the complex vertical transmission and the spatial mosquito dispersion. We characterize the threshold for a successful invasion, which is a bubble-shaped profile, called the “critical bubble”. The critical bubble is optimal in its release size compared to other spatial profiles in a one-dimensional landscape.  The fraction of infection near the release center is higher than the threshold level for the corresponding homogeneously mixing ODE models.  We show that the proposed spatial models give rise to the traveling waves of Wolbachia infection when above the threshold. We quantify how the threshold condition and traveling-wave velocity depend on the diffusion coefficients and other model parameters. Numerical studies for different scenarios are presented to inform the design of release strategies. This is a joint work with Tong Wu and James M. Hyman.