Description:

A fundamental pattern of many living cells is medial division followed by polarized growth. I will discuss recent advancements made in fission yeast, a model organism, where the integration of genetics, microscopy, and biochemistry has facilitated the development of mathematical and computational models elucidating the underlying biophysical mechanisms. Medial division during cytokinesis is powered by a contractile ring comprising actin filaments and myosin motor proteins. The assembly of this ring is orchestrated by "nodes," large protein assemblies forming a medial band on the plasma membrane. These nodes condense into a ring as actin filaments, polymerized by node-bound formins, are pulled by node-bound myosin. Nodes thus serve to stabilize long-range connections across the cell while also existing as structures between molecular and sub-μm scales. A defining characteristic of node proteins is their long intrinsically disordered regions (IDRs). I will present computational modeling and experimental efforts by collaborators demonstrating how phosphorylation promotes timely node assembly by modulating node IDR phase separation properties. Polarized growth requires non-equilibrium flows to create concentration gradients. I will argue that such gradients are established by a combination of a Turing-type mechanism based on activation of membrane-bound Cdc42 protein, coupled to membrane flows driven by vesicle secretion, which displaces Cdc42 inhibitors. The relative importance of reaction-diffusion versus transport by the membrane is revealed when we alter the mobility of Cdc42, either in theoretical models or experiments by our collaborators.

Dimitrios Vavylonis, Professor, Lehigh University

Host: Michelle Driscoll