Our goal is to understand how protocells developed signaling mechanisms that allowed them to communicate and coordinate their actions. The capability to respond to signals, move, and assemble into cohesive colonies would have significantly improved the protocells’ survivability and enhanced their functionality. Early protocells lacked complex biochemical machinery and thus, communication was most likely driven by fundamental physical/chemical mechanisms, including diffusion of molecules across the membrane. In this context, it is worth considering the behavior of primitive organisms, such as Dictyostelium discoideum (slime molds or social amoebas) who survive and replicate by releasing chemo-attractants, which drive them to move towards each other and aggregate into larger colonies. Based on the survival tactics of these primitive organisms, we hypothesize that this mode of communication—the release of signaling molecules, recognition of these molecules and motion in response to gradients of these molecules—served as a useful mechanism for protocell-protocell communication. To this end, we develop computational models that provide an ideal starting point for integrating both the spatial and temporal behavior of assemblies of protocells and investigating the role of physicochemical phenomena in enabling responsive, collective behavior. In these studies, micron-sized capsules release signaling inhibitor and promoter molecules, which modify the permeability of the capsules’ shells and create local adhesion gradients on an underlying surface. Hence, these capsules both sense and modify this environment. Due to this mode of signaling, these capsules can self-organize into various autonomously moving structures. Our findings also demonstrate the importance of noise and hydrodynamics in guiding the self-organization of the capsules. The results of these studies can provide some insight into communication and collective behavior among early protocells.
Anna C. Balazs
Chemical Engineering Department
University of Pittsburgh, Pittsburgh, PA