Biological Systems at Sub-cellular Scale: Investigation of G-actin Transport in Filopodia

Abstract

In our research of biological systems at the sub-cellular scale we focus on the cytoskeleton, particularly its components actin-filaments and microtubules, which are key mediators of axon growth and maintenance. Knowing how filaments and microtubules are regulated enhances our understanding of neural development, ageing, degeneration and regeneration. In the cytoskeletal machinery, finger-like, extremely narrow and long, membrane protrusions called filopodia act as sensors, facilitating proper cellular navigation and directed growth. Since explanations of dynamical and mechanical aspects of filopodia, centred in diffusion and transport processes, are being studied, we investigate the displacement of actins in the filopodia and discuss compensatory G-actin drift and diffusion towards the filopodia tip to supply the polymerisation of actins into filaments moving backwards. We conclude, through some simple calculations, that diffusion alone cannot provide the necessary actins to the polymerisation processes in all situations. Therefore, advection processes and Stokes equation need to be added to diffusion models to better simulate the colloidal fluid dynamics in filopodia cell-membrane protrusions.