Minimal in vitro systems shed light on cell polarity

Abstract

Cell polaritythe morphological and functional differentiation of cellular compartments in a directional manneris required for processes such as orientation of cell division, directed cellular growth and motility. How the interplay of components within the complexity of a cell leads to cell polarity is still heavily debated. In this Review, we focus on one specific aspect of cell polarity: the non-uniform accumulation of proteins on the cell membrane. In cells, this is achieved through reaction-diffusion and/or cytoskeleton-based mechanisms. In reaction-diffusion systems, components are transformed into each other by chemical reactions and are moving through space by diffusion. In cytoskeleton-based processes, cellular components (i.e. proteins) are actively transported by microtubules (MTs) and actin filaments to specific locations in the cell. We examine how minimal systemsin vitro reconstitutions of a particular cellular function with a minimal number of componentsare designed, how they contribute to our understanding of cell polarity (i.e. protein accumulation), and how they complement in vivo investigations. We start by discussing the Min protein system from Escherichia coli, which represents a reaction-diffusion system with a well-established minimal system. This is followed by a discussion of MT-based directed transport for cell polarity markers as an example of a cytoskeleton-based mechanism. To conclude, we discuss, as an example, the interplay of reaction-diffusion and cytoskeleton-based mechanisms during polarity establishment in budding yeast.

Motor-mediated clustering at microtubule plus ends facilitates protein transfer to a bio-mimetic cortex

“…We found that motor-mediated protein clusters formed at microtubule ends were able to transfer to the walls, but non-clustered proteins were not.We further show that this transfer mechanism leads to preferential cluster accumulation at chamber poles, when microtubules are confined to elongated microfabricated chambers with sizes and shapes similar to S. pombe. may in principle be formed, either based on reaction-diffusion principles and/or dependent on cytoskeletal processes [Vendel et al 2019], but the exact mechanisms are not yet understood. Here we focus on the principles behind establishment of polarized protein distributions in the model system fission yeast, where dynamic microtubules are essential in targeting cell-end specific factors to the cell poles.…”

A Cell Adhesion-Based Reconstitution Method for Studying Cell Polarity

“…In recent years, several methods have been developed that offer novel means of reconstituting polarity in non-polar environments ( Table 1). Several approaches have also been developed for prokaryotic and simple eukaryotic yeast cells (Vendel et al, 2019). Here, I describe an "induced polarity" assay protocol used in cultured Drosophila S2 cells that utilizes the cell adhesion protein, Echinoid (Ed), to reconstitute cortical polarity in these otherwise non-polar cells (Figure 1; Johnston et al, 2009).…”

Microfluidic trapping of vesicles reveals membrane-tension dependent FtsZ cytoskeletal re-organisation

“…In the future, it would be interesting to study the shapedependent effects on other reaction-diffusion and cell-polarity inducing systems, such as Cdc42. 39 Equally, the effects on other cell division systems than FtsZ, e.g. MreB, or cellular signalling, could be elucidated.…”