Reconstructing cell surface dynamics from lightsheet microscopy data

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Recent advances in light microscopy have made it possible to acquire fast high-quality 3D scans of single cells. The new techniques are so gentle that live cells can be followed over long periods of time without disrupting their normal behavior. The possibility to accurately reconstruct the outer cell envelope in 3D opens a new window on two distinct biological processes we are investigating, where the cell envelope bulges either outwards or inwards, in a very distinct manner.During blebbing, the first of these two processes, the cell envelope rapidly bulges outwards in form of a blister. It is an important mechanism found in cell locomotion, where blebs are directed to the cell front, for example in immune cells chasing pathogens, spreading tumour cells, and during development of organisms.Macropinocytosis, the second mechanism we are investigating, is the technical term for cell drinking. The outer cell envelope bulges inwards to form a cup like structure. In a process that is not yet understood, the lip of this cup closes, and fluid that previously surrounded the cell is being internalized. Macropinocytosis plays important roles in taking up nutrients for feeding, supporting for example the high demand of fast growing tumour cells. It also is relevant for sampling antigens by immune cells, and can be exploited by pathogens to invade cells. Contrary, it can be exploited as a route of entry for drugs into cells.Blebbing and macropinocytosis share commonality in that they both involve the shaping of the cell envelope under physical forces that are generated by molecules interacting with the envelope. These molecules belong to what is called the cellular cytoskeleton, a structure that is not static but needs to be constantly remodeled. Using a similar approach to tackle both problems, we will acquire detailed 3D scans of the cell envelope and image components of the cytoskeleton and its regulators that have previously been shown to play a role in blebbing and macropinocytosis.Advanced image analysis will then be used to generate spatial maps of the molecular events and deformations of the cell envelope, and how they change over time. These maps will be used to construct mathematical and computer models that help us to infer how molecular events relate to forces acting on the cell envelope. Previous models developed by us successfully predicted where on the cell envelope blebs are going to form, but lack of high quality 3D image data prevented us to enquire further how blebs grow and stop for example.We will take advantage of the new, fast 3D microscopy to investigate the mechanisms that lead to the bulging out or of the bulging in, of the cell envelope in Dictyostelium discoideum. Dictyostelium discoideum is an amoeboid type of non-animal cell in which blebbing and macropinocytosis have been well studied. Asking whether one of our previous discoveries, namely that bleb site localisation in Dictyostelium largely depends on cell geometry, also applies to animal cells, we will conduct a small study in blebbing cells during early development of zebrafish, where blebbing is known to play an important role.Long term goal of the project is to contribute to a better understanding of how the dynamic cytoskeleton can be programmed to fulfill so many different functions, ranging from cell locomotion and cell eating, to the immune response. And, how we could exploit this, for example to prevent entry of pathogens into cells or enhance the uptake of drugs.