Active cellular propulsion

Short term visitor's project

Amoeboid motion refers to the motion of objects through shape changes. It has long been recognized that cells undergo large shape changes during motion. Such amoeboid motion is typically categorised as as two-dimensional crawling (based on adhesion to the substrate) and three-dimensional motion. One of the possible modes of this three-dimensional motion corresponds to amoeboid swimming, where adhesive forces do not play a role. In such amoeboid swimming, it was shown that the mechanical properties of the cell play a role. In a typical biological environment, the cell is likely to be in a fluid with several nearby tissues and appendages. In such cases, it is clear that the cell will employ a combination of both modes to move. In order to attack this problem theoretically, it is essential to examine the key assumptions in the existing model and successively relax them and replace them with more realistic ones.

As a start we have considered methods which include traction on surrounding tissues and/or adhesion to substrates in amoeboid motion. In amoeboid motion, the cell can use these attractive forces to propel its motion. It is also clear that these adhesion based motion vs pure swimming motion will dominate during different stages of motion, so a combined model that allows for many different modes of motion is useful. A key assumption in our model of amoeboid swimming is that the membrane of the cell is inextensible. This was partially relaxed by endowing the membrane with a stretch modulus, but, nevertheless, the fluidity of the membrane is ignored and there was no flow in the membrane. Indeed, during motion, real cells show a large amount of actin recirculation within their membrane. The coupling of this flow to amoeboid motion is an exciting challenge which we will address during the course of this project. In this case, the mechanical and rheological properties of the cell will play an important part and results from experiments with model microcapsules and real cells will provide additional inputs to the models. For instance, the cortex viscosity which governs the fluidity of the membrane will be determined from experiments and these values will be inputs to the model. Thus the complementary expertise of the groups of the PI and the co-PI will be combined with the expertise of the international visitor to develop and test new models for cellular locomotion.