Stretching cells with Patricia Bassereau
Patricia Bassereau likes a challenge. Cell physics is an emerging field and her team is one of just a handful around the world working on developing new techniques to further research in the area. She makes giant liposomes, vesicles measuring a dozen micrometers across (thousandths of a millimeter in diameter), made from a membrane surrounding a liquid, like a simplified living cell stripped of its content. She holds these liposomes at one end using optical tweezers and pulls on the other end with a micro-pipette to form nanotubes.
By adding select proteins to these membranes, she can then study the effects of these tubes’ curvature on the proteins, and conversely, the effects of the proteins on the membranes’ curvature. She took a closer look at one protein in particular, ezrin, known for being present on cell membranes’ internal surfaces in abundant amounts, and in particular in outgrowths known as protrusions. She demonstrated that when ezrin is present alone, it is not particularly abundant in a curved membrane. But when combined with another protein, IRSp53, which prefers curved membranes, ezrin can be ‘recruited’. This information is key to understanding how membranous protrusions such as filopodia are formed, which allow cancerous cells to move around and invade other organs, forming metastases as a result.
Patricia Bassereau also presented her team’s work into myosin 1b, a protein that is much less well-known than its cousin, myosin II, involved in muscular contraction. Like ezrin, this protein binds to the membrane at one end and to another protein, actin, at the other end, forming a bridge between the two. Patricia Bassereau’s team showed that myosin 1b slows down growth in the actin filaments that form the skeletons of the protrusions, while sliding these filaments along the cell membrane. These results could help explain the disruptions observed by Evelyne Coudrier on neuron morphology when myosin 1b is not present.
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