Biological physics

My biological physics research is on liquid/liquid phase separation, and on the dynamics of proteins and RNA, in both cases inside cells.

Liquid droplets inside cells

We have known for a while that what looks very much like liquid/liquid phase separation occurs inside living cells, and that the resulting liquid droplets are at least correlated with function. For example, the wonderfully named protein Dishevelled can form liquid droplets inside cells, at least when biologists increase its concentration in a cell. These droplets are dynamics, molecules leave and enter them, and two droplets can coalesce. Over the last ten years, this field has really taken off with droplets of many different types being observed.

We still have very little idea of how many of these droplets contribute to the function of cells, or how cells regulate them. Above is just a simple simulation in which I turn on a chemical reaction about a third of the way through, and then accelerate this reaction two thirds of the way through. We have known since work of Glotzer and co-workers in the 1990s that a chemical reaction that cycles molecules through two states, can stop the growth of droplets, and you can see this in the movie above.

Transport in cells


The complex viscous energy-consuming fluid inside cells is very far from uniform, and very far from thermodynamic equilibrium. In a Physical Review Letter (arXiv), I suggest that larger particles (about 100 nm across) inside cells may move around in cells at least partly by surfing these gradients. Motion of particles due to concentration gradient is called diffusiophoresis, which is quite topical at the moment.

Older work

Modelling diffusion inside cells of the protein whose absence causes Duchenne muscular dystrophy

I have collaborated with muscle cell biologists on modelling the dynamics of the protein Dystrophin inside live muscle cells. Dystrophin is a medically important protein, the absence of this protein causes the genetic disease Duchenne Muscular Dystrophy. This work was published in eLife in October 2015. This site hosts the app used there. There is a news release on this work.

I was co-chair of the CECAM workshop ‘The Self-Organised Cytoplasm‘ in July 2014 (report here).