Microtubules are structural scaffolding within cells. They’re a bit like the poles in a tent, but they’re constantly growing and shrinking depending on what the cell needs. They’re made up of individual proteins that assemble into tubes by stacking onto each other like a spiral staircase. Similar structures are created from a protein from actin. Actin is one of the components of muscles and can contract to pull a cell into a particular shape. Until recently, it was thought actin only assembled into tubes in the cytoplasm, and existed as individual proteins in the nucleus.
An international collaboration between three research groups has just been awarded a grant to investigate these nuclear actin filaments using optogenetics. Optogenetics uses proteins that are sensitive to light to initiate changes inside cells. This study uses a protein that is folded over under normal conditions, but springs open when exposed to a certain kind of light. Hidden inside the closed version is a filament nucleation site. When the protein springs open microtubule proteins collect at the nucleation site and start to form actin filaments. This protein will be inside the nucleus of cells, and when these cells are exposed to light, actin filaments will form inside the nuclei.
These cells will be photographed using very powerful automated microscopes. Researchers can look at how the nucleus changes under different conditions by sticking fluorescent markers to particular proteins and watching them move around. They can see if the structure of DNA inside the nucleus changes by fixing the DNA in it’s current form, slicing it up, and then sequencing each piece to see which ones are usually stuck together.
This illustration was created for Dr Abderrahmane Kaidi who leads a research group at the University of Bristol.