In Nanoscopic Detail
For over one hundred years it was believed that the maximum resolution of a microscope is related to the wavelength of light and therefore optical microscopes could never be used to resolve objects of less than 0.2 micrometres. The three Nobel winners independently developed techniques to get around this limitation.
This work has enormous potential in the study of biological processes—individual virus particles or proteins can now be resolved in a cell using fluorescent imaging. This level of detail was previously only possible using techniques such as electron microscopy, which cannot be performed on live cells. Its use has already been demonstrated in my main area of research, the inherited disorder Huntington’s disease.
Neurodegeneration in Huntington’s is characterised by the build up of aggregates of mutant huntingtin protein in neuronal cells. The jury is still out as to whether these aggregates are the cause of neuronal cell death or the bodies’ way of clearing toxic huntingtin molecules from the cytosol. However, understanding how aggregates form is an important step in understanding how the disease progresses. Fluorescently tagged aggregates are large enough to be studied by regular microscopy but the bright signal from a dense huntingtin aggregate can swamp the signal from a smaller oligomer and individual protein molecules are not visible at all.
Moerner used his prize-winning technique of super-resolution imaging to define the distribution of genetically expressed fragments of the huntingtin protein in cells. Individual linear oligomers of ~80-100 nM were resolved in addition to small aggregates and larger inclusion bodies. In other words, Moerner was able, for the first time, to see aggregates in all stages of their formation and to hypothesize about the biological processes behind their formation.
The ultimate goal is to perform live-cell real-time studies of huntingtin aggregates forming and growing. Further extension using multicolored fluorescence may be possible, enabling the study of interactions between aggregating huntingtin and other proteins within the cell. This insight may help us identify new potential mechanisms to modulate the formation of aggregates and allow us to look at the effect of potential therapeutic intervention at the molecular level. For instance, can small molecules be identified that alter the rate of aggregation?
The Nobel committee has recognized eye-opening advances that will undoubtedly increase our understanding of a wide range of biological processes. Super-resolution studies have already been performed on protein aggregation in Alzheimer’s and Parkinson’s disease. Co-winner Hell focused his nanoscope on living nerve cells to study brain synapses and Betzig has used his technique to produce super-resolution images of cell division within embryos.