Quantifying the contributions of obstructions and protein-protein interactions to anomalous diffusion in cell nuclei
Date:
Authors
Matthew K. Daddysman, Michael A. Tycon, Christopher J. Fecko
Abstract
Most proteins exhibit anomalous subdiffusion in cell nuclei. The source of this behavior is not well understood but is commonly attributed to a combination of crowding and binding of proteins. In order to separate the contributions of these two effects, we measured the diffusion of unconjugated GFP in the polytene cells of Drosophila salivary glands using two-photon excited fluorescence recovery after photobleaching (FRAP). In polytene cells, we can resolve GFP diffusion behavior in nuclear regions containing chromosomes from regions devoid of chromosomes. Interestingly, we observed anomalous diffusion of GFP in the chromosomal regions only; GFP diffuses normally in the interchromosomal space of the polytene nuclei. This observation indicates that obstructed diffusion through chromatin is a primary source of anomalous diffusion in cell nuclei. Additionally, we measured the diffusion of GFP in crowded dextran solutions in vitro. At the dextran concentrations that result in the same diffusion coefficients as observed in the interchromatin space of polytenes, GFP also diffuses normally. These observations indicate that macromolecular crowding is likely not the source of nuclear anomalous diffusion.