Crowding Induces Entropically-Driven Changes to DNA Dynamics That Depend on Crowder Structure and Ionic Conditions.

Macromolecular crowding plays a principal role in a wide range of biological processes including gene expression, chromosomal compaction, and viral infection. However, the impact that crowding has on the dynamics of nucleic acids remains a topic of debate. To address this problem, we use single-molecule fluorescence microscopy and custom particle-tracking algorithms to investigate the impact of varying macromolecular crowding conditions on the transport and conformational dynamics of large DNA molecules.

Universal scaling of crowding-induced DNA mobility is coupled with topology-dependent molecular compaction and elongation.

Using single-molecule fluorescence microscopy and particle-tracking techniques, we elucidate the role DNA topology plays in the diffusion and conformational dynamics of crowded DNA molecules. We focus on large (115 kbp), double-stranded ring and linear DNA crowded by varying concentrations (0-40%) of dextran (10, 500 kDa) that mimic cellular conditions. By tracking the center-of-mass and measuring the lengths of the major and minor axes of single DNA molecules, we characterize both DNA mobility reduction as well as crowding-induced conformational changes (from random spherical coils).

The diagnosis of silicone breast implant rupture.

Magnetic resonance imaging of the breast in the diagnosis of silicone breast implant rupture is widely accepted to be the imaging study of choice for most women. Magnetic resonance imaging in the detection of silicone implant failure has been shown to have the highest sensitivity and specificity and has the ability to image the entire implant without the use of ionizing radiation. Unfortunately, some women are unable to have a magnetic resonance imaging examination of the breast because of contraindications such as cardiac pacemakers, aneurysm clips, and claustrophobia.