Spatio-temporal analysis of DNA damage repair using the X-ray microbeam

Cellular response to radiation damage is made by a complex network of pathways and feedback loops whose spatiotemporal organization is still unclear despite its decisive role in determining the fate of the damaged cell. The single-cell approach and the high spatial resolution offered by microbeams provide the perfect tool to study and quantify the dynamic processes associated with the induction and repair of DNA damage. The soft X-ray microbeam has been used to follow the development of radiation induced foci in live cells by monitoring their size and intensity as a function of dose and time using yellow fluorescent protein (YFP) tagging techniques. Preliminary data indicate a delayed and linear rising of the intensity signal indicating a slow kinetic for the accumulation of DNA repair protein 53BP1. A slow and limited foci diffusion has also been observed. Further investigations are required to assess whatever such diffusion is consistent with a random walk pattern or if it is the result of a more structured lesion processing phenomenon. In conclusion, our data indicates that the use of microbeams coupled to live cell microscopy represent a sophisticated approach for visualizing and quantifying the dynamics changes of DNA proteins at the damaged sites.

Characterization and parametrization in terms of atomic number of x-ray emission from K-shell filling during ion-surface interactions

When highly charged ions are incident on a surface, part of their potential energy is emitted as characteristic radiation. The energies and yields of these characteristic x rays have been measured for a series of elements at the Tokyo electron-beam ion trap. These data have been used to develop a simple model of the relaxation of the hollow atoms which are formed as the ion approaches the surface, as well as a set of semiempirical scaling laws, which allow for the ready calculation of the K-shell x-ray spectrum which would be produced by an arbitrary slow bare or hydrogenlike ion on a surface. These semiempirical scaling laws can be used to assess the merit of highly charged ion fluorescence x-ray generation in a wide range of applications.