In this issue

The Inherent Risks of Power Plants

Generation of energy in power plants, even of miniature size such mitochondria, carries on considerable hazards. Reactive oxidants, the by-products of aerobic respiration generated in mitochondria, induce DNA damage. Incessant oxidative DNA damage is considered to be the key factor in promoting cellular senescence, organismal aging, and predisposing to cancer. In their most recent article, Zhao and coworkers analyzed a relationship between oxidative DNA damage and DNA replication. The use of “click chemistry” to detect DNA replication concurrently with detecting DNA damage response allowed them to reveal that the latter occurs predominantly in DNA replicating cells. Of particular interest was the finding, by confocal microscopy, of a close association between the sites of DNA replication (“DNA replication factories”) and the sites of DNA damage (γH2AX foci). Their data indicate on particular susceptibility of DNA replicating cells to oxidative DNA damage and suggest that replication stress may be the critical event contributing to the aging-associated DNA damage.

In this issue: page 897

Pixels to Picograms - Weighing the Internal Compartments of Cells using the Deep Ultraviolet

From the flood of detailed color images that we see with fluorescence microscopy, we think we understand the basics of cell structure. But very little of this picture is actually known in absolute terms. How many picograms does a cell weigh? What fraction of this is comprised of nucleic acids? What percentage of those nucleic acids resides in the nucleus or in the nucleolus? How much protein is there in these compartments and in the cytoplasm, and do these quantities vary with cell cycle or metabolic factors? While some, but not all, the answers to these questions can be inferred by population averaging and calibrations with dyes, there are errors in such transfer measurements–since staining efficiency of extrinsic fluors is dependent on access and molecular packaging. In this issue, Cheung and coworkers at Boston University describe an updated version of wide-field ultraviolet microscopy that answers these questions with millisecond exposures and to a resolution of a single 200-nm pixel.

In this issue: page 920