Functional Imaging

The neural correlates of feeling sympathy. Decety, J. & Chaminade, T. Neuropsychologia 41, 127–138 (2003)

The authors use functional imaging to show that watching actors telling sad stories leads to activation of neural structures that are involved in processing emotion. It also activates a 'shared motor representation' network that includes the right inferior parietal cortex, and which is normally activated by both observed and executed actions. If the actors used emotive gestures and facial expressions, there was also a specific increase in activity in the left inferior frontal gyrus. These areas are proposed to form a network that is important for feeling sympathy.

Circadian Rhythms

Rhythmic histone acetylation underlies transcription in the mammalian circadian clock. Etchegaray, J.-P. et al. Nature 11 December 2002 (doi:10.1038/nature01304)

In mammals, the circadian clock is controlled by a transcriptional feedback loop. Clock and Bmal1 drive the expression of Per1–3, Cry1 and Cry2, and the Cry proteins in turn block Clock/Bmal1-mediated transcription. Here, Etchegaray et al. show that in the mouse liver, the Per1, Per2 and Cry1 gene promoters exhibit oscillations in histone acetylation that are synchronized with circadian rhythms. The data imply a new role for chromatin rearrangements in circadian rhythmicity.

Neurotrophic Factors

Brain-derived neurotrophic factor can act as a pronecrotic factor through transcriptional and translational activation of NADPH oxidase. Kim, S. H. et al. J. Cell Biol. 2 December 2002 (doi:10.1083/jcb.200112131)

As brain-derived neurotrophic factor (BDNF) can cause cell death, Kim et al. set out to explore the underlying mechanisms. They found that BDNF-induced neuronal death depended on the production of free radicals and the synthesis of new proteins. Microarray analysis revealed that BDNF increased the synthesis of a subunit of NADPH oxidase. The authors obtained evidence for the involvement of this enzyme in the death process, as blocking its activity prevented BDNF toxicity, but not with the antiapoptotic action of this neurotrophin.

Stem Cells

A nucleolar mechanism controlling cell proliferation in stem cells and cancer cells. Tsai, R. Y. L. & McKay, R. D. G. Genes Dev. 16, 2991–3003 (2002)

The authors identify nucleostemin as a nucleolar protein that is expressed in neuronal and other stem cells, as well as in cancer cells. When stem cells differentiate, the expression of nucleostemin decreases before they exit the cell cycle. Increasing or decreasing the levels of nucleostemin reduces stem cell proliferation, leading to apoptosis. The data point to a new nucleolar mechanism that controls the progression of stem cells through the cell cycle.