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[
Science,
2001]
Over the years, a steady stream of structural and regulatory RNAs have been identified. Three papers published in this issue on pages 853, 858, and 862 from the Tuschl, Bartel, and Ambros labs continue the tradition, but now prospecting for tiny RNAs of 22 nucleotides (nt). The chain of reasoning that simultaneously attracted these groups to 22 nt is convoluted but interesting.
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[
Nature,
2002]
Behavioral ecologists have shown that many animals form social groups in conditions. Neurobiological evidence for this behaviour has now been discovered in the nematode worm, Caenorhabditis elegans. On pages 899 and 925 of this issue, de Bono et al. and Coates and de Bono present striking results on the genetic, molecular and neural mechanisms underlying nematode social feeding. These discoveries provide tantalizing insights into the effects of stress in social groupings.
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[
Science,
1997]
In many situations-both normal and pathological-cells die as a result of an orderly, stereotyped cascade of cellular events. On pages 1122, 1126, 1129, and 1132 of this issue, four reports describe the molecular basis of crucial steps in this cascade. The importance of understanding the basis of this programmed cell death was spectacularly demonstrated recently through the rescue with cell death inhibitors of mice undergoing acute liver destruction.
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[
Nature,
2001]
The degredation of DNA is one of the hallmarks of programmed cell death (apoptosis). When forced to commit suicide, apoptotic cells - like good secret agents - grimly destroy their "instruction book," chewing up their genomic DNA into tiny morsels. Until now, only two DNA-destroying enzymes (nucleases) with a clear role in cell death were known, one in mammals and one in the nematode worm Caenorhabditis elegans. But, on pages 90-99 of this issue, Li and colleagues and Parrish and co-workers show that another nuclease, endonuclease G (endoG), also contributes to the carnage, and might even influence the likelihood that a cell will live or die.
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[
Nature,
1994]
One of the most satisfying moments in science is when different lines of investigation converge to yield a beautiful picture that opens up new perspectives. This happened last year when expression cloning of an epithelial sodium channel subunit revealed that the DNA encoding it was significantly similar in sequence to that of certain nematode genes, mutations in which lead to insensitivity to touch, neurodegeneration or both. Three reports on pages 463, 467 and 470 of this issue now suggest that at least three distinct subunits are used to build channel complexes in both mammals and the nematode Caenorhabditis elegans. Further, the new work provides insights into the relationship between subunit structure and function, and demonstrates a remarkable degree of functional conservation between vertebrates and invertebrates.
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[
Nature,
2001]
In all animals, the process of programmed cell suicide (apoptosis) is coordinated by enzymes known as caspases, which cut up key substrates in the cell. The dying cell is then neatly packaged, engulfed by neighbouring "phagocytic" cells, and cleared from the body without fanfare, leaving no evidence of the catastrophic events that preceded. It has always been assumed that there is a "point of no return" in this death cascade - at or shortly before the time at which caspases are activated - beyond which the process of cell execution proceeds inexorably. This view is challenged by Reddien et al. and Hoeppner et al. on pages 198 and 202 of this issue. It seems that cells in which caspases have been activated can in fact progress through a state of being "mostly dead", a stage that physically resembles the early phase of apoptosis but from
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[
Nature,
1998]
Cytochrome c leads a double life. When a cell is called on to commit apoptotic suicide, cytochrome c relocalizes from the mitochondria to the cytosol. There, it helps to activate the foot-soldiers of apoptosis - the death proteases known as caspases. How cytochrome c escapes from the mitochondria is still a matter of debate, but it is clear that certain elements within the apoptotic regulatory hierarchy do not condone such behavior. In particular, overexpression of the cell-death suppressors Bcl-2 and Bcl-xL prevents the release of cytochrome c, suggesting that these proteins act upstream of cytochrome c in the pathway to death. However, on pages 449 and 496 of this issue, Zhivotovsky et al. and Rosse et al. show that Bcl-2 can also protect cells downstream of cytochrome c release, forcing a re-evaluation of this newly acquired dogma.
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[
Nature,
1999]
Advances in human genetics have meant that the genes mutated in human diseases can be identified exclusively by their location in the genome. But how do we work out the cellular functions of the associated protein products? Reports on pages 383 and 386 of this issue begin to address this problem for two proteins - polycystin-1 (PKD1) and polycystin-2 (PKD2) - that are defective in human kidney disease. From their studies of the nematode worm Caenorhabditis elegans, Barr and Sternberg present evidence that homologues of the polycystins act together in a signal-transduction pathway in sensory neurons. Chen et al., by contrast, have used an oocyte-expression system in the from Xenopus laevis to show that a homologue of PKD2 is associated with the activity of a cation channel. These results support the hypothesis that polycystin-related proteins belong to a hitherto unknown class of signal-transduction molecules.