RNA

Sequence-specific inhibition of small RNA function. Hutvágner, G. et al. PLoS Biology 24 Feb 2004 (doi:10.1371/journal.pbio.0020098)

The authors show that 2′-O-methyl oligonucleotides that are complementary to small RNAs can bind to the RNA-induced silencing complex, and function as potent and irreversible inhibitors of RNA silencing in vivo and in vitro. As these oligonucleotides block the function of siRNAs and microRNAs in vivo, they will be useful for the functional characterization of the many small RNAs that have been identified recently. Furthermore, tethered oligonucleotides can be used to identify small-RNA-associated proteins, which might lead to new insights into the RNAi pathway.

Cell cycle

Recovery from DNA damage checkpoint arrest by PP1-mediated inhibition of Chk1. den Elzen, N. R. & O'Connell, M. J. EMBO J. 23, 908–918 (2004)

The G2 DNA-damage checkpoint prevents mitotic entry in the presence of DNA damage, but how the checkpoint is released and cell-cycle re-entry occurs is poorly understood. den Elzen and O'Connell have now identified the type-I protein phosphatase Dis2 as a key component of a checkpoint-release pathway in fission yeast. Dis2 specifically dephosphorylates, and thereby inactivates, the checkpoint-effector protein Chk1 kinase — but does not affect the function or phosphorylation of other checkpoint proteins.

Stem cells

Derivation of embryonic stem-cell lines from human blastocysts. Cowan, C. A. et al. N. Engl. J. Med. 3 March 2004 (doi:10.1056/NEJMsr040330)

A group led by Douglas Melton has derived and characterized 17 new human embryonic stem-cell lines that meet strict criteria for easy and routine in vitro cell culture. These cell lines are available to scientists with a Material Transfer Agreement, but only for non-commercial research purposes. Under current regulations, the cell lines cannot be used for research that is funded by NIH funds. Information on how to obtain the cells and detailed protocols are available at http://www.mcb.harvard.edu/melton/hues.

Molecular motors

A kinesin-like motor inhibits microtubule dynamic instability. Bringmann, H. et al. Science 303, 1519–1522 (2004)

The Xenopus laevis kinesin-like protein 1 (Xklp1) is important for chromosome-microtubule interactions and spindle-pole extension. Bringmann et al. now show that Xklp1 combines two properties that are characteristic of different classes of kinesin-like proteins: it is a fast, non-processive, plus-end-directed motor and inhibits microtubule polymerization and depolymerization. The inhibitory effect is mediated by a global structural change in the microtubule lattice that is induced by the presence of bound Xklp1.