Cell signalling

PAR-1 is a Dishevelled-associated kinase and a positive regulator of Wnt signalling. Sun, T.-Q. et al. Nature Cell Biol. 3, 628?636 (2001) [PubMed]

Dishevelled (Dsh), as well as regulating the Wnt?β-catenin pathway, also controls planar polarity through the Jun amino-terminal kinase (JNK) pathway. Sun and colleagues have now identified Drosophila PAR-1 ? an important regulator of polarity ? as a kinase that exists in a complex with Dsh. Activation of PAR-1 is needed for Dsh phosphorylation and potentiation of the β-catenin pathway, while inhibiting the JNK pathway.

RNA transport

Developmental changes due to long-distance movement of a homeobox fusion transcript in tomato. Kim, M. et al. Science 293, 287?289 (2001) [PubMed]

Until now, the functional significance of long-distance movement of messenger RNA in plants was unclear. Kim et al., however, have shown that, after grafting, a mutation that causes tomato leaves to be rounded can be transmitted from a mutant plant into a wild-type plant. Mutant mRNA was detected in the phloem sieve tubes and associated companion cells of wild-type plants, and accumulated in sites of known expression in wild-type plants.

RNA export

Messenger RNAs are recruited for nuclear export during transcription. Lei, E. P. et al. Genes Dev. 15, 1771?1782 (2001) [PubMed]

Export of mRNA requires processing, packaging, recognition by export factors and finally translocation through the nuclear pore. It is becoming increasingly evident that these processes are tightly linked. Here, the authors show that two Saccharomyces cerevisiae export factors, Npl3 and Yra1, are recruited to the mRNA as early as during transcription. Npl3 seems to be recruited before Yra1, probably through direct interaction with RNA polymerase II.

Cytoskeleton

Essential roles for four cytoplasmic intermediate filament proteins in Caenorhabditis elegans development. Karabinos, A. et al. Proc. Natl Acad. Sci. USA 98, 7863?7868 (2001) [PubMed]

Many genetically tractable organisms, including Drosophila and yeast, do not have intermediate filaments, whereas mammalian cells have over 50 isoforms. Caenorhabditis elegans now emerges as the perfect model organism to study intermediate filament function, as it only has 11 isoforms. The authors knocked out each of these genes by RNA interference and found phenotypes for five of them. Four of these are essential for development of the worm.