Language

Selective priming of syntactic processing by event-related transcranial magnetic stimulation of Broca's area.Sakai, K. L. et al. Neuron 35, 1177–1182 (2002)

Lesions of Broca's area cause aphasia, but it is not clear whether this effect is related to a syntactic or a semantic deficit. Sakai et al. used transcranial magnetic stimulation (TMS) to interfere transiently with the activity of Broca's area while subjects were required to judge whether a series of sentences were semantically or syntactically normal. They found that the effect of TMS was limited to syntactic decisions, highlighting the role of Broca's area in syntactic processing.

Neurological disorders

Intracellular ataxin1 inclusions contain both fast- and slow-exchanging components.Stenoien, D. L. et al. Nature Cell Biol. 30 September 2002 (doi:10.1038/ncb859)

Polyglutamine protein aggregates are dynamic.Kim, S. et al. Nature Cell Biol. 30 September 2002 (doi:10.1038/ncb863)

These two papers highlight the dynamic nature of polyglutamine protein aggregates. In the first article, the authors used fluorescence recovery after photobleaching to identify two types of ataxin 1 inclusions — aggregates in which ataxin 1 is rapidly exchanged with the soluble pool, and aggregates in which such an exchange is slow. As slow-exchanging aggregates contain high levels of ubiquitin but not of proteasomes, the authors suggest that proteasomes might fail to recognize the ubiquitinated substrates in this type of aggregate. In the second paper, the authors used the same technique and a related method (fluorescence loss after photobleaching) to reveal that the association of the chaperone Hsp70 with huntingtin aggregates is not irreversible, as was previously thought, but transient. This finding challenges the assumption that polyglutamine disorders affect neuronal function by sequestering essential components of the cellular machinery. The dynamic nature of polyglutamine protein aggregates highlights the potential of therapeutic interventions that aim to promote their dissolution.

Neurological disorders

A Drosophila fragile X protein interacts with components of RNAi and ribosomal proteins.Ishizuka, A. et al. Genes Dev. 16, 2497–2508 (2002)

Fragile X syndrome is a form of mental retardation that is caused by alterations in the function of the FMR1 protein. Studying the Drosophila homologue of FMR1 (Fmr1), the authors found that a complex of proteins that mediate RNA interference (RNAi) in the fly can interact directly with the Fmr1 protein. RNAi is an important gene-silencing mechanism that has been described mainly in Drosophila and plants. These findings raise the possibility that a regulatory mechanism of this type might also be related to human disease.