In Brief

Development

Cyclin-dependent kinase 5 phosphorylates disabled 1 independently of reelin signaling.Keshvara, L. et al. J. Neurosci. 22, 4869–4877 (2002)

Reelin and cyclin-dependent kinase 5 (Cdk5) have a crucial role in the control of neuronal migration during development; the independent disruption of these signalling pathways leads to comparable neuroanatomical defects. Keshvara et al. report that Cdk5 phosphorylates disabled 1, a molecule associated with reelin signalling. This observation is the first direct evidence of biochemical interactions between the two pathways.

Ageing

Degenerative age changes in white matter connectivity visualized in vivo using magnetic resonance imaging.Davatzikos, C. & Resnick, S. M. Cereb. Cortex 12, 767–771 (2002)

A cross-sectional and longitudinal imaging analysis of aged brains showed white matter abnormalities, particularly in the left hemisphere. More importantly, a comparison of these abnormalities with the volumetric changes that are commonly observed in ageing showed that the two measures were unrelated, and that the alterations in the white matter signal correlated more strongly with age. So, this kind of change in the white matter might be a more sensitive marker of preclinical degeneration states.

Axon guidance

Axonal protein synthesis provides a mechanism for localized regulation at an intermediate target.Brittis, P. A. et al. Cell 1 July 2002 (doi:10.1016/S0092867402008139)

As local receptor upregulation might affect growth cone responsiveness to guidance cues, the authors explored whether axonal protein synthesis participates in this upregulation. They found that severed axons synthesize proteins and export them to the membrane. Moreover, a sequence in the 3′ untranslated region of the ephrin EphA2 mRNA targets reporter genes to distal axon segments.

Synaptic transmission

Synaptotagmins I and IV promote transmitter release independently of Ca²⁺ binding in the C₂A domain.Robinson, I. M. et al. Nature 18 July 2002 (doi:10.1038/nature00915)

The C₂B Ca²⁺-binding motif of synaptotagmin is required for synaptic transmission in vivo.Mackler, J. M. et al. Nature 7 July 2002 (doi:10.1038/nature00846)

Synaptotagmin I seems to serve as the Ca²⁺ sensor during synaptic vesicle exocytosis. This protein has two C₂ domains that bind Ca²⁺, and these two genetic studies show that the C₂B, but not the C₂A, domain is important for vesicle fusion in Drosophila. In addition, Robinson et al. report that synaptotagmin IV can substitute for synaptotagmin I, indicating that it promotes release, rather than inhibiting it (as was previously thought).