Cell Biology of the Neuron

Axonal transport of mitochondria to synapses depends on Milton, a novel Drosophila protein.. Stowers, R. S. et al. Neuron 36, 1063–1077 (2002)

To satisfy synaptic energy requirements, mitochondria must be able to traverse the often considerable distance that separates a terminal from its cell body. Here, Stowers et al. identify a Drosophila protein, Milton, which regulates mitochondrial movement. Without Milton, mitochondria fail to migrate from the cell body to axons and terminals — by contrast, transport of synaptic vesicles is unaffected. Coimmunoprecipitation indicated that Milton is associated with the kinesin heavy chain, and might therefore be required for the kinesin-mediated movement of mitochondria.

Ion channels

Direct interaction with a nuclear protein and regulation of gene silencing by a variant of the Ca2+-channel β4 subunit. Hibino, H. et al. Proc. Natl Acad. Sci. USA 100, 307–312 (2003)

β-Subunits commonly regulate the functional properties of voltage-gated channels by a direct interaction with the pore-forming α-subunit. Here, the authors identify a splice variant of the β4 subunit of Ca2+ channels — β4c — that, in addition to modifying channel behaviour, regulates gene expression. To carry out this novel function, β4c directly binds to the transcriptional regulator CHCB2/HP1γ, markedly enhancing its gene-silencing activity.

Neurotransmitters

Synthesis of serotonin by a second tryptophan hydroxylase isoform. Walther, D. J. et al. Science 299, 76 (2003)

The rate-limiting enzyme in the synthesis of the neurotransmitter serotonin is tryptophan hydroxylase (TPH). Walther et al. show that mice without the gene that encodes TPH lack serotonin in the periphery but not in the brain, owing to the presence of a second isoform, Tph2, which is expressed only in the nervous system. The authors also found that Tph1 is expressed almost exclusively in the periphery. Tph2 is therefore more likely than Tph1 to be important for brain function.

Neurophysiology

Neuron-to-astrocyte signalling is central to the dynamic control of brain microcirculation. Zonta, M. et al. Nature Neurosci. 6, 43–50 (2003)

Signalling from neurons to astrocytes could provide the key to the increase in cerebral blood flow that accompanies neuronal activity, according to Zonta et al. The authors showed that astrocytes increase their intracellular calcium concentration in response to the release of glutamate from neurons that synapse onto them. This in turn stimulates the release of vasoactive agents from the astrocytes, which cause arterioles to dilate.