Cell biology of the neuron

Truncated TrkB receptor-induced outgrowth of dendritic filopodia involves the p75 neurotrophin receptor. Hartmann, M. et al. J. Cell Sci. 117, 5803–5814 (2004)

Truncated splice variants of the TrkB neurotrophin receptor are abundant in the adult rodent CNS, but little is known about their physiological functions. Hartmann et al. present evidence that the TrkB.T1 isoform interacts with the p75NTR receptor, thereby initiating a signalling cascade that induces outgrowth of dendritic filopodia. This could be one of the mechanisms that contribute to the formation of new synapses in the postnatal CNS.

Circadian rhythms

Circadian gene expression in individual fibroblasts: cell-autonomous and self-sustained oscillators pass time to daughter cells. Nagoshi, E. et al. Cell 119, 693–705 (2004)

The body's circadian rhythms are centrally controlled by the suprachiasmatic nucleus (SCN) in the brain, and oscillators in peripheral tissues were originally thought to lose their rhythms rapidly in the absence of SCN input. However, Nagoshi et al. now show that oscillations in circadian gene expression are sustained in a cell-autonomous manner in cultured fibroblasts, and although cell division causes a phase shift in the circadian cycle, the oscillations also persist in the daughter cells.

Sensory systems

Magnetoreception and its trigeminal mediation in the homing pigeon. Mora, C. V. et al. Nature 432, 508–511 (2004)

This study provides new evidence to support the idea that homing pigeons use magnetoreception to find their way home. Mora et al. were able to train pigeons to detect a magnetic field anomaly, but this ability was impaired by anaesthetizing the upper beak or attaching a magnet to it, or by severing the ophthalmic branch of the trigeminal nerve. The authors suggest that magnetite in the upper beak region is used to detect the magnetic field and the trigeminal nerve relays this information to the brain.

Stem cells

Chromatin remodeling and histone modification in the conversion of oligodendrocyte precursors to neural stem cells. Kondo, T. & Raff, M. Genes Dev. 18, 2963–2972 (2004)

Purified oligodendrocyte precursor cells (OPCs) can be converted to multipotent neural stem-like cells (NSLCs) that generate both neurons and glia, so they could provide a source of neurons for CNS repair. To investigate how this potential might be harnessed, Kondo and Raff analysed the molecular mechanisms that underlie the conversion of OPCs to NSLCs. They show that this process depends on the reactivation of Sox2 gene expression, which in turn depends on chromatin remodelling at the Sox2 promoter.