1. Neurofilament Turnover and Transport, Revisited
Stphanie Millecamps, Genevive Gowing, Olga Corti, Jacques Mallet, and Jean-Pierre Julien

The abundant neurofilaments (NFs) of the cytoskeleton are polymers of light, midsize, and heavy subunits. Although once thought to move unidirectionally, NFs can move bidirectionally along microtubules in a start-and-stop pattern. This week, Millecamps et al. focused on the transport and turnover of light subunits (NF-L). They generated mice that conditionally expressed a transgene encoding human NF-L under the control of doxycycline in mice that were either heterozygous (tTA;hNF-L;NF-L^+/-) or deficient (tTA;hNF-L;NF-L^+/-) for endogenous NF-L. Doxycycline treatment reduced hNF-L mRNA within a week, whereas the half-life of the protein was longer, 3 weeks in cerebellum. However, in large-caliber axons in the sciatic nerve, drug treatment did not diminish the existing stationary NF-L network in tTA;hNFL;NF-L^+/- mice. Breakdown of NF-L occurred spontaneously along the entire axon, not just at nerve endings. Accumulation of new hNF-L after cessation of doxycycline in tTA;hNF-L;NF-L^-/- mice also appeared synchronously along the nerve, rather than wave-like.

2. Zebrafish Pioneer Axons and PlexinA3
Julia Feldner, Michell M. Reimer, Jrn Schweitzer, Bjrn Wendik, Dirk Meyer, Thomas Becker, and Catherina G. Becker

Plexins, receptors for semaphorin signaling, are among the molecules that guide axon growth and pathfinding. Here, Feldner et al. unveil the molecular niche carved out by plexinA3 in primary motor axon guidance. The authors cloned plexinA3 from zebrafish and demonstrate its expression at the ventral edge of the embryonic spinal cord, specifically in the caudal and middle primary motor neurons (CaP and MiP), the axons of which regularly exit the spinal cord. Translation-blocking morpholinos of plexinA3 mRNA caused ab
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Contact: Sara Harris
sharris@sfn.org
202-962-4000
Society for Neuroscience
1-May-2007