Traffic at the Roundabout

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Science  06 Sep 2002:
Vol. 297, Issue 5587, pp. 1613
DOI: 10.1126/science.297.5587.1613b

The Drosophila nervous system has been used as a model system for studying the molecular signals underlying the developmental choices of axons at the midline. Growth cones that display the receptor Roundabout (Robo) are repelled from crossing the midline, whereas those featuring the receptor Frazzled are attracted across the midline. To prevent a return trip across the midline by axons that succeed in reaching the contralateral side, Robo is then up-regulated.

Keleman et al. show that commissureless (comm) regulates the exposure of Robo by altering its intracellular trafficking. When expressed alone in cultured cells, Robo is located primarily at the plasma membrane, whereas Comm is found in an internal late endosomal-lysosomal compartment. When expressed together, Comm associates with Robo as it emerges from the trans-Golgi network and carries it away in late endosomes, preventing Robo from entering the route to the plasma membrane. The authors suggest that either the timing of comm expression is specified intrinsically or retrograde signaling from the newly crossed growth cones serves to turn off comm and thus permit Robo to reach the surface once again. — NG

Cell110, 415 (2002).

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