Cover legend: A side view of the trunk of a 24-h-old transgenic zebrafish embryo in which motor neurons express green fluorescent protein under the motor neuron specific promotor hb9 is shown. False colors code for relative depths of green fluorescent protein positive somata and axons from deep (blue) to superficial (yellow), indicating rows of ventral motor axons on the left and right side of the trunk. In this embryo, plexinA3 expression has been reduced by morpholino injection resulting in aberrant growth of some motor axons (far left and right). For more information, see the article by Feldner et al. in the May 2, 2007 issue (pages 4978–4983).