Cover legend: Composition of three mouse retinal ganglion cells arbors in the superior colliculus. Individual retinal ganglion cells were labeled by injection and electroporation of plasmids encoding reporter proteins into the embryonic retina. Arbors in the superior colliculus of nine-day-old mice were imaged individually, superimposed in a single image, and artificially colored. Blue, red, and green arbors correspond to control retinal ganglion cells, while magenta and yellow axons come from retinal ganglion cells that ectopically express the rectifying potassium channel Kir2.1. Although all the axons reach similar topographic points in the superior colliculus, the Kir2.1-expressing axons do not arborize properly. For more information, see Benjumeda et al. (18208–18218).