The cover image shows multicolor-labeled tumor cells in a model of glioblastoma multiforme in the rat. Both unicolored and mix-colored tumor clones are visible in this image. This multicolor glioblastoma multiforme is generated by cotransfecting radial glia with plasmids encoding oncogenic HRasV12/AKT and three fluorescent proteins GFP, mRFP, and CFP. This new animal model takes advantage of piggyBac transposon-mediated somatic transgenesis and provides a new method to study sources of brain tumor heterogeneity. For more information, see the article by Chen and colleagues on page 742.