This schematic diagram shows the progenitor domains in dorsal (mixed colors) and ventral forebrain (yellow) regions of Nissl-stained embryonic day 12.5 mouse brain lacking Suppressor of Fused, a potent regulator of Sonic Hedgehog signaling. In these mutant mice, cortical progenitors are unable to maintain their dorsal forebrain identity and specification program, instead exhibiting properties of ventral forebrain progenitors. For more information, see the article by Yabut et al. Cover Image: Odessa Yabut. (pages 6872–6877).