Cover legend: GFP expression (green) was induced in a cohort of NG2-expressing glial cells using Cre-lox genetic approaches. Shown are GFP-expressing cells in corpus callosum, some of which remain in the progenitor state and express PDGFaR (blue) and others which have differentiated into oligodendrocytes and can be labeled with the monoclonal antibody CC1 (red). For more information, see the article by De Biase et al. in this issue (pages 3600–3611).