This image shows keratinocytes (green), proliferating cells (white), inflammatory cells (red), and cell nuclei (blue) associated with a skin tumor in a one-year-old mouse lacking PTEN, a protein that regulates cell growth and proliferation. Although loss of PTEN is associated with several cancers, it can also promote axon regeneration in the CNS and PNS. For more information, see the article by Meyer zu Reckendorf et al. (pages 2474–2491). Cover image: Sofia Meyer zu Reckendorf.