JNeurosci is publishing an Expression of Concern for the article, “TGFβ Signaling Regulates the Timing of CNS Myelination by Modulating Oligodendrocyte Progenitor Cell Cycle Exit through SMAD3/4/FoxO1/Sp1,” by Javier Palazuelos, Michael Klingener, and Adan Aguirre, which appeared on pages 7917–7930 of the June 4, 2014 issue. The editors have been made aware of questions about the reliability of the data presented in Figure 5J. JNeurosci will make a final decision on this article pending a full investigation and reproduction of the results and conclusions presented in the article.