Wnt and Notch signaling during murine T-cell development in the thymus. The roles of Wnt and Notch signaling in both normal and malignant development are indicated. The stages in which constitutively activated forms of molecules in the Wnt or Notch pathways lead to malignant transformation are still somewhat speculative. Data from various sources combining human and mouse models are summarized.^1–3  Illustration by A. Y. Chen.