Bazi [creativecommons license] from Wikimedia CommonsControlling gene expression in vivo forms the basis for genetic engineering for research and therapeutic purposes. Recently, Haifeng Ye and Martin Fussenegger (Eidgenössische Technische Hochschule Zurich, Basel, Switzerland) reported their success in developing a light-driven, synthetic biology mechanism to control transcription. To prove that the technique has therapeutic potential, they used it to control insulin production in a mouse model of type 2 diabetes.