Shown are gastrin-releasing peptide-producing (GRP) neurons in the suprachiasmatic nucleus (SCN) of a genetically modified mouse (Grp-iCre knock-in). Cre-dependent expression of mCherry (red), observed in the same neurons that endogenously express GRP (green), confirms that Grp-iCre mice express Cre recombinase specifically in SCN GRP neurons. This mouse line enabled Ruoshi Li and colleagues to manipulate SCN GRP neurons, leading to the discovery that artificial activation of these neurons induces a phase shift similar to that triggered by sunlight. Thus, these neurons may play a role in photic entrainment: the integration of light and non-light signals to regulate the circadian clock. See the article by Li et al. for more information on how SCN GRP neurons may contribute to photic entrainment. Cover image: Ruoshi Li and Takeshi Sakurai