The cells in our body follow a 24-hour cycle, the circadian clock. Disruptions of this cycle, for example by working night shifts, can cause disease. In recent years, it has become clear that the clock can be disrupted in individual organs or tissues. To study and potentially cure problems with the clocks inside our cells, Dutch and Japanese scientists created a compound that will elongate the 24-hour cycle and that can be activated or deactivated using light. They showed that it is possible to change the 24-hour cycle in cells or tissues to a 28-hour cycle by activating the compound. After deactivation, the cells and tissues returned to a near-normal cycle. The compound can be used to investigate the clocks inside our cells and may eventually be used to treat diseases that are caused by a disrupted clock. Reference: “Reversible modulation of circadian time with chronophotopharmacology” by Reference: Dušan Kolarski, Carla Miró Vinyals, Akiko Sugiyama, Ashutosh Srivastava, Daisuke Ono, Yoshiko Nagai, Mui Iida, Kenichiro Itami, Florence Tama, Wiktor Szymanski, Tsuyoshi Hirota and Ben L. Feringa, 26 May 2021, Nature Communications.