ArrestRed (the scientific name is H2B-tKR) is a novel optogenetic tool, which can be used to study the roles of specific cell populations in development, regeneration, and carcinogenesis. This is a chimeric protein composed of a tandem version of genetically-encoded photosensitizer KillerRed fused to histone H2B protein [Serebrovskaya et al., 2011]. Expression of ArrestRed in mammalian cells results in correct chromatin labeling and does not interfere with cellular division. The illumination of the ArrestRed expressing cells by intense green light leads to blockage of cell proliferation. The effect of ArrestRed activation lasts for about 24 hours, after that approximately 90% of ArrestRed expressing cells resume division. Repeated light illuminations allow to maintain cells in the non-dividing state for longer periods.

The inhibitory effect of ArrestRed on cell cycle progression is attributed to generation of reactive oxygen species (ROS) upon ArrestRed activation [Bulina et al., 2006]. Light-induced generation of ROS leads to massive damage of genomic DNA and activation of repair machinery. In turn, it causes cell cycle checkpoints activation and cell cycle arrest. After successful DNA reparation interphase cells restore normal proliferation.

• Reversible inhibition of cell cycle progression
• Activation by green light irradiation
• Direct expression and easy visualization in cell nuclei
• No exogenous chemical compounds required
• Recommended for transient blockage of cell division in vitro and in vivo