Cell cycle checkpoints are control mechanisms that ensure the fidelity of cell division and genome stability.They mainly include DNA damage-dependent checkpoints and DNA damage-independent checkpoint, the spindle assembly checkpoint.Defective checkpoints will predispose organs to cancers.At the same time, most chemotherapeutic drugs and radiotherapy target at these checkpoints.Thus, understanding molecular mechanisms of cell cycle checkpoint controls will benefit controlling cancers.In the context of checkpoint controls, my laboratory recently focuses on protein phosphatases and the primary microcephaly (MCPH) causative genes in breast tumorigenesis.Reversible protein phosphorylation by kinases and phosphatases is one of the most common mechanisms in controlling most, if not all cellular processes.The phosphorylated form of the histone variant H2AX at serine-139, γ-H2AX, is a marker for DNA double-stranded breaks (DSBs), and elimination of γ-H2AX at DSBs is required for DNA damage repair.