Required for checkpoint signaling in response to DNA replication stress; either resulting from normal embryogenesis or induced by the DNA synthesis inhibitor hydroxyurea (HU). It is not required for the G2 arrest resulting from DNA double strand breaks induced by ionizing irradiation (IR). Necessary for the timely phosphorylation of Cdk1 at the mid-blastula transition. May have a minor role in maintaining genomic stability in mitotic cells. Detected in the ovary but not in the testis (at protein level). Expressed during S phase, in a cell-cycle-dependent fashion. Expression levels are highest in embryos (0-4 hours old) and in the ovaries of adult females. Little to no expression in larvae and pupae (at protein level). Phosphorylated in response to DNA damage by IR and HU treatment. Phosphorylation does not require mei-41 or tefu. Hatch rate of embryos is less than one percent. Nuclear morphology of embryos is normal until the 10th nuclear cycle when the shape and size of nuclei becomes abnormal and surface nuclei also begin to exhibit an irregular distribution. The phosphorylation of Cdk1 at the mid-blastula transition (between 2 to 4 hours after egg deposition) is also severely delayed. Increased sensitivity to HU with reduced survival rates. In the eye disks from mutant third stage larvae treated with HU, there is a higher percentage of mitotic cells compared to untreated mutant larvae. Is insensitive to ionizing radiation; the percentage of mitotic cells is unaffected in the eye disks of larvae treated with IR, and IR-induced apoptosis in larvae also appears to be unaffected. Belongs to the claspin family. Truncated N-terminus.