title: Delayed and stage specific phosphorylation of H2AX during preimplantation development of gamma-irradiated mouse embryos.
abstract: Within minutes of the induction of DNA double-strand breaks in somatic cells, histone H2AX becomes phosphorylated in the serine 139 residue at the damage site. The phosphorylated H2AX, designated as gamma-H2AX, is visible as nuclear foci in the irradiated cells which are thought to serve as a platform for the assembly of proteins involved in checkpoint response and DNA repair. It is known that early stage mammalian embryos are highly sensitive to radiation but the mechanism of radiosensitivity is not well understood. Thus, we investigated the damage response of the preimplantation stage development by analyzing focus formation of gamma-H2AX in mouse embryos gamma-irradiated in utero. Our analysis revealed that although H2AX is present in early preimplantation embryos, its phosphorylation after 3 Gy gamma-irradiation is hindered up to the two cell stage of development. When left in utero for another 24-64 h, however, these irradiated embryos showed delayed phosphorylation of H2AX. In contrast, phosphorylation of H2AX was readily induced by radiation in post-compaction stage embryos. It is possible that phosphorylation of H2AX is inefficient in early stage embryos. It is also possible that the phosphorylated H2AX exists in the dispersed chromatin structure of early stage embryonic pronuclei, so that it cannot readily be detected by conventional immunostaining method. In either case, this phenomenon is likely to correlate with the lack of cell cycle arrest, apoptosis and high radiosensitivity of these developmental stages.
authors.affiliation: Division of Reproductive Medicine, Department of Obstetrics and Gynecology, Kasturba Medical College, Manipal 576 104, India.
authors.forename: Satish Kumar
authors.initials: SK
authors.lastname: Adiga
authors.forename: Megumi
authors.initials: M
authors.lastname: Toyoshima
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Shimura
authors.forename: Jun
authors.initials: J
authors.lastname: Takeda
authors.forename: Norio
authors.initials: N
authors.lastname: Uematsu
authors.forename: Ohtsura
authors.initials: O
authors.lastname: Niwa
mesh_terms: D000818:Animals; D017209:Apoptosis; D001757:Blastomeres / Q000378:metabolism; D002843:Chromatin / Q000648:ultrastructure; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D004307:Dose-Response Relationship, Radiation; D047108:Embryonic Development; D005260:Female; D005455:Fluorescent Antibody Technique; D005720:Gamma Rays / Q000009:adverse effects; D005865:Gestational Age; D006657:Histones / Q000378:metabolism*; D020287:In Situ Nick-End Labeling; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D010766:Phosphorylation; D011247:Pregnancy; D015053:Zygote / Q000378:metabolism* / Q000528:radiation effects
chemical_list: D002843:Chromatin; C468783:H2AX protein, human; D006657:Histones