@misc{oai:repo.qst.go.jp:00067437,
 author = {Kanda, Reiko and Shang, Yi and Hayata, Isamu and 神田 玲子 and 尚 奕 and 早田 勇},
 month = {Aug},
 note = {Okadaic acid and calyculin A, inhibitors of serine/threonine protein phosphatases, can induce premature chromosome condensation (PCC) at any stage of the cell cycle in human peripheral lymphocytes.  In the present study, we investigated unstable nature of a ring chromosome observed in PCC preparations, which is an indicator of the newly developed biodosimetry.  Human peripheral lymphocytes irradiated in vitro or in vivo were cultured and treated with okadaic acid.  Air-dried slides were made in warm and humid conditions, and processed according to a dual staining method developed for the successive application of Giemsa staining and pan-centromeric FISH painting on the same metaphase.  In PCC preparations, we observed cells in late G2 phase and cells in late M phase.  In cells at late M phase, 10-20 % of the rings lacked their own partner of sister chromatids (single-chromatid ring), irrespective of exposed dose. Microscopic observation, data on distribution patterns of centromeres in rings and on the intercentromere distances in dicentric rings indicate that some of single-chromatid rings might be formed by sister chromatid exchanges (SCE) occurred in a chromosome-type ring thereby joining strands of two rings followed by transformation into one ring.  These single-chromatid rings were less stable in vivo than chromosome-type rings. Many researchers indicated that the ionizing radiation itself was a poor inducer of SCE, and that the seeming radiation-induced SCE was a consequence of radiation-damage to agents to differentiate sister chromatids, such as BrdU.  These ideas were supported by the observation that SCE was induced only in the first cell cycle following irradiation of BrdU-substituted cells.  The present study proved that the in vitro and in vivo irradiation induced SCE in the absence of these agents, and that SCE accelerated the instability of rings by means of the secondary transformation of rings., 第１２回国際放射線研究会議},
 title = {Radiation-induced sister chromatid exchanges observed in a ring chromosome},
 year = {2003}
}