@misc{oai:repo.qst.go.jp:00070565,
 author = {Ariyoshi, Kentaro and Kakinuma, Shizuko and Takabatake, Takashi and Shinagawa, Mayumi and Kadono, Kyoko and Nishimura, Mayumi and Shimada, Yoshiya and 有吉 健太郎 and 柿沼 志津子 and 高畠 貴志 and 品川 まゆみ and 角野 響子 and 西村 まゆみ and 島田 義也},
 month = {Sep},
 note = {Background: Age–at–exposure is a critical factor that influences the risk of radiation leukemogenesis. Whereas adult C3H/He mice are prone to develop myeloid leukemia after ionizing-radiation (IR) exposure, fetal and neonatal mice are resistant. Nakano et al. reported that dose response of chromosomal translation in hematopoietic cells was not observed in mice irradiated in utero or soon after birth. They hypothesized that the fetal or neonatal hematopoietic stem cells are genetically highly sensitive to ionizing radiation, so that the aberrant cells disappear soon after IR exposure. The purpose of this study was to determine the sensitivity to IR of developing hematopoietic cells both in vitro and in vivo. 
\nExperimental procedures: After in vivo gamma-ray irradiation to the 1 week-old to 14 week-old C3H/He mice, the survival of hematopoietic progenitor cells was determined by both colony forming assay in vitro using MthoCult kit and spleen colony formation assay in vivo. The gene expression profiles of bone marrow cells from 1 week-old and 8 week-old mice were also examined. 
\nResults: A marked reduction in the number of colony forming cells was observed after in vivo irradiation in the 1 week-old mice; the colony forming unit-granulocyte macrophage (CFU-GM), burst-forming unit-erythroid (BFU-E) and colony forming unit-spleen (CFU-S) of irradiated 1 week-old mice were more radiosensitive than those of older ages. Interestingly, in vitro irradiation did not show age difference between 1 week-old mice to 14 week-old mice. This suggests that in vivo microenvironment and/or its response to IR critically affects the radiation sensitivity of hematopoietic progenitor cells.
Further, the gene expression profiles of bone marrow cells revealed that expression of cytokines and chemokines which can stimulate hematopoietic progenitor cell growth or survival, were reduced in 1 week-old mice compared to those of 8 week-old mice. 
\nConclusion: These results demonstrate that hematopoietic progenitor cells of neonatal stage are radiation sensitive, which may associate the lack of expression of survival cytokine and chemokine after ionizing radiation., 14th International Congress of Radiation Research},
 title = {Radiation-induced marked reduction in hematopoietic progenitor cells in infant leukemia prone C3H/He mouse},
 year = {2011}
}