Purpose: Several past studies using a mouse model of radiation-induced AML (rAML) have shown that hemizygous deletion of the Sfpi1 gene (HDSG) is an initiating event for the development of rAML. In this study, we examined the difference in frequency of HDSG in hematopoietic stem cells (HSCs) Rich hematopoietic Cell population (HRCs) from bone marrow (BM) and spleen of C3H mice irradiated with 3 Gy X-rays. Materials and methods: 8-weeks old male C3H mice were irradiated 3Gy of whole body X-ray (1 Gy/min) and mice were sacrificed at 1, 4, 8, and 26 weeks. Then, HSPCs were isolated from BM of femur and spleen, the frequency of HRCs with Sfpi1 gene deletion was analyzed by fluorescence in situ hybridization (FISH). Results and conclusions: The frequency of HRCs with HDSG in both BM and spleen was increased 1 week after X-irradiation. Then, the frequency of HRCs with HDSG in BM showed a gradual decrease from 4 to 26 weeks, whereas HRCs with HDSG in spleen remained high, even at 26 weeks after X-irradiation. HDSG is less likely to be eliminated, particularly in the spleen, after X-irradiation. The spleen as well as BM of the femur may be major sites of rAML development.
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