| Estimate the dose of ionizing irradiation is key to diagnose and therapy on the damage of nuclear irradiation. The methods we have already used have some deficiency such as poor speciality, high background, short time it last and too complex and time-consuming to examine. Following IR induce cell cycle stagnate become the hotspot of radiobiology, gene expression in transcription level also become highlight.GADD45(Growth arrest and DNA damage gene 45)is studied regularly in recently years. It is a downstream gene of p53 and has close relation with cell cycle arrest. There are over twenty articles about GADD45 gene expression change following IR induction overseas. Armed Forces Radiobiology research Institute of USA give the first report about use gene expression change of GADD45 as biodosimetry in February 2002.In order to study the relation between GEC of GADD45 and dose it received, we used MNC of human as test object. We used Reverse Transcription-Polymerase Chain Reaction to measure relative mRNA of this gene.First we choiced the primer from literature and verified it on the genbank. Amplified the purpose gene and B-actin in the same tube. After agarose gel electrophoresis, we used PCR software to analyse the result and used GADD45/B-actin as relative expression of GADD45.MNC from 100ml whole blood were diluted with PBS and collected in 6 centrifuge tubes. These MNC were exposed to the following nominal doses:0, 1, 2, 3, 4, and 5Gy. After that, we diluted cells with RPMI media containing 10% calf serum and prepared for RNA extraction at specified intervals after irradiation (0h, 4h, 8h,16h, 20h,and 24h).Each tests has 36 independence studies, and repeat 3 times. The means+standarderror were used as results and use SARS software to analyse them. The data in each time intervals of each dose were compared with OGy and use origin software to draw a graph in order to find the relation between gene expression and doses. Results are follows:Datum of blank group had no statistic difference with each other. In Oh point after irradiation, datum of different doses had no statistic difference too.After irradiation, GADD45 gene expression of every dose (1-5Gy) increased and had statistics difference (p<0.05). At every time point we observed, the increase of gene expression were dose-dependent. And at 20h point, the relation between them was accord with linear.At every dose point, the tendency of gene expression change were same: They increased after irradiation and reach peak at 4 hour after. After that they decreased, but at 24hour after irradiation, they were not come back to the initial.According to the results, we got the conclusion. X-ray can induce the increase of GADD45 gene expression. It is identical with X-irradiation induced G1 arrest and the gene expression changes. It proved the important role which GADD45 gene played in IR-reduced Gl arrest. In this study we found that the GADD45 gene increased dose-dependently and the tendency was same at different time point. So this technology may be a new efficient biological dosimetry tool applicable in radiation therapy applications and early-response accident biodosimetry.
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