Study of effect of ionizing radiation on germline cells

目的研究高能重离子微束辐射对后生动物秀丽隐杆线虫生殖系细胞的位置效应。用方位角变化场（AVF）回旋加速器发射的220MeV 12C5t粒子的光栅扫描宽束或准直微束照射生殖系细胞，观察细胞周期阻滞和凋亡情况。在L4幼虫期用宽光束照射全身，可阻止生殖细胞增殖。在L4期用微束局部照射性腺臂尖端区域时，观察到同样的阻滞。当微束照射幼龄妊娠期生殖腺臂粗筋素区时，生殖腺发生辐射诱导的细胞凋亡。相比之下，未辐照的邻近区域或对面性腺未引起阻滞和凋亡。在c-abl-1 （Abelson小鼠白血病病毒细胞对应物的哺乳动物同源物）突变体中也证实了类似的结果，该突变体对辐射诱导的细胞凋亡高度敏感。此外，我们证明了一些编码凋亡细胞死亡激活因子和分泌表面蛋白的基因在电离辐射后上调。其中一些也因线粒体DNA复制缺陷而上调。这些结果表明，微束辐照是有用的，以表征组织特异性，局部生物反应的辐射在生物体。在局部辐照区观察到DNA损伤诱导的细胞周期阻滞和凋亡，但在线虫中几乎没有“旁观者效应”。

To investigate positional effects of radiation with an energetic heavy-ion microbeam on germline cells using an experimental model metazoan Caenorhabditis elegans. The germline cells were irradiated with raster-scanned broad beam or collimated microbeam of 220MeV 12C5t particles delivered from the azimuthally varying field (AVF) cyclotron, and subsequently observed for cell cycle arrest and apoptosis. Whole-body irradiation with the broad beam at the L4 larval stage arrested germ cell proliferation. When the tip region of the gonad arm was irradiated locally with the microbeam at the L4 stage, the same arrest was observed. When the microbeams were used to irradiate the pachytene region of the gonad arm, at a young gravid stage, radiation-induced apoptosis occurred in the gonad. In contrast, arrest and apoptosis were not induced in the non-irradiated neighboring region or the opposite gonad. Similar results were confirmed in the c-abl-1 (mammalian ortholog of cellular counterpart of Abelson murine leukemia virus) mutant that is hypersensitive to radiation-induced apoptosis. In addition, we demonstrated that several genes encoding apoptotic cell-death activators and secreted surface proteins were upregulated after ionizing radiation. Some of them were also upregulated by defect of mitochondrial DNA replication. These results indicate that the microbeam irradiation is useful in characterizing tissue-specific, local biological response to radiation in organisms. DNA damage-induced cell cycle arrest and apoptosis were observed in locally irradiated regions, but there was little, if any, ''bystander effect'' in the nematode.