COMPLEMENTATION OF THE NIJMEGEN BREAKAGE SYNDROME DEFECT

奈梅根断裂综合征(NBS)是一种罕见的遗传性人类疾病 以免疫缺陷、小头畸形、发育迟缓为特征 和癌症易感性。受国家统计局影响的患者不显示 小脑性共济失调或毛细血管扩张是共济失调的两个突出症状 毛细血管扩张症患者。然而，在细胞水平上，NBS和AT细胞 对电离表现出明显的过敏性 DNA双链断裂修复中无可测量缺陷的辐射； 抗辐射的DNA合成和染色体不稳定。两行 有证据支持这样的假设，即NBS的基因不同于 AT基因：微细胞介导的人类11号染色体转移(携带 AT-基因)导入NBS-细胞不能补充表型[19]/遗传学 来自五个不同家庭的证据，每个家庭有两个受影响的兄弟姐妹 从父母那里继承了不同的等位基因 包含AT基因的染色体11q也排除了ATM基因 NBS的原发缺陷[24，25]。 我们在这个提案中的总体目标是进一步描述来自 有NBS家族的患者受到这种疾病的罕见的限制。 因此，我们将创造保留小鼠染色体的NBS细胞杂交 将在低剂量率下选择用于抗辐射的碎片 辐射。随后，互补的染色体区域可以 FISH和聚合酶链式反应定位。匿名DNA标记间距3.5厘米摩根 (约3.5兆字节)将测试存在的距离或 在抗辐射和辐射敏感的杂交种中不存在。这种类型的 分析允许对染色体区域进行统计推断 含有NBS基因的。通过精确定位NBS基因的定位 到最小的区域(小于1兆数据库)，我们应该能够识别 使用传统的克隆方法或通过 利用人类基因组计划积累的信息。在……里面 此外，我们将在下文中进一步描述DNA损伤反应 并将研究NBS的染色体修复动力学 细胞。NBS基因的鉴定将增加我们对 参与细胞对电离辐射的反应的途径和 影响辐射敏感性的因素。

Nijmegen Breakage syndrome (NBS) is a rare inherited human disorder characterized by immune deficiencies, microcephaly, developmental delay and cancer susceptibility. Patients affected by NBS do not display cerebellar ataxia or telangiectasia, two prominent symptoms in Ataxia telangiectasia patients. However at the cellular level NBS and AT cells are indistinguishable showing marked hypersensitivity to ionizing radiation with no measurable defect in DNA double-strand break repair; radioresistant DNA synthesis and chromosomal instability. Two lines of evidence support the assumption that the gene for NBS is distinct from the AT-gene: Microcell-mediated transfer of human chromosome 11 (carrying the AT-gene) into NBS-cells fails to complement the phenotype [19]/ Genetic evidence from five different families with two affected siblings each who inherited different alleles from their parents for the region on chromosome 11q containing the AT gene, also excludes the ATM gene as the primary defect in NBS [24,25]. Our overall goal in this proposal is to further characterize cells from patients with NBS families is restricted by the rarity of this disease. Hence we will create hybrids with NBS cells retaining mouse chromosome fragments, which will be selected for radioresistance under low dose rate irradiation. Subsequently the complementing chromosomal region can be mapped by FISH and PCR. Anonymous DNA markers spaced in 3.5 centiMorgan (about 3.5 Megabases) distances will be tested for the presences or absence in radioresistant and radiosensitive hybrids. This type of analysis allows a statistical deduction of the chromosome region containing the NBS gene. By pinpointing the localization of the NBS gene to a minimal region (less than one Megabase) we should be able to identify candidate cDNAs using either a traditional cloning approach or by utilizing the accumulating information of the Human Genome Project. In addition, we will further characterize the DNA damage response following ionizing radiation and will study the kinetics of chromosome repair in NBS cells. Identification of the NBS gene will add to our understanding of the pathways involved in the response of cells to ionizing radiation and to the factors governing radiation sensitivity.