COMPLEMENTATION OF THE NIJMEGEN BREAKAGE SYNDROME DEFECT

奈梅亨断裂综合征（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NBS影响的患者未显示 小脑共济失调或毛细血管扩张，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 无法区分，显示出对电离 在DNA双链断裂修复中没有可测量缺陷的辐射; 抗辐射DNA合成和染色体不稳定性。 两行 有证据支持NBS基因不同于NBS基因的假设。 AT基因：微细胞介导的人类11号染色体（携带 AT-基因）进入NBS-细胞未能补充表型[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， 从父母那里遗传了不同的等位基因， 染色体11 q含有AT基因，也排除了ATM基因， 第一个问题是NBS [24，25]。 我们在这项提案中的总体目标是进一步表征来自 NBS家系患者因其罕见性而受到限制。 因此，我们将创建与保留小鼠染色体的NBS细胞的杂交细胞 碎片，将在低剂量率下被选择用于辐射抗性 辐照 随后，互补染色体区域可以是 通过FISH和PCR定位。 匿名DNA标记间隔为3.5厘摩根 （约3.5兆）的距离将被测试的存在或 在辐射抗性和辐射敏感性杂交体中不存在。 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。 通过精确定位NBS基因 我们应该能够识别的最小区域（小于1兆字节） 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 此外，我们将进一步表征DNA损伤反应， 电离辐射，并将在NBS研究染色体修复的动力学 细胞 NBS基因的鉴定将增加我们对 参与细胞对电离辐射反应的途径， 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.