Development of genome analytical systems for identification of causative genes in rat models for human diseases

在了解健康和疾病的生物学和遗传基础方面，大鼠具有许多独特的特征和优势，而且绝大多数人类疾病的大鼠模型是独一无二的，在其他物种中没有已知的等同物。在本课题中，我们对大鼠遗传图谱和大鼠-小鼠-人比较基因组图谱进行了改进，以便对人类疾病大鼠模型的致病基因进行遗传分析和定位克隆。合成的大鼠图谱由5682个冗余标记组成，遗传长度为2028 cM。近年来，在新建立的大鼠基因组辐射杂交（RH）图谱的基础上，建立了大鼠-小鼠-人全基因组比较图谱。我们报告了基于小鼠遗传图谱的第4版比较图谱，并对其完成度进行了评价。在小鼠遗传图谱上，大鼠-小鼠同源图谱的保守区总长度为1199 cM（75%）。此外，我们还通过定位克隆鉴定了突变小鼠和大鼠的致病基因。1)小鼠的淋巴增生（aly）突变是常染色体隐性的，其特征是全身淋巴结和佩耶氏病的缺失，脾脏和胸腺结构紊乱并伴有免疫功能低下。我们发现aly等位基因携带一个点突变，导致nf -kb诱导激酶（NIK）的氨基酸取代。与野生型Nik的转基因互补成功。2)震颤大鼠表现为缺席样癫痫发作和中枢神经系统海绵状变性。通过定位克隆，在天冬氨酸酰化酶基因所在的关键区域发现了基因组缺失。因此，在检查的任何组织中均未检测到天冬氨酸酰化酶活性，并且在突变体大脑中显示n -乙酰- l-天冬氨酸（NAA）的异常积累。有趣的是，将NAA直接注射到正常大鼠脑室会引起类似于震颤大鼠的缺席样癫痫发作。

The rat has many unique features and advantages for understanding the biological and genetic bases of health and disease, and the great majority of rat models for human diseases are unique without known equivalents in other species. In this research project, we have improved the rat genetic map and rat-mouse-human comparative genome map to facilitate genetic analysis and positional cloning of causative genes in the rat models for human diseases. The resultant integrated rat map consists of 5,682 redundant markers, spanning a genetic length of 2,028 cM. Recently, a genome-wide rat-mouse-human comparative map based on newly developed radiation hybrid (RH) map of the rat genome has been reported. We have reported the 4th version of our comparative map based on mouse genetic map and its evaluation in respect of the completion. The total length of the conserved regions in the rat-mouse homologous map spans now 1199 cM (75%) on the mouse genetic map. In addition, we have identified the causative genes in mutant mouse and rat by positional cloning. 1) The alymphoplasia (aly) mutation of mouse is autosomal recessive and characterized by the systemic absence of lymph nodes and Peyer's pathches and disorganized splenic and thymic structures with immunode-ficiency. We found that the aly allele carries a point mutation causing an amino acid substitution in Nf-kb-inducing kinase (NIK). Transgenic complementation with wild-type Nik was successful. 2) The tremor rat exhibits absence-like seizures and spongiform degeneration in the central nervous system. By positional cloning, a genomic deletion was found within the critical region, in which aspartoacylase gene is located. Accordingly, no aspartoacylase activity was detected in any tissues examined and abnormal accumulation of N-acetyl-L-aspartate (NAA) was shown in the mutant brain. Interestingly, direct injection of NAA into normal rat cerebroventricule induced absence-like seizures similar to those seen in tremor rats.