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

大鼠在理解健康和疾病的生物学和遗传学基础方面具有许多独特的特征和优势，并且绝大多数人类疾病的大鼠模型是独特的，在其他物种中没有已知的等同物。在本研究项目中，我们改进了大鼠遗传图谱和大鼠-小鼠-人比较基因组图谱，以便于对人类疾病大鼠模型中的致病基因进行遗传分析和定位克隆。由此产生的综合大鼠图谱由5，682个冗余标记组成，跨越2，028 cM的遗传长度。最近，一个全基因组的大鼠-小鼠-人比较地图的基础上新开发的辐射杂种（RH）的大鼠基因组图谱已被报道。本文报道了以小鼠遗传图谱为基础的第四版比较图谱的构建及其完成情况。在大鼠-小鼠同源图谱中的保守区域的总长度跨越小鼠遗传图谱上的1199 cM（75%）。此外，我们还通过定位克隆的方法在突变小鼠和大鼠中鉴定了致病基因。1)小鼠淋巴发育不全（aly）突变是一种常染色体隐性遗传病，其特征是全身淋巴结和派伊尔氏径缺失，脾脏和胸腺结构紊乱，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的转基因互补是成功的。2)震颤大鼠表现出失神样癫痫发作和中枢神经系统海绵状变性。通过定位克隆，发现该基因组缺失的关键区域内，该酶基因所在。因此，在所检查的任何组织中均未检测到N-乙酰基-L-天冬氨酸（NAA）的活性，并且在突变体脑中显示出N-乙酰基-L-天冬氨酸（NAA）的异常积累。有趣的是，直接注射NAA到正常大鼠脑室诱导的失神样癫痫发作类似于震颤大鼠。

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.