Production of Down syndrome model mice based on fine genetic information of human chromosome 21.

唐氏综合征（DS）或21三体综合征，是由人类21号染色体（HC 21）的三个而不是两个拷贝遗传引起的。很难鉴定每种表型的关键基因，因为部分21三体患者的数量有限，即使是完全21三体患者的表型也高度可变。因此，已生成DS小鼠模型并用于研究表型-基因型相关性。我们分析了人类染色体21q22.3上基因的转录本、结构和功能。基于这些信息，我们专注于小鼠10号和17号染色体同源区域的基因，以产生新的DS小鼠模型。与藤田卫生大学的Tuneko Okazaki博士和她的同事合作，选择含有整个靶基因的BAC克隆，并使用人类人工染色体（HAC）作为载体转移到小鼠胚胎干（ES）细胞中。使用这些含HAC的ES细胞，我们已经产生了嵌合小鼠，其具有携带人类染色体21基因的HAC。随后的遗传杂交表明，HAC稳定地传递给后代。对携带HAC的“transminicromosomal（TMC）”小鼠的各种组织中的HAC上的三个人基因（CBS、U2 AF 1、U2 AA）的RT-PCR分析揭示，人基因在小鼠组织中的表达模式与在人组织中的表达模式相似。然而，人CBS基因在小鼠各种组织中的表达水平低于内源性小鼠对应物的5%。我们推测人类基因表达水平的降低是由于小鼠转录因子的种属特异性。

Down syndrome (DS), or trisomy 21, is caused by the inheritance of three instead of two copies of human chromosome 21 (HC21). It is difficult to identify critical gene(s) for each phenotype because the number of patients with partial trisomy 21 is limited and the phenotype is highly variable in patients with even full trisomy 21. Therefore, mouse models for DS have been generated and used to study phenotype-genotype correlations. We have analyzed transcripts, structure and function of genes on human chromosome 21q22.3. Based on the information, we focus on genes in the regions homologous to mouse chromosomes 10 and 17 to generate novel mouse models for DS. BAC clones containing the entire target gene(s) were selected and transferred into mouse embryonic stem (ES) cells using a human artificial chromosome (HAC) as a vector in collaboration with Dr.Tuneko Okazaki and her colleagues at Fujita Health University. Using these HAC-containing ES cells, we have generated chimeric mice harboring a HAC that carries human chromosome 21 gene(s). Subsequent genetic crossing showed that HAC was stably transmitted to progeny. RT-PCR analysis of three human genes (CBS, U2AF1, CRYAA) on HAC in various tissues of "transminicromosomal (TMC)" mice harboring a HAC revealed that the expression pattern of human genes in mouse tissues is similar to that in human tissues. However, expression level of human CBS gene in various mouse tissues was less than 5% of endogenous mouse counterpart. We speculated that the reduced expression level of human gene was due to species specificities of mouse transcription factors.