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

唐氏综合症（DS），或21三体，是由人类21号染色体（HC21）的三个副本而不是两个副本遗传引起的。由于患有部分21三体的患者数量有限，并且即使患有完全21三体的患者的表型也高度可变，因此很难确定每种表型的关键基因。因此，已经建立了DS的小鼠模型，并用于研究表型与基因型的相关性。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，我们将重点放在小鼠染色体10和17同源区域的基因上，以建立新的小鼠DS模型。与藤田卫生大学的tuneko Okazaki博士及其同事合作，选择含有整个目标基因的BAC克隆，并使用人类人工染色体（HAC）作为载体将其转移到小鼠胚胎干细胞（ES）中。利用这些含有HAC的胚胎干细胞，我们培育出了携带人类21号染色体基因的HAC嵌合小鼠。随后的遗传杂交表明，HAC稳定地遗传给后代。RT-PCR分析了三种人类基因（CBS、U2AF1、CRYAA）在携带HAC的“transminicromosomal （TMC）”小鼠的各种组织中对HAC的影响，发现人类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基因在小鼠各组织中的表达水平低于内源性小鼠对应基因的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物种特异性。

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.