Dominant negative effects of HNF-1β mutation on the development of MODYS in transgenic mouse models

肝细胞核因子-1 α（hepatocyte nuclear factor-1α，HNF-1α）和HNF-1β是转录激活蛋白，属于同一同源异型蛋白家族。这些基因的突变分别导致年轻人3型成熟型糖尿病（MODY 3）和MODY 5。HNF-1α和HNF-1β在体外可形成同源或异源二聚体，并与相同的靶DNA序列结合。另一方面，HNF-1α表达的减少导致小鼠糖耐量异常，而HNF-1β表达的减少则不会导致小鼠糖耐量异常。因此，我们推测HNF-1β基因的显性负效应而非HNF-1α基因突变在MODY的发生中起重要作用。本研究的目的是建立过表达显性负性HNF-1β突变蛋白的转基因小鼠，并试图阐明MODY 5的发生机制。在本课题的研究过程中，我们构建了能表达HNF-1β突变蛋白的载体，并将其注射到小鼠受精卵中。然而，遗憾的是，迄今为止，我们还没有得到任何阳性转基因小鼠。其原因可能是载体不适合在小鼠体内表达，或者表达的突变蛋白对小鼠胚胎发育有一定的毒性作用。现在我们正在研究这些可能性。与载体相关的是，我们最近成功地制备了一种β细胞特异性过表达氨基酸转运蛋白的转基因小鼠。因此，我们计划将突变的HNF-1β cDNA转化到该载体上，用于注射表达氨基酸转运蛋白。

Hepatocyte nuclear factor-1α (HNF-1α) and HNF-1β are transcriptional activator proteins and belong to the same homeoprotein family. The mutations of these genes are responsible for maturity onset diabetes of the young 3 (MODY3) and MODY5, respectively. HNF-1α and HNF-1β can form homo- or hetro-dimer and bind to the same target DNA sequences in vitro. On the other hand, a decrease of HNF-1α expression in mouse caused glucose intolerance but a decrease of HNF-1β expression in mouse did not. So, we hypothesize that the dominant negative effect of HNF-1β but not HNF-1α mutation is crucial for development of MODY. In this study, we aim to make a transgenic mouse that over-expresses a dominant-negative HNF-1β mutant protein and try to elucidate the mechanism for the develomnent of MODY5. In the term of this project, we made some vectors by which the dominant-negative HNF-1β mutant protein could be expressed and injected these vectors to some fertilized mouse eggs. Unfortunately, however, we can not get any positive transgenic mouse until now. The reason is that the vectors would not be suitable for the expression in mouse, or that the expression of the mutant protein would have some toxic effects on the development of mouse embryo. Now we are checking about these possibilities. In relation to the vector, we recently succeed to make a transgenic mouse that over-expresses a kind of amino acid transporter in β cell specifically. So we plan to change the mutant HNF-1β cDNA to this vector which we used for the injection to express the amino acid transporter.