| Research Abstract |
Gene targeting is a useful method for the analyses of molecular functions in vivo. However in the interpretation of the results of knockout mouse studies, there are two problems. One is that the gene disruption occurs in the whole body, but not in the restricted region. Secondly, since the gene expression starts early in development, gene targeting results in developmental defects and compensatory regulation of other genes. Because of these problems, it has been difficult to precisely determine the role of the molecules in mediating synaptic plasticity and leaning in the mature brain.
Recently, a spatio-temporally restricted gene targeting system was developed. This method is based on the P1 phage Cre/loxP recombination system, where the Cre gene and a mutated ligand binding domain of the human progesterone receptor gene were fused to produce the CrePR gene. The recombinase activity of the CrePR protein is induced by the synthetic steroid, RU486, but not by endogenous hormones. By generating mutant mice in which the CrePR gene is expressed in a region-specific or cell-type specific manner, it has become feasible to achieve spatially and temporally regulated gene targeting.
We have established a mouse line which can be used to mediate inducible gene recombination specifically in cerebellar Purkinje cells. In the generated mutant mice (D2CPR), the CrePR gene is specifically expressed in Purkinje cells under the control of the GluRδ2 gene promoter. The GluRδ2 gene is abundantly and specifically expressed in the Purkinje cells. When these mice were crossed with a reporter mouse line carrying the lacZ reporter gene under a universally active promoter, CrePR-mediated expression of β-galactosidase was induced specifically in the mature Purkinje cells by the artificial progesterone receptor ligand RU486.
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