Because genetic manipulation occasionally disrupts the expression of the neighboring genes, the chromosomal locus where the transgene has been integrated should be identified in the use of transgenic organisms. By using a new blend of thermostable DNA polymerase, we established a highly efficient method of inverse polymerase chain reaction for this purpose. By using this protocol, we successfully determined the vector integration sites of 2 mouse lines, NSE-tTA and tetO-Cre, the combination of which is a useful tool in neuroscience research. On the basis of this information, we quantified the relative expression amount of the chromosomal genes adjacent to these transgenes and found that the insertion of the tetO-Cre vector significantly altered the mRNA level of one of the examined genes. Considering the potential risk of the insertion effect, we recommend that the vector integration sites of any transgenic lines should be determined routinely by using this method, and that the expression levels of their neighboring genes should be determined.
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