Analysis of expression patterns in the brains of tet-off promoter mice

In traditional transgenic mouse models for neurological diseases, the transgene is constitutively expressed in invariable brain regions. The „Tet-Off-System“ developed by Dr. H. Bujard (ZMBH Heidelberg) however allows the generation of inducible transgenic mouse models and flexibility in the selection of the targeted brain regions. This system is based on two constructs: The promoter construct controls the expression of the so called tTA (Tetracycline transactivator) gene product. The binding of this protein to a Tetracycline responsive element (TRE) in the responder construct induces the transcription of the gene of interest. The expression can be blocked by the addition of Tetracycline which allosterically inhibits the tTA protein. In order to assess whether a specific promoter mouse line is suitable for the generation of a disease model the knowledge of the brain regions in which the transgene will be expressed is indispensable. The expression pattern of the promoter mouse line states whether the transgene will be targeted to the desired brain regions and in which brain regions a phenotype or pathology is to be expected, respectively. For this reason we studied the expression pattern of available Tet-Off promoter mouse lines with known expression in the brain (Prion protein (Prp) promoter, Ca2+/Calmoduline-dependent protein kinase II (CamKII) promoter). We crossbred these mouse lines with responder mice transgenic for the lacZ reporter gene. The expression of beta-galactosidase in brain regions with promoter activity was detected using X-Gal as beta-galactosidase substrate resulting in a blue staining. For an overall view entire mouse brains were stained. Brains were sectioned for a detailed analysis of the localization of beta-galactosidase, and composite images of whole sections were generated. The visualization of this expression data in a 3-D brain atlas facilitates the future goal-directed generation of inducible mouse models using the Tet-Off-System.