Generation of transgenic mouse line with prostate-specific expression of codon-improved Cre recombinase.

Background: Genetically engineered mouse models are useful tools to decipher molecular mechanisms of diseases. As for prostates, a rat probasin promoter has been widely used to drive prostate-specific gene expression. To optimize its codon usage to that of mammals, we used codon-improved Cre recombinase (iCre) for prostate-specific Cre- loxP recombination.
Materials and Methods: We generated transgenic mice that express iCre driven by conventional probasin promoter in a prostate-specific manner (PB-iCre). Linearized PB-iCre transgene deoxyribonucleic acids (DNAs) were microinjected into pronuclei of fertilized mouse embryos. The integration of the transgene was confirmed by Southern blot analysis. A line of transgenic mice expressing a sufficient amount of iCre mRNA in its prostate was selected. To test recombinase activity of PB-iCre in vivo , its offspring was crossbred with Pten ^flox/flox mice in which murine prostate adenocarcinoma is reported to occur upon excision of loxP -flanked regions.
Results: Eight founder animals were obtained, all of which showed germ line integration of PB-iCre transgene by Southern blot analysis. Among them, the prostate from only one line (line 58) expressed a sufficient amount of iCre mRNA. This line was crossbred with Pten ^flox/flox mice to generate PB-iCre58/ Pten ^flox/flox . As a result, 12-week-old PB-iCre58/ Pten ^flox/flox mice presented with prostate adenocarcinoma that was histologically similar to human cribriform prostate cancer of Gleason grade 4.
Conclusions: We have successfully established a transgenic mouse line that expresses iCre in a prostate-specific manner.