A 914-bp promoter is sufficient to reproduce the endogenous prolyl oligopeptidase gene localization in the mouse placenta if not subject to position effect

Abstract

Prolyl oligopeptidase (POP) is a widely distributed multifunctional protein which has an endopeptidase activity to cleave a Pro-X peptide bond. In spite of numerous studies about POP, the mechanism by which its transcription is controlled has not been well investigated. Here we generated transgenic mice bearing a transgene which contained a 914-bp POP gene promoter linked to the enhanced green fluorescent protein (EGFP) gene to assess the in vivo promoter activity. We established six transgenic lines with different copy numbers, but no EGFP signal was observed in four lines due to a high level of DNA methylation, which suggested that the transgene was subject to position effect. However, in the other two lines, we detected the EGFP expression in many tissues, and its placental localization showed a similar change to POP. A strong EGFP signal was observed in the junctional and labyrinthine zones of E10.5–E12.5 placentas and in the junctional zone and the maternal decidua after that. This placental gene activation might be attributed to AP-2γ because we detected its binding to the POP promoter. In contrast, we did not obtain any evidence that EGFP was expressed in a similar pattern compared with POP in the ovary. The current data demonstrated that the 914-bp promoter had sufficient activity to reproduce the POP localization in the placenta if it was not subject to position effect and suggest that the regulatory mechanism of the POP gene expression differs between tissues.