Use of PB-Cre4 Mice for Mosaic Gene Deletion

Andreas Birbach,Wei Yan

doi:10.1371/journal.pone.0053501

Abstract

Transgene expression from short promoters in transgenic animals can lead to unwanted transgene expression patterns, often as a byproduct of random integration of the expression cassette into the host genome. Here I demonstrate that the often used PB-Cre4 line (also referred to as “Probasin-Cre”), although expressing exclusively in the male prostate epithelium when transmitted through male mice, can lead to recombination of loxP-flanked alleles in a large variety of tissues when transmitted through female mice. This aberrant Cre activity due to Cre expression in the oocytes leads to different outcomes for maternally or paternally transmitted loxP-flanked alleles: Maternally inherited loxP-flanked alleles undergo recombination very efficiently, making female PB-Cre4 mice an efficient monoallelic “Cre deleter line”. However, paternally inherited loxP-flanked alleles are inefficiently recombined by maternal PB-Cre4, giving rise to mosaic expression patterns in the offspring. This mosaic recombination is difficult to detect with standard genotyping approaches of many mouse lines and should therefore caution researchers using PB-Cre4 to use additional approaches to exclude the presence of recombined alleles. However, mosaic recombination should also be useful in transgenic “knockout” approaches for mosaic gene deletion experiments.

Highlights

Transgene expression in transgenic animals is often achieved by a short promoter element which ideally should constrict gene expression to a specific tissue of interest
In order to verify this hypothesis, I set up a number of test breedings using PB-Cre4 line together with a line carrying a loxP-flanked allele of the tumor suppressor Pten used in our studies
When breeding male mice carrying PB-Cre4 in addition to a Pten flox allele and a Pten wildtype allele to wildtype females, a normal distribution of the Pten flox and Pten wildtype allele in the offspring was observed

Summary

Introduction

Transgene expression in transgenic animals is often achieved by a short promoter element which ideally should constrict gene expression to a specific tissue of interest. Use of these small expression units and the classic transgenic technique of pronuclear injection lead to random integration of the unit in the genome. Transgene expression is not under sole control of the short promoter element, and of the host locus. This leads to aberrant transgene expression patterns in many transgenic lines with expression in tissues not primarily targeted [1]. Use of multiple transgenic lines and/or cloning and analysis of the integration site can help in explaining the pattern

Methods

Results

Conclusion