Placenta‐specific gene activation and inactivation using integrase‐defective lentiviral vectors with the Cre/LoxP system

Transgenic and knockout studies have advanced our understanding of the genetic control of embryonic development over the past decades. However, interpretation of the phenotype of mutant mice is potentially complicated, since the commonly used knockout approach modifies both the fetal and placental genome. To circumvent this problem, we previously developed a placenta‐specific gene manipulation system by lentiviral vector transduction of embryos at the blastocyst stage. In the present study, by combination with the Cre/LoxP system, we successfully demonstrate placenta‐specific gene activation and inactivation in EGFP reporter mice and Ets2 floxed mice, respectively. Transient expression using integrase‐defective lentiviral (IDLV) vectors diminished the toxic effect of Cre expression and solved the dilemma of mosaic recombination with lower concentrations and toxic effects with higher concentrations of Cre recombinase. We also show that placenta‐specific Ets2 disruption causes embryonic lethality and reconfirmed the critical role of Ets2 during placentation. This technology facilitates both gain and loss of gene function analyses in placental development during pregnancy. Since IDLV vectors can efficiently transduce a variety of cell types similarly to wild‐type vectors, our IDLV‐Cre strategy is potentially useful for a wide range of applications. genesis 47:793–798, 2009. © 2009 Wiley‐Liss, Inc.