A rare and transient subpopulation of mouse embryonic stem (ES) cells can express high levels of transcripts that are found in two-cell (2C) embryos. These cells lack the typical inner cell mass pluripotency markers Oct4 (Pou5f1), Sox2, and Nanog but can contribute to the development of both embryonic and extraembryonic tissues. It was found that these ES cells cycle in and out of the pluripotent 2C-like state.
The most highly activated sequence repeat in two-cell (2C) embryos is the MuERV-L (murine endogenous retrovirus with leucine tRNA primer) family of retroviruses and their corresponding long terminal repeat (LTR) promoters (Mt2_mm).
In order to indelibly mark these cells and follow their fate, a transgenic mouse line incorporating MuERV-L regulatory elements driving expression of a tamoxifen-inducible Cre recombinase was created (2C::ERT2-Cre-ERT2).
When crossed with Gt(ROSA)26Sor floxed stop lacZ reporter strain (see Stock No. 007905), progeny may be treated with 4-hydroxytamoxifen (4HT) to detect nuclear Cre expression in MuERV-L Gag+ cells. ES cells derived from these mice that are cultured in 4HT show a steady increase in the percentage of reporter-positive cells.
