![Blastocytes_left](/system/files/styles/mdc_header_1_mdc_mobile_1_5x/private/2018-02/Header_murine-Blastocystes_1.jpg?h=e9777f68&itok=K5YwMfLi)
ES cell injection into a mouse embryo
The injection of ES cells at an earlier time-point, i.e. the 8-cell-stage, leads to an F0 generation of mutant mice that is completely ES cell-derived and allows immediate phenotyping.
In 2007, Poueymirou et al. developed a laser technology to perforate the zona pellucida followes by injection of the ES cells into the perivitelline space (published in Nature Biotechnology). This was a major technological advance to facilitate the injection of eight-cell-stage embryos.