Efficient allele conversion in mouse zygotes and primary cells based on electroporation of Cre protein

•Cre-loxP recombination can be mediated via Cre protein electroporation.•Electroporation of Cre protein is efficient in mouse zygotes and primary cells.•Cre protein electroporation can be combined with zygotes obtained from IVF.•Cre protein electroporation has no toxic effects on electroporated zygotes. Cre-loxP recombination system is a powerful tool for genome engineering. One of its applications is found in genetic mouse models that often require to induce Cre recombination in preimplantation embryos. Here, we describe a technically simple, affordable and highly efficient protocol for Cre protein delivery into mouse zygotes by electroporation. We show that electroporation based delivery of Cre has no negative impact on embryo survival and the method can be easily combined with in vitro fertilization resulting in a significantly faster generation of desired models. Lastly, we demonstrate that Cre protein electroporation is suitable for allelic conversion in primary cells derived from conditional mouse models.