The targeting vector was designed to insert an eGFPCreERT2 (GCE) fusion protein coding sequence and loxp-flanked neo selection cassette into just after the stop codon of the last exon of Olfm4 gene, making use of the endogenous poly A signal. Positive clones were injected into blastocysts to establish the mouse line. The neomycin selection cassette was excised in vivo by crossing the mice with the PGK-Cre mouse strain.