A transgenic construct containing the rabbit Beta-globin (RBG) intron, a sequence encoding Cre/ESR1 (Cre recombinase fused to a mutant estrogen receptor ligand-binding domain (ERT2)) under the control of the acinar cell-specific rat elastase 1 (Cela1) promoter, and a rabbit Beta-globin polyadenylation cassette was made and injected into B6SJLF1 oocytes. (J:121254)