LoxP sites were inserted on either side of the single coding exon. The open reading frame for a membrane tethered human placental alkaline phosphatase (hPLAP) was placed after the second loxP site. An FRT-flanked neomycin selectable marker used for ES cell selection (located just downstream of the alkaline phosphatase reporter) was removed by flp-mediated recombination. (J:175369)