5.5 kb of upstream bovine AMELX gene sequence plus untranslated exon 1, intron 1 and part of exon 2 was fused to a partial mouse Amelx cDNA that encodes the M180 isoform from exon 2 to part of exon 5 and a partial bovine AMELX CDNA that encodes the rest of exon 5 and exon 6, and was followed by a bovine polyadenylation signal sequence from the bovine AMELX gene. RT-PCR analysis demonstrated that this transgene is expressed in first mandibular molar teeth in 3-5 day old pups. Western blot analysis demonstrated that transgenic protein was expressed in first mandibular molars. Two lines of mice were produced; in addition to line 87, line 31 was also created.