The amelogenins are the predominant matrix proteins in developing enam
el and are crucial for proper enamel mineralization. Transgenic mice w
ere constructed in order to identify the segment of the amelogenin gen
e required for specific expression in enamel organ cells. A 3.5 kb fra
gment of the bovine X-chromosomal amelogenin gene that includes a TATA
box, the transcription initiation site, and 32 bp of exon 1 was linke
d to the betagalactosidase gene and injected into fertilized mouse egg
s. Newborn transgene positive mice expressed betagalactosidase activit
y in developing teeth treated with the chromogenic substrate Xgal. Foc
i of ameloblasts were positive in newborn mice; stain intensity and nu
mber of positive ameloblasts increased in 1-day and 2-day postnatal mi
ce. Some of the adjacent stratum intermedium cells also were positive
in the tater stages. Targeting of the transgene to the enamel organ wa
s specific; the only other cells observed to be positive were macropha
ges, which have endogenous betagalactosidase activity. (C) 1994 Wiley-
Liss, Inc.