OVEREXPRESSION OF AN AGOUTI CDNA IN THE SKIN OF TRANSGENIC MICE RECAPITULATES DOMINANT COAT COLOR PHENOTYPES OF SPONTANEOUS MUTANTS

The classical mouse fancy Agouti gene is responsible for the wild-type coat color where hairs are banded black and yellow. The Agouti gene e ncodes a 131-amino-acid secreted protein product that regulates phaeom elanin synthesis by melanocytes in mice. Mice with a dominant mutation at this locus, AY, develop a yellow coat color, obesity, and diabetes , as the result of a deletion that results in ectopic overexpression o f the Agouti gene mRNA in all tissues examined. Obesity and diabetes i n A(y) mutant mice could be caused by circulation of the protein, or l ocalized action in specific tissues as a paracrine factor acting in ce ll-cell communication. To test these two possibilities, the Agouti cDN A was overexpressed in the skin of transgenic mice using either the Ty rosinase-Related Protein-1 or the keratin-14 (K14) promoter, the latte r with and without an intron. The K14 promoter directed high constitut ive levels of expression of Agouti mRNA in the skin, and several lines of transgenic mice exhibited coat colors resembling dominant Agouti a llele phenotypes. Two highly expressing K14-Agouti transgenic lines, w ith light-yellow pelage, were analyzed for obesity and hyperglycemia. The transgenic mice were not significantly different from the controls (P > 0.05), indicating that the Agouti product does not act as an end ocrine factor. RNase protection assays revealed a correlation between the levels of dorsal and ventral skin expression with pigmentation/pha eomelanin phenotypes. Co-injection experiments with the Agouti transge nes and other transgenes demonstrated co-integration of the two constr ucts at the same chromosomal site in approximately 95% of F1 progeny, allowing transgene inheritance to be visibly detected. (C) 1996 Academ ic Press, Inc.