A TRANSGENIC MOUSE ASSAY FOR AGOUTI PROTEIN-ACTIVITY

The mouse agouti gene encodes an 131 amino acid paracrine signaling mo lecule that instructs hair follicle melanocytes to switch from making black to yellow pigment. Expression of agouti during the middle part o f the hair growth cycle in wild-type mice produces a yellow band on an otherwise black hair. The ubiquitous unregulated expression of agouti in mice carrying dominant yellow alleles is associated with pleiotrop ic effects including increased yellow pigment in the coat, obesity, di abetes and increased tumor susceptibility. Agouti shows no significant homology to known genes, and the molecular analysis of agouti alleles has shed little new light on the important functional elements of the agouti protein. In this paper, we show that agouti expression driven by the human beta-ACTIN promoter produces obese yellow transgenic mice and that this can be used as an assay for agouti activity. We used th is assay to evaluate a point mutation associated with the a(16H) allel e within the region encoding agouti's putative signal sequence and our results suggest that this mutation is sufficient to cause the a(16H) phenotype. Thus, in vitro mutagenesis followed by the generation of tr ansgenic mice should allow us to identify important functional element s of the agouti protein.