Influence of maternal phenotype on metabolic differentiation of agouti locus mutants in the mouse.

The results of extensive breeding experiments indicate that the phenotypic differentiation of embryos carrying the viable yellow, A( vy), or mottled, a(m), mutations is influenced to a major extent by the agouti locus genotype and the strain genome of the dam. The A(vy)/a and a(m)/a genotypes are each expressed in a spectrum of coat color phenotypes. These can be grouped into two classes, mottled and pseudoagouti.-In a reciprocal cross of C57BL/6JNIcrWf and AM/Wf-a(m)/a(m) mice, 29.5% of the offspring of C57BL/6 dams were of the pseudoagouti phenotype, whereas no pseudoagouti offspring were produced by AM strain dams.-Mottled yellow A(vy)/a mice become obese and tumor formation is enhanced in these mice in comparison with the lean pseudoagouti A(vy)/a siblings.-In two different reciprocal crosses using four different inbred strains, the proportion of pseudoagouti A(vy)/a offspring differed according to the strain of the dam. Regardless of strain, mottled yellow A( vy)/a dams produced significantly fewer pseudoagouti A( vy)/a offspring than did black a/a dams.-The data suggest that metabolic differentiation of A(vy)/a zygotes into phenotypic classes with different susceptibilities to obesity and tumor formation is influenced to a considerable degree by the metabolic characteristics of the oviductal and uterine environment of the dam.