Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Biology and Microbiology


The lethal yellow (AY/a) mouse is a productive model to study melanogenesis, genetic obesity, maturity-onset diabetes, immunosuppression, and infertility because overexpression of a single gene causing agouti protein synthesis is the sole source of these problems. Agouti protein modifies signal cascades in a number of specific cell types. One important effect of agouti gene expression is modification of tyrosinase (E.C. activities of which there are three: tyrosine hydroxylase, dopa oxidase, and DID oxidase. We measured dopa oxidase activity of agouti (A wJ / A wJ), lethal yellow (AY/a), and black (a/a) mice over 5, 8, 11, and 14 days of regenerated anagen hairbulbs. The results show significant differences between all three genotypes over 5, 8, and 11 days of regeneration as well as significant differences between black/agouti as compared to yellow at day 14. Ratios of dopa oxidase activity of black, agouti, and yellow samples at day 5 are 6:4:1; at day 8 are 3:2:1; at day 11 are 5:5:1; and at day 14 are 4:4:1. The agouti mouse hair is unique in that initially, black pigment is produced for three days, followed by a shift to form yellow pigment for three days, and then shift back to black pigment formation to finish the hair growth cycle. Agouti protein is synthesized only during the yellow phase of agouti hair production. This produces the classic agouti hair shaft possessing a black tip, a subterminal yellow band, and a black shaft. Dopa oxidase activity in hairbulbs of the agouti mouse (A wJ / A wJ) parallels that of the lethal yellow mouse (AY/a) during phaeomelanin (yellow pigment) synthesis, and simulates dopa oxidase of the black mouse (a/a) during periods of eumelanin (black pigment) synthesis. These data further support the hypothesis that agouti-regulated dopa oxidase activity is a critical factor in the determination of whether melanocytes synthesize black pigment ( eumelanin) or yellow pigment (phaeomelanin).

Library of Congress Subject Headings

Mice -- Genetics Melanocytes Hair follicles Oxidases Lethal mutation Melanins -- Synthesis



Number of Pages



South Dakota State University