Fig. 7. Proposed biochemical and molecular mechanisms for pigment synthesis and patterning. (A) Dopa-melanin, dopamine-melanin and NBAD scelerotin are products of discrete branches of a common biochemical pathway. Yellow, Tan and Ebony proteins are rate-limiting enzymatic steps in the formation of black, brown and tan pigments, respectively. The ‘?’ indicates the activity of an unknown gene that regulates pigment patterns in the absence of tan (P. J. W., unpublished). (B) Development of the abdominal pigment stripe in D. melanogaster requires spatial regulation of Yellow, Ebony and Tan. Boxes represent a section of abdominal tergite as shown in the far right panel. Yellow expression is gray, Ebony expression is yellow and our prediction of Tan expression is brown. The combined action of these patterns is to induce the formation of black melanin in the stripe where Yellow is expressed, tan pigment anterior to the stripe where Ebony is expressed alone, and brown melanin in the stripe where both Ebony and Tan are present. The combination of black and brown melanins produces the final appearance of the stripe.
