Fig. 2. Expression of Edar, Edaradd and Eda in the developing feather tract. (A) In situ detection of ß-catenin transcripts shown as an example of the pattern exhibited by a class of `early genes' during development of the femoral tract. Expression begins as a band (yellow bracket) at the distal border (yellow arrowhead) and spreads towards the trunk. It is repressed in interfollicular epidermis and increased in the epidermal placodes. The first bud to form is marked by an asterisk. Younger buds are added sequentially within a row (red arrow) and additional rows arise progressively closer to the trunk (black arrow) as development progresses so that rows closer to the trunk have buds at earlier stages of development than those more distal on the leg. (B,E,H) Edar is expressed in a similar pattern. Initial diffuse expression (B) becomes restricted and upregulated in the nascent placode (B,E). (C,F) Initial diffuse Eda expression (C) becomes restricted to interfollicular skin (F). (D,G) Edaradd expression resembles that of Edar (B,E) at all stages analyzed. In older embryos, Edar expression persists in feather bud epithelium (H), whereas Eda is detected in the posterior and distal regions of the most mature buds (I). Embryos were harvested at day 7.5 (A), day 7.25 (B-D), day 8 (E-G) and day 10 (H,I).