Fig. 4. Timing of gene expression changes. Gene expression was compared in the left and right femoral tracts. (A) Four rudiments lacking Eda expression are observed in the left femoral tract, (B) six rudiments with localized Edar expression are observed in the corresponding row of the right tract and additional rudiments are observed in the next row. Corresponding rudiments are noted by black arrows; rudiments with local Edar expression but without a corresponding region of suppressed Eda expression are marked by red arrows. The left femoral tract (C) shows three well-resolved spots of Bmp2 expression, while the right femoral tract (D) shows a single well-resolved spot of Edar expression (black arrow). While local Bmp2 expression in the next rudiments to form is well resolved (C, red arrow), Edar expression in the corresponding rudiments is not (D, red arrow). (E,F) By contrast, three well-defined spots of Bmp4 expression are observed in the second row of follicles on the right leg (E, black arrows) when, in addition to the corresponding spots of Edar expression (F, black arrows), two additional spots are observed in the corresponding row on the right leg (F, red arrows). (G,H) Comparison of Eda expression (G) and Bmp2 expression (H) reveals additional rudiments with local Bmp2 expression within the corresponding row (black arrows), and an additional row of rudiments expressing Bmp2 (red arrows).