Figure I.

The relationship of Ds, Fj gradients and proposed Ft and Fz activity gradients in the eye and wing. (a) In the eye, Ds is expressed in a gradient that is highest at the poles, and low at the equator. Fj expression is highest at the equator and low at the poles. Thus, the Fz activity slope and Fj gradient are opposite to the Ds gradient. (b) In the wing, Ds is high proximally and low at the distal end and Fj is again the opposite. In contrast to the eye, however, the Fz activity slope is the same as Ds and opposite to Fj. Fz is expressed evenly in both eye and wing; a Fz activity gradient is inferred from genetic data. In summary, the slope of the Fz ‘activity’ gradient and Ds–Fj expression gradients (regulating Ft ‘activity’) have the relative opposite directions in the two tissues, suggesting that interactions between Fz–Fm-group and Ft–Ds-group factors, if any, must be more complicated than a simple one way regulatory input.