Fig. 1. The pros enhancer and eye development. (A) Schematic of the developing third instar eye-antennal disc complex. Anterior, top; posterior, bottom. The So/Eya expression domain is colored red. Positions of the morphogenetic furrow and PPN zone are shown. Black dots represent differentiating photoreceptor and cone cells, and show the progressive differentiation of cells from the furrow to the posterior disc margin. (B) Molecular analysis of the pros enhancer and transcription factor-binding sites. The original pros enhancer reporter is shown at the top, as a fusion of four tandem copies with hsp27-lacZ. Various constructs used in this study are shown below, including the full-size enhancer fragment fused to pros-lacZ and hsp70-lacZ. Deletion mutants of the fragment are presented below those. The transcription activity of each enhancer construct is presented as a qualitative scale from a β-gal pattern that completely mimics the Pros pattern (+++), to a β-gal pattern that exhibits variegated expression in R7 and cone cells (+ and ++), to no expression (-). Multiple independent transgenic lines were assayed for each construct. Colored triangles indicate putative transcription factor-binding sites based on their similarity to consensus-binding sequences. Their identities and locations in the pros enhancer region are indicated. Putative sites for which there are experimental binding data that confirm their binding-site activity (this paper) (Xu et al., 2000) are marked by an asterisk.