Spatial expression pattern of expL3 promoter activity detected with a lacZ reporter construct. The lacZ reporter construct expL3/lacZ contained a 948-bp upstream promoter region fused to the β-galactosidase (lacZ) gene. Ax2 cells (panel A) and STATa null cells (panel B) transformed with expL3/lacZ were allowed to develop on filters until the mound (a), tip (b, c), first finger (d), slug (e), late slug (e’ and e” for STATa null), Mexican hat (f), and culminant (g) stages. To detect expL3 expression, staining was carried out at 37°C for 4 h. Arrows indicate the position of pstO cells where the difference of staining pattern between Ax2 and STATa null strains were observed. The bars represent 0.5 mm.