The most distal conserved module, A, is a silencer that restrains olSix3.2 expression to the anterior neural plate. (a) Drawings to the left of the panel are schematic representations of the different constructs (cI to cV) used to study the potential regulatory activity of modules A to C, whereas the tables to the right summarizes the presence (+) or absence (-) of enhanced green fluorescent protein (EGFP) reporter expression observed with each construct and corresponding to the endogenous olSix3.2 expression domain (NE) or with an ectopic posterior expansion (EPE). The A module with silencer activity is depicted in purple. (b to d) Bright field images, and (e to g) epi-fluorescence dorsal views of cII transgenic embryos at different stages of development (as indicated). Note that the domain of EGFP expression is progressively expanded in the caudal direction (arrows in panels e and f), invading the spinal cord at St36 (panel g). Equivalent patterns were observed with the cIII and cIV transgenic lines. Dotted lines in panels e to g indicate the caudal limit of endogenous olSix3.2 expression.