Fig. 7. Activity of the E1 enhancer is increased in the chick spinal cord when the low affinity Pax6 binding sequence has been replaced with a consensus binding site. Labelling for ß-gal (A,C,E,H), GFP (B,D,F,I) and Pax6 (G,J), of chick neural tubes harvested 6 hours (A-D) or 48 hours (E-J) after electroporation with the constructs E1ßglobinlacZ (A,B,E-G), consE1ßglobinlacZ (C,D,H-J) and CMVGFP (B,D,F,I). In A-D, neural tubes are shown in dorsal views and the electroporated side is towards the bottom. Activity of the E1 element is low at this early stage (HH stage 13-15), and introducing a consensus Pax6 binding sequence at the E1.1 site significantly increases activity of the E1 element (C). The dashed lines outline the shape of the neural tube. In E-J, -ß-gal and -GFP stainings were performed on the same transverse sections of spinal cord, and -Pax6 staining on adjacent sections. Activity of the E1 element at this stage (HH stage 21-22) is confined to a medial domain of high Pax6 concentration (F,G), whereas the modified element consE1 is active in a broader domain that includes cells expressing low Pax levels (I,J).

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