Figure 6.
The BMP-AE mediates a conserved Smad-responsive function in the Drosophila and vertebrate CNS. (A) Schematic representation of the chick neural tube electroporation experiment with the sequence of the wildtype and mutated dad13-BMP-AE. (B) Expression of an octamerized version of a wildtype and mutated BMP-AE with an EGFP reporter at 24 hpe. The wildtype reporter displays strong EGFP expression in dorsal-most part of the neural tube, whereas the mutant reporter does not show any activity. An RFP control plasmid is co-electroporated with the EGFP reporters to indicate the efficiency of electroporation. Pax7 immunostaining indicates the dorsal region of the spinal cord. (C, D) Co-electroporation of a phosphomimetic form of Smad1 (Smad S/D) strongly increases and expands expression of the wildtype BMP-AE throughout the whole neural tube (C), but does not activate expression of the mutated version (D). (E) Schematic representation of the Drosophila transgenesis experiment where the Van26 genomic fragment has its BMP-AE motif replaced with a BMP-AE taken from the X. laevis bambi enhancer. (F) Nuclear DsRed expression driven from the Van26AEbambi-BMP-AE-nlsDsRed reporter in control and wit mutants third instar larval VNCs. The mean±SEM number of nuclei per VNC that express the reporter is indicated at the bottom of each panel. Reporter activity was significantly reduced in wit mutants (P = 0.0079 two-sided Wilcoxon rank-sum test). At least five VNCs were analyzed for both genotypes.