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Fig. 4 A 336 bp regulatory region upstream of wt1b is necessary and sufficient for expression in the pronephric glomeruli. (A) Deletion constructs were generated using plasmid pBS-wt1b-GFP (row 1). Construct numbers are indicated on the left. Dark gray bars represent the GFP gene, yellow bars represent the 2.1 kb region between NdeI and ClaI sites or subfragments thereof (shown in higher magnification in rows 5-12). At least 40 embryos were investigated for GFP expression in the glomeruli, which are located ventral of the third somite, 24 hours after injection of the respective reporter construct. For quantification, the number of embryos with GFP expression in the glomerulus was divided by the total number of GFP-positive embryos (GFP expression anywhere in the embryo). +++, >40%; ++, 20-40%; -, <5%. (B) Overlay of brightfield transmission and fluorescence images of stable wt1b-coreProm and wt1b-coreProm-wt1bEnh transgenic embryos (dorsal view). The first three somites are numbered and are marked by parentheses.