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Fig. 5 sp5l transcription is induced by ectopic Wnt and repressed by interference with Wnt signaling. (A) Ectopic expression of sp5l at the animal pole of embryos injected with 10 pg wnt8 RNA, 6 hours after injection at shield stage (right panel, dorsal view), compared with wild-type expression in embryos injected with equimolar amounts of GFP RNA (7 pg, left panel). (B) Overexpression of dominant-negative TCF rapidly abolishes sp5l expression. Fish heterozygous for heat-shock-inducible dominant-negative TCF-GFP [Tg (hsp70:δTCF-GFP)w26] were outcrossed to wild type, the resulting embryos heat-shocked for 15 minutes or 30 minutes starting at the 1-somite stage and the whole clutch fixed immediately. In situ hybridization for GFP (light brown) in addition to sp5l (blue) was performed to identify transgenic embryos. sp5l expression is severely reduced in 100% (n=21) of transgenics 15 minutes after induction of the transgene (middle panel), and completely abolished in 100% (n=24) of transgenic embryos after 30 minutes (right panel). (C-F) Expression of sp5l in WT, wnt3a, wnt8 and wnt3a/wnt8 morphants at the 3-somite stage.