Forced expression of the putative antimorphic form of zebrafish syndecan-2 (dS2) mimicked the weak syndecan-2 morphant phenotype. Wild-type embryos were injected with either 9 pg EGFP expression construct or a mixed solution of 7 pg dS2 and 2 pg EGFP expression constructs. (A-B) Bright field images (A, EGFP-injected embryo; B, dS2-injected embryo) showing normal morphology. (C-D) bp-GFP filter set images. Mosaic expression of EGFP was observed in each case (C, EGFP-injected embryo; D, dS2-injected embryo). (E-F) Microangiography analysis. Microangiography was also performed on embryos at 48 hpf, using TRITC (tetramethylrhodamine-5(and 6)-isothiocyanate)–dextran. EGFP-injected embryos showed normal circulation (E). Embryos injected with dS2 showed reduced or a lack of intersegmental vessels (F, arrowheads) in a subset of injected embryos (65%, n = 22). Analysis of flk-1 expression by in situ hybridization was performed as a separate measurement of blood vessel development. (G-H) In situ hybridization. (G) flk-1 expression in a wild-type embryo. (H) dS2-injected embryo, showing reduced or a lack of flk-1 expression in some intersegmental vessels (arrowheads). (I) Summary of results from in situ analysis of flk-1 expression. A significantly higher fraction of the dS2-injected embryos showed reduced flk-1 expression than was observed in wild-type syndecan-2 DNA or GFP (control) DNA injections. (J) Summary of results from microangiography analysis showing synergy between dS2 DNA at 1.5 pg and syndecan-2 MO at 1 ng in generating embryos with vascular defects (compare column 3 with columns 1 and 2). No synergy was observed between syndecan-2 DNA at 1.5 pg and syndecan-2 MO at 1 ng (column 4). Error bars indicate SE. Original magnification, × 5 (A-B); × 5 (C-F); and × 10 (G-H).