Zebrafish syndecan-2 is most similar to vertebrate syndecan-2. (A) A homology tree showing clustering of zebrafish syndecan-2 (gray shading) to the vertebrate syndecan-2 family. (B-G) In situ hybridization. Original magnification, × 5 (B-D); × 10 (E-G). (B) Expression of syndecan-2 mRNA in a wild-type mouse embryo at embryonic day 9.5 showing expression in the head and along the trunk (arrowheads). (C) A mouse embryo at embryonic day 9.5 treated with labeled sense mouse syndecan-2 mRNA probe. (D) A transverse section of a mouse embryo at embryonic day 9.5. The level of the section is indicated by the white line in B. The dark purple staining indicates expression of mouse syndecan-2 RNA. Similar to zebrafish syndecan-2, mouse syndecan-2 is expressed in the dorsal neural tube (arrowheads) and the cells surrounding the right and the left dorsal aorta (arrows). The notochord is indicated by double arrowheads. (E) flk-1 expression in a wild-type embryo. (F) flk-1 expression in a syndecan-2 MO–injected embryo, showing a lack of intersegmental expression. (G) flk-1 expression in an embryo coinjected with syndecan-2 MO and human syndecan-2 expression construct. Sprouts of intersegmental vessels were observed (arrowheads). (H) In situ analysis of flk-1 expression from 5 injection experiments. In each case, a higher fraction of embryos showing intersegmental expression of flk-1 was observed in embryos coinjected with syndecan-2 MO and human syndecan-2 expression construct compared with those injected with syndecan-2 MO only. Error bars indicate SE.