Syx-b and amot morphants show a common ISV phenotype. (A) Knockdown of zebrafish syx-b using 2 nonoverlapping morpholinos, MO1 and MO2, resulted in identical ISV migration defects. The sprouts in syx-b MO arrest at the horizontal myoseptum. (B) In syx-b morphants, outgrowth of the ISV tip cells was delayed. With time, defective ISVs appear to form lumens that are capable of anastomosing with neighboring vessels. The truncated ISV phenotype was observed in embryos after 52 hours after fertilization (hpf). Due to the severity of the phenotype, the dorsal longitudinal anastomosing vessel (DLAV) does not form. In all panels, anterior is to the left and dorsal is to the top.