miR-27b controls tip cell fate via Dll4. (A) Representative images of zebrafish vasculature in miR-27b, Dll4, and double miR-27b/Dll4 morphants. Arrowheads indicate disconnected, hyper-migratory tip cells (MO-Dll4 [1]) and excessive branching (MO-Dll4 [2]) in Dll4 morphants. Note decreased sprout length, lack of branched tip cells, and decreased filopodia formation in miR-27b morphants and restored phenotype in double morphants. Broken line indicates that the image is a composite of 2 independent photomicrographs of the same field taken in different focal planes (B-C). Quantitative analysis of experiment shown in panel A. *P < .0002 and **P < .00007 between control and miR-27b knockdown. (D) Expression of flt1 in miR-27b, Dll4, and double morphants. Note increased Flt1 mRNA on miR-27 knockdown and normalized phenotype of the double morphants.