Laminin and Fibronectin Cooperate to Guide Endothelial Self-Organization During Intersegmental Vessel Formation

Endothelial sprouts must integrate cell-intrinsic self-organization with external guidance cues to build stereotyped vascular patterns. During zebrafish intersegmental vessel (ISV) formation, the extracellular matrix in the intersomitic space is enriched in laminin and fibronectin, but how these cues guide sprouting remains unclear. We integrated live imaging, perturbation experiments, rescue assays, and mathematical modeling to test whether these matrix components canalize endothelial behavior. Partial loss of laminin or fibronectin slowed endothelial sprouting without abolishing overall ISV formation. In a hybrid mathematical model coupling endothelial self-organization to a deformable extracellular matrix, reduced matrix density predicted slower sprouting and increased vessel fusion. Consistent with this prediction, combined laminin and fibronectin knockdown produced severe ISV mispatterning, including ectopic fusion events and network-like vascular arrangements. Chimeric fibronectin mRNAs rescued vascular patterning and associated somite defects. Comparison of lama1/lama4/fn1a and lama1/lama4/fn1b morphants suggested that somite disorganization exacerbates ISV defects, but is not required for them. Together, our results support a guided self-organization model in which laminin and fibronectin cooperate with other tissue cues to confine endothelial self-organization to the intersomitic space and ensure