Abstract
Endothelial guidance is very important for vascular network expansion during development. It involves the induction of endothelial cell (EC) into tip and stalk cell potential at the growing angiogenic sprout. The tip cell is located at the leading edge of growing sprout, which responds to guidance cues to direct the EC migration. Meanwhile, the stalk cell trails behind the tip cell proliferates in response to guidance cues. The hierarchical organization of sprouting vessels is critical for vascular morphogenesis under normal or diseased conditions. Previously, our group has discovered a novel protein called thrombospondin type I domain containing 7A (THSD7A) that is highly conserved among the vertebrates. During zebrafish vascular development, it is a guidance cues required for directing EC migration. We have also shown Thsd7a is related to the growth path finding of angiogenic intersegmental vessels (ISV) and parachordal chain (PAC), as morpholino (MO) knockdown of Thsd7a gene expression affects ISV sprouting and PAC patterning. However, whether Thsd7a has a role in regulating tip and stalk selection during vascular development is unknown. Using transgenic zebrafish as the research system, we found THSD7A morphant displayed distinct phenotypes that are very similar to the phenotype after loss of notch-delta like 4 (dll4) signaling. This implies thsd7a may involve in the notch-dll4 signaling pathway during vascular development. Real Time-quantitative PCR data further showed that expression levels of notch1b and its downstream targets, VEGFR2/3, were down-regulated in the thsd7a morphants. In addition, in situ hybridization analysis on the thsd7a morphants revealed notch1b has an aberrant expression pattern in hindbrain, spinal cord and heart. These data indicated that zebrafish Thsd7a could regulate endothelial tip and stalk cell selection via notch-dll4 signaling during development. Interestingly, we found knockdown of Thsd7a also affect neuronal growth in the spinal cord, which suggest the association of Thsd7a and notch signaling in neurovascular interactions. Taken together, our data strongly suggests that Thsd7a may be a regulator on endothelial tip and stalk cell selection during angiogenesis. These findings could offer an opportunity for developing THSD7A targeting therapy in angiogenesis-related diseases in the future.