Abstract
The common guidance cues share by the neural and vascular systems are under precise control of complex neurovascular interactions. As expected, some factors initially identified as angiogenic factors also serve as neuronal guidance molecules during development. These molecules are thus named as “angioneurin”. Previously, our group has discovered a novel protein called thrombospondin type I domain containing 7A (THSD7A) that is highly conserved among the vertebrates. We first found that THSD7A is able to mediate endothelial cells migration and tube formation during angiogenesis. We later showed that zebrafish thsd7a ortholog is a neural protein required for intersegmental vessels (ISVs) patterning during development. Recently, we further revealed that the functional THDS7A is a soluble N-glycoprotein that promotes endothelial cell migration via a FAK-dependent mechanism. However, the exact origin of zebrafish thsd7a and its effect on neural system remains unclear. In this study, we discovered that zebrafish thsd7a is expressed in the primary motoneurons. Morpholino (MO) knockdown of Thsd7a activity resulted in aberrant primary motoneuron pathfinding and ISV sprouting in the Tg(kdr:EGFP/mnx1:TagRFP) double transgenic zebrafish. Specifically, rostral motoneuron (RoP) axon and the parachordal chain (PAC) were either absent or distorted in the thsd7a morphants. Strikingly, the morphant’s phenotypes are reminiscent of those observed in the netrin1a and deleted in colorectal cancer (dcc) morphants shown in the literatures, implying that thsd7a may involve in the netrin1a signaling during neurovascular development. The Real Time-quantitative PCR analysis (RTq-PCR) and in situ hybridization (ISH) results showed that netrin1a expression level was indeed decreased in the thsd7a morphants. Moreover, RoP axon and PAC defect could be rescued by the addition of netrin1a mRNA. Our findings indicate that zebrafish Thsd7a is a neural protein expressed in primary motoneuron. It is required for PAC and RoP axon formation by regulating netrin1a expression. Taken together, our data supports the notion that Thsd7a is a potent angioneurin involved in the developing and/or remodeling of both neural and vascular systems. Finally, the neurovascular guidance function of Thsd7a may offer a unique therapeutic potential in the future.