An α-Smooth Muscle Actin (acta2/αsma) Zebrafish Transgenic Line Marking Vascular Mural Cells and Visceral Smooth Muscle Cells

Mural cells of the vascular system include vascular smooth muscle cells (SMCs) and pericytes whose role is to stabilize and/or provide contractility to blood vessels. One of the earliest markers of mural cell development in vertebrates is α smooth muscle actin (acta2; αsma), which is expressed by pericytes and SMCs. In vivo models of vascular mural cell development in zebrafish are currently lacking, therefore we developed two transgenic zebrafish lines driving expression of GFP or mCherry in acta2-expressing cells. These transgenic fish were used to trace the live development of mural cells in embryonic and larval transgenic zebrafish. acta2:EGFP transgenic animals show expression that largely mirrors native acta2 expression, with early pan-muscle expression starting at 24 hpf in the heart muscle, followed by skeletal and visceral muscle. At 3.5 dpf, expression in the bulbus arteriosus and ventral aorta marks the first expression in vascular smooth muscle. Over the next 10 days of development, the number of acta2:EGFP positive cells and the number of types of blood vessels associated with mural cells increases. Interestingly, the mural cells are not motile and remain in the same position once they express the acta2:EGFP transgene. Taken together, our data suggests that zebrafish mural cells develop relatively late, and have little mobility once they associate with vessels.血管系统壁细胞包括血管平滑肌细胞（vascular smooth muscle cells, SMCs）与周细胞（pericytes），其功能为稳定血管并为血管提供收缩力。脊椎动物壁细胞发育的最早标志物之一为α平滑肌肌动蛋白（α smooth muscle actin, αSMA，编码基因acta2），周细胞与血管平滑肌细胞均可表达该蛋白。目前尚无斑马鱼血管壁细胞发育的在体模型，为此我们构建了两种转基因斑马鱼品系，可在表达acta2的细胞中驱动绿色荧光蛋白（Green Fluorescent Protein, GFP）或mCherry的表达。借助该转基因斑马鱼，我们可追踪胚胎及幼体阶段斑马鱼壁细胞的活体发育进程。acta2:EGFP转基因动物的表达模式基本模拟内源acta2的表达：最早于受精后24小时（24 hpf）在心肌中出现泛肌肉表达，随后依次波及骨骼肌与内脏肌。在受精后3.5天（3.5 dpf）时，动脉球（bulbus arteriosus）与腹主动脉（ventral aorta）中的表达标志着首个血管平滑肌细胞表达的出现。在后续10天的发育过程中，acta2:EGFP阳性细胞的数量以及与壁细胞相关的血管类型均显著增多。值得注意的是，壁细胞不具备运动活性，一旦表达acta2:EGFP转基因便会固定于原位，不再发生位移。综上，本研究数据显示斑马鱼壁细胞发育相对较晚，且与血管结合后几乎无移动能力。